Cooling Issue

[Jim Garry]

Hi everybody. Happy New Year!

My car is a Cheetah (sportsracer). It is used for autocrossing. Has a front radiator. Suzuki 1000 engine. It has cooling issues because the air intake for the radiator was never meant to have to deal with the front wing that is now used. But with the installation of a fan on top of the radiator, things were OK. The system contains about 4.5 to 5 qts of water with water wetter. I ran this way for several years with mostly no cooling issues.

Last season there were some much bigger cooling issues and although I can't say for certain, I believe it was due to a change in fuel which was recommended by someone. Went from 108 or 110 leaded to about 102 unleaded with ethanol. But I didn't come to that conclusion until September. Here's what I tried during the season to help the problem:

• (Fan was already in place since years earlier. Can't fit anything larger.)
• Davies Craig EBP40 - surprisingly yielded no improvement
• Improved routing of lines (I know this is vague as I've written it but an automotive engineer made the design suggestion) - no improvement
• Top of the line racing radiator (forget the name at the moment) - shockingly no improvement
• Cut a hole in the bodywork and ducted the air out from the radiator - Temps dropped 15 degrees!
• Returned to leaded high octane - temps dropped another 5 degrees.

Yet on a 90 degree day, water temps still get up pretty high. Not critical but getting there. About 230 and climbing after a 60 second run later in the day and oil temps are established (say bout 200ish maybe a bit higher).

So now I suspect the air flow. Here are the intake and exhaust air areal measurements:

The area of the opening at the nose of the bodywork is 61.5 sq inches.
The area of the exhaust through the ducting on the top of the bodywork is 91 sq inches.

So far so good.

But when I installed the new radiator which was about double the thickness of the old VW radiator, there was a reduction in air entering the radiator behind the air opening at the bodywork. That area is bounded by the splitter below the rad and the radiator itself and is only 47 sq inches!

So 61.5 sq in of open area at the nose, funneling down to 47 into the radiator, and then 91 exhausting out the top of the bodywork.

Is this a problem?


Thanks for any advice guys.

P.S. In the photo with the thicker radiator, the shrouding on top of the radiator is not level left to right because it was just laid on top for the photo. The air gap is normally even left to right.

[mikey]

Make the fan shroud better, close up any air gaps between the edges. Makes a big difference. The shroud should cover the entire radiator and funnel to the fan, with tight tolerances and good seals.

[Fred Michael]

Is the wing that you mentioned keeping air from entering or exiting the rad? Pictures of the wing would help.
Is the new radiator single pass or double pass or...?
Have you asked the Cheetah experts at the dsrforum, in particular Kevin Mitz?

[Will Velkoff]

Something simple to try - pressure test the cap and cooling system. I was chasing an overheating problem that gradually got worse for no apparent reason, ended up having a weak cap, and also a small leak in a connection that was not visible until we pressure tested the system and went up and down with a flashlight and mirror.

[Jim Garry]

Make the fan shroud better, close up any air gaps between the edges. Makes a big difference. The shroud should cover the entire radiator and funnel to the fan, with tight tolerances and good seals.

I agree. Everything is very tight. Thanks. Good suggestion.

[Jim Garry]

Something simple to try - pressure test the cap and cooling system. I was chasing an overheating problem that gradually got worse for no apparent reason, ended up having a weak cap, and also a small leak in a connection that was not visible until we pressure tested the system and went up and down with a flashlight and mirror.

If it was a weak cap, would water as steam be coming out? No water is lost as far as I can tell.

[Jim Garry]

Is the wing that you mentioned keeping air from entering or exiting the rad? Pictures of the wing would help.
Is the new radiator single pass or double pass or...?
Have you asked the Cheetah experts at the dsrforum, in particular Kevin Mitz?

Rad is double pass.

Air comes out fine; wing doesn't affect discharge at the top. It does impact air coming in as described in op, but the fan has always pulled enough air in. So I'm wondering if the loss of area at the radiator as described in first post is an issue. ??

