Thermostat coincidentally gone bad?

[Ted Idlof]

I'm about to change out my thermostat but the timing of it going bad, if it has, is strange. Looking for other ideas on what might be going on with the car not getting cooled properly if at all.

My car has run on the cool side including needing tape on the screens even with ambient temps in the high 70's, low 80's. It takes 15 min to warm up from cold to 170 with a thermostat which has always worked fine (predictably).

But I had to replace the right side radiator after getting hit in the sidepod last race. With it buttoned up and ready to test, I added my coolant as I have in the past, just filled up the swirl pot and added more coolant as it burped. However this time when starting it up, the temps went from cold (60F) to 190 in about 8 minutes. I put a fan in front of the sidepod and it kept climbing til I shut if off at 210. So, I'm thinking the thermostat is stuck closed/plugged. Does that seem logical; that I have no or almost no circulation? God forbid the water pump quit instead.

Other thoughts observations: 1) I have a 3 psi water pressure sensor and the light didn't go off until 190F when it usually goes out at 150. 2) The lines off the top of the radiators provide a way for air to escape back to the swirl pot, right? 3) And even if I had a problem with the replaced radiator, the left side one should still be working and keeping the temps reasonable just sitting in the garage idling.

Your thoughts please.

While y'all are collecting your thoughts and insights, I'll go replace the thermostat now and hope something strange happened with it.

Edit; took the thermostat out; no change.

[J Leonard]

Are the vent lines from rad to swirl pot plugged?

[Ted Idlof]

shouldn't be since it was the same ones on there before. But something is plugged. Guess I'll check that before I put a new radiator on.

[Ted Idlof]

So says my FM mechanical mentor Derry O. I'll crack the bleed line and squeeze the hoses at the bottom first thing tomorrow before I replace the radiator.

[DanW]

So says my FM mechanical mentor Derry O. I'll crack the bleed line and squeeze the hoses at the bottom first thing tomorrow before I replace the radiator.

If the hoses have air in them, you will hear the air when you squeeze them quickly. Bleed and try again.

[Dave Cutchins]

I have a similar problem anytime I drain the system and then refill.
I remove the thermostat and watch the flow and check to see if coolant is flowing through the bleed lines back to the swirl pot.
With the engine running, I have used my compressor to force the coolant though the block by covering the swirl pot opening with a damp rag and using an air gun. That usually removes the trapped air. Just work fast before the water gets too hot.

[Jon Jeffords]

It sounds like the system isn't bleeding sufficiently when filled.

The key to a proper 'first fill' procedure is for air to escape out of the system (at the high points) as it is being filled with coolant, to the point where the water pump will not loose its prime when the engine is fired.

You will know if the water pump looses its prime by putting your hand on the coolant hoses or radiators. If the engine is hot and the hoses are not, either the thermostat is still closed, or the pump is surrounded by air and not circulating the coolant.

If you have bleeds running to the swirl tank, you should see a nice 'pee stream' from the bleeds when the cap is off and engine is running (thermostat open), indicating the bleed lines are clear.

Two suggestions:
Remove the bleed lines and blow compressed air through them to make sure they are clear of debris (usually rust for those of you with cast iron engines).

Remove the thermostat. Manually force it open, and insert an aspirin to temporarily hold it open. Reinstall the now-jammed open thermostat, and sloooowly refill the system. The open thermostat may allow the system to bleed more efficiently, and will dissolve once the system has been successfully filled.

[Ted Idlof]

Checked all the bleed points and bleed lines and they are clear and water moves thru.

Started it up and the pipes, radiators and bleed lines got warm after just a couple of minutes, so some water is moving, But it still is heating up much quicker than normal. Went from 58 to 130 in 5 minutes.

The radiator was a used spare in good condition a few years ago, but it was a few years ago. putting on a new one w/ fingers crossed.

Edit: the thermostat is out and I did put an air hose in the top as suggested.

[scorp997]

a thermostat doesn't limit the MAX temp, but limits the MIN temp in a system. A properly operating thermostat will allow an engine to warm up very quickly, then the radiators will have to regulate the upper temps.

If your "130" is in degrees F, you don't have any issue, if in C you probably do.

[Ted Idlof]

I just took the thermostat out to make sure I had max circulation. I'll put it back in when I've fixed the problem.

130F is not the concern, it's how fast it got there. Going up 70 F in 5 minutes is faster than it usually did before. Which is why I've concluded water is circulating, the system is burped and the rad I had on was working, just not very well.

[Dave Cutchins]

Ted, depending on where your temp sensor is, an air pocket in the block impeding the flow would cause the temp to rise faster than normal until proper flow is established. Keep working at it, you probably still have some air trapped.

I installed an auxiliary electric water pump in the right side pod to help keep the engine from overheating when standing still. It also aids in pushing coolant thru the system to get the air removed and establishing good flow before starting the engine.

