Too much radiator pressure

bchrismer

bchrismer

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Hey Fellas,

Long time since I have visited the Ford Barn, but I have a quick question regarding my latest '40 Ford project.

My "beater" panel truck has the '40 Flathead motor from my '40 stake truck. Because the stock radiator was in really bad shape, and trying to throw this thing together on a tight budget, I bought an aluminum radiator that came with a 16lb cap.

Due to the gearing, I can drive the truck at highway speeds turning around 2500RPM, but if I drive more than 100 miles, it pushes at least a gallon of coolant out of the radiator.

I haven't seen any steam in the exhaust nor any milky oil in the engine, but I have seen some coolant droplets on the top end of the dipstick and the driver side head seems to have some "mositure" around it more than it used to when I ran it in the stake truck with a stock radiator and 4lb cap.

Back in 2014, we did have that head off to fix a broken valve guide, so I am wondering if the 16lb pressure cap is creating too much pressure for the head gasket?

This morning, I bought a 7lb cap, hoping to reduce the pressure in the system and retorqed the nuts on the head to 55lbs, topped off the radiator and took it for a spin to get it up to operating temp.

Before I yank the head off for a new head gasket, I wanted to get some thoughts on whether I'm heading down the right path. I don't know what kind of pressure the stock head gaskets will withstand before it blows them out.

Thanks.
 

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I suspect that you are using a shallow cap. Probably need a "deep well" cap.
I wouldn't use a 16psi either.
 
If you have moisture on the head, no amount of re-torquing will stop the leakage. You have apparently compromised the stud sealant on the studs that go through to the water jacket. Losing that much coolant, however, doesn't sound likely from that single source. Rather than jury rig the studs under the nuts, you may wish to pull the head and the offending studs to apply proper sealant to the stud threads, and replace the head gasket while you're at it.
 
As stated " do you have a recovery system?"
The 7007 cap is meant for a recovery system.
If it were mine I would install a recovery tank and be sure not to overfill the radiator to start with to see how it performs.
 
A 16 pound cap will cause top tank to expand and possibly "blow" at the seams. There's a formula for calculating what internal pressure the cap will produce.
 
And the reason for 16 lbs is to rise the boiling point . Do you need that . I thought 7 lbs was a lot
 
Sometimes, you have to go back to ground zero and analyze what you have and work from there. The "some coolant droplets on the top end of the dipstick" statement gives me pause.
 
Step-down said:
And the reason for 16 lbs is to rise the boiling point . Do you need that . I thought 7 lbs was a lot
Click to expand...

No, that flathead has always ran cool. The aluminum radiator came with the 16lb. I bought the 7lb because it was the first one that came up on the list. It appears that O'Reilly has the 7004, which is a 4lb. I may pick that up tomorrow and roll with it.

No, I don't have a recovery tank on the panel truck. I can always add one of those.

The dipstick is a typical flathead dipstick with the flat metal cover on the top. My assumption is that the coolant droplets that are on it are either from what's pushed out of the overflow tube going down the highway and blowing back under the hood or it is seepage from the lower edge of the head gasket. Again...the oil in the pan isn't milky looking, so it doesn't appear to have any real water leaking into the pan.

I've never run recovery tanks on any of my '40s, and the radiators usually find their happy place with the coolant level an inch or so above the core.

I'm planning on making a 100 mile run up to my sister and brother-in-law's house on Sunday, and am planning to take the panel truck. I'll let it cool down after I get there and see what happens with the 4lb cap. If the coolant level is down into the core, I'll plan to swap the head gasket next week before driving it up to St Louis.
 
You need to determine where the leakage is. Put on an overflow jar, even temporarily, to see if the radiator is overflowing. If it is, the radiator cannot handle the water from the engine pumps, which I would think means it is clogged. If the jar is not getting filled, look elsewhere (radiator hoses, head gaskets, etc) A gallon of water in 100 miles is quite a leak. There should be water all over the engine.
 
For what its worth, the later '40s used 4 lb caps with a stock brass radiator. As many know but I had to learn, I had to keep the (cold) coolant level about 2 inches below the cap, otherwise the coolant would just be forced out the over flow tube.

I wonder whether the gaskets in the cooling system, including head, are capable of resisting 16 lb pressure. One would suspect so.
 
Drbrown said:
For what its worth, the later '40s used 4 lb caps with a stock brass radiator. As many know but I had to learn, I had to keep the (cold) coolant level about 2 inches below the cap, otherwise the coolant would just be forced out the over flow tube.

I wonder whether the gaskets in the cooling system, including head, are capable of resisting 16 lb pressure. One would suspect so.
Click to expand...

Yeah, that's pretty much the question I was initially looking for an answer for, but I threw out more info that caused more questions.

After a closer inspection of the head, I think what I am seeing on the lower edge of it is oil drips from the return line that has a little seepage on it, although the initial thought was a coolant seep.
 
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