'61 230 HP overheating

[Peter V.]

My '61 230 HP, after more than 20-30 minutes running time, reaches an operating temperature of 160-180 (rarely higher). After shutting off the engine, coolant "percolates" into the expansion tank and out the overflow tube. Never more than a cup, sometimes less. If I'm home, I catch the coolant in a pan, otherwise I end up soiling someoe else's property.
My radiator is a replacement brass unit, not the factory designed aluminum Harrison. It appears to be somewhat smaller than the Harrison.
I theorize that the lower capacity of the replacement radiator is unable to accomodate the expanded volume of coolant and venting it out throught the overflow, rather than making its way back into the radiator.
Any thoughts????

[Duke W.]

Re: '61 230 HP overheating

Stop topping it off with coolant. Let it seek it's own level, and if it doesn't overheat, you're okay. I'm assuming you still have the remote expansion tank with the pressure cap and no pressure cap on the replacemehnt brass radiator.

Shutting off the engine causes "heat soak" - residual heat in the engine heats up and expands the coolant. Once it runs out of expansion air space the coolant will overflow.

The expansion tank should only be about half full - COLD.

You should also check that your Vacuum advance control is functional and meets spec.

Duke

[Peter V.]

Re: '61 230 HP overheating

Duke,

The expansion tank is never more than half full. Do you think the capacity of the brass radiator is the issue?
Also, what does the vacuum advance have to do with it?
THANKS!!

[Duke W.]

Re: '61 230 HP overheating

It shouldn't expel coolant unless the exansion tank runs out of air space? What's the pressure rating of the cap and have you tested it? (Most auto parts stores have cap pressure testers.)

A dead VAC can cause heat buildup at idle. Since they are easy to check...

Duke

[Peter V.]

Re: '61 230 HP overheating

Duke,
I believe the cap is 14 lbs. but should check again. It's the standard repop from CC for the '61 expansion tank. I haven't tested it.
Others have suggested I just keep letting it do this until it stops, suggesting (as you have) that the coolant needs to seek the proper level in the system. Since it does not run hot or leak fluid during operation, that may be all I can do.
Once again, do you think the capacity of the brass radiator is a contributor to this issue?

[Timothy B.]

Re: '61 230 HP overheating

Peter,

When during normal driving does the cooling system go under pressure? I would start by having the repro cap tested for max pressure relief.

[Duke W.]

Re: '61 230 HP overheating

When you say "capacity" I'm not sure if you're talking about heat transfer or physical capacity, but if it's not overheating it has sufficient heat transfer capacity, and the physical capacity is not an issue.

Pressure test the cap, replace if necessary, and from the expansion tank half full when cold, let the coolant seek it's own level and see what happens.

A fourteen psi cap won't release until the coolant gets up to about 260F, so your "repro" cap is suspect. If you need a new cap, buy a proper name brand OE replacement from a local parts store. A lot of this "repro" stuff may look "original", but doesn't meet OE performance specs.

Duke

[Jack H.]

Re: '61 230 HP overheating

Also, check for 'crud' embedded in the cap's rubber gasket and/or on the sealing lip of the expansion tank. Plus, mechanics with a Stant pressure checker, can run it two ways:

(1) Connected to an adaptor to verify the rad cap.
(2) Connected to the cooling system in lieu of the rad cap.

The second application of the pressure checker will verify the basic cooling system's 'plumbing' integrity. Do you have loose inter-connect hose(s)???

On 'could' the replacement brass radiator be a cause factor, nobody is really qualified to comment since we don't know WHAT replacement brass radiator you've installed (mfgr/make/model)...

But, as Duke said, each car is going to have its own 'quirks' associated with the EXACT level of coolant fill that's 'just right' for that car. Most mechanics intentionally over-fill the system (compensate for trapped air bubbles in the block, Etc. that will naturally 'burb' themselves out during initial heat/cool cycles). They typically advise customers to EXPECT some 'minor' degree of coolant expulsion for the first 2-3 hot engine shut-down episodes.

The amount of coolant expelled should decrease progressively and STOP with the system finally reaching its 'natural' fill level. So, as others have advised, if the car isn't running HOT when you're underway on the road, don't worry. And, don't keep re-filling the system--you're only pro-longing its attempt to find the correct fill level...

[Peter V.]

Re: '61 230 HP overheating

Thanks for all the help. I'll get the cap tested (or replaced), and keep an eye on the operating temp.

[Doug F.]

Re: '61 230 HP overheating

duke is correct, repo caps are for show purposes only, cc and others sell a late model stainless steel AC delco cap that don't look too bad and actually works, i'm running about the same setup as you in my 61 270 hp and don't have a problem even here in the desert southwest

[Stan G.]

Re: '61 230 HP overheating

I put a C C repop on my 58 230 hp at first , always ran hot , put cheap auto parts cap on let it seek its own level runs fine now .Resist the temptation to top it off every time . As long as it runs cool leave it alone .

[John G.]

Re: '61 230 HP overheating

you might try running the heater to "burp" the air

[Peter V.]

Re: '61 230 HP overheating

Finally got around to replacing the repop cap with a 15 lb. NAPA cap listed as correct for the '61 Corvette. No more post-running overflow! Not correct for judging, but fully functional for driving.