[Art Smith]

Jim-

is the new thicker heat exchanger single or double row? if double row, why? is there space for a second and/or third fan in parallel? if not, what has to move?? how are the heat exchanger tanks vented? and to where? is there space to duct high pressure air from in front of your tires to the front side of your heat exchanger? what's the heat exchanger's core area?

under the heading of fault isolation suggest you draw a cartoon with ALL the flow areas AND path lengths AND changes in direction annotated including the fan. have you measured the pressure differential across the heat exchanger vs flow? ....the flow through the core? do you have the performance spec's for the fan you're using? .......air flow vs voltage?? there is no substitute for diameter when it comes to heat exchanger fans. early on I measured two 10" fans and two 12" fans looking for packaging relief from my baseline single 16" fan and the results were NOT close! I'm guessing your 1-liter Suzuki makes more power than any of my 1600cc Kent's and that implies a larger cooling requirement.......................

your symptoms suggest to me not nearly enough air flow through the core

Art
artesmith@earthlink.net

[ChristopherBernard]

Jim,
Performance of a prop fan drops drastically with any additional resistance.
Best to avoid quick changes in direction of air flow, etc.
There appear to be some "dead" spots in terms of air flow. For example, it's likely the only significant air flow is at the round opening to the fan. This, together with the added resistance of the thicker core could net less cooling capacity than your previous set up.
20 years in HVAC for customers like IBM and others with massive clean room facilities and extremely dangerous chemical exhausts, third party verification of performance gave me some decent experience in avoidance of problems in this area but applications where space is limited are always a challenge. Call me. PM me if you haven't got my number.

Chris

[Fred Michael]

With that wing, there is no possible way you are getting adequate inlet flow

[TDI PILOT]

1. Try replacing your thermostat with a new OEM one.
2. Make sure you have the routing of the hoses correct.
3. Start the car (cold) and after it runs for a few minutes touch the hoses coming into the radiator and the ones coming back out to the motor. Make sure they are BOTH hot, this verifies flow.
4. Crack the air bleed screw on the water pump if the engine has one. Bleed all air out after engine is warm.
5. Make sure the swirl pot is the highest point in the cooling system, ensure the top of it is higher that the valve cover on the motor.
6. Replace the radiator cap with a new one.

[2BWise]

With that wing, there is no possible way you are getting adequate inlet flow

I agree with this comment. That wing is going to create a large low pressure zone above and ahead of the radiator inlet. That's opposite of what you need to get adequate flow.

How is the electric water pump wired? Can it be run with the engine off? Back when I was doing FSAE we ran dual electric water pumps which could be powered with the engine off to cool when the car was sitting stationary.

[Jim Garry]

The wing is the same one I've had for years. There has never been more than an occasional problem because the fan was pulling enough air. Keep in mind this is for Solo. 60 second runs at most. Afterward I can run the water pump with the engine off if needed.

You all have listed a ton of great points! But I shouldn't have listed all the issues that I did in my original post. Here's the real question I wanted to know about:

Intake area in the fiberglass = 61 square inches
Intake area into the radiator with the old, thin radiator = 60
Intake area into the radiator with the new thick radiator = 47
Exhaust area post-rad = 91

In the past, the intake area to the radiator was 60 square inches. Now it is 47. This is due to the thicker radiator cutting down the flow area into it. See sketch (not to scale, exaggerated for clarity of discussion).

So, would going back to the old radiator which is not as efficient as this new one actually relieve the situation?

[Purple Frog]

Any chance with all the changes you made you wired the fan in reverse?

Thicker rad core requires stronger fan. Get a bigger fan and make sure it is tightly shrouded so all air goes through the fan.

Weld a bleeder screw in the top of rad as it sits in the car.

[hdsporty1988]

This being solo with such a short run time, it seems to me that you might have a water volume issue which should be more with the new radiator. You probably already thought of this, but is the temperature even across the radiator? With your layout it would be very easy to have an air pocket at the top right corner.

[Jim Garry]

Any chance with all the changes you made you wired the fan in reverse?

Thicker rad core requires stronger fan. Get a bigger fan and make sure it is tightly shrouded so all air goes through the fan.

