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Old as Dirt!
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I frequently see posts concerning coolant leakage from the cooling system on Perkins 4-108 engines. For a while we had a similar problem that appeared to be at the fill cap on the heat exchanger but we couldn't tell whether it was from the cap itself, from the tubing connecting the expansion tank to the fill throat or just where. I didn't think it could be from the fill cap as ours was a Perkins original equipment item purchased only a few years ago from TransAtlantic Diesel (for nearly $50.00!!!). Every effort to track down the source of the leakage proved unsuccessful until a friend indicated he's had similar problems and "solved" it with a filler Cap from the local NAPA auto parts store. Considering the relative newness of the Perkins cap, I couldn't imagine that could be the source but, for the sake of the exercise...

The replacement cap, that "solved" our leakage problem is a NAPA Radiator Cap (10 PSI), Part Number 703-1708, at a cost of $5.49 plus tax.

An inspection of the rubber gasket on the NAPA cap shows that it is at least twice as thick as that on the Perkins cap and rather more pliable which was evidently all that was needed to resolve our difficulty. Because of the low cost, I picked up a spare for our stores locker, just in case the problem recurs as the cap ages in use (although I don't expect that).

FWIW...
 
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When I replaced the pressure cap on my yanmar 3gm30f, I took the old cap to a local auto mechanic who looked at the cap and said" its a 9 pound cap. I asked him how he know that and he said its engraved on top see: pointing to a 9 engraved into the top of the cap. As it later turned out it was 0.9 Kg per square cm. The decimal point wasn't clearly visible and there was no leading zero. I bought a 10 psi cap that fit but what I really needed was 12.8psi
 

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Old as Dirt!
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3,487 Posts
Discussion Starter #3
When I replaced the pressure cap on my yanmar 3gm30f, I took the old cap to a local auto mechanic who looked at the cap and said" its a 9 pound cap. I asked him how he know that and he said its engraved on top see: pointing to a 9 engraved into the top of the cap. As it later turned out it was 0.9 Kg per square cm. The decimal point wasn't clearly visible and there was no leading zero. I bought a 10 psi cap that fit but what I really needed was 12.8psi
In the case of the Perkins, "10 PSI" is inscribed on the original equipment cap which seems to comport with the listing in the shop manual for the engine (according to our Diesel mechanic).
 
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