1966 and later BB thermostats

[Ronald L.]

Re: 1966 and later BB thermostats

With my current configuration, rebuilt pump, ne hoses, heater core radiator and new fan clutch, mine tends to hug the 210 point as long as we are at speeds of 25 or more. With these cooler days it stays at that 10 o'clock bar to the left of the 210 mark except when we go 80 plus on the highway where it is back up to 210.

[Joe R.]

Re: 1966 and later BB thermostats

This is where I got mine, and it works great. However, a hot running (210 degrees+ and over 230 in stop and go driving) BB is not a myth but a very common occurrance. It can be solved, but take it from a person who did about a dozen things (many suggested by Duke) to fix it, it takes much time and work to solve the hot running BB.

Michael,

My L72 used to run just fine with no overheating issues (once we replaced a bad fan clutch!) even in 95 - 100 degree weather. I found the thread I was thinking of, the owner reports are a bit of a mixed bag. So it doesn't dispel the myth as handily as I originally thought. But you're right, it can be solved. I wonder how they ran when they were new. I have a real hard time believing Chevy would have released "hot runnin'" big blocks to the public! Anyhow, here's the thread I mentioned:

https://www.forums.ncrs.org/showthre...79886&uid=9347

Joe

[Timothy B.]

Re: 1966 and later BB thermostats

Don't you guys know the weather was not that hot back then..

Ever heard of global warming

[Michael J.]

Re: 1966 and later BB thermostats

HeeHee, love the Algore factor for this subject! But I also think Joe's thread link pretty much captures the range of outcomes with an old BB. Some are fine, some overheat, and some are trailered so much who knows . I do know at a recent regional I asked all the BB owners about it, my informal survey indicated 75% had "heat problems" (not sure how bad) mentioned by the owners. One of the biggest issues I think is how the bone-headed GM engineers failed to put an expansion tank on the BBs, so when it gets hot it pukes what looks like gallons on coolant on your garage floor. Being a careful and proper car guy, you put more in (since the radiator looks half empty when you take the cap off after it cools down), and when she goes over 220 again, it happens all over. I even went so far as to put a coolant recovery system (closed system) on it. It didn't help the overheating when it stops, but at least I didn't have to clean up the garage floor all the time after driving it around.

But, there are fixes I think probably work, but I too would be curious if new BBs had issues. A 44 year old one with so many things that get old and messed up is one thing, but surely GM wouldn't have had that with new cars. I never knew anyone with a new BB C2 or C3 'Vette (I lived in a poor neighborhood), but maybe some veterans here can remember.

[Michael W.]

Re: 1966 and later BB thermostats

One of the biggest issues I think is how the bone-headed GM engineers failed to put an expansion tank on the BBs,

Huh? All Corvettes prior to '73 had expansion tanks. They were either internal to the rad or external. Neither system was meant to be filled up to the top. All cars go through a heat soak phase after shutdown, with or without an expansion tank.

[Domenic T.]

Re: 1966 and later BB thermostats

This is where I got mine, and it works great. However, a hot running (210 degrees+ and over 230 in stop and go driving) BB is not a myth but a very common occurrance. It can be solved, but take it from a person who did about a dozen things (many suggested by Duke) to fix it, it takes much time and work to solve the hot running BB.

If your BB has the correct end gap on the rings you can damage them or find them broken at 230. But if they were not file fit (as in a standard rebuild) they have a random end gap and you may be lucky as they just scratch the cylinder walls a little.
I would look at your cooling system. I live in a hot place and you can't drive them that hot if you care about them.

DOM

[Michael J.]

Re: 1966 and later BB thermostats

If your BB has the correct end gap on the rings you can damage them or find them broken at 230. But if they were not file fit (as in a standard rebuild) they have a random end gap and you may be lucky as they just scratch the cylinder walls a little.
I would look at your cooling system. I live in a hot place and you can't drive them that hot if you care about them.

DOM

I have, I did the "dozen things" and it is fixed.

[Michael J.]

Re: 1966 and later BB thermostats

Huh? All Corvettes prior to '73 had expansion tanks. They were either internal to the rad or external. Neither system was meant to be filled up to the top. All cars go through a heat soak phase after shutdown, with or without an expansion tank.