[Ted Idlof]

I'm out of radiators to put on and out of time to worry about it. I think the system is purged, and an "almost new" rad I got from my Shoe String racing teammate looks to be performing better than the one I had.

Going to the track Friday for the weekend, so we shall see.

New question: The new one I bought from the local Bug shop (as I have in the past) and a nearly identical new one from World Speed that my partner had are both longer than the ones I've always had. So I'm at a loss as to how these longer ones are supposed to be mounted. Is there a longer V hangar and some other gyrations you need to do to attach it to the frame? I see no variations on Mo's parts page.

this whole experience has been a head scratcher. Guess I've been pretty lucky heretofore with the 4-5 radiators I've replaced without a hitch.

[Roland V. Johnson]

check the gage.(electrical or mechanical?)......have seen several not reading correctly lately.

[mikey]

Ted,
As others have noted, t-stats help a motor warm up and if you're not overheating then it isn't stuck closed.
Consider this - what if it was previously stuck open, but 'fixed' itself when you did the swap? When you removed the t-stat, did the warm up time equal what it was before you did the radiator work?

Mike

[sflaten]

On some cars we have had to drill a 1/8" hole in the tstat flange to allow trapped air to bleed out on start up. Otherwise the air fools the tstat thinking I is cooler than the actual hot water temp.

[Ted Idlof]

sflaten, the thermostat had the hole in the flange and I took the thing out first thing to make sure it was not the culprit. I won't put it back in til I run at least one session.

Mikey, my concern is that the car is/was warming up much quicker now without the thermostat than before with the thermostat. Much of the time the temps on track were barely above 160F and maybe got up to 180 with a lot of tape on the screeens. I realized I had a problem when I saw temps jump up to 190 in less than 10 minutes just idling at 1800 RPM in the garage.

Anyway, in summary, I'm sure I had an air blockage at first and then had a marginal rad on there. I think I might be OK now with the rad I have on there since it looks near new but not brand new. I got it from my team mate and he's not real sure where it came from and what the condition is, but my last idle test and driving around the cul-de-sac suggested I might be OK. We'll see.

Roland, the gage looks to be accurate; it reads ambient air temp when stone cold and "feels" accurate when it gets hot; it's just how fast it gets hot is my concern.

[scorp997]

I have to admit I'm not familiar with the coolant system in a Mazda FM rotary, but many engines (my old BMW comes to mind) have a coolant bypass passage that REQUIRES the t-stat to block this bypass when warm . If ran without the t-stat the coolant would never get to the radiator and the car would overheat.

Rotary engines do NOT take well to overheating, and I suspect the era of donor for FM had emmision systems (like the coolant bypass for quick warm up). I would really make sure your engine is ok to run without one before removing the t-stat.

[Albatross]

Observe the t-stat's function by taking it out of the car and watch what it does in a pot on the stove as the water temp increases towards boiling. Put a cooking thermometer into the pot also to observe what the t-stat does co-incidental with the observed temperature rising towards boiling.

[tige00]

Yes a rotary has a coolant bypass and needs to be plugged if not yout not running a t-stat

[tige00]

Yes a rotary has a coolant bypass and needs to be plugged if your not running a t-stat

[brownslane]

Also, thermostats slow the passage of water through the radiators and allow for a greater exchange of heat. it is common to see temps run higher and get there faster with no thermostat installed.

If the rads are up to temp, the hoses are all hot, and a T-stat installed, then you have an issue with heat exchange...to me it would seem the rads may be pooched....

I got the same deal with my V12 Jag. Everything is as good as it gets. All tested. the rad "looked" fine...and was pooched. New rad, INSTANT drop of 20 degrees.

I hope things work out...

Best, Tom

[Albatross]

Sorry, I don't believe that I'm the only one that doesn't understand what poooched means?
And, English is my mother tongue. Please define.

[Ted Idlof]

To brown lane. Re thermostat slowing flow & improving heat exchange. Eric Purcell told me same thing just minutes before I saw ur post. Never heard that before but it makes sense.

Anyway no problems @ T-Hill. Temps were 89 yesterday & I ran 175-180 w/o the t-stat so I guess I have a good rad. Put the t-stat back in & ran 182 this morning in 75F w 8" duct tape on the screens.

[glenn cooper]

"Overthinking it"?

I was really leaning towards something up with the water pump or impeller...

You sort of groaned at the prospect of changing the water pump (if my Coop-sense was fully warmed up), not sure if you are aware of the super sano and quick method of double nutting the H2o pump studs and pulling THEM out and lifting the whole thing out w/ engine in-car.
New pump can go back on with bolts of proper length, preinstalled in pump.

I do recall folks back in old SMPS days running w/o t-stat, so no bypass would need to be blocked on that gen engine at least, which as I recall is made from JDM housings, which are different from N American import, probably w/ emission items?