Engine overheating

Post here issues with diesel engines on PDQ yachts
John&Ria
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Re: Engine overheating

Postby John&Ria » Tue Apr 11, 2017 2:01 am

An update: We just tested the engines after annual maintenance, which included new water pumps (one was leaking), a chemical flush of the heat exchangers, and inspection of the exhaust elbows (both good). Although it took somewhat longer to get there, at WOT the starboard engine still ran up to 200 degrees, at which time we throttled back to fast cruise. At that pace the temperature was steady at 175.

Next step will be to replace the thermostat.

sailkane
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Re: Engine overheating

Postby sailkane » Thu May 04, 2017 5:45 pm

Quick check.... swap the thermostats from starboard engine to Port engine and then do the test at WOT

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Re: Engine overheating

Postby John&Ria » Mon May 08, 2017 10:02 pm

Thermostat on starboard engine swapped out, but overheating at WOT persists. Next step will be to see if we can diagnose where/how the problem is occuring by using an IR thermometer while running at full load. I plan to be at the helm while our mechanic slaves over the hot engine at 20 mph.....

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Re: Engine overheating

Postby sailkane » Tue May 09, 2017 10:14 am

I am battling a similar problem...except one of my engines runs 15 degrees hotter all the time.

I did have a situation 2 years ago where the engine only overheated at wot and went back to 175 when reducing the throttle.
I found the rear raw water cooler cap where the raw water enters the heat exchanger and exits out , has a gasket that separates the input from the output had failed. The symptoms of low pressure pushing water through the heat exchanger was ok but as the throttle increased and the water pressure increased it would not go through the heat exchanger but push right out the exit cap, causing the overheat.
The water followed the path of least resistance.

Good luck.

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Re: Engine overheating

Postby John&Ria » Tue May 09, 2017 12:03 pm

Thanks Sailkane. I will share your story with our mechanic. One question - was the leak at the exit cap leaving much water in the bilge under the engine? Part of our puzzle is that the engine bilge is dry, with no sign of either water or coolant there. The coolant retainer tank drops by a few inches and requires topping up periodically on the problem engine, but there's no sign of where the coolant goes.

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Re: Engine overheating

Postby sailkane » Tue May 09, 2017 6:13 pm

No leaking. The inside of the cap is split in half...the gasket covers the outside perimeter and across the center diameter. Top half of the cover is the input water to the heat exchanger, bottom half is the output of the heat exchanger. If the inner gasket is not on correctly then the back pressure goest right out to the bottom of the cap and out the hose.

This happens if someone has taken off the cap to inspect the heat exchanger and put it on again. You only notice the problem at full throttle.

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Re: Engine overheating

Postby John&Ria » Wed May 10, 2017 12:50 am

Thanks for the additional information. It definitely sounds like it's worth a look. I'm not sure if it will make any difference, but for the record what model of Yanmar do you have?

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Re: Engine overheating

Postby duetto » Wed May 10, 2017 8:00 am

with regard to coolant loss and no trace. common causes would be a blown head gasket or in this case the o-ring/gasket on the ends of the heat exchanger. let's eliminate the head gasket for the time being. the bad end cap gasket would explain both the coolant loss AND the heat spike (b/c of the raw water bypassing the heat exchanger per analysis in this thread). i do think that a pressure test would zero in on it. test coolant via heat exchanger cap. test raw water (need to make end cap plug). if both show leaks you've found your problem. unfortunately, i think that you'll be taking the end caps off the heat exchanger.
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sailkane
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Re: Engine overheating

Postby sailkane » Wed May 10, 2017 9:52 am

We have the 75 hp Yanmar. MV 34 year 2005.

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Re: Engine overheating

Postby John&Ria » Wed May 10, 2017 11:21 am

Thanks again sailkane, I appreciate the assistance.

John

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Re: Engine overheating

Postby John&Ria » Wed May 10, 2017 11:25 am

Thanks too duetto for your latest post. I plan to share all of this with our mechanic.

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Re: Engine overheating

Postby John&Ria » Thu Jun 01, 2017 12:43 am

At long last a solution to our overheating issue. While removing the end caps to replace the gaskets and o-rings of the heat exchanger - as suggested on the Forum - we decided to pull the core. Much to my mechanic's amazement he discovered that the core was installed upside down and backward, restricting the flow of coolant. Once reassembled properly with the new gaskets and o-rings installed, the engine performed perfectly. i.e. rock steady at 175 degrees, even at WOT (3200 rpm).

As the engines only had 340 hours on them when I purchased His Idea, and the heat exchanger has nopt been apart until now, it would appear that the installation error occurred at the time the engine was manufactured. I would expect (hope?) this is a very rare event, but if you experience a similar overheating problem that is difficult to resolve, it might be worth a check.

Thanks to all who came to my assistance by sharing their experience and providing useful advice.

John

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Re: Engine overheating

Postby duetto » Thu Jun 01, 2017 7:05 am

great news!
john & diane cummings

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Re: Engine overheating

Postby wrnole » Thu Jul 20, 2017 11:09 pm

John,

When your HE core was removed, what was the position of the "opening" in the shield? Were they on top, bottom or side? I just pulled my starboard HE and sent out for cleaning. I was looking at the Yanmar Service Manual and the diagram has the "opening" on the side. Mine were on the top. I'm not sure if the diagram is correct. I'll probably call Yanmar tomorrow.

Thanks,
Richard
"Soul Sauce" Hull 24

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Re: Engine overheating

Postby duetto » Fri Jul 21, 2017 6:19 am

i believe the openings are oriented to the side, facing the thermostat housing. i think this orientation will make the ridge in the endcap line up with centerline of the he bundle.
john & diane cummings

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