I live in the southern part of Florida and this week is the first time I have ever driven my 71 in temperatures below 70. Usually the temperature gauge needle sits right at 210 after warming up on the road or in traffic in either case it sits right at 210 and has never over heated. The radiator is two years old (aluminum) the water pump, hoses, thermostat are all about two years old as well. Upon warming up the needle on the temperature gauge moves past 210 ever so slightly and then settles back at 210 I always thought that was from the thermostat opening up. I drove my car to work on Tuesday morning its was in the high 50,s as usual the needle move past 210 and then settled back at 210 however when I got on the open road at speeds of 55 mph the needle on the temperature gauge started to climb to 215 and from there float back and forth between 210 and 215. When slowing down to 40 mph it dropped to 205 then slowly back to 210. At first I thought maybe the lower radiator hose was collapsing at the higher RPM but when setting still in neutral and revving the engine 2500 and holding it there (same RPM as 55) it stays at 210. A friend suggest that it could be possible that the cooler air pushing through the radiator is enough to close the thermostat? I have never heard of a thermostat closing after a engine warms up. The actual engine temp is unknown the sending unit is a aftermarket that was recommended by members of this forum as being closely calibrated to the factory original so I really do not know if 210 is really 210 or 180 or what.
Thanks for any suggestions or thoughts

 

First, Vero is in the middle of Florida.

Your friend is correct, tstats do modulate and depending on the capability of the radiator, the tstat could be almost closed. It usually only happens at very cold below freezing temps.

Your temp swing is only 10° total and that's well within the tolerances tstats are rated for.
Sounds like you may have a 195° one in there. That's what I use in S Florida (Ft Lauderdale).

You may want to use an IR temp gun on the tstat housing or better yet a remote pyrometer so you can test actual temps while driving. Always good to know.
You also may want to insure you have the best tstat available, good ones usually don't swing much.

 

My daughter's 4 cylinder import started varying the temp reading----normal...then cold....then normal....two weeks later she said the temp needle started climbing to normal---past normal--it finally pegged out---the engine overheated....by the time she could park in a safe location (2 minutes) the coolant was boiling out thru the overflow tube....the head was toasted---but still in warranty.

(I removed the original T-stat....it was jammed/cocked CLOSED---SEEMS IT COULDN'T FIND ITSELF TO JAM OPEN !-----evident that it was damaged upon installation since the brass bulb had drag marks where it constantly rubbed against the metal housing while in use...If she would have told me sooner, I would have replaced the T-stat before it seized closed.

Be careful with your Vette engine!

 

Hey Noonie
Thanks for confirming my thoughts and the possibilities. It was not as cool this morning in "the southern part of central Florida" and the gauge was a little more steady. I will replace the thermostat this weekend with a better one and see what happens. I have been wanting a IR gun now I have good reason to buy one.
Thanks Again
Scott

 

Hey DG
Things like this are always in the back of my mind. I will be replacing the thermostat this weekend.
Thanks, Scott

 

I think I'd stop worrying about minor fluctuation on the gauge and watch the road instead.

 

Advise taken Mike,
Thanks

 

Your daughter's car overheated. Based on what he posted, Roco's car is not overheating.