06-12-05, 09:13 PM
When driving the car for a while, came home and turned off car, coolent poored out the bottom and I popped the hood and it was boiling inside the coolent resevoir, could this be the thermostat not funcionting right? Car is an '89 d'Elengance.
(Sorry, slow connection and it double posted)
It could be, the overflow is intended to catch the boil over.
The basic reason for the boilover is the engine was running, and all was ok, but suddenly the pressure that was there just dropped, as the pump isn't turning anymore, keeping things in check. So it boils instantly.
1. Check coolant concentration, should be around 50/50 mix.
2. Check coolant temp (on board diagnostics? my 94 FWB can) Is it near overheating now? A bad thermostat can cause this if it sticks closed.
3. Check for bad cap, it should hold pressure to 15 psi. Remember, you don't get boilover unless the pressure in the system exceeds the cap pressure. GM caps last a LONG time if kept clean from crude on the seal. My Cutlass went over 200K on the factory cap, and it still tested good.
4. Pressure test cooling system. If not enough pressure, it will boil at too low temp. This may also show stuff from step 5.... Remember, water will not boil until around 220-225 degrees F under 15 psi pressure, but lower the pressure suddenly, and it is instant boilover.
5. Check for bad head gasket (emissions test of an open radiator cap)
Too much coolant vs water can cause headaches. Water boils at 212F under standard pressure. Antifreeze mixed 50/50 boils around 260-275F. with a 15 psi cap. But pure antifreeze will boil much lower. Pure water can handle more heat and pull it away from the engine faster than antifreeze/water mix. But the temp range it can handle is much less.
My 85 Cutlass with a 77 Olds 350 did as you describe after I did a hard WOT run from 60-100 mph. And it did blow the gasket (cyl #7). I stuffed some stop leak in and it behaved for a while. I sold the car, made him aware of it, and it drove for a few more years before it leaked after sitting for 8 hours at the person's work, and hydrolocked the engine and broke the nose off the starter when they cranked it. Then the car sat for about 6 months, eventually got sold to a new owners who was clueless, and had some kids who claimed they knew how to swap head gaskets, and they "fixed" it. It wasn't pretty. They had no clue what a torque wrench was. It is sad... It runs, but not like it should. Rocker arms took the hardest hit. I don't even want to know if they knew what a torque sequence is....