'67 BB radiator, coolant recovery
I am about finished getting my '67 BB ready for it's first chapter judging in a couple of weeks, and am now experimenting a bit as I will be driving it about 90 miles to the judging (love those extra points). I have been concerned about the radiator throwing out coolant, and with coolant, like blood, a little looks like a lot. I filled the radiator to about 1" below the cap seat. I installed an el cheapo coolant recovery tank, a small one that fits neatly beside the radiator. I then did a series of test with different caps. I replaced the RC-15 cap with an RC-36 (closed system cap), an RC-26 (from my '66 SB), and a NAPA 16 lb. cap. I ran the car about 45 minutes with highway 70 mph and stop and go mixed for each cap. When I got back to the garage (and the temp was about 195-200 at the end of the drive) I would observe the amount of coolant that ran into the tank. Each time about 1 1/2 pints would run into it, and of course by morning when it cooled down it was all sucked back into the radiator. All the caps did the same thing. So my question is, now can I take the 1 1/2 pints out and assume the radiator will not overflow with my RC-15? Also, will the temps be the same with the 1 1/2 pints out? Then I am wondering what a coolant recovery closed system is supposed to do that is better than an open system. Thanks for any opinions.
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Big Tanks In the High Mountains of New Mexico -
Re: '67 BB radiator, coolant recovery
Coolant expands when it heats up. What your experiment shows is that you have too much coolant in the system when filled to 1" below the cap. If you only fill it (cold) to the "Full Cold" line down on the side tank, it won't burp any coolant out through the overflow hose. It's not boiling (that won't happen until 265*F with a 50-50 coolant mix and a 15# cap), it's just expanding normally, but you have to provide expansion room in the system for it.
If you fill it again to 1" below the cap, it will find its own "happy level" all by itself after a couple of driving cycles, and won't dribble again. -
Re: '67 BB radiator, coolant recovery
John.......
If you fill it again to 1" below the cap, it will continue to "burp" out as you note. I think what you meant to say (in your closing statement) is that if you fill it to the line shown on the side of the tank (as you also state), you'll be ok and it'll find it's own "happy level".......
Take care,Comment
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Re: '67 BB radiator, coolant recovery
Bob -
No, I meant what I said - either approach will have the same result; if it's over-filled (1" below the cap), it will burp a couple of times, until the coolant level is correct (adequate expansion space created), and won't burp again - it will correct the over-fill issue all by itself if he just leaves it alone.
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Re: '67 BB radiator, coolant recovery
Thanks for the input. I should have told you my radiator doesn't have a "fill to" mark or line (just a "Harrison" embossing on the side), so that is why I was running the experiment to find where that might be. But, at the level it wants to be at after several cycles, it is about 5 inches below the cap neck cold. That seems like a lot of air space with several rows of radiator coil empty. But I guess that is OK. It does seem the coolant recovery mode with the tank is more "comforting" to me pyschologically. I will put the tank back on after judging. I do wonder how many points I would lose with the tank hooked up and an RC-15 cap. Couldn't be too much since you are just removing the drain hose from the neck and replacing with the tank and hose.Big Tanks In the High Mountains of New MexicoComment
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Re: '67 BB radiator, coolant recovery
Yes, not all of these Harrison radiators had the 'FULL' emboss on the side... Seems the service replacement versions deleted that aspect of construction.
John's right when he tells you there needs to be an internal air space to accommodate natural coolant expansion/contraction. That's why these radiators were NOT filled to the top. The 'FULL' emboss on the side of originals was really just an approximation of where the fill line would/should be...
Most mechanics intentionally overfill the system to accommodate air bubbles trapped in the engine that will naturally 'burp' out when you first start/run. They tell the customer to expect 'some' degree of coolant overflow for the first 2-3 heating cycles with the amount of coolant 'puked' by the system to decrease and then STOP when the system finds its 'natural' expansion level.Comment
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Re: '67 BB radiator, coolant recovery
Thanks for the info. I do see why the cars now all have a coolant recovery system and even the C2 SBs had an expansion tank. You do wonder why the engineers didn't put the same kind of system on the BBs. Guess they were not as smart and competent as the ones who did the SBs.
Big Tanks In the High Mountains of New MexicoComment
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Re: '67 BB radiator, coolant recovery
That's a matter of opinion (what's a smart design)... It's not just BB cars that lacked a discrete coolant expansion/recovery tank. My '71 SB with A/C uses a Harrison copper/brass radiator without external expansion tank (all expansion is internal) and so did other other GM vehicles.
What's 'unintelligent' about eliminating the cost of a discrete expansion tank, its mounting hardware, expansion tank to radiator interconnect hose and the hose clamps necessary to maintain pressure seal integrity?
About the only 'advantages' I can see to having all the coolant expansion hardware external to the radiator are:
(1) The overall silhouette of the radiiator is somewhat reduced.
(2) It's a bit less likely for the owner to either fill the cooling system 'short' or fail to detect a coolant low situation that would result in the upper portion of the radiator becoming exposed to air, oxidizing and losing thermal transfer efficiency due to the oxidation...Comment
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Re: '67 BB radiator, coolant recovery
The general fill requirement when coolant recovery systems became standard in the mid seventies was to fill the radiator/expansion tank to the top leaving no free air space.
So as the coolant expanded it flowed into the recovery tank, and back into the radiator as the system cooled leaving no free air space, and air was effectively purged.
IMO, this is an excellent system, and it can be adapted to any vintage Corvette, but for a big block I recommend a recovery tank capacity of at least 1.5 quarts, preferrably 2 quarts, and maintain about half-a-quart in the coolant recovery tank when the engine is cold.
With a coolant recovery tank there is no need to open the cap to check coolant. As long as the cold level remains stable, the system is full. If the cold level in the coolant recovery tank decreases, the system may have a leak.
Coolant recovery tanks can be hidden behind the rear of the inner fender apron and easily removed for judging.
DukeLast edited by Duke W.; April 29, 2010, 10:13 PM.Comment
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Re: '67 BB radiator, coolant recovery
Thanks for the info. I do see why the cars now all have a coolant recovery system and even the C2 SBs had an expansion tank. You do wonder why the engineers didn't put the same kind of system on the BBs. Guess they were not as smart and competent as the ones who did the SBs.
Michael I think you've misunderstood the configuration of the system. All C2 Corvettes have an expansion tank. Some are intregral with the radiator, typically the copper/brass type, the others are external similar to yours.
A coolant recovery system as Duke describes did not appear on Corvettes until 1973 MY.Comment
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Re: '67 BB radiator, coolant recovery
Leave the coolant recovery tank on the car. It's an excellent upgrade. It adds a small additional "margin" to the already "marginal" cooling capacity of BBC Corvettes.
Besides, when you take your expensive Corvette to the drag strip, the recovery tank is required.Comment
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