white smoke and overheating on MD7A - Page 2 - SailNet Community
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post #11 of 15 Old 07-04-2010
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I think Gene has it right about water boiling through the exhaust, then cooling off again in a cycle. After connecting a clear hose between the thermostat and exhaust elbow on my MD11C, I could see bubbles coming through just as the temperature begins to fall during the heating/cooling cycle that has been happening in my motor. Both heads have been off (one replaced) and water passages are reasonably clear in heads and cylinder jackets after a recent Rydlyme flush.

Has anyone solved this problem by replacing the manifold? It looks pretty rough, and although water is getting to the overheating back head, it obviously isn't enough.

Thanks,
Bob
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post #12 of 15 Old 07-05-2010
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A non contact thermometer can find the hot spots and probably give you a good idea where the blockage is. It is difficult to clean using any kind of solution if things are completely blocked because the solution can not get to the problem. But you can do a good job with a stiff wire and a hose to wash it out. I worked on my manifold for several hours and got it very clean by poking the wire in all the passages. If you need to pull the heads to do this you will need to plug all oil passages and the cylinders. This is the kind of problem that generally does not cost much if you do it yourself but it takes a lot of time and is messy.

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post #13 of 15 Old 07-06-2010
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Several years ago I took everything apart, had the cylinder liners pressed out, and did a full de-scaling by hand. It ran well for a long time after that, but the back cylinder always ran hotter to the touch. Now wishing I had picked up an IR thermometer years ago, I can measure temperatures just over 200F where the rear head and manifold meet, but only 150-160F on the front.

The manifold on this MD11C had a previous problem that I haven't seen on any boards before: one side of yoke-shaped frame of the thermostat came loose so it was hanging on one mount, vibrating against the iron manifold. The lower temperature was masked by the temp cycling previously described so by the time it was discovered the thermostat had worn a hole clear through to the lower manifold chamber. A patch made with JB Weld is still holding, but makes me consider replacing the manifold to protect my recent investment in a new head.

The old head, incidentally, suffered a corrosion hole between the exhaust port and water jacket. I'm told this is a common way for the head to fail (it lasted 30 years..). It seems as though early in the leak, small amounts of water were corroding the valve guide and starting problems there before bigger symptoms like lots of steam or a hydrolock cropped up.
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post #14 of 15 Old 07-06-2010
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Volvo MD11C - more cooling details

Several years ago I took everything apart, had the cylinder liners pressed out, and did a full de-scaling by hand. It ran well for a long time after that, but the back cylinder always ran hotter to the touch. Now wishing I had picked up an IR thermometer years ago, I can measure temperatures just over 200F where the rear head and manifold meet, but only 150-160F on the front.

The manifold on this MD11C had a previous problem that I haven't seen on any boards before: one side of the thermostat's yoke-shaped frame came loose so it was hanging on one mount, vibrating against the iron manifold. The lower temperature was masked by the temp cycling previously described so by the time it was discovered the thermostat had worn a hole clear through to the lower manifold chamber. A patch made with JB Weld is still holding, but makes me consider replacing the manifold to protect recent investment in a new head.

The old head, incidentally, suffered a corrosion hole between the exhaust port and water jacket. I'm told this is a common way for the head to fail (it lasted 30 years..). It seems as though early in the leak, small amounts of water were corroding the valve guide and starting problems there before bigger symptoms like lots of steam or a hydrolock cropped up.

-Bob
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post #15 of 15 Old 07-06-2010
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I'm not a big fan of Harbor Freight tools but I did pick up one of their infared (gun type) thermometers and it works great. I got it to measure and trend temperature data on my Volvo MD7A engine that has some, relatively minor, overheating issues. The thermometer was a little less than $30 on sale and seems pretty accurate.
I'm following this thread with interest - thanks to all the contributors.
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