How Much Of The Radiators Should Be Blocked Off?

I’ve got a Track Day at Willow Springs scheduled for the 20th. I made up some 1/8” aluminum plates to block off part of the oil and water radiators. On the past Track Days I blocked off about 1/3 of each radiator but the car ran too cool and wouldn’t rev past 4000 Rpm and would run rough for the first lap or two. I would warm up the car to about 200* before I left the grid, but it was cold outside and the car would cool off.

My question for all of you that are more experienced than me is, can I block off 1/2 of each radiator with larger aluminum plates?

Is anyone closing off the intakes with duct tape?

What does everyone do?

You need to manage airflow to reach target operating temperatures. Operating temps are affected by ambient, wind, inlet size, and your driving. If you are not pushing the car to the limit then you need to block a lot more airflow.

since you are not sure what you need in terms of percentage blocking of the inlets you might want to fashion a block off that can be quickly adjusted.

but you can also just use racers tape (gaffers tape).

Thanks Mikey. So blocking off 50% or more of the radiators is acceptable to get the operating temps correct?

Sorry for the dumb questions, I’ve never had a car without a thermostat.

My current P2 car is running with 75% airflow blocked. Coolant temps are running 180 degF on a 65 degF ambient day.

I use various sizes of Garolite sheets (available from McMaster-Carr) taped over the radiator surface (inside the duct).

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Originally Posted by David Ferguson

My current P2 car is running with 75% airflow blocked. Coolant temps are running 180 degF on a 65 degF ambient day.

I use various sizes of Garolite sheets (available from McMaster-Carr) taped over the radiator surface (inside the duct).

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Hi Dave, thank you.

We’ve got some friends that retired and moved to Paso. They live in a community about 1/2 hour out of town, near a small shopping center that has a gas station, pizza place and a market. Are you near there?

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Originally Posted by Extreme1

Hi Dave, thank you.

We’ve got some friends that retired and moved to Paso. They live in a community about 1/2 hour out of town, near a small shopping center that has a gas station, pizza place and a market. Are you near there?

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I know serious racers all remove them but I'd run a t stat.

Run a thermostat.

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Originally Posted by t walgamuth

I know serious racers all remove them but I'd run a t stat.

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Why would you not have one? Even in go karts I always had a thermostat. It's a cheap sensor and no thermostat just seems like asking for trouble, potentially very expensive trouble. :(

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Originally Posted by Extreme1

Thanks Mikey. So blocking off 50% or more of the radiators is acceptable to get the operating temps correct?

Sorry for the dumb questions, I’ve never had a car without a thermostat.

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A wide open thermostat still restricts flow. Yeah, in SoCal we always run hot, right? So the thought is to increase flow.

Part of the reason you want to slow flow is to allow the coolant to absorb/take-on the heat so it can carry the heat to the radiators.

If flow is too fast the heat can't transfer effectively into the middle/whole of the water flow.

Think if it like your hand and fire. You can zip your hand through the fire and not get burned. Go slowly and you get the heat!

Check the PFM manuals. I don’t recall if that cooling system was designed for use with a t-stat or not.
starracecars.com lists a t-stat housing SKU: 100-524 so my assumption is you can and should run a thermostat.

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Originally Posted by Spengo

Why would you not have one? Even in go karts I always had a thermostat. It's a cheap sensor and no thermostat just seems like asking for trouble, potentially very expensive trouble. :(

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tstat is not a sensor and can fail. It’s not uncommon that people pull them out. The OP is not having any issues cooling so the lack of restriction leading to too much flow and not enough heat transfer time as beerbudget describes is not the issue here. But it is an important point because it is possible to overheat some systems if the flow is too fast.

Oil temp is critical.
Too cold and it will go into limp mode which sounds like what you have experienced. I believe that anything below 160* will trigger the limp mode.
You are going to want to see 180* oil temp while warming up your car. Target 200* while on track. 240* is probable death to the engine so you need to be mindful and adjust your blocking accordingly. 50% or even more is not uncommon on cold days but like Mikey said how you drive the car will definitely cause variances

Go thru the Resources on starracecars.com
Lots of helpful info on there

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Originally Posted by mikey

Check the PFM manuals. I don’t recall if that cooling system was designed for use with a t-stat or not.
starracecars.com lists a t-stat housing SKU: 100-524 so my assumption is you can and should run a thermostat.

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I wasn’t aware that there is a thermostat available for a PFM. I’ll look up that part number.

If you know, is that thermostat for the water or oil? I can’t keep the temperature up high enough in either one. The track days at Willow Spring are all in the winter months and it’s cold there. 32* when I get there at 7am and a high of 60*ish during the middle of the day.

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Originally Posted by Fred Michael

Oil temp is critical.
Too cold and it will go into limp mode which sounds like what you have experienced. I believe that anything below 160* will trigger the limp mode.
You are going to want to see 180* oil temp while warming up your car. Target 200* while on track. 240* is probable death to the engine so you need to be mindful and adjust your blocking accordingly. 50% or even more is not uncommon on cold days but like Mikey said how you drive the car will definitely cause variances

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Yes, limp mode is what’s been happening. The last track day I had 1/3 of the oil and water radiators blocked off. This time it will be 1/2 of both of them, and a roll of duct tape nearby. Thanks for the target temps, that’s what the Resource Guide says also.

