Okay, I just noticed something weird. My car runs at 190 steady as long as it's on after warm-up. I shut it off today after driving and stayed in the garage to work on my other motor when I noticed that over the next 45 minutes or so that the temp gauge indicated that it went from 190 up to around 235, and then back down. I've thought up three possibilities.

1) My gauge is messed up. Unlikely cause it seems accurate but possible.
2) The heat tries to bleed out through the temp sender, making it indicate higher.
3) All cars do this and I just never noticed.

What's up guys?

Thanks.

 

electric gauge or mechanical? if its electric id say your sending unit is bad.....mechanical gauges tend to do that b/c they dont have air flow keeping the wire cool....(heat radiation).........But im sure its just a gauge problem.....motors dont get hot when they set not running

 

Yeah, I didn't think so. I'm pretty sure it's mechanical because its a big fat hose, like 1/4 inch or so in diameter made out of rubber. The red-necks that owned the car before me put it in when the voltmeter/oil pressure/temp gauge in the dash cluster went out.

 

Mine is doing exactly the same thing. I just rebuilt the engine and the entire cooling system is new, even a new fan clutch. Put in a 195 stat and it runs at 195-200. When you shut it off, after about 1-2 mins. the gauge goes up to 235-240 and the overflow tank starts boiling from the bleedoff. I changed the stat to 180 last night but I haven't driven it enough yet to see what happens. I expect temp to go up some right after shutting off the engine but not 45 to 50 degrees. I hadn't thought about radiant heat to the gauge capillary but the you can hear it boiling after a couple mins. I ran it with the radiator cap off to see if maybe the head gasket was leaking but no bubbling in the radiator. I'm stumped. Ideas anyone?

 

Mine does it too. It always has, and all of my cars always have. I'm pretty sure its a normal thing.

When the car is off there is no longer any water circulation to cool the water jacket, and the parts that were hotter heat the water further.

dlturner- boiling is certainly not normal! I would try to pressure test the system. at 240 it should not be boiling i the system holds proper pressure.

 

I've never pressure checked one. What's the best way, pressure gauge in the temp sensor hole? What kind of reading should I get?

 

Replace the radiator cap, I was told to do this but have yet to do so because my car is a garage diva. My car does just as your describing, it runs perfectly fine temp wise, but after i shut it off the coolant boils out of the overflow. Try it, and let me know if it works, besides a new cap is only 6 bucks so how could you go wrong?

 

The first culprit, like LegalDisaster said, is probably the radiator cap. The cab should hold about 15 psi of pressure before releasing into the overflow. If it releases early you will have low pressure and a boiling problem.

 

I haven't noticed mine boiling though. Is there anything I should correct? How important is it that I correct this?

 

Some heat build up after the motor is no longer circulating coolant through the radiator is normal.

JamesC

 

180 stat and/or new radiator cap seems to have solved the problem. Drove it for 30 min in 90 deg temp and no boiling after shutdown. Holds 185-190 while driving.