Radiator Cap 7 PSI?

[dclamm]

Got my '71 Z radiator back from the rad shop today (had a blown tube that was sealed off and two others leaking that were repaired). It's been re-cored at least once as it's a 3 row core.

The radiator guy (good old guy in the business for awhile) recommended going to a 7 PSI cap (vs the 13 psi I run) to relieve some stress on the old cooling system. Said it wouldn't affect the running temp much but would increase the longevity of the various components/gaskets (including his repair I presume).

Opinions on this? I know it would lower the boiling point, but would that just cause more overflow when stopped? (I don't have an overflow tank on it). Would it cause any other problems? My engine is stock, no mods, don't drive it hard. I took the A/C condensor out so has good flow, 180 thermo.

Wondering if this is a legit suggestion and if anyone else has tried it good/bad.

Dave

[d240zx2]

7psi is one-half atmosphere. I'd think you'd need at least one.....

My original radiator does peachy-keen with a 15 psi cap. No problems at all.

[EScanlon]

7psi is one-half atmosphere. I'd think you'd need at least one.....

If he were living in vacuum...

E

[MikeW]

It seems to me that without an overflow tank having a lower pressure cap would make it more likely that you'd lose coolant and overheat. I agree that the lower pressure cap would reduce strain on the whole system only because the cap would never let the pressure get higher than the 7PSI. According to how stuff works a 15 PSI cap raises the boiling point by 45 degrees F. Let's assume that 7 PSI would raise it by 20 degrees (212 up to 232). You can then consult your antifreeze container for the boiling point of varying mixtures. Instead of 50/50 (antifreeze/water) you could go to 60/40 which would also raise the boiling point.

For normal driving I doubt you'll have a problem. The fact that you're at sea level also helps. If you do a lot of stop and go traffic in hot weather then I'd start to worry. The bottom line is I think you'll be fine with 7PSI as long as it never actually opens up.

Edited June 29, 2010 by MikeW

[Z train]

He's telling you 7 pound cap so his repair lasts longer.

[barth4567]

That does not sound right to me. Been running a 13lb cap forever on my 1972 I think I would put a new radiator in if it was me. Just put one in mine last year and it was less than $200.00. Those old radiators are just not worth messing around with. Just my opinion:)

[Z train]

Low pressure caps are for cooling systems that are structurally "challenged" shall we say.In the SW,i wouldn't screw around with a questionable radiator.

[dclamm]

Thanks for the comments. I'm going to stick with the 13 PSI cap for now and keep an eye on it (not a daily driver, still sorting things out so not going too far from home, plus the old lumpy tires limit me to 50MPH, new ones on order). Put some miles on it today and no leaks at all and no overflow, temp normal. Once I'm confident enough to venture out in it will likely get a new radiator.

Dave

[Z train]

Seeing as how you are in OC,i would look into an aluminum radiator.THe extra money will be well spent.