I installed ones of those overflow bottles from Summit , it feeds into the bottom and and I suppose if it fills up it will overflow through the top. My question is I don't get that purge of coolant when the car is hot , likewise I don't get the draw back from the overflow as it cools. Is that action a function of the radiator cap I use? ( which is an old Robert Shaw 15lb.) I have the overflow bottle on the other side of the radiator from the cap, but the distance I wouldn't think would matter.

Distance from the cap shouldn't matter and the 15# is about right...

I like the looks of those tall recovery tanks from Summit... good choice. graemlins/thumbsup.gif

Are you sure your fluid quantity is up to proper levels? Or are you concerned your pressure is low?

Is your recovery tank pressurized? I'm not familuar with what you are describing. If it's not pressurized the recovery tank is only in play if the pressure in the radiator core goes above the 15 lbs the cap is rated at. If you are not over powering the cap you'll never see any overflow. If I over fill my rad, it purges once when hot and I shut it off and that's it. If it is a pressurized tank then I would think you need a cap that will let the rad pressure into the recovery tank.

Look on the inside of the cap in the center. There should be a small metal disc that seals against a rubber washer. It is held up against the underside of the cap by a small internal spring. You should be able to pop it open by pulling it down with very little pressure. That is where the suction comes from as the car cools down. I think the old style caps may not have this feature.

-Mark.

KWIK , the jug is cool, I got the clear one (well sort of clear ) such that I could monitor the level. I even machined an aluminum bracket to hold it off the core support , anodized it blue. Looks clean, too bad it doesn't work like I expected,

DJ, I almost wonder if the cap should be in the 14lb range , my other Camaro has a 14 lb cap, so I'm not really sure what pressure I should be running. I pressure checked the radiator, off the car not long ago, and we pumped it up well beyond 15lbs. The overflow jug has seals on it that I would expect can hold at these modest levels. I wondered about that , but for a sanity check I looked at my Suburban's setup ( factory obviously ) and that is set up the same way , feeds into the bottom , but the cap is vented. I had a post about running hot while cruising at 3K rpm, maybe the two issues are related. I have been trained to think that way, but intuitively, I wouldn't think a faulty cap would cause me to run hot at higher rpm.s??

Stingr, I do have the seal in the bottom of the cap, but I wasn't aware of that functional check you described, I will check it out. I wasn't really sure how to check to see if it was releasing at the prescribed psi, but it would help to see if it moves at all.
Thanks.

If you don't run hot enough to raise the coolant above its boiling point (265 degrees with a 50-50 mix and a 15# cap), it'll never puke past the pressure release and dump to the overflow bottle (a good thing). If it did, and you have the correct cap with a pressure/vacuum valve in it, it will draw the puked coolant back into the system as it creates a vacuum as it cools down. Radiator cap pressure ratings have absolutely nothing to do with operating temperature - that's determined only by the radiator's heat rejection capability and the airflow through it; all the cap does is determine the temperature at which the coolant will boil. graemlins/thumbsup.gif