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Old 01-10-2012, 13:56   #16
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Join Date: Jul 2006
Location: Chesapeake Region and Maine
Boat: 42' Bob Perry sloop
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Re: Perkins 4-108 Corrosion on new heat exchanger

Mike,

Yeah, you're right. The 4-108 is nowhere near a 50hp engine as some claim. I put it closer to 30hp.

The super duper mechanic who finally put me straight (a friend I flew down to St. Thomas after dealing with local mechanics, including ex-pats, for years) told me that if the heat exchanger were working properly and if the engine were not over-propped, it should be possible to to push that engine wide open for a long time without overheating.

After doing his magic -- and finding several things wrong -- he made me power at full speed from Nanny Cay in the BVI up the Drake Channel to Cooper Island. Sure enough, no overheating.

But, that was with a NEW heat exchanger, and everthing tweaked up right.

After I fitted the larger heat exchanger a couple of years later (having again experienced overheating), I've had no more problems.

Conclusion: that heat exchanger on the 4-108 is too small, especially if you're sailing in warm water temps in the tropics.

Re: RPM, I can power at 2500-2600 indefinitely, but use a lot of fuel. I find that 2300-2400 suits me better. My boat has a 17" 3-blade MaxProp and weighs about 27,000 lbs.

Bill
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