Do all Yanmars overheat? It seems anytime I motor my Yanmar over about 2600rpm the thing wants to overheat.Ive been thru the whole system from fresh water intake to exhaust(shy of taking the heat exchanger off) and havnt found a reason for the overheating. The Yanmar manual does list overpower as a possible reason for overheating. It has the proper salt water sensor and thermostat. Have checked raw pump/impeller etc. It seems to be no problem if I keep the rpms at 2500 or less. The boat is a 1988 H 37.5 and the engine has approximatly 600 hours on it. Any suggestions? thanks
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Paul Akers
It once happen to me also
I have an '88 L37 (3HM35F) and it happen to me once also when I was running at high rpm's. I had it maxed out (3200 rpm's) after doing what a mechanic told me and it overheated after about 10 mins. I let it cool down, and never went there again. I usually run mine about 2400 with no problems and get 5.5 kts.
I have an '88 L37 (3HM35F) and it happen to me once also when I was running at high rpm's. I had it maxed out (3200 rpm's) after doing what a mechanic told me and it overheated after about 10 mins. I let it cool down, and never went there again. I usually run mine about 2400 with no problems and get 5.5 kts.
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Rich
Mixing Elbow?
I'm assumming when you say you've been through the whole system you've checked the raw water mixing elbow? I've always heard that this is the most likely cause of overheating. You need to make sure that it hasn't corroded to the point that it's blocking the flow of water. Sometimes it's hard to tell if it's blocked.
I'm assumming when you say you've been through the whole system you've checked the raw water mixing elbow? I've always heard that this is the most likely cause of overheating. You need to make sure that it hasn't corroded to the point that it's blocking the flow of water. Sometimes it's hard to tell if it's blocked.
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Tim Gabrielse
2500 RPM
I agree with Paul. I have a 1987 Legend 37 and I never run it over 2500RPM. and we still run at 6 to 6.5 kts. Anything over 2700 it will over heat. I went over the cooling system last year with a fine tooth comb to make sure everything was OK, and it was. A suggestion given to me was to increase the diamater of the fresh water intake hose and thru hull fittings. Tim Gabrielse Legend 37 - BLAZE
I agree with Paul. I have a 1987 Legend 37 and I never run it over 2500RPM. and we still run at 6 to 6.5 kts. Anything over 2700 it will over heat. I went over the cooling system last year with a fine tooth comb to make sure everything was OK, and it was. A suggestion given to me was to increase the diamater of the fresh water intake hose and thru hull fittings. Tim Gabrielse Legend 37 - BLAZE
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Paul Sealock
Overheating Yanmars
Yanmars do over heat but it isn't right. I have a 92 L37.5 and had an overheating engine. It got progressively worse over several years. It would get hot at high RPM (2800) so I reduced to 2400. This helped but eventually I would detect steam coming out the exhaust. I removed the mixing elbow and attempted to clean it out. This helped a little but not enough. Finally, I bit the bullet and bought a new mixing elbow (had to buy all three parts plus gasket for $290) and installed. After a couple of false starts, got a tremendous exhaust water flow. Last week motored to Bellingham and back (some sailing) for a total of about eighteen hours of motoring at 2900 RPM averaging 6.7kts for the trip. Everything went fine except for an incident next to Saddlebag Island but that's a whole other story. Bottom line, if your boat is more than five years old and you motor often, change the mixing elbow because it is clogged and you have reduced water flow. Also make sure the raw water strainer in front end of water intake has an evenly seated cover or you may suck air into the line causing reduced air flow also. Good Sailing. Paul
Yanmars do over heat but it isn't right. I have a 92 L37.5 and had an overheating engine. It got progressively worse over several years. It would get hot at high RPM (2800) so I reduced to 2400. This helped but eventually I would detect steam coming out the exhaust. I removed the mixing elbow and attempted to clean it out. This helped a little but not enough. Finally, I bit the bullet and bought a new mixing elbow (had to buy all three parts plus gasket for $290) and installed. After a couple of false starts, got a tremendous exhaust water flow. Last week motored to Bellingham and back (some sailing) for a total of about eighteen hours of motoring at 2900 RPM averaging 6.7kts for the trip. Everything went fine except for an incident next to Saddlebag Island but that's a whole other story. Bottom line, if your boat is more than five years old and you motor often, change the mixing elbow because it is clogged and you have reduced water flow. Also make sure the raw water strainer in front end of water intake has an evenly seated cover or you may suck air into the line causing reduced air flow also. Good Sailing. Paul
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Jim Ewing
Troubleshooting