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Originally Posted by Extreme1

I wasn’t aware that there is a thermostat available for a PFM. I’ll look up that part number.

If you know, is that thermostat for the water or oil? I can’t keep the temperature up high enough in either one. The track days at Willow Spring are all in the winter months and it’s cold there. 32* when I get there at 7am and a high of 60*ish during the middle of the day.

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I just looked at that thermostat housing on Starracecars.com and it’s a water thermostat housing.

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Originally Posted by Extreme1

I just looked at that thermostat housing on Starracecars.com and it’s a water thermostat housing.

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correct. Add thermostat at least 160F rated. That’s colder than target but the PFM cooling system is marginal in warm weather and you can get into a bit of a thermal runaway situation if the cooling loop doesn’t open up early enough. Daytona was always a bear for me with so much of the lap at full throttle. Every lap just hoping to get to the bus stop section of the back straight before it overheated.

anyway once your water temp is up into operating range the oil temp will come up accordingly as well.

Also keep in mind that you can always warm up in the paddock longer. PFM has no problem building heat while idling stationary. I actually used fans in the garage at home to prevent overheating when just idling the motor.

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Originally Posted by mikey

Also keep in mind that you can always warm up in the paddock longer. PFM has no problem building heat while idling stationary. I actually used fans in the garage at home to prevent overheating when just idling the motor.

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Yes thx. I just ordered a leaf blower for my buddy in the paddock to blow into the water radiator, until the oil temps come up.

I just looked at my car. It has the thermostat housing on it. I just need to remove the hose and stick my finger in there to see if it has a thermostat. I’m thinking not, it was bought from Juncos Racing.

If it was run without a thermostat, then it probably has/should have a 'plug' in the housing that needs to be removed. That plug slows the coolant flow (so it has time to dissipate the heat) when there isn't a thermostat. I run a 180 degree thermostat and VP Racing Stay Frosty race coolant and I never see more than 195 degrees on the coolant - and that's in 98 degree ambient air pushing the car hard. The Stay Frosty dropped my coolant temperature by at least 10 degrees over straight water. Make sure you get the right thermostat. It has to be tall enough to block off the passage (where the 'plug' I mentioned would be) when it's closed.

And you must not have a cooling fan. I highly recommend adding it. I can idle on the grid and it just cycles on and off keeping the coolant around 185 to 190 degrees. No more leaf blowers or wondering if it's going to overheat before you get moving.

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Originally Posted by CSasfai

If it was run without a thermostat, then it probably has/should have a 'plug' in the housing that needs to be removed. That plug slows the coolant flow (so it has time to dissipate the heat) when there isn't a thermostat. I run a 180 degree thermostat and VP Racing Stay Frosty race coolant and I never see more than 195 degrees on the coolant - and that's in 98 degree ambient air pushing the car hard. The Stay Frosty dropped my coolant temperature by at least 10 degrees over straight water. Make sure you get the right thermostat. It has to be tall enough to block off the passage (where the 'plug' I mentioned would be) when it's closed.

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Okay thx!

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Originally Posted by CSasfai

And you must not have a cooling fan. I highly recommend adding it. I can idle on the grid and it just cycles on and off keeping the coolant around 185 to 190 degrees. No more leaf blowers or wondering if it's going to overheat before you get moving.

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No I don’t have a cooling fan. Maris gave me his before he moved back to Europe, but I haven’t installed it yet. I’ll have to look at that more closely.

I hate idling in the staging area and watching the temps go up too high.

Question: where is the thermostat that cycles the fan on/off/on? Is it built into the fan? Can you send me a link so I know what to get?

Mine is triggered by the MoTeC system, so I can go in and program under what circumstances it comes on (e.g., coolant more than 190 and car speed less than 5 MPH).

Be careful adding a radiator fan. It is only convenient for idling in the paddock or if stuck on grid for a loooong time. At speed a radiator fan is restricting airflow and hurts overall cooling system performance. They are absolutely useless above 35mph.

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Originally Posted by mikey

Be careful adding a radiator fan. It is only convenient for idling in the paddock or if stuck on grid for a loooong time. At speed a radiator fan is restricting airflow and hurts overall cooling system performance. They are absolutely useless above 35mph.

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The auxiliary fan can be quite small. I added one to my 85 Reynard on a switch. When the temp got up there I'd just flip the switch and in five minutes it was cool. At speed the fan will windmill so not restrict flow all that much, imho.

Okay I wanted to thank everyone for their help.

I had a great track day at Willow Springs today. It was 46* when I got there and had both radiators halfway blocked off with aluminum plates. The engine and oil temps were good, about 180* water and 165* oil. As the day got warmer the water temps rose to 213* max. The oil never went above 180*.

Later in the day it was 74* and I removed the plate in front of the water radiator and left the one halfway blocking the oil radiator. Doing that cooled off the water temp to 180ish and the oil stayed at 165ish.

I was pushing myself and ran out of talent and spun in turn 3 and ended up backwards in the dirt. No damage but the car wouldn’t start so the truck had to tow me back to the pits. My buddy got a good laugh at that.

Glad to hear you had a good time. I've been a flight instructor for more than 30 years and it's like learning to fly an airplane. At first, you're working hard just trying to learn the basics then before long, it all starts to come together and you get more and more comfortable.