Weld a bleeder screw in the top of rad as it sits in the car.

At idle, hot air blows out the top with good speed.
Pretty big fan already. I can research for bigger ones.
Have a bleeder screw.

Thanks Frog.

[Jim Garry]

This being solo with such a short run time, it seems to me that you might have a water volume issue which should be more with the new radiator. You probably already thought of this, but is the temperature even across the radiator? With your layout it would be very easy to have an air pocket at the top right corner.

Good points. I have wondered about water volume. I think it would help to increase it. But not sure where I could find a place in the car for another couple of quarts.

Temp is pretty good across the rad.

Thanks much.

[Jim Garry]

So do you think this isn't part of the issue?

[DaveW]

So do you think this isn't part of the issue?

The thick radiator (more flow resistance), the decreased area at the front of the radiator, and the wing blocking the air entrance at the front are all possible contributors.

Water volume in the long run, makes little difference. In short bursts more water volume means slower response to both heating and cooling.

However, IMO, the wing blocking the entrance is the greatest issue. You may need a fan for airflow enhancement especially when you are not at speed.

[Art Smith]

So do you think this isn't part of the issue?

Jim-

jumping ahead of your cartooning effort, it's my sense you're NOT looking for "An" issue but rather a collection of "issues"! the suggested cartoon was recommended as both a device to collect relevant design data AND to change the focus from things to the system. finned-tube heat exchangers aren't hard and there's a great deal of material available on how they work. the hard part of heat transfer is cramming it into a small irregular space and then attempting to provide it minimum air flow; under those circumstances it comes down to details AND attention to detail! from your problem statement heat exchanger water flow rate AND inlet air temperature are fixed. that leaves the product of core area and air flow rate as the only cooling system design degree of freedom....................... heat transfer goes up with increasing air flow rate and/or increasing core area (assuming fixed coefficient of core heat transfer AND equal air flow rate through the core across the core's face). smoke, oil, or CFD will confirm your current installation is getting little, if any, dynamic pressure recovery from behind the wing. with little or no dynamic pressure recovery to promote air flow through the heat exchanger core, you're left with only the pressure differential from the fan. it's been my experience there's two problems with fans: air flow drops off with pressure (either back pressure OR pressure drop through the core) AND they have to be spaced away from the heat exchanger core to assure something approaching equal air flow across the face of the heat exchanger core. the attached collage shows experimental hardware used to explore the cooling system design trade space for a FFord. the experimental hardware implementation is dated but the cooling system concepts examined are still applicable today! to help with the decimal point, for a 1600cc Kent I'm currently using a single 16" fan that flows north of 3000cfm using a 2" space between the core face and the heat exchanger core with a 1/2" edge radius. a simple descriptive geometry solution for a spaced circle to rectangle transition is more than adequate. it's my experience that a sealed transition is not negotiable! without one it's my opinion that best-on-best you're likely to be using only half the projected area of your fan of your heat exchanger core which clearly isn't the answer!

Art
artesmith@earthlink.net

[Jim Garry]

. You may need a fan for airflow enhancement especially when you are not at speed.

Thanks Dave. I have a pretty big fan currently. I suppose I could research to find a larger one but this one is big relative to the space I have available.

Jim

[Jim Garry]

