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Old 09-06-2015, 12:11   #1
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Diesel overheated

I'm new to this forum and new to ocean sailing. I recently bought a boat with a Westerbeke 40, built in 1978 with 1800 hours.
I checked the engine before taking it out and found the coolant level a little low and topped off with 8 oz. of water.
I hired a captain/instructor to teach me docking instructions inside the harbor.
Day 2, the captain had me check oil and water again before going out to sail. This time we found the reservoir completely out of water and kept poring until we found the water running into the bilge. I immediately called a nearby diesel mechanic who said there was a leak to the water heater and would just plug off for now, so we could sail that afternoon
We went about a mile past the breakwater and the alarm went off and steam started filling the cabin from the motor.
The captain motored us back in just past the breakwater and shut off the engine and then sailed back in.
I am wondering how long an engine like this can run typically before ruining the engine? (The mechanic said the engine must have had an air bubble)

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Old 09-06-2015, 12:22   #2
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Re: Diesel overheated

Cast iron engines, both head and block, are very tolerant of overheating. Over the years have run a number of engines without coolant because of stupidity on my part or mechanical failure. All seemed to work just fine after. Did not run any of them to seizure, however. As long as the engine didn't seize up, you probably did no damage to it. If the problem is water blockage on the raw water cooling side, you should check the impeller in the pump. Running them dry for a long period can damage the vanes on the impellor.

I nursed my 3GM30 Yanmar back to the slip by adding coolant as it boiled away because of lack of cooling water caused by critters in the raw water intake. Several hundred hours later it is still doing fine. If I would have thought about it more clearly, should have called for a tow. Don't recommend doing that.

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Old 09-06-2015, 13:04   #3
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Re: Diesel overheated

I agree about a cast iron head being resistant to cracks if overheated. Aluminum will crack if there is no coolant in the head. There are kits you can buy at an auto parts store that will tell you if any exhaust is getting into the cooling system, a sure sign of cracks; however, smaller cracks can occur that will not leak exhaust into the cooling system until they get larger. Will a magnet stick to the head (the top part of the engine not including rocker are cover)? If so, do not worry. If aluminum head, pull it and take it to a shop that specializes in welding aluminum automobile heads. Have them pressure test and weld any cracks that are found. Aluminum heads weld easily. Cast iron is more difficult to weld and can crack if scale develops inside the engine where coolant circulates, especially with direct raw water cooling.
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Old 09-06-2015, 14:48   #4
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Re: Diesel overheated

Thanks for your prompt replies!
The engine did not seize while running.
I might add that after we were towed a short distance inside the harbor from the Harbor Patrol Dock to our slip the engine was again turned on for just a minute or 2 to reverse gear to slow approach. The engine started and acted normally, though still hot.
The next morning, I looked at dipstick and did not find the oil to be milky, but normal looking.
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Old 22-06-2015, 16:52   #5
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Re: Diesel overheated

I am rebuilding a Perkins diesel that overheated and seized. This was due to a lack of water thru the raw water circuit. Raw water pump had been run so long that the impeller was shredded (cam had worn down to sharp edges), passages thru the oil cooler and heat exchanger were blocked up. So, the whole system has to be in good order. You might want to check all the components.
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Old 22-06-2015, 17:12   #6
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Re: Diesel overheated

Whenever I do any engine work, I won't leave the slip without testing the engine to fully warmed-up, for at least 20 minutes. I use reverse gear and moderate RPM. Haven't snapped the dock lines or cleats yet!

Once after bleeding the fuel system, the engine cut out after 10 minutes with an air bubble. I'd rather find this out, in the slip.

I suggest before going out again, that you make sure the engine is running right and not overheating.

I haven't seen any mention of the raw water flow. Is there a healthy flow of cooling water out of the exhaust? Is the seacock for the raw water even open?

The first thing I do after starting the engine, is look over the stern and check the raw water flow. Then the voltmeter, to check charging. After a couple of minutes, the coolant temp gauge should be registering.
Bristol 31.1, SF Bay.
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Old 22-06-2015, 17:23   #7
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Re: Diesel overheated

What can happen if it really gets hot is the rings can loose some of their tensile strength and you can start to develop blowby which starts to pressurize the case.

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