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post #1 of 5 Old 07-09-2003 Thread Starter
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I have one of these faithful motors in my ''78 Islander Bahama 30. Original motor with very good compression. The only issue I have is the soot that it produces at cruising RPM (2200). It covers the stern of the boat at the waterline and up for about 3 inches. I have re-pitched the prop from over to under pitched with some reduction, but not elimination of the soot. I have replaced the exhaust elbow and ensured that the air cleaner is clean (no back pressure and or lack of air). Anything that I''ve missed? If these engines are prone to produce soot, is there a non-damaging way of removing this soot from the gelcoat and paint?
On the same engine, it runs hot at 2200rpm, around 200 to 250 degree. Raw water cooled. The water pump is in "like new" condition and the thermostat has been cleaned and in good condition. The through hull is also clean, as is the strainer. Any ideas?
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post #2 of 5 Old 07-10-2003
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Volvo MD7A

Try a Cetane booster. Many of the older engines require a higher cetane number than what is commonly found nowadays. Just like octane has been reduced in common ''regular'' grade gasoline, so too has cetane been reduced in diesel fuels. My old Yanmar will soot with the available fuels but with a cetane booster (added to the fuel) it doesnt.
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post #3 of 5 Old 07-10-2003
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Volvo MD7A

Ah... The old MD7A. 2200? Get the revs up to 2400 - 2600 and that may take care of some of the sooting problem. It always seamed to wash off well enough with just soap and water scrubbed lightly with a washcloth.

I had a lot of cooling problems too and had to back flush the motor on a couple of occasions. At around 500 lbs., she''s a heavy motor with casting thickness to handle seawater cooling but the water jackets and ways are a tad small so they tend to block up easily.

I guess I took care of the problem once and for all and evicted that patent thing from my bilge along with all of its superfluous paraphernalia. Then I hung an outboard motor on the stern and life has been wonderful ever since!
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post #4 of 5 Old 07-10-2003 Thread Starter
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Abandon an jewel like the MD7A?!? That''s like saying goodby to an old Atomic 4 (which I have done!). No, for the price I''ll be sticking with this one for a while. It''s still in great shape. I will try the flush as well as the Cetane booster. Thanks for the info.
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post #5 of 5 Old 07-14-2003
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I recently had the same overheating problem with my Volvo MD11C. 1) I had an abstruction in the raw water inlet valve. 2) I removed the exhaust manifold and had it boiled out.
It now runs cooler and discharges more water out of the exhaust. If the manifold has never been off and boiled out that maybe the annswer to your heating problem.
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