yanmar 3gmf overheat and low rpm

[Jim Oursler]

I sure need help. Have a persistent heat alarm at high forward throttlle.

RPMs are down in forward and reverse. See tests run below:
HIghest Engine speed 3400 rpm in neutral, no overheat
Highest speed 3100 rpm tied at dock in reverse, no overheat
Highest speed 2700 rpm tied at dock forward, overheat
When motoring highest speet..2700 rpm, overheat
No overheat motoring at 2000 rpm.

Note, wasnt until these tests that I noticed low rpms.. I just thought it was a dirty bottom that held me to 4.5 knots from usual 6-7.

Boat environment is freshwater, same dock since delivery new in 83.
I am going to list a lot that I have done that had no effect. Now I am beginning to wonder if it is my old two blade propeller original equipment propeller.

Have in past month done following, with no improvement:
1. replaced seawater pump impeller (this has a closed cooling system with heat) Old impeller looked good. Hose tight.
2 Replaced thermostat and temp sense alarm.
3. Cleaned seawater strainer.
4. Used high pressure water hose to blow out water intake.
5. Good steady stream of exhaust water.
6. Pulled heat exchanger, checked every tube for gunk or blockage.. none.
7. Haven't replaced mixing elbow, but it is 7 years old on fresh water system.
8. Triple checked cooling level. No air above thermostat. Bled that area
9. Overall, engine runs smooth .. and will run all day at low rpm, around 2000.
10. intake hoses look good as well as right angle hose at exhaust mixer.

This engine is reliabel and has run a lot.. not since I bought it in 99.

 

[Jim Oursler]

change run a lot at end of my post to "not run a lot"..mostly into and out of harbor.

 

[Bill Roosa]

Sounds pretty classic to me

She runs fine but when you really put a load on her she overheats.
You have a restriction in the raw water circuit. Since you have checked everything else and the mixing elbow is actually a restriction to begin with I'd pull it and check.

The raw water flow is sufficient to cool the engine when you don't load it up but with the increased load and lower RPM (from a fixed prop operating in forward) the flow of water is insufficient to cool the engine.

 

[Steve Dion]

Assuming that there are no restrictions (including the mixing elbow) I would check the prop to determine if it is matched to your engine.

1. R/R the mixing elbow.
2. Check all the hoses when running at high RPM under load (possible collapsing).

Other than that, you may need to check your head gasket. I can't think of much else that you have not done.

 

[Vinny]

Jim,

First thing is to be sure the RPM's are what the tach indicates they are. Borrow a photo tack and check RPM's. If they are correct then recheck the mixing elbow. The boat next to mine was having the exact same problems and the engine was turning 3,300 when the tack indicated 2,600. Also the valve clearance was way off (to loose). We set the valves backed it down on the tack to 2,100 and it runs fine as frogs hair. No over heat no oil pressure problems nothing.

 

[Ron McCoy]

Change out the mixing elbow. Seven years of use is a long time, even in fresh water. Remember they're made of cast iron steel, they rust and corrode and will restrict water flow when they do. Results: Engine overheat.

 

[petersea]

As others are advising check elbow but I was under the impression the coked up elbow was a salt water issue. Operating in fresh water it should last almost forever. Let us know what you find out. Other then that the tach could be suspect as suggested. You may also want to get a temperature gun to check the water temp on engine to see if it is truly overheating. Can you hold you hand on the exchanger when it says it is overheating ?? Do you have a gauge or buzzer ?? Could be a bad gauge. Other then that I am thinking as you are you may be overproped. Compare your prop size to other boats like yours and see how they compare but I would be surprised that after all this time it is the prop. Being overproped is often associated with heavy black exhaust at higher rpm's and sometimes a fuel sheen on the water ?? Any of these problems ? ? What does your exhaust look like ?? That being said you should be able to get 3200 to 3400 rpm in gear at full throttle. Sorry for all the questions. Keep up updated what was wrong.

 

[Jim Haynie]

Anything that makes prop extremely inefficient will cause these same symptoms. Mine was simply a lot of barnacles on prop, but a bent prop, oversized prop, shaft bound by too tight cutlass bearing or packing gland will all also cause these symptoms.

 

[Jim Oursler]

yanmar and overheat

Thanks to all. Have been traveling and now need to get back out to the boat.

The 2 blade fixed prop came with the boat in 83. No black smoke. Exhaust is clean.

Temp sensor has been changed, it turns on a buzzer when it hits high temp, so not that. Had same problem of over heat with old sensor.