My '67 L71 had the original Harrison brass radiator, and if it had an internal expansion tank, I failed to see it when I opened the radiator (RC-15) cap. The radiator, after running at 210-220 for a while, when cooled, showed the coolant level in the radiator to be about 7-8 inches below the neck. Is that the "expansion tank" you are talking about? If so, I much prefer the one on my '66 L79 which never overflows at most temps it runs at. To just add room at the top of the radiator shows poor engineering design IMO, it is probably why the BB radiators have such bad corrosion and deposit buildups in the top 8 inches.

[Joe R.]

Re: 1966 and later BB thermostats

One of the biggest issues I think is how the bone-headed GM engineers failed to put an expansion tank on the BBs, so when it gets hot it pukes what looks like gallons on coolant on your garage floor. Being a careful and proper car guy, you put more in (since the radiator looks half empty when you take the cap off after it cools down), and when she goes over 220 again, it happens all over. I even went so far as to put a coolant recovery system (closed system) on it. It didn't help the overheating when it stops, but at least I didn't have to clean up the garage floor all the time after driving it around.

Michael,

I went through the overfilling of my radiator with the subsequent puking coolant all over the garage floor a couple of times. Then I noticed that there is a fill cold line on the radiator below the cap. The expansion tank is built into the radiator.

Joe

[Michael W.]

Re: 1966 and later BB thermostats

Joe is correct. Overfilling a system and eliminating a portion of the expansion room will make them puke everytime, makes no difference if the tank is internal or external.

[Michael J.]

Re: 1966 and later BB thermostats

Joe is correct. Overfilling a system and eliminating a portion of the expansion room will make them puke everytime, makes no difference if the tank is internal or external.

Yes, mine had that fill line, but it was about three inches below the neck. Filled to that line (I never filled to the top), it would overflow about a pint or two if the temp got above 210., and of course the heat soak after shutdown. I found by filling it 7 inches below the top it would not puke during normal driving around I do. But, all that changed when I replaced the old clunker radiator with a DeWitt's direct fit aluminum. The heating also changed of course, it doesn't overheat anymore. And I fill the DeWitt to within 2 inches of the top, it doesn't have an internal expansion tank I guess.

But here is a question I have been thinking about for Corvette radiator and cooling design. I have had many classic '60s vintage cars and none of them have needed an expansion tank, internal or external. Even with my '68 1/2 428 Cobra Jet Mustang, and my current '64 Dodge Polara 500 426 wedge engines, I can fill those to within 2 inches of the top of the radiator and no issues. Why is it that Corvettes required expansion tanks while no other BB, or SB engines of that era did? Is it becasue the 'Vettes just all run hotter and need them? The physics of water expansion at temps is not different for differnt cars. Any ideas?

[Michael W.]

Re: 1966 and later BB thermostats

The air space inside the radiator is the expansion space. Different systems need different sized spaces. Corvettes after '72 did away with expansion tanks and (finally) converted to a non-pressurised coolant recovery type system.

[Michael J.]

Re: 1966 and later BB thermostats

OK, but the '60s Ford and Mopar cooling systems were pressurized (both have 15 pound caps), so why did they need so little air space (I just measured my Dodge 426, it is 1" below the neck), and the 'Vettes so much? Why couldn't GM engineer that into the 'Vettes?

[Joe L.]

Re: 1966 and later BB thermostats

The air space inside the radiator is the expansion space. Different systems need different sized spaces. Corvettes after '72 did away with expansion tanks and (finally) converted to a non-pressurised coolant recovery type system.

Mike------


Actually, GM never referred to the pre-73 radiator tanks, integral or external, as "expansion" tanks. They did served that secondary purpose but they were always referred to and functioned as "supply" tanks.

ALL Corvettes, from 1953-2010, have radiator SUPPLY tanks, either integral, external, or both. 1973 and later also have coolant recovery tanks.

[Michael W.]

Re: 1966 and later BB thermostats

True enough Joe, but the terminology is not mine. Better calling it an expansion tank than the more common 'surge tank'.