Overheating engine...

[Doug/Karen]

Our Yanmar 3GM30F engine overheated earlier this Spring. We have a new repair shop owner on the lake this year and I decided to give this problem to him as a "get acquainted" job. He diagnosed the problem as a broken impeller and proceded to fix it with the comment that our engine is one of Yanmar's "European" models, Serial No. E3030. Apparently, the European models have a different impeller housing that required him to get a slightly different impeller replacement kit.

Next time out with the boat under power, it again overheated. This time, his diagnosis revealed a melted plastic O-ring seat that would take a little longer to source. Meanwhile, he came up with a homemade fix that he said would serve us well until the damaged part came in.

Next time out with the boat under power, it again overheated. Now he has said that he is not certain whether the problem is the water pump itself or the thermostat. Given that the thermostat is a much less expensive solution, I encouraged him to go there first, but, in the meantime, I began thinking this problem has probably been experienced by a number of my fellow Hunter Forum members and perhaps I should submit this thread.

Any comments, as always, will be appreciated.
Doug.

 

[Rick D]

Doug, when my 3GM overheated, I found that the exhaust elbow was clogged thus severely restricting the flow of raw water through the heat exchanger. Good luck; it would be the first thing I would check.

 

[Jeff]

My 3GM30F has over heated twice. The first time was the impeller. The second time it was the failed cork gasket on the strainer basket cover. Air was getting in at high RPM's. It was pretty easy to buy a piece of cork and remake that gasket.

 

[navigator97]

Doug, Rick's point is a good one. Can you determine how many engine hours since the mixing elbow was last changed? I would generally not like to go over 500 engine hours between replacements. Being a little anal, I keep track of engine hours on each trip (however long or short) and note the engine hours at the time of any engine part change out, oil change, coolant change, etc.. Another routine check is the Raw Water Intake Strainer, to be sure it's not clogged as well as the hose from the intake sea cock and the strainer. Good luck with your ongoing diagnosis.

 

[Steve Dion]

The elbow is a possibility but probably not the issue. Doug/Karen are located in fresh water.

If he ends up replacing the water pump you may want to consider the US version if that is possible. It will be easier to get impellers in the future.

Are you kicking water out of the exhaust while idling and underway?

I would also check all of the hoses/thru hull to be sure that the hoses are not collapsing or something in the engine intake.

 

[Rick D]

Ah, Steve was good to point that out. While it certainly reduces the possibility, it doesn't eliminate it. So, I think I'd pull off the front of the heat exchanger to look at the tubes and to be sure there isn't any missing impeller pieces blocking the flow (had that happen too) after you do the hose inspection, etc. Another very long shot is a bad run of impellers a while ago which spun on their shafts after a while and caused problems. Another issue was growth blocking the intake thru-hull one time. Running a gun cleaner through it took care of that issue, another simple check.

 

[Doug/Karen]

Thank you all for your comments. At the moment, the repair shop owner has informed that he discovered one of his hands had left the belts untensioned after doing the impeller/pump inspection. After re-tensioning them, he has run the engine several times both in and out of gear with no further overheating. With the Missouri Governor's Cup Regatta coming up this weekend, we will see how that works for us.

 

[Don Lucas]

the repair shop owner has informed that he discovered one of his hands had left the belts untensioned after doing the impeller/pump inspection.

WOW! Another quality boatyard worker