Jim-

jumping ahead of your cartooning effort, it's my sense you're NOT looking for "An" issue but rather a collection of "issues"! the suggested cartoon was recommended as both a device to collect relevant design data AND to change the focus from things to the system. finned-tube heat exchangers aren't hard and there's a great deal of material available on how they work. the hard part of heat transfer is cramming it into a small irregular space and then attempting to provide it minimum air flow; under those circumstances it comes down to details AND attention to detail! from your problem statement heat exchanger water flow rate AND inlet air temperature are fixed. that leaves the product of core area and air flow rate as the only cooling system design degree of freedom....................... heat transfer goes up with increasing air flow rate and/or increasing core area (assuming fixed coefficient of core heat transfer AND equal air flow rate through the core across the core's face). smoke, oil, or CFD will confirm your current installation is getting little, if any, dynamic pressure recovery from behind the wing. with little or no dynamic pressure recovery to promote air flow through the heat exchanger core, you're left with only the pressure differential from the fan. it's been my experience there's two problems with fans: air flow drops off with pressure (either back pressure OR pressure drop through the core) AND they have to be spaced away from the heat exchanger core to assure something approaching equal air flow across the face of the heat exchanger core. the attached collage shows experimental hardware used to explore the cooling system design trade space for a FFord. the experimental hardware implementation is dated but the cooling system concepts examined are still applicable today! to help with the decimal point, for a 1600cc Kent I'm currently using a single 16" fan that flows north of 3000cfm using a 2" space between the core face and the heat exchanger core with a 1/2" edge radius. a simple descriptive geometry solution for a spaced circle to rectangle transition is more than adequate. it's my experience that a sealed transition is not negotiable! without one it's my opinion that best-on-best you're likely to be using only half the projected area of your fan of your heat exchanger core which clearly isn't the answer!

Art
artesmith@earthlink.net

Thanks Art. That was a lot of concept you got across.

You hit the nail on the head with your statement that, "the hard part of heat transfer is cramming it into a small irregular space ...".

Regarding, "they have to be spaced away from the heat exchanger core to assure something approaching equal air flow across the face of the heat exchanger core", I understand. The problem is that the more space it is given, the more area for intake flow that I lose. Currently I have a little less than 1" space between the rad and the fan. If I go to 2", then the area for intake flow goes from the original of 60 sq inches, to the current 47 sq in, to something like 35 sq inches.

I will keep all of your points in mind as I progress forward (and other suggestions too!).


Jim

[Peter Olivola]

So do you think this isn't part of the issue?

That is a significant reduction in inlet area and while you may not have had problems with the wing before, it's highly likely you created a combination that has reduced or even cut off, airflow to the radiator when in motion.

[Fred Michael]

When I saw your pictures of the two installations the first thing I thought I noticed was that they were at different angles. Since you have now confirmed that, yes that is definitely a contributing factor.
Some radiator fin arrangements are VERY restrictive to the airflow as well. If you could actually measure airflow of both rads it may surprise you. Not easy to do, I know.
Is the temp getting high during the runs or just while sitting between runs? While both are important, the temp while moving with the engine under load is more of a concern than heat soak between runs...to a point, obviously.
If you need more cooling between runs a fan feeding into the inlet can be a big help as long as the electric water pump is doing it's job properly.

[S Lathrop]

My experience is that increasing the surface area of the cooling system is the only way to get better cooling. Found this out as we developed the Zink Z10. Thicker never worked for us.

The thicker core may have actually resulted in a less efficient system. The air slows down as it passes through the core and as such is not taking the heat away as well as it would passing through the thinner core.

Your drawing also shows a reduction in the efficiency of the air flow. The air has to make a much sharper turn.

You might try removing the floor pan under the radiator and add a larger kick up at the exit of the radiator. This might increase the air flow to the radiator. Dumb idea but given where you are sitting now, I would try it.

[Jim Garry]

When I saw your pictures of the two installations the first thing I thought I noticed was that they were at different angles. Since you have now confirmed that, yes that is definitely a contributing factor.
Some radiator fin arrangements are VERY restrictive to the airflow as well. If you could actually measure airflow of both rads it may surprise you. Not easy to do, I know.
Is the temp getting high during the runs or just while sitting between runs? While both are important, the temp while moving with the engine under load is more of a concern than heat soak between runs...to a point, obviously.
If you need more cooling between runs a fan feeding into the inlet can be a big help as long as the electric water pump is doing it's job properly.

The problem is during the run. Interestingly, on a tight course there is no cooling issue but on open, fast courses where the percentage of full throttle is large, the temps are very high. If I put a co driver in the car who is not familiar with the car's handling capabilities, the car will cool down a small amount on that run but then increase again on my run. (Not trying to tout driving skills; just an interesting observation to pass along.)

[Jim Garry]

My experience is that increasing the surface area of the cooling system is the only way to get better cooling. Found this out as we developed the Zink Z10. Thicker never worked for us.

