Question1966 Oldsmobile Delta 88, 425ci
After driving a few miles, or 40 miles, when the engine is turned off, the radiator drain rubber hose next to the radiator cap releases between a pint and a quart of coolant in either case. Coolant system holds correct pressure, tested by Mechanic. I replaced the radiator cap, no difference in coolant drainage. Coolant was 50/50 concentration. 1-1/2 months ago engine overheated (cause was leaking heater valve). I had the thermostat (180° per specs in my CD manual) replaced at that time as well. The engine does not overheat when I'm driving in stop and go traffic or 65mph. My Mechanic suspects the radiator is blocking water flow, or the water pump is not circulating the coolant enough. Could the thermostat have gotten stuck in a near closed position? I don't have a temperature gauge on this engine yet, so I couldn't monitor the temperature changes.
AnswerHello Carl,
It looks to me that you've looked at the right things thusfar. Assuming your mechanic is correct, that flow is the problem, a complete reverse flush of the cooling system to clean as much gunk out of the block and the radiator is a first step. Flow still a problem? Check the radiator for for deposits and plugging. Having it boiled out by a radiator shop is good preventative maintenance anyway for a car that old if it hasn't been done recently. While the thermostat could be partially closed, you'd have much more problems with overheating while driving than you do. Also, don't forget to check your radiator hoses for
"soft spots", sidewall separation or collapse. It's not unknown for a hose to look OK at idle and then partially collapse while on the road.
More unusual but possible, water pump could be part of the problem here too. There are pump flow specifications and ways to measure throughput although few do this and simply replace the pump. There also are such things as high output pumps made for cars like performance Chevys (what else!) but I don't know if any are made for a 425.(they might because 425 were used in 4-4-2's)
Failing all of the preceding, there are other alternatives to enhance cooling/manage the "burping". For the former, going to an aftemarket, either/both, larger or aluminum radiator can do the trick. Another enhancement is an external, electric radiator fan. Finally, if nothing works and the car still performs acceptably, consider installing a coolant recovery system similar to what the OEM's have made almost standard equipment since the seventies. Sources such as Summit Racing Equipment carry most if not all of these items or could point you in the right direction. The big downside of all this if you're into originality is that none of these options were standard equipment in 1966 and will require modifications to the car to install and use.
Obviously, this is a complex but common old car subject. The one thing you didn't state was whether the burping was present before the overheating event or started following it. If the later is the case, it's certainly a clue that would lead more toward the engine internals such a warped heads or blown head gasket(s).
You just need to peel back the onion one layer at a time, test, then move on to the next alternative. I always go with cheapest/easiest first for obvious reasons. Dirt and/or deposits are the most likely cause, followed by mechanical then to band aids like the cooling fan.
Good luck on that great car!!
Bob
