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tj924 · Posted: Sat Mar 12, 2005 2:09 pm Post subject: New radiator cap

Picked up a new radiator cap today for about $8.00. Not a genuine one but after reading the Haynes I thought a 16psi cap would do the trick. Fits on perfectly but haven't started the car since putting it on.

Does 16psi sound OK. I can pick up the same size in a 13psi but while that is within spec (book says it should open between 12.something & 16.something) I thought the high-end may be better.
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TJ
Silver '82 924 NA 5-Speed Manual

brit vw boy · Joined: 18 Feb 2005 Posts: 59 Location: oxford, england

Paul · Posted: Sat Mar 12, 2005 6:57 pm Post subject:

TJ, a higher pressure cap raises the boiling point of the coolant which is a good thing.

The downside is that all of the gaskets and hoses will now be subjected to higher pressures (3 pounds per square inch of surface area, assuming you had 13 psi before).

tj924 · Posted: Sat Mar 12, 2005 9:17 pm Post subject:

Paul · Posted: Sat Mar 12, 2005 9:54 pm Post subject:

If it fits and doesn't leak, it will be fine. It only builds up that much pressure when the system has been overfilled or the motor is overheating.

tj924 · Posted: Sat Mar 12, 2005 10:24 pm Post subject:

Paul · Posted: Sun Mar 13, 2005 7:43 am Post subject:

Yes, I would bleed it at the same time.

From a cold motor, the level in the tank near max, and the cap on tight, just loosen or remove the bleeder plug and start the motor. I usually block the throttle with a screw driver at the throttle body to obtain about 1200 rpms.

Let the car warm up, as soon as the fluid starts flowing from the bleeder smoothly, while leaving the car running, replace the plug.

Then let it warm up until the fans kick in and shut it down. I follow this procedure everytime I take the radiator or coolant (depending which one the car has) cap off.

tj924 · Posted: Sun Mar 13, 2005 6:43 pm Post subject:

Thanks Paul, that makes much more sense than the Haynes. The way I read it, Haynes indicates to bleed the system with the rad cap off as well. When I did it your way, coolant spat out of the hole for a few minutes, then started running out instead of spitting. Replaced the bleeder plug & ran for a few more minutes until the fan came on (temp guage read about 1/2 way). Rad cap & surrounding area still cold to the touch so definitely no leaks.
_________________
TJ
Silver '82 924 NA 5-Speed Manual

Paul · Posted: Sun Mar 13, 2005 6:49 pm Post subject:

Glad to hear, good work!

As long as your coolant level when the car is cold is above the minimum mark, you're good to go.