Ok one of my friends has a 95 integra ls with 36,000 original miles on the motor and car....When he is driving on the fwy at about 70 for a couple mins then when he slows down approaching traffic he noticed that the temp. gauge went from the normal position to dropping down in temperature....Almost going back to full cold!!! Then when traffic picks up the temp. gauge goes back to the normal operating temp position....One person suggested it could be the sign of a bad headgasket...Radiator is a couple months new along with the hoses... any suggestions??

 

Since it doesn't really cost anything, my first step is usually to fully bleed the cooling system. Especially since components have been taken apart in your case. Air trapped in the system can do strange things, and it can be a bitch to get it all out.

I like to use the kit that comes with a big yellow funnel and various radiator fittings. They're like $25-30 I think. You attach it to the radiator and fill it like half way. This way, you don't have coolant bubbling out, don't have to add coolant constantly, and the high point of the system is raised so bubbles come out better. After you get it attached, start the car and make sure the heater is on since coolant also flows through there. While the car is warming up, occasionally feel the hoses. The top should get hot while the bottom should feel cool/warm. If the t-stat is working, when the temp gauge gets near the middle it should open and the bottom hose should also get hot. At this time you can see if the fan is working since it should start cycling on/off. Another good thing about the funnel kit is it's easy to see if oil is in the system since it will work it's way up and mix with the coolant in the funnel (headgasket).

I don't think it's a stuck open thermostat since the engine would never really get to operating temp. Water pump would cause overheating. I don't know if a headgasket can cause this. Is he losing coolant or blowing smoke?

 

Sounds like air in the system. Bubbles love to float around where the temp sensor is located.

First off you should jack the front of the car up, remove the rad cap, and start it. Allow the engine to reach operating temp. and the thermostat to open. Top off your radiator as the air escapes. Reinstall the cap and go take it for a test drive. Temp gauge back to normal?

While you're doing this, look for oil specs (black/milky looking dots) in the coolant.

Also check that all of the hoses and radiator he installed recently are not leaking..

 

His thermostat is stuck open

 

I would check the cooling sensors on the left f the head. that was my problem on my 95dc2

 

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Also check the one wire temp sensor sensor. I had a similar problem and a new one fixed it.


P.S. the pic actually shows how to test it also. Unplug it, connect a gator clip to the yellow/grn wire and the other end to a body ground, turn ignition on then turn off before it goes all the way to H!

if the needle moves, then the gauge is ok and the sending unit is bad.