Overheating Question

[jimalley]

Had overheating issues at new Hampshire Sunday in my Miata. Dash light came on and Temp was close to 140F. I shut it down and pulled in. Hope I havent damaged a new engine. I unloaded tonight and strted to look for reason. After investigation found out that there was no thermostat in place. Is this my problem?

[boywonder]

I'm no mechanic but...

Are you sure it wasn't 240º? My car isn't warm until over 160º. And no, not having a thermostat shouldn't cause you to overheat. If anything not having a tstat would make it harder for you to get heat during the colder seasons.

Check the wiring to your dash light.

[JeffYoung]

240 is borderline but you should be ok. If you hurt anything it would probably be the head gasket. Do a compression check and see what you get and go from there.

The lack of the t-stat COULD cause a problem, but I doubt it. Some cooling systems need the restriction the t-stat provides. Wtihout it, the coolant actually flows through the radiator too fast and does not have time to cool. Not sure if that is the case with a Miata cooling system -- go ask on the SM board. THey probably have the answer off hand.

[xr4racer]

I do not know about Miatas, but the lack of a thermostat in most racecars forces too much water too fast through the radiator not allowing it to cool. Most racecars have a thermostat or at least a flow restrictor.

matt

[xr4racer]

Since Jeff beat me to the punch, make sure you do not have an air pocket in the system.

matt

[rhygin]

Jim... guage sensors seem to be a maint item in my mind. So... get it pretty hearted up and flowing in the drive way (garage if you are lucky) and pull the cap and stick a temp sensor into the water moving passed. I have used a turkey thermometer and a temp sensor from a multimeter... try it... see what happends and let me know. i am betting on a bubble in the system even though you think there is no way that can be the case. Was with me....

at 240... bad stuff is or is about to happen... that is a lot of heat for a miata in my experience.
BB

[kevin22]

I also run no thermostat, so i don't think thats our problem. I would start with flushing the system and using a air compresior to blow out the radiator fins, also I would change the cap.

[joeg]

Did you actually confirm it was overheated (see coolant coming out of any expansion tank), ever try the heater? vapor smell?

[Wreckerboy]

Most of the SM and SSM cars I've seen at Summit, mine included, run either no thermostat or a gutted stock one. I would suspect your lack of stat is not the problem. Miatae are particularly sensitive to missing pieces like the splash shield under the radiator, which contributes greatly to cooling. Also, make sure that the area between the core support and the bumper is blocked off to assure cooling air flows through the radiator and not around it.

Lastly, you said this is a new engine. (Lots of assumptions follow.) Depending upon what you had in place before, it is possible you are now making more horsepower and thus heat than you were before. It is possible to overwhelm the stock radiator even with a SM/SSM build. If any of this is the case, it is time to consider an aftermarket radiator. When my new motor went in last year (SSM build) it quickly caused my temp guage to read much hotter than it had previously, and that was with the ducting and shields in place and a good stock radiator. A decent aftermarket piece solved the problem for me.

YMMV.

[Russ Myers]

DO NOT get it heated and then pull the cap, that"s a damn good way to scauld yourself. cars must have some type of restristion in the passage to force coolant to the rear of the engine. With no restriction, coolant just cools the front of the engine. Lisle Tools make a real cool funnel that attaches to the rad neck, find it at NAPA. That alows you to run the engine with no cap, and not make a mess all over the driveway.

Russ

[MMiskoe]

Temps at the radiator cap and temps at the #4 piston are two different things since the front cools more than the front due to the coolant routing. Taking the temp at the radiator won't tell you much.

Check that you didn't have an air bubble in the system. If you let it idle w/ the cap off and the fluid level doesn't change much, you've got it full. If the fluid level rises as the temp increases this indicates there is an air bubble somewhere (air expands a lot as it heats, water not so much).

A quick check of the radiator is to pull it and put your hand over the bottom outlet and fill it w/ a hose. When its full, pull you hand off the bottom. If it doesn't gush out the radiator is not flowing right. Not very scientific but its a start.

[rhygin]

Correct... do not pul a hot cap... see if there is a gap after it has heated. I bet it is an air bubble as I went through the whole "oh no, I broke the engine" deal and it was an air bubble deal.

[jimalley]

Thanks for all the feedback. I have been away from the computer so I ahvent been able to respond.

1. Yes the temp was 240F.
2. I Am going to install a gutted thermostat to slow the flow and see if that doesn;t cool better.
3. I am running a Ron Davis radiator so I think it should be adequate for the engine!
4. I will investigate for air pocket.

Thanks again.

[ner88]

Jim
240 reading with a real gage?
YOu're not assuming the factory gage is correct, right.
We have a 220 lite setup in one of our cars and it often goes off below that??
You should run a t-stat, ecu monitors temp and can change things if getting wrong readings.
Have you checked fuel mixture and timing on a dyno? Otherwise you're just guessing......
Was the radiator cooling fan working?

[jimalley]

The temp is comming from the cpu to my AIM Dash. Not sure of the accuracy of the AIM uniy but I assume it should be close!

The cooling fan is not working. Will change the fan first and then see if the relay and CPU are doing there thing.