I will borrow a tach to verify correct reading.

I will check mixing elbow, although in fresh water.

I will probably adjust valves...once I determine how to find TDC.

Thanks to all for the help.

As others are advising check elbow but I was under the impression the coked up elbow was a salt water issue. Operating in fresh water it should last almost forever. Let us know what you find out. Other then that the tach could be suspect as suggested. You may also want to get a temperature gun to check the water temp on engine to see if it is truly overheating. Can you hold you hand on the exchanger when it says it is overheating ?? Do you have a gauge or buzzer ?? Could be a bad gauge. Other then that I am thinking as you are you may be overproped. Compare your prop size to other boats like yours and see how they compare but I would be surprised that after all this time it is the prop. Being overproped is often associated with heavy black exhaust at higher rpm's and sometimes a fuel sheen on the water ?? Any of these problems ? ? What does your exhaust look like ?? That being said you should be able to get 3200 to 3400 rpm in gear at full throttle. Sorry for all the questions. Keep up updated what was wrong.

 

[Jim Oursler]

Hi Vinny,
I need tips on setting valve clearance on the 3GMF. How do I find TDC for cyliner 1?

 

[Dan Johnson]

Jim...

assume you have checked the raw water strainer if you have one. We get long weeds floating here on the Chesapeake. I had a friend's boat get one balled up in the hose line before the strainer--strainer basket was empty but flow was restricted. Used an air compressor to blow it back out--used the ball valve like you'd fire a torpedo.

Have the tach RPM checked as Vinny suggested. Just did it on my H34 and found the Yanmar tach reading 8 to 10 percent low.

 

[Jim Oursler]

Re: Jim...

Hello,
My original email listed a who lot of stuff including raw water intake.
I wonder what I will learn with a tachometer test, as my big problem is overheat at high RPMs.
Regads,
Jim

 

[Vinny]

Jim,

The correct way is to find the mark on the flywheel through the cover. That being said is easier to say than do. What I did is removed the valve cover then just hunted the TDC for the #1 cyl. by feeling the rockers for both intake and exhaust until I was close to TDC. Then check the flywheel for the exact mark. The engine I was setting was so far off that anything would have been an improvement. The setting is 0.2±0.03mm for both intake and exhaust cold. Someone used a .2" instead of .2mm. Big difference. Anyway .2mm is 0.0079" so I used a .007" and adjusted it loose, then used a .008" as a go no go. If the .008 did go it was still too loose and had to be re adjusted. I think you could use just the .008 and do a tight fit adjustment and be OK due to the slight tolerance allowed and a bit loose is better than to tight.

Don't forget a new cover gasket. Good luck.

 

[Dan Johnson]

Vinny...

Great advice! Did many a race engine valve adjustment the same way!

 

[Vinny]

Re: Vinny...

Thanks Dan,

Some time what comes natural (after years of doing it) isn't so natural to a person doing it for the first time. I think we all forget that at times. It's like the driving directions" Oh it's just up this road a bit (3 miles) and turn at the Amoco (which is now a BP) station (which way?), you can't miss it". Easy if you been there before.

 

[Jim Oursler]

Yanmar 3gmf overheat

Well, I didn't solve the overheat, but have quieter engine after adjusting lifters using old fashioned method.

Original problem and continuing problem : yanmar 3gmf in h34 overheat at high RPMS, not at moderate speed.

Realized today that I have not replaced or checked my heat exchanger filler cap, which is akin to a radiator cap, rated 60. Could this be the culprit?

Now I have added to my long list of what is not the problem:
1. Replaced mixing elbow (only had minor blockage, and a reminder to all to not attempt unless you have a four foot cheater bar for pipewrench, and a solidly mounted vise)(the connector pipe that has right and left handed pipe threads was almost rusted through) (3gmf has 2 syles of mixing elbow,straight and curved, plus 2 syles of water inlet pipe..straight and a right angle)
2. Replaced hose from heat exchanger to mixing valve, and assured not crimped.
3. Replaced intake hose from through hull.
4. adjusted valves/lifters to .008 (definitely quieter)(needed lithium grease to hold valve cover gasket in place)
5. Used Prestone cooling system cleaner to remove any crud in engine cooling system.

