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post #1 of 15 Old 11-08-2006 Thread Starter
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overheating diesel

I just purchased a 1973 Morgan 36 Outisland. The previous owner tells me of two problems with the diesel engine. The engine is a 42hp Perkins.

1. When motoring the engine overheats when going over the hull speed, which is about 7.4 knots.

2. When sailing, the engine overheats and has to be started every 1/2 hour to re-cool. I imagine this is because the prop is turning, but if put in reverse wouldn't it not turn. Would a folding prop solve this problem? It currently has a 3 blade prop.

I appreciate any advice you have.

Thank you.
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post #2 of 15 Old 11-08-2006
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1. Check the impellor or blockage in the cooling system. This often causes overheating.

2. Could you explain the second problem more. You shouldn't have to restart the engine every 1/2 hr. while sailing.

When the prop spins under sail, it has no effect on the engine because the transmission is in nuetral.
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post #3 of 15 Old 11-08-2006 Thread Starter
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Thanks for your reply, I will check the impellor in the spring.

As for the second problem, I don't know much more than that. The previous owner said the engine would overheat while sailing and he had to start the engine every 1/2 hour. Doesn't make sense to me either, but I've never had a diesel engine before, I thought it was a common problem easily fixed. I'll have to talk to him and get more info.
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post #4 of 15 Old 11-08-2006
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Try to get more information then check back. Restarting a stopped engine to keep it from overheating sounds rediculous. Hopefully there's no hidden problems. A good site for engine ?'s is www.torresen.com
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post #5 of 15 Old 11-08-2006
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First Congrats on your new boat!!!

Start by checking the thermostat & the impeller. Not a bad idea to check the flow of water from the the through hull. If that fails to do it, I might suggest removing your heat exchanger, take it to a radiator shop and they will soak it in acid, If that doesn't do it I 'm at a loss.

As far as restarting it while sailing to cool it, this makes no sense to me. Good practice is too run your motor at idle for a few minutes after motoring to cool down the engine a bit, but why its developing heat while its off, just doesn't make sense. Maybe the previous owner lost their mind at sea somewhere?

As far as the engaging the prop, always keep it in gear, preferably in reverse for most trannies. A folding prop wouldn't make a difference in the heat build up but it would make a difference in your sailing performance. Some transmissions, not engines (to my knowledge) can become hot by the shaft turning while sailing because they use a pump to cool the transmission while the engine is running.

Sounds suspicious or someone got their information wrong. I'll be interested to see if any others have experienced similar things...umm???

Last edited by T37Chef; 11-08-2006 at 04:18 PM.
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post #6 of 15 Old 11-08-2006
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ST joint the sailnet Morgan site... great bunch of sailors and very much into maintaining these older classics. There are many threads on over heating on that site.

2ond... I have a Morgan 384 and you should put the transmission in reverse while sailing. Hearth transmissions and the manual will confirm this. However it is very unlikely that the engine would heat up when it is off..so I would check the instrument that says it is... I would bet the gage is at issue in both situations.

3rd pushing an engine past the boats hull speed is fruitless. All your doing is working the engine harder than needed. The 42 horse engine is more than adequate at less than wide open. Our 50 never runs over 2200rpms while you will find other on the Morgan site that run over 3000. The prop seems to be the deciding factor. When you go to the Morgan site we had a discussion about 8 weeks ago about this exact thing. Someone changed props and angels a number of different times until he found the correct one so his engine did not overheat.

Good Luck, you've got a great boat.

John
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post #7 of 15 Old 11-08-2006
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Even the reduction should not get hot because the friction plates are not being compressed by the piston. I build transmissions, and this makes no sense to me-
putting the trans in gear will not do anything as there is no hydraulic pressure. Why don't you sail around a while and then put your hand on the unit and see if it really is getting hot, and post. My money (one cent) says it won't be.
Oh yeah- trying to go past hull speed is pointless, all you are doing is stressing the reduction under steam, or loading the rig under sail.
BTW, that ketch won the Pepsi Americas' sail this year singlehanded...
(had to brag!)

Last edited by empresa; 11-08-2006 at 05:04 PM.
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post #8 of 15 Old 11-08-2006
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My first guess is the impeller. Do you make good water? If this is a yes, my second guess is the heat exchanger. Older diesels will get clogged up over the years and even though they are making good water, they do not pull the heat off well. Third, check your REAL temperature at the block. The sending units for most boats (temperature) are awfully notorious for being way off. It may be nothing more than a temp gauge malfunction.

How does your oil look? I don't know if I can explain it with words, but it should be a smooth black or dark brown. Does it smell charred? Also, if the oil has any kind of a white or milky aspect to it, you should really have a diesel mechanic take a good look at it before using it again. That could mean water intrusion.

Regarding the engine over heating while it is off???? That sounds like a farse to me. It would seem illogical that the prop could be spun fast enough to cause that much friction on the cylinder walls to overheat an engine that is not even on???!!! Also, the comment about running the engine to cool it off, can actually be a yes if you have a turbo. The turbo on my tractor has to be cooled off if it has been worked hard by running it at idle for a few minutes. My little offshore fishing boat had a similair issue. Still, most sailboat diesels do not have turbos, but it is always a good idea to let your diesel run at idle for a few minutes after running it hard (even without a turbo).

I am no diesel mechanic, just some of my observations. Just be glad you have a secondary means of propulsion... a one that is a lot more fun (sailing).

- CD
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post #9 of 15 Old 11-08-2006
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Engine overheating when pushing to hull speed is not uncommon. As you try to exceed hull speed the power demands on the engine skyrocket. On an older engine this is usually just a sign of a collection of problems. Weak impellor, disintegrating hoses, clogged heat exchangers, etc. Usually not a single thing (it it were, the engine would overheat at normal cruise). It is just a reduction of maximum cooling flow. Don't ignore it, but it is not a deal breaker.
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post #10 of 15 Old 11-08-2006
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I also had an over heating issue with higher rpm's on a new boat. I think I solved my problem with new hoses from raw water intake to water pump (older ones were soft and compressed when the engine compartment got hot), replaced thermostat, and removed (temporarily) raw water strainer as the hose conecttions were reducing the inner diameter of the raw water hose and restricting flow.
Water flow thru exhaust has increased and problem seems solved. Next step would be repair/replace heat exchanger.
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