Temporary Engine Overheating?

[Roger S.]

Drove the '73 Corvette to Carlisle Thursday from Richmond, Va. While waiting in the downtown Carlisle traffic the temp gage went from 200 to 250+ in about 5 minutes. Pulled the car to the curb and turned it off, opened the hood and checked to see that nothing obvious was wrong. We got back in the car and started it up, pulled back into the traffic and the temp started back down. By the time we went two blocks the temp was back to 200. On Friday while waiting 25 minutes to get out of the fairgrounds the temp stayed at 200.
Could the fan clutch be a problem? Any other things to check out?
Roger

[Wayne P.]

Re: Temporary Engine Overheating?

I would replace the thermostat. I have seen them cause intermittant problems before freezing shut.

[Jack W.]

Re: Temporary Engine Overheating?

agree, stuck stat could be the culprit for such shennanigans

[Michael H.]

Re: Temporary Engine Overheating?

Roger,

This may be totally incorrect but it is possible that if you have only had this problem once, it could have been caused by the fact that you were sitting behind a car in traffic that was sending hot exhaust from a tailpipe directly into your radiator. It doesn't take a drastic change in air inlet temp to have quite an effect on radiator performance, especially if the system is on the edge anyway with already high outside temps. I don't see a thermostat that is already open suddenly closing for no aparent reason in traffic but I suppose it's possible.

I was in a parade once with the 66 and I was right behind another big block 67 that was sending hot exhaust into my radiator and my normally cool running motor started shooting up near 240. I backed off and put a little more distance between us and eventually the temp started to drop back to the 220 range.

Michael

[Patrick H.]

Re: Temporary Engine Overheating?

One more thought is that if the system had recently been drained and filled with fluid, an air bubble might have worked its way loose and caused the problem. A long shot, but a possibility.

Patrick

[Stephen W.]

Re: Temporary Engine Overheating?

Well let take another look. Sitting in traffic what is the most vital part of the coolong system? The fan... If the fan decides it is hot and doesn't want to lock up you have no fan or cooling air being drawn through the radiator. By stopping it's possible it decided to work again. You only mentioned a problem while stopped and if it was a bad thermostat it would happen on the road regardless. I also agree an open thermostat has no reason or force applied to close it. With the engine hot and shut off try spinning the fan by hand. You should feel a good resistance when hot. I had my fan clutch go bad in my truck and it reacted the very same way you described.

[Patrick H.]

Re: Temporary Engine Overheating?

My 72 has a marginal radiator, and only overheats at rest.

Patrick

[Roger S.]

Re: Temporary Engine Overheating?

When I stopped to check under the hood I did spin the fan to check on the clutch. With a moderate pull the fan turned about a 1/8 to a 1/4 of a revolution. Sitting in the garage and cool the fan will spin about a 1/2 of a revolution.
Once I noticed the temp went up I backed off of the car in front of me three car lengths and then speed up and slowed down four times to get some air over the radiator, but I figure this was too little to late.
With the 3+ hours of interstate driving could the fan clutch have absorbed too much heat to engage the fan? That evening and Friday with no long distance driving and sitting in traffic the cooling system worked fine, especially in the 25 minute wait to get out of the fairgrounds.
I think I may obtain another fan clutch an install it.
Roger

[Stephen W.]

Re: Temporary Engine Overheating?

I think its a matter of eliminating the possibilities. Someone mentioned an older radiator with marginal cooling that would overheat in slow traffic. That seems to be a consistant and almost predictable situation which doesn't seem to fit your problem. The thermostat is also not likely in your situation. With my truck it reacted very much the way you described. I had a fairly new radiator and thermostat so I knew they were not the problem. I too tried to spin my fan and it felt like it had some resistance but once I installed the new clutch I could tell how weak it really was. The clutch eliminated my problem with overheating in morning traffic. I also feel the 3 hours at highway speeds effected the performance of your already worn or weak clutch.