Radiator Cap Operation

[Joe C.]

I have an RC27 cap on my 1965 Corvette's reservoir tank, which is a 15 pound cap. I bolted a plastic coolant recovery tank just behind the reservoir, and want to ensure that the system will function correctly. The goal is to keep the reservoir full to the top, and function as a "recovery" or "closed" system (not a simple "catch can").

What must I look for in a rad cap? Is the RC 27 OK? What is the difference, if any, between a cap used for an "open" and "closed" system?
Thanks in advance.

[Dick W.]

Re: Radiator Cap Operation

To make the recovery tank work, you will have to purchase the correct cap, pressure wise, for a recovery system.

[Michael W.]

Re: Radiator Cap Operation

Joe,

Try an RC33 which is the OEM article for real Corvettes.

[Terry M.]

Re: Radiator Cap Operation

Joe,

Try an RC33 which is the OEM article for real Corvettes.

You go Mikie.

[Edward J.]

Re: Radiator Cap Operation

Joe, I know a few weeks ago you had a post about the broken shaft on your water pump, I received august vette vues mag. there was a chevrolet tech. service bulletin, on broken shafts on water pump.dated june of 1971, it had to do with the elimanation of center reinforcment on the water pump pulley, There was a balance issue due to the pulley not resting flat against the water pump. and also they are talking about the alignment of the yellow mark on fan clutch and the blue mark on water pump, these were used for balancing reasons, I not sure if these marks were around on the mid year cars, but if not, they go on to say using a dail indicater to check for run out, should be less the .006 in.

sorry guys for hopping in on this thread.

[Joe C.]

Re: Radiator Cap Operation

I'd sure like to know what might be different about the RC 27 v the RC 33, as they are both 15# caps.

The RC 27 just might be working OK as it is now, but I do want to understand how/why. Seems that nobody over at Stant, Gates, Be Cool, DeWitt's , etc can quantify the difference(s) (if any). AFAIK, the caps for both the "open" and "closed" (as used on the so-called "real" Corvettes.............1973 and later) have dual function of relieving pressure, and reversing to allow air (or coolant, in a "recovery" or "closed" system) to re enter upon cool-down.

The RC 27 cap that I have in place, is one of a collection of used caps I have, from who knows where. If you Google AC RC 27 you'll see a plastic cap, which has superseded the stainless steel RC 27 that I have. This stainless RC 27 cap was used on Cadillacs and other GM vehicles circa 1969-1970. It closely resembles the RC 33, except for the lettering stamped thereon.

The only difference between these two, I believe, is the addition of an upper rubber gasket on later caps (such as the RC 33 used for "real" rubber bumpered Corvettes of vintage 1973 and later) which was not used on the caps designed for "open" systems. ALL pressurizing radiator caps, which were used beginning in the early 1950's, have the lower, rubber disc, which maintains pressure against the cap spring.

[Joe C.]

Re: Radiator Cap Operation

Joe, I know a few weeks ago you had a post about the broken shaft on your water pump, I received august vette vues mag. there was a chevrolet tech. service bulletin, on broken shafts on water pump.dated june of 1971, it had to do with the elimanation of center reinforcment on the water pump pulley, There was a balance issue due to the pulley not resting flat against the water pump. and also they are talking about the alignment of the yellow mark on fan clutch and the blue mark on water pump, these were used for balancing reasons, I not sure if these marks were around on the mid year cars, but if not, they go on to say using a dail indicater to check for run out, should be less the .006 in.

sorry guys for hopping in on this thread.

Thanks Ed. Short answer is NO, there are no alignment marks, and 1965 SHP pulley does NOT call for the backup reinforcement disc next to the hub. The hub was pressed (by me) onto the failed shaft with .006" runout, according to Mister Stewart. I believe that a combination of that runout, along with the belt being somewhat tight, and the "pinch point" created by the ball bearing design, all collaborated to cause the failure. These three items taken collectively, leave very little safety margin, and the fact that the engine sees RPM's over 7000 should not be a factor. I maintain that there was a flaw in the shaft.