Previously had:
1. replaced seawater impeller.
2. cleaned seawater filter.
3. removed and assured no blockage in heat exchanger tubes.
4. replaced thermostat
5. replaced temp sensor.
6. assured no air in the closed cooling system
7.checked that water exiting freely through exhaust.
8. for those who think it is the 2 bladed prop. that is original equipment.
9. This boat has never been in saltwater.. since 1983 delivery to freshwater Lake Texoma.
10. checked, verified no blockage at water inlet through hull.
11. belts for seawater and closed cooling system pumps are tight.
12. no black and no white smoke. clean exhaust.
13. have a flexible coupling between transmission and prop shaft.
14. Before someone says, check the closed system impeller.. that is a stainless steel impeller.
15. no water in oil, no oil in water.

Allright guys.. what next?
Jim

Jim,

The correct way is to find the mark on the flywheel through the cover. That being said is easier to say than do. What I did is removed the valve cover then just hunted the TDC for the #1 cyl. by feeling the rockers for both intake and exhaust until I was close to TDC. Then check the flywheel for the exact mark. The engine I was setting was so far off that anything would have been an improvement. The setting is 0.2±0.03mm for both intake and exhaust cold. Someone used a .2" instead of .2mm. Big difference. Anyway .2mm is 0.0079" so I used a .007" and adjusted it loose, then used a .008" as a go no go. If the .008 did go it was still too loose and had to be re adjusted. I think you could use just the .008 and do a tight fit adjustment and be OK due to the slight tolerance allowed and a bit loose is better than to tight.

Don't forget a new cover gasket. Good luck.

 

[petersea]

Jim, yes the cap could be causing a problem especially if it was not holding pressure. A 60 psi cap rating sounds pretty high double check that you have the right cap. If I remember correctly the cap is 15 psi or less. As far as the fresh water water pump they do go bad but it should be pretty easy to see water flow (with the cap off and thermostat open) It is possible the impeller is slipping on the shaft. Not a very likely thing but you have seemed to have tried everything else. You truly have done all the normal thing ( except the cap I would try asap but not real convinced that is the problem) Check the following link and you can send a e email to this guy He used to run a big yanmar shop in Australia and maybe he can be of some help or know of a trick every one else has missed. Good Luck and keep us posted. www.yanmarhelp.com

 

[petersea]

http://www.yanmarhelp.com/index.htm try this link if other one did not work

 

[kloudie1]

Jim, the only thing I didn’t see in your comprehensive list is the raw water strainer .. Not that it is dirty, .. The top gasket on mine was leaking air into the raw water pump at high RPM.. My strainer is an old GROCO, don’t know if it was original or is like yours but the handle on the basket is stiff enough to keep the top lid from seating properly on an old cork gasket.. I noticed the corrosion around the lid, but until I read a post to that effect here, I didn’t think that could be a problem.. I never saw water leaking out of the lid, but to get corrosion, it must have been, sometimes.. The gasket looked good but it was much compressed. I rebuilt the strainer.. MainSail did a photo spread on it.. It is pretty simple., but I don’t think the cork gasket is the right material and I will soon make a good spongy Buna-N gasket to replace the cork one.. Now my engine doesn’t overheat at high RPM.. Yes I changed most of the same stuff you did along the way.. radiator cap is marked with 60, but I think that is kilopascals ?? Would be about 9 psi .. If the gaskets and springs are free and in good shape, and your catch tank is working correctly, the cap is probably OK..

 

[Jim Haynie]

There is still one more item of evidence nobody seems to have noted. I replied once that it might be anything that puts more load on engine than normal (such as heavily fouled prop). I have no experience with fresh water, but I'm assuming barncles are not there?? But there are other things such as pieces of fishing line and ropes that get tangled on props. Does your packing gland drip a bit as it should, or is it tightened down too much and binding shatf. the clue that leads me back to these ideas is that you mention no overheat and higher RPMS when in reverse and tied to dock. The prop is not exactly symetrical and it operates with less efficiency (ie less drag on the engine as it moves less water) in reverse. So, you are only having the problem whne trying to put forth maximum effort with the prop. My boat has the original two blade prop, but if I get a crab pot line wrapped even twice or a good load of barnacles, I have EXACTLY same symptoms as yours. Have you actually gone below and checked prop? Have you tried loosening up on the packing gland a good bit and re-run your tests even if it is dripping considerably? Maybe it is worn out from long term overtightening and now only way to stop the excessive drip is bind it up entirely?? You may have wasted some effort and $$$ on things in your list above that would cause overheating even in neutral idling, but you did not show any evidence that you proved there is no excessive load on the prop or shaft.