Overheating '81....well sometimes........

Okay folks, I have a minor overheating (actually just running hot) problem with my 81. I recently installed new intake, carb, and distrib., and tuned with new plugs, new wires, and advanced the timing to around 15 initial, and 36 in by 2800 rpm.

I have replace t'stats (twice), I have yanked the intake and replaced (twice), and I have checked for vac leaks, which I can't find. I don't believe I have any air locks.

Now the problem: When I take the car out and just baby it around without getting on the gas hard, it runs about 190-200. I can drive it this way just cruising around not getting over 45 mph, and it will stay fairly steady.

As soon as I punch it and start running the car hard, the temps immediately start going up in the 220-230 range. If I get on the highway and try to run over 65 mph it will do the same thing. What's going on here? The fan clutch seems to be operating properly.

The car does have the original rusty water pump on it, but it's not leaking. Car appears to have very little circulation when taking the cap of the radiator and looking after warm up. (Should their be a noticeable swirl of circulation?) T'stat is opening, and hose is getting hot.

I am not running lean........

I have retarded the timing to around 12, and ran it their for a while, that didn't help......

Any clues?

I have an even better problem, but I'll wait to solve this one first.....

Starting with the simple things is always my approach and usually works out to be something simple, but here's a long shot...how old is the radiator cap? I was having similar probelms. I replaced the old cap and ended up shaving about 10 degrees off the highway speed temps. I see your '81 has the air dam, but mine was missing, so I installed the factory type and that shaved another 10 degrees off. I'm currently running 190 (180 thermostadt) consistantly and that's without the air flow seals that surround the radiator to funnel the wind.

My .02, I hope it's worth something

New rad. cap.......

[goertz]

shroud still there?

Yep, but I did remove the air dam on top of the rad that went to the old air cleaner hookups.........

[JohnZ]

If the lower air dam is in place, it cools OK around town but heats up at highway speed, there are several possibilities:

1. Inoperative vacuum advance.

2. Collapsing lower radiator hose.

3. Simply an old radiator beyond its service life; corrosion and scale builds up in the tubes and acts as an insulator, cuts the heat rejection capability in half.

The cap has no effect on operating temperature; all it does is determine the temperature at which the coolant will boil (and puke). A 15# cap, with a 50-50 coolant mix, will raise the boiling point to 265*F.

[jdp6000]

The rubber front spoiler directs the air up to the rad...is it still there??

Jim

Yep......front spoiler is their......

I'm under the impression it's either the radiator (which was supposed to have been cored out, and btw...it wasn't running hot before my mods but it was wintertime), the water pump which may be siezed up, or an airflow problem to the rad......

I have the new water pump, so that will be the next elimination.

I don't believe it's the timing or vac advance (which is working by the way), I my lower hose is firm with spring in place.

This is weird. As long as I'm just out of the garage and moving at 45 or below without stopping, it fine. If I sit and Idle it starts to run hot, and if I get on the highway it runs hot.........

[jdp6000]

Which "T" stat do you have? i.e. open and close? Have you tried a 160? Fan usually doesn't kick in until 230 plus or minus so thats not your problem. Is the rad full?

If the water pump is old maybe you should consider changing it. There aren't too many things that will cause your problem provided the engine is running good.

Jim

I have the 160 in now, but I have also tried the 180 with no big difference...

I had a thought.......(ouch)......Is it possible that the fan clutch is slipping at higher rpms therefore the overheating? Fan seems fine when I spin it by hand, and it won't completely free wheel. It seems to spinning fine at idle......Naw, that don't make sense cause it will run hot while I sit in idle, then cool down at an even pace of 40 or so.........Nevermind......

[jdp6000]

Well....I guess we are back to the water pump then. Try changing that and see what happens.

Are you sure your stat works? Temp should climb but when the stat opens it should drop. Mine works like a clock. Do you notice a rise and drop in temp.??

Jim

I have tested the t'stats in boiling water, and they are opening. When my temps come up, they just continue to rise, and never really drop, just stay steady until I go fast or goose it. Yep, I'm thinking water pump, or radiator. For whatever reason I just don't think I'm getting the proper circulation...

My engine will get so hot that you could cook an omlette on it in a minute.....

Next rainy weekend.....it's water pump replacement time, then the rad.........

What are the odds that a rusty 24 year old water pump is still working properly?

[goertz]

if your waterpump was siezed, this would be evident by the large amounts of smoke and burning rubber smell right before the belt breaks. waterpumps ALWAYS PUMP, no matter what, the only way they fail is when they leak, and even then, they still pump. i'd pop for one of those nice aluminum radiators.