Mister Stewart, at my request, has located and installed a FAG shaft/bearing assembly using needles instead of balls with a 5/8" diameter shaft. This will make for a stouter shaft due to the larger minor diameter required for the needles as opposed to the balls.

[Dick W.]

Re: Radiator Cap Operation

The only difference between these two, I believe, is the addition of an upper rubber gasket on later caps (such as the RC 33 used for "real" rubber bumpered Corvettes of vintage 1973 and later) which was not used on the caps designed for "open" systems. .

Bingo, the only difference!

[Michael W.]

Re: Radiator Cap Operation

I'd sure like to know what might be different about the RC 27 v the RC 33, as they are both 15# caps.

The RC 27 just might be working OK as it is now, but I do want to understand how/why. Seems that nobody over at Stant, Gates, Be Cool, DeWitt's , etc can quantify the difference(s) (if any). AFAIK, the caps for both the "open" and "closed" (as used on the so-called "real" Corvettes.............1973 and later) have dual function of relieving pressure, and reversing to allow air (or coolant, in a "recovery" or "closed" system) to re enter upon cool-down.

As Dickie confirms, the rubber gasket is the key. This secondary seal is required for the radiator to effectively draw coolant from the recovery tank during cooldown. In this respect, my Corvette sucks in a way yours presently doesn't.

[Joe C.]

Re: Radiator Cap Operation

As Dickie confirms, the rubber gasket is the key. This secondary seal is required for the radiator to effectively draw coolant from the recovery tank during cooldown. In this respect, my Corvette sucks in a way yours presently doesn't.

I wonder if you and Dickie would have known that before I mentioned it. If you'ze did, you should edumenicate the employees of the companies I mentioned earlier.

So, early yesterday morning, I took the rubber seal off of another spare cap that I have, and put it on the AC RC-27.

I'm real happy now that I don't have to use a part (RC-33) from a bubber rumper model.

Ya goin ta Carlisle?

[Michael W.]

Re: Radiator Cap Operation

So, early yesterday morning, I took the rubber seal off of another spare cap that I have, and put it on the AC RC-27.

I'm real happy now that I don't have to use a part (RC-33) from a bubber rumper model.

Ya goin ta Carlisle?

Just making ya work a bit, and glad to hear that your car will suck even more now.

G110 is not in the cards this year, the stars are not aligned despite best efforts.

[Dick W.]

Re: Radiator Cap Operation

I wonder if you and Dickie would have known that before I mentioned it. If you'ze did, you should edumenicate the employees of the companies I mentioned earlier.

So, early yesterday morning, I took the rubber seal off of another spare cap that I have, and put it on the AC RC-27.

I'm real happy now that I don't have to use a part (RC-33) from a bubber rumper model.

Ya goin ta Carlisle?

I ain't spent the last 55 years a foolin' round with old cars and trucks, workin' in parts departments of dealerships, pulling wrenches, swappin' and a tradin' fer nuttin'

[Francis F.]

Re: Radiator Cap Operation

I ain't spent the last 55 years a foolin' round with old cars and trucks, workin' in parts departments of dealerships, pulling wrenches, swappin' and a tradin' fer nuttin'

Dick,What did you spend da last 55 years foolin' around fer ?
Fran

[Dick W.]

Re: Radiator Cap Operation

Dick,What did you spend da last 55 years foolin' around fer ?
Fran

'cause I could

[Joe C.]

Re: Radiator Cap Operation

I ain't spent the last 55 years a foolin' round with old cars and trucks, workin' in parts departments of dealerships, pulling wrenches, swappin' and a tradin' fer nuttin'

Well..............I'm glad to see that you learned SOMETHING.
(Talkin' 'bout you knowin' 'bout the radater cap upper seal.)