I've got a '93 L37.5 and the motor (if I remember right) has a continuous duty RPM of 3400. Theoretically I should be able to run at this RPM for days on end without damage to the engine. (assuming I wanted to burn 2 gal/hr). I have run days on end at 3000 RPM with no overheating. With the work you've done so far (assuming that you have got good flow through the mixing elbow as suggested) I think you might want to look at the heat exchanger. With a boat as old as yours with such light use on the engine I can imagine all sorts of opportunities for growth, corrosion and scaling in the heat exchanger any of which might reduce your cooling water flow. Jim "Prospect"
I've got a '93 L37.5 and the motor (if I remember right) has a continuous duty RPM of 3400. Theoretically I should be able to run at this RPM for days on end without damage to the engine. (assuming I wanted to burn 2 gal/hr). I have run days on end at 3000 RPM with no overheating. With the work you've done so far (assuming that you have got good flow through the mixing elbow as suggested) I think you might want to look at the heat exchanger. With a boat as old as yours with such light use on the engine I can imagine all sorts of opportunities for growth, corrosion and scaling in the heat exchanger any of which might reduce your cooling water flow. Jim "Prospect"
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Walt Turner
Over heating of Yanmar on 37.5
I had the same problem. I wrote in here to HOW and was told to check the mixing elbow on the exhaust. It was terrible, had to replace, now the boat cruises at 3000 RPM without over heating. Total cost was $153.00 and an hour of my time. I tried soaking the elbow for 48 hours, waste of time.
I had the same problem. I wrote in here to HOW and was told to check the mixing elbow on the exhaust. It was terrible, had to replace, now the boat cruises at 3000 RPM without over heating. Total cost was $153.00 and an hour of my time. I tried soaking the elbow for 48 hours, waste of time.
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Alex
Mixing elbow 2
On my 29.5 I disassamble and clean mixing elbow almost every year !!(200 hours),and I think of replacing it next year. It is an occurance on many Yanmars (mixing elbow getting cloged )as I read on HOW over the years , especially on salt water enviroment. Running the engine regulary at high RPM (80-85% of max)for at least half an hour ( if it doesn't overheat..) is suppose to avoid this . and is benefitial in general to engine 'health'.
On my 29.5 I disassamble and clean mixing elbow almost every year !!(200 hours),and I think of replacing it next year. It is an occurance on many Yanmars (mixing elbow getting cloged )as I read on HOW over the years , especially on salt water enviroment. Running the engine regulary at high RPM (80-85% of max)for at least half an hour ( if it doesn't overheat..) is suppose to avoid this . and is benefitial in general to engine 'health'.
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SteveC
A mixing elbow will corrode...
and that's a fact of life... The water that mixes internally will eventually corrodes the internal metal causing the eventual restriction and blockage. No matter how much you 'wash' and how you run your engine, it WILL need replacing after a period of time. Around my neck of the woods(Long Island Sound) we get approximately 500/600 hours before it causes problems and MUST be replaced...
and that's a fact of life... The water that mixes internally will eventually corrodes the internal metal causing the eventual restriction and blockage. No matter how much you 'wash' and how you run your engine, it WILL need replacing after a period of time. Around my neck of the woods(Long Island Sound) we get approximately 500/600 hours before it causes problems and MUST be replaced...
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Gene Gruender
Possibly the heat exchanger
I have the older 3qm30 in my H37 cutter, but found the heat exchanger was causing my overheating problems. My boat was built with an aftermarket heat exchanger, not the one built onto the motor. I had a new one made 50% bigger for about 10% more than the original replacement one would have cost. It is a good possiblity that the heat exchanger is part of your problem.
I have the older 3qm30 in my H37 cutter, but found the heat exchanger was causing my overheating problems. My boat was built with an aftermarket heat exchanger, not the one built onto the motor. I had a new one made 50% bigger for about 10% more than the original replacement one would have cost. It is a good possiblity that the heat exchanger is part of your problem.
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Roger Mummah
Yanmar Mixing Elbow
My Yanmar guy, who has become my best friend, says to replace the mixing elbow every 4 years whether it needs it or not. The things get clogged with carbon. Ours lasted from 1983 until 1999 on our 2GMF (Hunter 31). When I replaced it, it had only a small passage for the exhaust water.
My Yanmar guy, who has become my best friend, says to replace the mixing elbow every 4 years whether it needs it or not. The things get clogged with carbon. Ours lasted from 1983 until 1999 on our 2GMF (Hunter 31). When I replaced it, it had only a small passage for the exhaust water.
