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Old 24-09-2021, 14:33   #1
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Coolant Fill Cap for 1982 Universal M-40

I had a coolant service done on my old sailboat; one thing the mechanic identified as an issue was that the coolant fill cap wasn't holding pressure. It had an aftermarket 14PSI rated cap, and he thought that was a bit high for an engine like this. He recommended I replace it with the properly rated one.

...but I can't figure out what the rated one is. There's no specification for the coolant fill cap on any of the Universal documentation I can find.

What PSI rating should I go with, and why?
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Old 25-09-2021, 06:22   #2
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Re: Coolant Fill Cap for 1982 Universal M-40

9-15 PSI according to Westerbeke. Page 14.


https://www.westerbeke.com/technical...hnical_man.pdf
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Old 26-09-2021, 04:51   #3
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Re: Coolant Fill Cap for 1982 Universal M-40

Huh. I couldn't find that anywhere. Thanks!
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Old 26-09-2021, 09:32   #4
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Re: Coolant Fill Cap for 1982 Universal M-40

Regarding the 'why', not sure, but if it were me I'd go with the lower range if I could find one. My understanding is that the higher pressure cap is to increase the boiling point of the coolant in the F/W side of the system.

Since your engine is designed to operate at 195F max, 17 degrees below the boiling poiint of plain water, the lower pressure in the system would help guard against fresh and salt water mixing due to less-than-perfect sealing between the two 'sides'...
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Old 26-09-2021, 16:04   #5
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Re: Coolant Fill Cap for 1982 Universal M-40

If you take those spec's to a NAPA store, they will fit you out with the correct after market radiator cap. The M-30 and M-40 are basically the same engine and that what those of us that have the M-30 do. If you PM me, I'll get you the exact part number.
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