H28 Yanmar overheating at 3000 RPM

[eliems]

2GM20F and the alarm goes off after an hour at 3000 RPM, is this normal?

Sea strainer is clear, coolant is up, impellor is new, should I replace the thermostat?

Engine has 2000 hours on it and is otherwise in perfect condition.

I did once screw up with the sea valve and destroyed an impellor (little pieces poured out and perhaps some went in to the elbow).

If I run at 2800 RPM it doesn't happen.

 

[Ralph Johnstone]

Check the mixing elbow by hand for temp. at 3000 RPM after an hour. It should be warm at most. If not, time to start checking:

1. Raw water pump condition.
2. Blockage in the mixing elbow.
3. Blockage in the exhaust line.
4. etc.
5. etc.

 

[kloudie1]

Not normal and probably not your thermostat. Did it just start after you replaced the impeller? couple of things if it did.. There have been some reports of the impeller slipping on the shaft that is it could be not turning as fast as the shaft. That should get worse pretty fast as the rubber wears.. Is the belt tight enough? OK, next is more complicated.. Get two gaskets, Yanmar part # 128695-44070. Drain your coolant then pull the covers off the heat exchanger bundle. Some of the old impeller parts may have gotten into the tubes and the waterflow may be partially blocked.. Get a 9mm pistol cleaning rod about a foot long and brush the insides of the tubes. Clean the outside of the tubes too but you won't be able to get at most of em .. there is a cover on the outside.. don't try to take it off. If you aren't comfortable with this kind of work, get a good mechanic to do it.. Next, make sure your raw water strainer gaskets are good, especially the top clean-out one. They can admit air under high flow and cause strange overheating.. Happy Hunting, eliems

 

[Cmp1110]

Isn't 3000 kind of high for one hour, mine yanmar will heat up if I run that hard 3000 is almost max power versus 2600 cruise I believe it is rated at full power for only 10 min or something like that

 

[eliems]

Isn't 3000 kind of high for one hour, mine yanmar will heat up if I run that hard 3000 is almost max power versus 2600 cruise I believe it is rated at full power for only 10 min or something like that

That's the thing, if there is nothing wrong and the motor just does not want to run at 3000 then I could be looking and replacing everything with no results.

This is the 18 hp so perhaps not normal for a bigger motor but normal for mine?

ps: Belts are tight. This has been going on for 500 plus hours so can't be slipping impellor, more likely elboe blockages from the rubber bits but shouldn't they break down after a time and leave the system?

No one thinks it is likely the thermostat?

I will try the hand on the mixing elboe test, should be warm but not hot to the touch?

 

[Steve Dion]

Eliems: I would guess it is your mixing elbow.

Have you ever inspected it? The manifold and elbow are a real SOB to get appart. They get coked up after 400-500 hrs. Some owners just bite the bullet and replace the entire setup. They are quite often corroded/rusted and can only be taken apart with a torch and some large tools.

 

[Steve Dion]

Isn't 3000 kind of high for one hour, mine yanmar will heat up if I run that hard 3000 is almost max power versus 2600 cruise I believe it is rated at full power for only 10 min or something like that

These engine should run all day at 2800-3000 RPM. They have a max rating of 3600 and can be run continously at 3000 RPM.

http://www.yanmarhelp.com/operate.htm

If you are having issues it can be your prop, bottom condition etc.

 

[Stu Jackson]

more likely elboe blockages from the rubber bits but shouldn't they break down after a time and leave the system?

Common misconception. The rubber does not break down and disappear. What happens is once a vane breaks off, which occurs from a failure at the point where the vane meets the hub, or at the point where the vane end gets a tad wider near the tip, the piece(s) break off and clog pipe elbows from the pump, the hose to the HX and the HX themselves. These are usually not tiny little pieces, but pretty hefty chunks.

They don't breakdown. Why? 'Cuz if they did, you wouldn't want that same material to BE your impeller, would you?

 

[Dave602]

At the end of last season my 2GM20F would overheat same as yours. My speed was also going down. During spring commissioning had a diver clean my prop of "Moderate to Heavy growth". No more problems this season. Speed is up, she will run at 3000rpm all day in very hot weather. Not one overheat this season. Just something else to add to the list of things to check.

 

[Benny17441]

After an impeller failure the system should be flushed thoroughly to help prevent blockages. Soft hoses are prone to collapsing and they may also become partially blocked by salt and mineral deposits and foreing matter that gets past the strainer.

 

[brigadoon340]

One addition to the comments above. I had a couple occurences of overheating and checked the strainer, changed the belt and made sure it was tight, changed the oil, oil filter and airfilter, replaced the impeller, checked the mixing elbow and still had overheating issues. What finally fixed it for me was nothing more than a little bit of grease / lubricant on the o-ring by the impeller. Apparently, when I replaced the impeller, I forgot to re-lubricate and the seal was just loose enought to suck in air instead of water. Hope this helps if you still have issues.

 

[mr c]

Mine did the same thing. Opened up the heat exchanger and several tubes were clogged and I took off the mixing elbow and it was partially clogged. Cleaned both out and no problems this year. I can't even believe its the same engine.