BBC 468ci cooling problems

[pwrunt3pte]

hey guys, I recently got a 1955 GMC 1st series with a chevy 468ci engine. I'm having problems with the cooling system on this truck, and I'm begining to think the engine is junk. i just recently got the truck to idle and noticed coolant being pushed out the overflow bottle. I figured i needed to burp the system, so i left the radiator cap off and started the truck. the temp climbed to about 210 degrees and when the truck idled, coolant was flowing out the top the radiator because i had the cap off. when i revved the engine a little the flow of coolant would go back down and remain in the radiator. I turned it off and coolant poured out of the radiator like a guyser. I'm new to this so any suggestions would be appreciated

[chev3600]

What do you have for a fan setup? aluminum or stock radiator?

[pwrunt3pte]

I bought a aluminum U.S. radiator. It is a drop in replacement and has a two row design with 1" wide cooling tubes. I bought a universal electric fan with shroud that mounts behind radiator. according to the classic industries book it moves 1950cfm. thermostat is a 195, going to try a 180.If you have a similar engine, what would you suggest? the 468ci is in a 55 gmc 1st series pickup

[chev3600]

I wish I had a similar setup! I have seen cooling issues on many different vehicles. Some resulting from inefficient electric fans, no shrouding, fan too small, etc. Also ignition timing / lean mixture can cause it to run hotter. Your rad sounds like its fine. Is the fan the largest size you can fit? I've even run a hose on a radiator while idling to see if reducing the temp will be enough. Just a small spray to cool it down a little.

Just some ideas, hope it helps.
High pressure cap? no 3-6 lbs.

[pwrunt3pte]

I thought I had everything covered as far as the cooling system went. The fan on there is the biggest they sell that will fit that radiator. I'm going to run a compression test on it to see if i have a leaking head gasket. If that comes back ok, I'll replace the t-stat and check the timing again. Thanks for your input.

[dwcsr]

First off 210 is not over heating, 210 is not over heating, 210 is not over heating. Your system is doing as it should. Cap off at 210 water will come out of the radiator, shut it off and it will gyser out. Its from the water sucking the heat from the cylinders and heads and boiling out. This is normal on an open system. The system will burp itself once you have enough coolant in it.

With the cap on and the over flow bottle that holds about a half gallon at about 1/3 full cold you should see water at a higher level when its hot. A 180 stat will not make a 210 motor cooler that a 195 stat. The purpose of a stat is to keep a consistant "minimum" temp not a maximum temp.

What psi is the cap?
What pulleys are you running, Undersized?
1950 cfm is not enough to cool a 468. You need to get up to 4500 -5000.
If you have room try a Mark VIII fan 18" 3500 cfm or so.

This is what I did to mine. 4 1500 CFM fans. It will idle in 100 degrees and stay at 200F.

[pwrunt3pte]

thanks Dave for the help, I like the setup you have. I'm looking in the summit racing catalog now to see what I can come up with. What would you recommend for pulley size and radiator cap psi?

[dwcsr]

Cap PSI should be between 14 and 18. But thats with a brass/copper radiator. Check with US radiator on yours. The pulley should be the stock one I don't know the diameter, maybe someone here has one they can measure for you.

[pwrunt3pte]

well, did a compression test today and my worst fears were confirmed. Need a new engine. cylinder 1,2,3,4,6,8 were around 178-182psi. Cylinder#5 was 130psi and cylinder#7 was 90psi. Don't know if i should get it rebuilt or buy a crate engine or something.

[dwcsr]

do a head gasket and save your cash. unless its a high mileage motor