Sure wish I could figure this out. Thought it was the cam and timing. Other than trying a stock rebuilt clutch, not sure what to do. I have the same clutch and radiator you have.

 

Just wanted to verify something that was stated earlier in this discussion. If I move the fan slightly more into the fan shroud that it will reduce the airflow rather than increase it?

 

John answers this question on the first page of this thread. I just went back and read this whole thing. It's gotta' be something simple.

If your engine temp starts at cold and steadily climbs off the top end of the guage, whether you're idling or moving, you have to have a flow or heat transfer problem. It wouldn't be the fan or fan clutch. It wouldn't be some minor problem in your timing curve. It likely wouldn't be anything to do with a lean mixture. If it was mixture problems you'd have bad driveability problems, not just a little stumble off idle like you report.

I haven't seen anything posted that indicates you are pushing coolant out your overflow past the radiator pressure cap. Is this happening?

Going back to the fixation on the fan issue, I've run my '63 fuelie all Summer with NO FAN on it. 90-95 degree heat. Runs down the highway at 175 with a rated 180 thermostat. I can drive it into town, around the courthouse square 4-5 times and through 7-8 stoplights out to the Wal-Mart lot and by this time, the guage will be about 185-190. The vacuum timing is plumbed into manifold vacuum currently. I've also had it plumbed to venturi vacuum as it was designed. It makes little difference on engine temp under those same driving conditions.

The engine in this car that preceeded the current one was a stock configuration 327-300. Unknown history. 180 thermostat. With a fan, it ran all the time 185-195.

Both engine temps were verified by a mechanical surface temperature guage. I have no idea why the first engine ran hotter than the replacement unless the head and water jackets of the first engine were partially plugged with sediment. The second engine was overbored .060, the first I don't know.

Maybe this will get you thinking in a slightly different direction.

 

May be a shot in the dark but several years ago I experienced similar overheating symptoms on my Grand Wagoneer after installing a rebuilt water pump. I pulled the radiator cap and noticed a low coolant flow. Turns out the impeller in the water pump was slipping on the shaft. No more rebuilt parts for me.
Bud

 

I am surprised that the cam switch didn't fix it. There is no apparent reason why it should be running hot. Did some water passages get blocked during the rebuild? The radiator should have plenty of margin for cooling any small block engine. Having read all that you have done, I would definately switch the fan clutch to see if that is the culprit. What a mystery! Good luck finding the problem.

Dave

 

I appreciate the comments. To answer Mike's question, I usually don't let it get hot enough to spew coolant. If I let it get hot enough, it will spew a little.

When I put the new cam in, I took the heads off to check them out and look at the coolant flow. Everything seems ok there. The water pump is new and seem to be flowing coolant. I could put a high flow pump on, but from what I have read that probably won't make a difference.

 

Given the comments though, if it a flow problem, it might make sense to swap the water pump.

 

Forget the high flow pump.

"If I let it get hot enough, it will spew a little."

This could lead me to believe you're overfilling the oflo bottle. Are you filling it to the cold mark? If the engine is truly getting hot, it will not spew a little, it will spew a whole lot! And it will gurgle and rumble and grumble. Is it doing this?

You "could" stick a clear vinyl hose on in place of your top radiator hose and observe the coolant flow through your cooling system at different rpm's. That may tell you something.

 

Mike

I know this is a super old thread on overheating but its a new issue to me. I have a 63 327 powerglide. It idles fine, runs fine but....not at idle. The temp will climb and it will spew out the overflow cap if Im so inclined as to let it. When running 180 is the temp but at idle or in traffic there seems to be no limit as to how high it will go. It goes slowly but it goes.

The only non stock item is an open air filter set up, maybe from a 67, vs a dual snorkel. Shroud, etc all good, fan recently replaced, radiator is about 8 years old and looks good. Coolant looks like it came out of the bottle.

Any thoughts?

Thanks
Frank

 

You should start a new thread but check thermostat, fan clutch and that the lower radiator hose has a spring in it and is not collapsing..

 

Read the Duke63 stuff. It is absolutely, positively a dead vacuum advance on the distributor.

 

Thanks, I will try to find that. Im new to the hobby, wouldn't the vac advance issue cause other issues at idle etc?

Regards
Frank

 

sounds like no air flow thru rad at idle and car sitting still.
which points to fan clutch

 

That's a logical conclusion but that's not it. Trust me, that's what I do and nine times out of ten it's the timing issue. Of course you need to make sure the fan clutch is working but rapid rising idle temps is usually the vacuum can.

 

This problem is real easy to check....
Get set up with a timing light and check the timing as specified in the manual. Before disconnecting everything, plug the vacuum hose back onto the distributor and the timing will jump an additional 15-18 degrees over the static timing. If it doesn't, you have a problem.
This overheating problem is real easy to prove...
If the timing does not increase 15-18 degrees, then simulate the advance function by turning the distributor. Add the 15-18 degrees manually but do not drive the car. Let it idle and see what happens then. You should be able to idle for 45-50 minutes with no issues. Again, do not drive the car like this. Change the timing back to the static setting before driving and get a new vacuum can

 

Read this - it will help you understand how your Corvette cooling system works and will help you diagnose your problem.