rwsduc

Back in June I replaced the factory radiator cap on my 92 with a generic cap from a local auto parts store due to a bad rubber seal. In the days that followed, the coolant reservior overflowed and I got a low coolant light. I had new hoses and a waterpump in a closet for years and decided to replace the old hoses and waterpump, along with an OEM radiator cap. Everything has been fine until just today I noticed the surge tank was very low and the overflow tank is completely full. I replaced every single hose including the hard lines running from the overflow tank to the surge tank. I haven't replaced the overflow tank, but I did clean it out thoroughly when I replaced the hoses. I don't see coolant leaking anywhere, have no white smoke in the exhaust, no coolant in my recent oil change, and don't smell coolant in the cabin. Suggestions as to what to look at next?

sailorsteve

Did you have any coolant problems before you replaced the pressure cap?

rwsduc

Nothing serious, I just noticed the operating temp had been consistently hotter than in previous Florida summers by 10-15 degrees.

After changing the pump, hoses, & cap (OEM), steady running temp is 197-200.

chrldo

you probably need to bleed the air out of your cooling system. there are 2 bleed valves , 1 is on top of the thermostat housing(looks like a bolt in a bushing) and 1 on the front of throttle body , drivers side. i reccomend you buy a factory service manual. YOU CAN NOT GET ANY WATER ON THE OPTISPARK DISTRIBUTOR located under the water pump. air in the system will cause higher temp readings and overboil of tank. you dont want to replace the optispark. check the forum on optispark.

tahoemedic

Head temp should be around 185-200, and waterpump temp should be 200-220

rwsduc

I bled it per the Helm manual almost two months ago and didn't experience any of the problems that I've read about various people encountering after draining the cooling system (overheating, etc). Amen on not wanting to replace the opti! My first one got fried shortly after I bought her in 2004 when an upper radiator hose blew out. I installed a Delteq opti direct and have been trouble free since. Someone suggested on another forum that I do a cooling system pressure test to make sure there isn't a crack in the heater core or radiator (preventing the system from drawing fluid out of the overflow back into the surge tank). I don't want to replace a heater core for sure, or even the radiator, but they're both original as far as I know.

desertmike1

Time for a Block test kit, you have the classic signs of a leaking LT1 head gasket...temps wondering/recovery tank levels! etc.

Hot Rod Roy

An overflowing coolant reservoir is an indication of a radiator cap that isn't sealing properly. This prevents the coolant from being drawn back into the radiator as the engine cools when the engine is turned off. Try bending the tabs on your cap a little to be sure you're getting a tight fit on your radiator neck. Any damage to the sealing surfaces in the neck of your radiator? Your "generic" cap might not have fit right. Some forum members have had similar experiences, but I see you've already tried replacing that cap!

rwsduc

Thanks Roy, I took a good close look at the filler neck today and noticed two hairline cracks at about 10 & 2 oclock (with the inlet hoses being 12oclock) starting at the top of the opening where the larger of the two seals mates with the neck. The section between the two cracks will move slightly with moderate pressure. Safe to say I found my air leak. I'll look up replacement surge tanks tonight as I don't think soldering this will be an option with the plastic tank being so close to the filler.

Minkest

Did the new expansion tank solve the problem?