Yanmar 2GM20F overheating.

[kcscoop]

I have a 1987 Hunter 31....Had a problem one weekend when I was running under power......I heard a clinking sound coming from below. Sounded like a zinc on the prop shaft may have come loose. Monthly dive service said all was fine on bottom. When running we could here the clinking...... I was only able to get about 1500 rpms. at full throttle. Made it ok to our destination. On return trip had same issue ....along with the temp gauge started to climb past the normal 180 to about 220. I pulled back on the throttle to just a bit above idle, and the temp came back down. Now back at the dock the engine runs fine, no clinking, revs up to over 3000 rpm and idles perfect. Watching the temp at the dock it steadily will climb past 180 till my alarm comes on. I've read other overheating issues on here and have started my process of elimination. New belts, proper tension. Tested thermostat, opened in a pan of hot water. My next move is to change the seawater impeller. I do have a sea strainer.....have not checked it yet. Fresh water pump they say is bullet proof.....then come the heat exchanger. ANY ADVICE would be greatly appreciated. What should be my next move?

 

[MitchM]

1) how old is your coolant? coolant too old can lose a lot of capacity , yan mar recommends changing it each 300 hours 2) did you ever clean your heat exchanger? 3) any chance there is a piece of raw water impeller stuck in your heat exchanger? 4) is your overflow tank topped up to full? 5) are you losing coolant?

 

[kcscoop]

1)new coolant 2) never had heat exchanger out to clean, hoping to find prob before having to tear it apart. 3) Maybe 4) yes 5) no. Sound and not getting full rpm under pwr,,,,,is puzzling me

 

[LeoLambert310]

check your raw water pump impeller and a quick check feel the raw water outlet hose if hot then no flow as it should be the same temp as the inlet.

 

[Benny17441]

One of the overheating causes that may accompany a loss of RPM is a clogged exhaust mixing elbow. It will restrict raw water cooling flow and engine combustion exhaust restricting RPM. There is always the possibility of a compound fault, drain the water separator and replace the primary and secondary fuel filter elements. Do replace the raw water impeller.

 

[kcscoop]

Thanks guys, will try everything, what could be making that clinking sound? Only hear it when in gear running full throttle.

 

[mz4wheeler]

Thanks guys, will try everything, what could be making that clinking sound? Only hear it when in gear running full throttle.

With the boat tied to the dock put it in gear and slowly rev it up until you get the sound... Really swirls up the marina [grin]. Look below at all the engine components. Might just be something shaky loose, like an alternator bracket or motor mount. This also heats up the engine fast too.

 

[Ralph Johnstone]

I heard a clinking sound coming from below

Can't guess how that noise is related to overheating but this is an easy one to check but expensive to replace ..........

 

[kcscoop]

Would a clogged elbow reduce RPMs to about 1500... only when running in gear? I have no problems when in neutral .....revs up to 3300 and very responsive.

 

[kappykaplan]

Yes.

 

[kcscoop]

clogged elbow don't effect rpms in neutral ?

 

[kappykaplan]

Didn't affect me when I had the dreaded clog.

 

[kcscoop]

Thanks Kappy....going to work on it this weekend, going to do the raw water impeller.....then tackle the elbow, and hope that's it, keeping my fingers crossed it not the heat exchanger. The clinking sound....gonna try putting it in gear at the dock ( think I will do that at night) LOL. and see where the noise is coming from. I want to thank all you guys for your feed back....all is welcome. KC

 

[Ralph Johnstone]

Would a clogged elbow reduce RPMs to about 1500... only when running in gear? I have no problems when in neutral .....revs up to 3300 and very responsive.

When in neutral, it takes very little fuel to goose the engine up to 3,300 RPM as there's minimum resistance.

When in gear, there's much more resistance so much more fuel is injected to try to get up to speed. That fuel produces much more carbon dioxide which causes back pressure in the mixing elbow hence less RPM.

 

[Ralph Johnstone]

I want to thank all you guys for your feed back....all is welcome. KC

A small gratuity is expected by all if this solves the overheating problem.

If not, we said "nuuuuuthing" as stated by Sgt. Shultz in Hogan's Heroes .

 

[kcscoop]

LOL....$$... Thanks again will post results on what I find, and pics to help anyone in the future with this same type of prob. KC

 

[kcscoop]

Started at seacock...removed hose to sea strainer, opened valve and no issues there. Sea strainer basket was full of sea grass. rebuilding it now...waiting on gaskets. Hope this is my overheating problem. Heat exchanger was fine. Only thing left is the mix elbow. Could the sea strainer being clogged not get me full RPMs while running?

 

[Ralph Johnstone]

Could the sea strainer being clogged not get me full RPMs while running?

A clogged strainer would only result in overheating of the engine which would not affect the RPM's.

 

[kcscoop]

Thanks again Ralph for the feed back......Should have the gaskets today for the sea strainer. Soaked the brass in vinegar ......WOW like new. I will have all in place this weekend....have gone thru everything, seacock, sea strainer, raw water pump, heat exchanger, only two things left....mix elbow and fresh water pump. If overheating prob is gone.....I will take out and run, but this time with someone down below too see whereabouts the clinking sound is coming from. Ralph, here's a dollar two ninety eight....don't spend it all at one time, LOL. Or you can divide it out accordingly to all who left feed back....again many thanks to all members of this forum.. KC

 

[Ralph Johnstone]

Soaked the brass in vinegar ......WOW like new.

Now vinegar is something I've never tried. Always gone with something more expensive and dangerous but with dubious results. Thanks for the idea.