Just remember a simple concept - the thermostat does nothing to control the upper temp range. All it controls is the lower range (I have seen mentioned in other threads installing a 'hi-flow' thermostat but all I get are weird looks from the guys behind the parts counter when I ask for one!). All issues related to high operating temperatures are problems with heat exchange not being carried out properly.

I have to agree with other checks mentioned already - belts, hoses, water pump, airflow issues, and radiator condition. In a thread in the Body forum it was mentioned that removing the front license plate and bracket will add some more airflow. But if you live in a state where both front and back plates are required that may not be a 'legal' option to try.

Garry,

Did you ever solve your problem?

Cooling in C3's has always been critical and marginal as they've grown older. You need to start from easist to check to the most difficult to take care of.

One question first...have you built up the engine in any way? More horsepower without increasing cooling system capability can cause problems as well.

The history of these cars suggests you check the seals around the radiator as many have suggested. You also need to make sure you actually have a problem. I also have a Brand X muscle car I thought was overheating and it turned out to be a bad guage. From your description that doesn't sound likely.

Since it runs normal temp at idle and low speed, I would concentrate on three things...pressure test your radiator and cap to make sure they are holding pressure (let the pressure stay attached for at least 12 hours at 15-16 pounds pressure). The other considerations are the lower radiator hose and the radiator possibly being restricted. The lower hose is not under positive presure like the upper, and can collapse at higher speeds if its internal spring has deteriorated away, and restrict coolant flow.

If you end up re-coring your radiator, see about getting a core with more fins per inch. That will increase the cooling area and efficiency without increasing the physical size of the radiator.

There can be other potential causes of your problem, but these are the ones to concentrate on first.

Gunslinger
Frederick, MD
'78 Silver Anniversary L82

i've been doing little things nothing has helped so far this is what i have planned to do one weekend , there are some small areas around the radiator and i mean small, that i will plug them with foam but do see how they can affect the air flow getting around the radiator much. my daughter gave me a chrome licience plate for fathers day and it would break her heart if i removed it , i plan on lowering it maybe 1 or 2 inches to allow more air flow. i have already removed the center grill behind the plate. i have noticed the level in the radiator slightly low everytime i check it. i don't see any leaks and plan on retorquing the heads, thinking maybe a leaking headgasket. i will replace the orgional water pump and put it away in a safe place and install a new one. I haven't decided stock or high flow one, as the hoses and radiator can only flow so much and if the fluld travels through the radiator too fast it cannot release enough heat. i will replace both upper and lower hoses. and plan placing a spacer 3/8-1/2 inch between the pump shaft and the fan this will place the fan blades fully inside the shrould so they pull the most air through the radiator. if this dosent help the the orgional radiator will be pulled and cleaned. i had the AC working for a short time till the orgional main hoses blew so now have that to install.

Gary

Try removing the license plate for just a test run. See if it makes a difference, as it sure did on my car. You can put it back on, but if it works, then you know where your problem is. Then you decide, run cool/break her heart or continue running hot. Only you can decide.

Mark

I had a simular problem & found that my front spoiler, was bent back under & the center peice was missing .. I bought the parts & it was an easy fix.
I've since just added a "BE Cool" radiator & dual electric fans, and in town & on the highway it just barely gets to 190* + it has a tranny cooler and I;m sure that that must be good for it.

i know it ran cooler befor i put it o thats wht i want to try lowering it to see if it will allow enough air to pass over it. all the front spoilers are in place and good condition