Yanmar 3gm35h cooling problems

[jwhusted]

My Yammer 3gm35h has been working flawlessly for over 20 years in my Pearson 36-2. This season intermittent no flow out exhaust. Entire raw water cooling system taken apart including the exhaust manifold. Impeller which looked good was replaced. Will run well for 2-3 hours then water will trickle out or stop pumping out exhaust. Belt is properly tensioned. Again entire water flow examined and wide open. Next AM will start and have good exhaust, again will run well for 1-2 hours at 2500 then stop pumping out exhaust. How can I check if there is a problem with this totally mechanical water pump.

Pearson 36-2 1989, coastal sailing off the N.J. shore

[AA3JY]

Age of hoses? Possible hose collapse..

[bensolomon]

Sounds like you may have to replace the sea water pump.

[Wotname]

First we need to know the actual model AFAIK Yanmar did not make a 3GM35h. They did make a 3HM35 and a 3HM35F. They also made a 3GM30 and a 3GM30F and perhaps a 3GM30H.

Is it a coolant cooled engine or a direct raw water cooled engine?

If it is direct raw water cooled engine, the water gallery in exhaust manifold could be clogging up. When the engine is cold, the thermostat directs the raw water away from the exhaust manifold and directly into the exhaust mixing point. Once fully warmed up, the thermostat directs the water through the exhaust manifold, if the manifold is clogged, the water flow is now restricted.

[bil56]

"Impeller which looked good was replaced"
and the pump cover ?

[jwhusted]

Thanks, Yanmar is 3HM35F not was I had thought. Pump cover was ok. It is fresh water cooled. Recently the hot water heater was removed when it rusted out. The raw water was then short circuited to the engine block. Each section of the raw water course was disconnected and there was excellent flow demonstrated. all the way through and into the muffler. When exhaust water stopped, just steam would be produced.

[Howler]

I'd check the heat exchanger (if that model has one) where internal coolant "meets" raw water. I'd also check the mixing elbow where raw water is mixed with exhaust gases before exiting. Both are known to get clogged over time.

[captstu]

It is hard to tell from the discussion, but I assume the fresh water section (with appropriate antifreeze) is circulating and is overheating? If so, that part of the circuit is working. At your engine's age, you might need some Barnacle Buster to clean your heat exchanger???

The 3GM series is notorious for clogging of the exhaust elbow where the hot salt water is injected into the exhaust stream - the symptom is little or no raw water flow out of the exhaust. If the elbow was last replaced over 700 hours ago, replace it! A cheap fix compared to the overheat and blown head gasket caused by the clog. The older ones were cast aluminum with a steel or bronze nipple threaded in near the top of the elbow. The new ones are either exact replacement or for a bit more money all stainless steel. The stainless ones have no lifetime limit and are better for high use engines. https://www.ebay.com/itm/23242524291...BoCKL0QAvD_BwE

[Granfalloon]

I had similar issues with a Yanmar 2GM. I did a remove and replace on the Mixing Elbow. - The old one was seriously coked up. I soaked it with acid and chipped a bunch out and saved it for a backup. In ant event Problem Solved.

Engine hours at the time were around 759 hrs.

In addition, after the engine was warm, I would increase RPM to around 3000 for a minute and do this going out before raising the sails and on my return. Operating at low RPM tends to cause the build-up.

[sinnerman]

Dumb question, but did you verify that your raw water thru hull fitting / valve is not plugged?

My story:

After installing BRAND NEW thru hulls and valves , when I went to fire up my air conditioning for the first time since the job, there was no water flow through the cooling pump.

Back tracing the pump / filter, I discovered that the thru-hull was blocked with some unknown crap.

I had to run a stiff wire through the valve to clear it.

Barnacles, sea life, plastic, disposable diapers (yuk), all can find their way to block the intake.

My two cents.

Cheers.

[bil56]

I do not agree (for direct sea cooling engines) :

if the engine is turned off hot after a little heavy use, the calories remain in the cylinder head and the temperature rises, crystallizing the salt more quickly
it is therefore advisable after use to leave the engine idling without load to lower the general temperature ...

[gonesail]

you say you checked the mixing elbow .. when did you replace it? that thing can cause a lot of problems .. especially if you are seeing any steam in the exhaust.

[alamoana]

I would chase the problem with an IR temperature gun if available. You will find it fast. Good luck

[jwhusted]

Thanks for the help. Thinking it through, I believe it’s related to us re-positioning the raw water hoses, which extends slightly above the pump, likely causing an intermittent airlock. We’re going to re-adjust the hoses and see if that does the trick. Thanks for the IR heat gun suggestion. I happen to have one I’ll check that out as well. Thanks a lot jim

[roverhi]

Replace the mixing elbow. The 2gm20f in my new to me boat had less than 200 hours on it when the water out the exhaust suddenly diminished. Engine had been started occasionally but not run long enough to warm up thoroughly over a couple of years. Owners had died and good samaritans periodically started the engine while issues with the estate were cleared up. It can only take a few hours run time for that