What size radiator cap would be good for my 454/425hp th400. 4 core radiator? Currently,It has a 15Lb cap. Is this good? should it be higher or lower?

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–Joe454–
"67 Malibu"

joe
I run a 17 on my 67/427. no fluid loss, and runs about 195.I know,but this still does not answer your question, just trying to give peice of mind, have a good one. 67rat member #199

I used to use a standard 16lb. cap on my Griffin radiator and during a long, hot cruise session, I would always have some fresh, hot overflow coolant inside the coolant recovery bottle.

At a local speed shop here in Houston (BushHog's Racing), I picked up a racing radiator cap rated at 22-24lbs. I haven't even thought of this until you posted the above question, but I have noticed no more overflow going into the catch bottle and my engine temps refuse to get above 180 during a midday drive here in 'hot' Houston.

I do not understand the exact relationship between specific pressure caps and a radiators capacity to keep an engine cool. Maybe someone else has the answer as to why a stronger cap works better at keeping an engine cooler. The Griffin radiator I am using is about 1 year old so I am not too concerned about building excessive pressures - it should be able to handle it.

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70' Malibu - 383 'Dental Gas' Inhaling Stroker! Gold Member #39
Chevellz Alwayz!

I'm not sure of the exact #'s but every pound of presure will lower the boiling point a few degrees.

Wes, are you running steel braid water hoses? that seems like a lot of pressure on rubber ones.

I have seen the intake gaskets blow out around the water ports from high pressure also.

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Philip Valentine
Team Chevelle Member #42 GOLD
philip@chevelles.com

To all, The correct answer is that 1# of pressure raises the boiling point 3 degrees. A 15# cap should be plenty of pressure. Just make sure the cap is good,it can be pressure tested with the same tester as the cooling system.

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Leo Paugh
Maryland Chevelle Club #017

Philip, no I am not using steel braided radiator hoses. I use the OEM rubber hoses but I am not even sure that my cooling system is building too much pressure in the first place - but then again, how could you tell when you have a 22-24lb cap? What would be a sign that there is too much pressure in the cooling system? I am not sure.

As I said earlier though, this setup never gets over 180 under REALLY hot conditions. My two electric fans pull a combined 3,900 cfm across the radiator and I use a 160 thermostat. The largest fan is a puller and the smaller one is a pusher. When things start to cool off here in Houston (November - geeeez!!), I will turn off the smaller fan and swap in a 180 thermostat.

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70' Malibu - 383 'Dental Gas' Inhaling Stroker! Gold Member #39
Chevellz Alwayz!

wes are you using other than a 50/50 mix of water and anti-freeze? i've always thought that containing that pressure would raise the temp (like a pressure cooker builds more heat so they cook faster)and do you use an engine driven fan or just electrics. i've always been on the edge of overheating and you sound like you may have an answer. thanks john

Hey John, my coolant mix is closer to a 60/40 water/coolant ratio. The bigger electric fan is called the 'Black Magic' by Flexalite and is rated at 2,800 cfm. It is positioned to cover the top right corner of the radiator, which is the hottest part (nearest to the radiator hose inlet). The smaller one is a standard 12" Flexalite pusher fan rated at 1,100 cfm. Adding that smaller fan and installing the 160 thermostat really did the trick in my opinion. It shaved about another 10-14 degrees off. The smaller fan runs at all times and the big fan has an adjustable thermostat that turns on at 160 degrees.

The Griffin aluminum radiator I use is their direct 70' Chevelle replacement 2 row (big 1 inch each) and I think I got it from Jeg's as well. Hope this helps!

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70' Malibu - 383 'Dental Gas' Inhaling Stroker! Gold Member #39
Chevellz Alwayz!

I am running a flexa lite dual electric fan. it is really noisy( loud hummm. ) does eveyone just put up with that or do i have a worn out fan? also does the catch can need to be higher or lower than the radiator filler?
sorry about adding to this post
thanx for your help
justin