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Hi All,
I'm looking for a 4psi radiator cap that will work with a recovery tank on the M37.

The 4psi caps I have seen all lack the second (upper) seal that seals to the OD of the filler neck. They will not pull any expelled coolant back into the system when it cools. I suspect there's something out there that will work, but have not found it. I looked at making a seal, but the added thickness was an issue.

Andy

Let me get it straight,....you are in this situation?

You got it.

Just curious why you need a recovery system? The truck was engineered without one to handle any hot, desert climate on earth.

Even with global warming.

PoW

Keep the fluid level at the max.
Allow quick visual inspection of system level
Eliminate coolant loss
Easy if I can find a cap!

I think I found a cap that will do the trick.

Gates 31348 Heavy-Duty Radiator Cap

Once I learned that the filler neck/cap is referred to as a "size B" I did some digging and found a 7psi cap for a closed cooling system. My current cap is 4psi and designed for an open cooling system. I should have the cap soon and will give it a try then post the results.