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Gene Gruender
burned mixing elbow
Everyone else has clogged mixing elblws - mine burned a hole through it! On an 800 mile passage from Isla Mujures, Mexico (on the Yucatan) to Corpus Christi, Texas it developed a hole on the side, just about where the exhaust and water meet. We had hot exhaust blowing into the engine compartment. I'm guessing that over the years the alternating heat from when it was used and rust when it was not just ate it up. I had checked it for buildup inside several times but never found any. I ended up patching it with some spare exhaust hose split down the side and a bunch of hose clamps. Gene Gruender Rainbow Chaser
Everyone else has clogged mixing elblws - mine burned a hole through it! On an 800 mile passage from Isla Mujures, Mexico (on the Yucatan) to Corpus Christi, Texas it developed a hole on the side, just about where the exhaust and water meet. We had hot exhaust blowing into the engine compartment. I'm guessing that over the years the alternating heat from when it was used and rust when it was not just ate it up. I had checked it for buildup inside several times but never found any. I ended up patching it with some spare exhaust hose split down the side and a bunch of hose clamps. Gene Gruender Rainbow Chaser
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Eric Lorgus
Beware flabby impellers
Matt: I have a 87H285 with Yanmar 2GM20GF. Last summer I had several overheats caused by a clogged water inlet (grass at the marina). Each time I shut down the engine immediately, cleaned the inlet, and resumed. But eventually I got an overheat alarm that wasn't caused by a clogged inlet, or any other discernible problem. After a lot of trial and error, it turned out to be the impeller! I had obviously looked at the impeller, and had disassembled, checked, and reassembled the pump unit many times. Each time the impeller checked out visually, but what I wasn't aware of was that it had become soft, possibly from the repeated incidents of running dry. Having exhausted all other possible causes, I decided to replace what I thought was my perfectly good impeller with a brand new one. Eureka! That was it. And when I had both the new and old in my hands, the difference was obvious. Which proves the old adage about try replacing the impeller first. It’s very easy to do, & relatively cheap. From this incident I also decided to no longer carry old impellers as spares, and now keep only virgins on board (impellers that is).
Matt: I have a 87H285 with Yanmar 2GM20GF. Last summer I had several overheats caused by a clogged water inlet (grass at the marina). Each time I shut down the engine immediately, cleaned the inlet, and resumed. But eventually I got an overheat alarm that wasn't caused by a clogged inlet, or any other discernible problem. After a lot of trial and error, it turned out to be the impeller! I had obviously looked at the impeller, and had disassembled, checked, and reassembled the pump unit many times. Each time the impeller checked out visually, but what I wasn't aware of was that it had become soft, possibly from the repeated incidents of running dry. Having exhausted all other possible causes, I decided to replace what I thought was my perfectly good impeller with a brand new one. Eureka! That was it. And when I had both the new and old in my hands, the difference was obvious. Which proves the old adage about try replacing the impeller first. It’s very easy to do, & relatively cheap. From this incident I also decided to no longer carry old impellers as spares, and now keep only virgins on board (impellers that is).
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Bob Blackmann
2800 rpm
I have a 1988 Legend 37. I cruise under power at 2800 rpm's and have not had an overheating problem. Cruising speed is 7 to 7 1/2 kts. On occasion, have run at 3200 rpm's for several minutes, with no problems. Sounds like you have water flow restricted somewhere. Good luck, Bob
I have a 1988 Legend 37. I cruise under power at 2800 rpm's and have not had an overheating problem. Cruising speed is 7 to 7 1/2 kts. On occasion, have run at 3200 rpm's for several minutes, with no problems. Sounds like you have water flow restricted somewhere. Good luck, Bob
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Colin McNaught
Yanmar overheating
Hi Matt, I have had similar problems with the engine (Yanmar 3HM35F) on my Vision 36 which should have a similar hull performance to your 37.5. Overheating occurs at revs above 2800. I would recommend (and am planning to myself this Fall) cleaning the heat exchanger. This is not a difficult process according to another Yanmar owner in our Marina here who has done it early this year. The inside of the tubes may be cleaned by purchasing wooden doweling of an appropriate size. I remember when my boat was new (1991) that tha cooling system could handle 3000 revs. Good Luck. Colin
Hi Matt, I have had similar problems with the engine (Yanmar 3HM35F) on my Vision 36 which should have a similar hull performance to your 37.5. Overheating occurs at revs above 2800. I would recommend (and am planning to myself this Fall) cleaning the heat exchanger. This is not a difficult process according to another Yanmar owner in our Marina here who has done it early this year. The inside of the tubes may be cleaned by purchasing wooden doweling of an appropriate size. I remember when my boat was new (1991) that tha cooling system could handle 3000 revs. Good Luck. Colin
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