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Old 08-30-2020, 02:49 AM   #1
DMMuir
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Default Radiator Cap

the gasket on mine is shot, but I see a few options. What would have been the correct for a 40 deluxe? 4# cap?
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Old 08-30-2020, 06:01 AM   #2
Terry,OH
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Default Re: Radiator Cap

The original cap is not a pressure cap. Adding a pressure cap will eventually bulge the upper brass tank of the radiator.
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Old 08-30-2020, 07:10 AM   #3
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Default Re: Radiator Cap

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Originally Posted by Terry,OH View Post
The original cap is not a pressure cap. Adding a pressure cap will eventually bulge the upper brass tank of the radiator.
DMMuir, Terry is as usual, correct.
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Old 08-30-2020, 12:49 PM   #4
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Default Re: Radiator Cap

DMMuri did not ask about a pressure cap, he asked about a gasket. Is not the part of an original cap that seats against the radiator cap called, and in fact is a gasket?
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Old 08-30-2020, 01:51 PM   #5
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Default Re: Radiator Cap

I kind of asked about both.
Non pressure is good to know. The gasket on mine is looking rough, but if it isn't sealing pressure it's likely not as big of a deal as I was thinking.

I was thinking the pressure may help it run a bit cooler, but that's a no.

I will continue working on the correct air directors and think about flushing the engine and having the radiator boiled out.

Thanks everyone
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Old 08-30-2020, 02:01 PM   #6
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Default Re: Radiator Cap

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I was thinking the pressure may help it run a bit cooler, but that's a no.
Increasing the pressure in the cooling system does not help with lowering the coolant temperature, it raises the temperature at which the water will boil. That allows you to operate the engine at a higher temperature, which has a lot of benefits. But it will be running at a higher temperature, so no help if you are trying to lower the operating temperature. Flowing coolant continues to remove heat from the internal metal surfaces until it reaches it's boiling point. Once the coolant is boiling it's ability to transfer the heat from the metal surfaces is greatly reduced. The higher the pressure in the coolant the higher temperature it can run at until it reaches it boiling point.

The older Ford v8 radiators were not designed for pressure systems and will not tolerate much.
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Old 08-30-2020, 09:39 PM   #7
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Default Re: Radiator Cap

DM. I don't know if the '40 rad cap and the '46 rad cap are comparable, but I "fixed" mine with some hi-temp black silicone seal, and planned to buy a replacement. I ran a 1/4" high bead of silicone around the existing gasket, at midpoint between the center metal disc and the outer perimeter of the gasket. I placed the cap gasket side up on the workbench, placed a piece of waxed paper over the rad cap, and placed a 1/2" x 4" x 4" piece of flat bar on top. Left it for two days to set, peeled of the wax paper, trimmed the outer edge with a knife and installed it. I ran it for one summer, before replacing, and no leaks.
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Old 08-30-2020, 10:47 PM   #8
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Default Re: Radiator Cap

Original side fill '40s were Not pressurized. They would dump water thru the top tube. Right??? Newc
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Old 08-31-2020, 08:16 PM   #9
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Default Re: Radiator Cap

I did not realize a 1940 required a non pressure cap.I have been running a 4# for years.What would be the chances of it running cooler with a non pressure cap?Who sells the best non pressure cap?
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Old 08-31-2020, 08:31 PM   #10
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Default Re: Radiator Cap

Caps or pressure have nothing to do with running temperature. It has to do with the boiling point.
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Old 08-31-2020, 08:48 PM   #11
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Default Re: Radiator Cap

A pressure cap on a 40 radiator still will not build any pressure. The overflow tube goes straight to the atmosphere.
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Old 08-31-2020, 09:53 PM   #12
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Default Re: Radiator Cap

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A pressure cap on a 40 radiator still will not build any pressure. The overflow tube goes straight to the atmosphere.
DOH, I knew this too, but just didn't put it together.....
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Old 08-31-2020, 10:55 PM   #13
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Default Re: Radiator Cap

Correct me if I'm wrong but with the overflow tube coming off the side of the filler neck, if you are using a pressure cap it pressurized the system and overflows or releases thru the tube once that pressure is reached? If the correct pressure cap is used.

Wouldn't a pressure cap of at least #4 be beneficial if you lived at a higher elevation to raise the boiling point?
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Old 08-31-2020, 11:16 PM   #14
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Wouldn't a pressure cap of at least #4 be beneficial if you lived at a higher elevation to raise the boiling point?
Yep, it would raise the boiling point.
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Old 09-01-2020, 10:56 AM   #15
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Default Re: Radiator Cap

A pressure cap on a '40 will work well only if you also install a Skip Haney 3# overflow tube cap.
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