The thicker core may have actually resulted in a less efficient system. The air slows down as it passes through the core and as such is not taking the heat away as well as it would passing through the thinner core.

Your drawing also shows a reduction in the efficiency of the air flow. The air has to make a much sharper turn.

You might try removing the floor pan under the radiator and add a larger kick up at the exit of the radiator. This might increase the air flow to the radiator. Dumb idea but given where you are sitting now, I would try it.

I would try that Steve but the splitter is underneath. Good idea though.

[hdsporty1988]

One variable that might help is, what water temperature are you starting your runs at? You mentioned that on a hot day runs end at 230 how many degrees does it climb?

[Peter Olivola]

The problem is during the run. Interestingly, on a tight course there is no cooling issue but on open, fast courses where the percentage of full throttle is large, the temps are very high. If I put a co driver in the car who is not familiar with the car's handling capabilities, the car will cool down a small amount on that run but then increase again on my run. (Not trying to tout driving skills; just an interesting observation to pass along.)

And on open courses your top speed and time spent at speed is higher. As I said, you may have created a situation where the combination of wing and reduced radiator inlet results in higher speed chocking off the airflow.

[DaveW]

The problem is during the run. Interestingly, on a tight course there is no cooling issue but on open, fast courses where the percentage of full throttle is large, the temps are very high. If I put a co driver in the car who is not familiar with the car's handling capabilities, the car will cool down a small amount on that run but then increase again on my run. (Not trying to tout driving skills; just an interesting observation to pass along.)

That is a major clue. You are not getting enough air through the radiator at high speeds. A fan is only effective in a cooling system at low velocities where the vehicle-to-ambient-air velocity difference is small. No fan that I know of can create air velocity near what an effective air intake can create at speed. In your case, the fan is maintaining a minimum air velocity through the radiator, but at high speed there is not enough air velocity or heat transfer.

As Steve said, often a thick radiator is less effective than a thin one for a combination of reasons:
1. air flow is slower due to radiator restriction
2. even if air flow were not reduced, the air heats up as it flows thru the rad, and efficiency of the last 1/3 of the rad thickness is minimal
3. the above effects are magnified if the air intake to air exit pressure difference is low - the big front wing is surely reducing this

[Art Smith]

Jim-

one other thought that needs running down (courtesy of the shower this morning): have you measured your water flow through either or both of the heat exchangers? dual pass heat exchangers by their very nature reduce the water flow area by a factor of two AND increase the path length through the heat exchanger by a factor of two. for equal water flow rate, the velocity through the heat exchanger has to go up that same factor of two for the increased path length; as a rule neither is good for water side pressure drop across the heat exchanger..................... as a consequence, most of the time a dual pass heat exchanger presents a larger pressure drop to cooling system water flow. if you're attempting to use the Suzuki water pump, the dual pass heat exchanger just might be the straw that broke the camel's back! adding a simple electric "booster" water pump would be a easy experiment but my money is ALL on inadequate air flow! it may be time to start thinking about a "cooling blister" or "locally raised hood" to obtain the space needed for adequate air flow............ your wing all but guarantees there's likely to be little or no aero drag penalty! if the previously mentioned cartoon doesn't work for you, maybe a section through the air's flow path to scale will do the trick. 2" between the heat exchanger and the fan was the smallest number I could make work with respect to effectively equal air flow across the face of the core (ie: hand held anemometer). incorporation of an electric fan in Vikings and Swifts incentivizes extreme creativity on the path length for the cooling system..............................

Art
artesmith@earthlinnk.net

[Jim Garry]

Thanks Art.

Lots to think about.

[Jim Garry]

One variable that might help is, what water temperature are you starting your runs at? You mentioned that on a hot day runs end at 230 how many degrees does it climb?

Always try to have starting temperature below 200. Sometimes i can get it to 185 at the start line.

But starting at 185 for the second run of the day results in a finish line temp of 220. But starting at 185 for the 8th run of the day can result in a finish temp of 235.

As the day goes on, there seems to be less ability to deal with temp.

But that could be due to learning the course and being able to maintain full throttle longer.

