Yanmar over heating

Bill Roosa · Oct 8, 2011

What is your max continuous RPM?
Check your strainer it may not be clogged but might be restricting enough so that at high RPMs it causes an over heat condition

seadaddler · Oct 9, 2011

Cooling

Could be a few different things and check water coming out exhaust when at low rpm's at dock in neutral and than with higher rpm's and check how much water coming out and compare.
Also could be clogged up cooling system and may need cleaning and also check mixing elbo.
Nick

kloudie1 · Oct 9, 2011

After the strainer, if you have another episode, check these others .. They all start as higher RPM problems but get worse.. Water pump drive belts for tightness, both of 'em .. the small elbow after the heat exchanger where raw water enters the exhaust mixing elbow.. and finally the exhaust elbow itself to be sure that the exhaust opening is not partially plugged and the raw water side is clear and flows water freely..
3400 RPM is the rated continuous speed for that engine, but the tachometer may be off by a bit.. get a true RPM reading to compare to what the tach is telling you .. The handheld tachometers are fairly inexpensive. http://www.harborfreight.com/digital-contact-tachometer-66400.html
There are optical ones (non-contact) too that are only $10 or so more..

Steve Dion · Oct 9, 2011

Has this been a problem in the past?

If you mixing elbow is clear you may want to check the heat exchanger and then check the prop. This together with the proper sized prop/pitch can cause these problems too.

It was common to have over-pitched props on this generation of H31 & H34's.

tkbio · Oct 10, 2011

thaeni said:
I have a Yanmar 3GM30F. While motoring I increased the RPM to
3400 for about 40 min then the over heat alarm went off. I stopped
the engine and checked the impeller and all was OK. I restarted and
continued on at 2500 RPM for another 2 hrs with no over heat. Any ideas
why it over heated at 3400 RPM ?
Thanks

I had this problem and it turned out to be that some of the channels in the heat exchanger were clogged with salt deposit. I took it apart and cleared the blocked channels with a wire. Pretty easy to do. Now I make sure to flush and drain it before winter layup.

Rod10027 · Oct 10, 2011

You might want to check your belts fro slippage at the higher RPM... my 2QM15 was doing the same... impellar was first thought... a belt adjustment solved the problem...

Dan Johnson · Oct 10, 2011

Water intake...

If after you've checked belt, impeller, and strainer, try checking the size of the thru-hull water intake for the engine. Most Hunters seem to be a bit undersized. Running at 3,400 RPM you're putting a strain on the amount of water that can be pulled through what is commonly about a half inch ID thru-hull and hose feed through a strainer to the raw water pump.

Though anecdotal, I've heard that running the 3GM30F harder than cruising RPM over time will result in over-heating due to the lack of enough water flowing through the heat exchanger. Some owners have increased the thru-hull and hosing to 3/4" to compensate.

As you are sailing in Lake Michigan, I doubt if it's clogged strainer tubing due to salt. Could be silt clogged though.

captainpat · Jan 15, 2012

3400 rpm's sounds high for the Yanmar 3GM30. I believe that is the max. It should be run at about 2700-2800.

whatfiero · Jan 15, 2012

RE : Yanmar overheat

I second the max rpm theory It's 3200 on the 2gm20 and 1 hour max run time for 3400 I feel 3000 is a safe cruze speed to avoid problems

John T1594 · Jan 15, 2012

PRM's

I have a 2000 3GM30F. The Engine plate says Max RPM 3,600, Continuous Rating 3,400 RPM". The sweet spot on my boat (H340) is about 2800 RPM for low noise & vibration and best fuel consumption and boat speed.

captainpat · Jan 16, 2012

Re: PRM's

My '90 35.5 had an older 3GM30 which may explain the max rpm difference then what John states. However, if the newer Yanmar is rated 3,600 max I would opt to cruise at 2,800-2,900 which represents the 80% of max that is often recommended. Thaeni's boat is a '92 I believe, which would have the older Yanmar like I had. I ran mine most of the time at 2,700-2,800 with occasional bump ups to 3,100 for short periods of time. I would sometimes max it out for a minute or so every once in a while to check on the foulness of the bottom and to blow out any carbon build-up. I'm thinking that if "thaeni's" boat is overheating after as long as 40 minutes it's probably not due to many of the common overheating problems, which should make themselves evident much sooner - especially at that rpm setting. I would suggest lowering the continuous operating rpm's to 2,900-3,000 or so and see what happens.

Crazy Dave Condon · Jan 17, 2012

The owner did not mention the year of his boat but the above suggestions are all good with the impeller being checked first, any clogging at the water intake, hoses, strainer, etc.

When the 29 hp Yanmar first came out appx 8 years ago or in that time range, not enough "bundles" I think cooling coils were added causing that engine to overheat. More had to be added to correct this situation.

Bill Roosa · Jan 17, 2012

A surefire way to tell if the HE is minimal is if the water temp gage changes temp with changing power levels. the thermostat SHOULD keep the water a a fixed temp. If the thermostat is open all the time then the HE determines the engine temp. this would be an indication of the HE not being robust enough to remove all the engine heat without increasing the water temp to increase heat flow. which is why your temp gage has that region with both green and red lines IMHO