[Jim Garry]

That is a major clue. You are not getting enough air through the radiator at high speeds. A fan is only effective in a cooling system at low velocities where the vehicle-to-ambient-air velocity difference is small. No fan that I know of can create air velocity near what an effective air intake can create at speed. In your case, the fan is maintaining a minimum air velocity through the radiator, but at high speed there is not enough air velocity or heat transfer.

As Steve said, often a thick radiator is less effective than a thin one for a combination of reasons:
1. air flow is slower due to radiator restriction
2. even if air flow were not reduced, the air heats up as it flows thru the rad, and efficiency of the last 1/3 of the rad thickness is minimal
3. the above effects are magnified if the air intake to air exit pressure difference is low - the big front wing is surely reducing this

I'll certainly try out the thinner rad.

The difference in top speed between me and a driver who isn't familiar with the car is only about 5 to 8 mph. Makes a big difference in course time. But would the difference between 72 mph versus 79 mph show up in coolant issues?

[BLS]

"As the day goes on, there seems to be less ability to deal with temp."

Higher ambient temperature?

[DaveW]

I'll certainly try out the thinner rad.

The difference in top speed between me and a driver who isn't familiar with the car is only about 5 to 8 mph. Makes a big difference in course time. But would the difference between 72 mph versus 79 mph show up in coolant issues?

If the cooling system were more efficient, probably not. But if it is restricted in airflow, then the internal air velocity increase enabling an increase in heat transfer with speed is obviously smaller than needed, so longer throttle application is not balanced due to the compromised heat transfer.

[hdsporty1988]

Always try to have starting temperature below 200. Sometimes i can get it to 185 at the start line.

But starting at 185 for the second run of the day results in a finish line temp of 220. But starting at 185 for the 8th run of the day can result in a finish temp of 235.

As the day goes on, there seems to be less ability to deal with temp.

But that could be due to learning the course and being able to maintain full throttle longer.

I think the end of day probably has to do with higher ambient temperatures which reduce cooling and everything in the engine bay would be "heat soaked" thus causing water temperature to rise. The heat has to go somewhere! Which brings up another question. Did you change anything that would have decreased airflow from the engine compartment? Have you considered louvers or something to allow heat to escape?

[Jim Garry]

Did you change anything that would have decreased airflow from the engine compartment? Have you considered louvers or something to allow heat to escape?

Take a look at my photos from early in the thread.

[cjsmith]

As Dave mentioned earlier, I would expect the front wing is reducing the amount of air that is entering the inlet and the disturbed air coming of the back of the wing could reduce the low pressure area where the air exits the body. Assuming the sun is out during most of your runs, the ground temperature can be 120 to 150 deg F. You are taking the air just a couple of inches above the ground, the incoming air is close to the temperature of your water there isn’t a lot of differential to reject heat into. Could you make a duct opening outside the front wing,( near the tires on both sides) similar to a break duct and rout it to a plenum that would feed the inlet. Have you thought about trying to lift the front wing to increase air flow underneath? In between runs could you use an electric leaf blower to increase air flow over the radiator to drop the temps if there is room….
The air flow pattern through the cooling system isn’t optimal. You are forcing the air to make a lot of turns, hence the air has to make an S shaped pattern to travel through system. More bends mean less flow. I see this in the R&D labs when designing new air-conditioning systems. I assume the air used to discharge behind the front wheels. Is that blocked off now or is it open? I was wondering if the front wheel discharge would help you on the high speed courses?
As Steve mentioned, if you can maintain constant flow a thicker radiators can work, if you can’t you can lose capacity or stay the same due to the pressure drop. As the air absorbs heat as it goes through the radiator, the potential to pick up heat is reduced the farther it goes. A radiator with increased surface area and a larger opening and discharge might help.

[S Lathrop]

If you really want to solve this problem, I think you are going to have to mover the radiator / radiators to a place where you can get 200 to 300 square inches of surface area with cores that are 2" thick or less.

You may be able to improve what you have a bit but not as much as you really need to. Anything short of a lot of square inches will be fruitless.

Sorry to be the barer of bad news.