Yanmar 1GM10 Overheating

[scottb34300]

Hi. I have a 1994 Yanmar 1GM10 that has recently started overheating. I have replaced the impeller and gasket. I have been advised to run the engine with anti-freeze and leave it in the engine for about 30mins followed by flushing with fresh water, (the engine is saltwater cooled).

Can anyone suggest anything else?

I don't know whether this may have anything to do with it, however, when running at high speeds I sometimes get a black liquid (not oil) coming out of the exhaust.

<hr width=100% size=1>Scott.

 

[Jools_of_Top_Cat]

what state is your oil in, is cooling water getting into oil. Is the oil level remaining or are you topping up often?

is clean water coming out of the hose at slow speeds, how long will it run before overheating.

If you pull the outlet water hose off the exhaust elbow is there a good stream of water flowing. Is the thermostat opening?

just looking for ideas

<hr width=100% size=1><font color=blue> Julian </font color=blue>

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[scottb34300]

I frequently replace the oil. The oil level never falls down. Clean water is coming out of the exhaust at slow speeds, apart from when the engine is run at top speed and a black liquid comes out. It runs at top speed for about an hour before overheating.

Hope this helps.
Scott.

<hr width=100% size=1>Scott.

 

[Jools_of_Top_Cat]

without seeing it I can only guess that this is carbon mixing with water. Deisel engines throw out copious amounts of carbon when over worked, or over revv'd.

Is it possible that you are running the engine too hard or have too large a prop fitted. When you say top speed, is that to the rev limiter or top boat speed.

How long has this been happening, is it a new occourance, have you changed anything recently. Pounding a little engine at full revs for an hour is not best practice I think, but again I am not there to see.

Some thoughts though;

head needs cleaning, all carbon residue removed (this will make the engine run hotter)

Water system needs overhaul, to mix carbon in with cooling water to me sounds like not enough water flowing through exhaust.

Prop is incorrect for engine forcing you to run engine too fast to get anything reasonable from the boat.

Anything in these that might sound familiar?

These are just thoughts, as I said I am working in my head here.

<hr width=100% size=1><font color=blue> Julian </font color=blue>

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[pete]

Hi
I have the same engine and also had the black water problem at high revs, My trouble was a knackered exhaust valve seat and the water came out like ink, With the overheating, check the mixing exhaust elbow for blockage and the inner tubing for perforations (a common fault on these engines) also check impellor brass bush has not come unbonded from rubber, is the pump front plate worn ?
I fitted a globe (run dry) impellor to mine this season it pumped ok when moored but when the boat speed went up it could not over come the suction effect on the skin fitting, when compared to a original impellor it was about half a millimeter less in width with the old impellor back in everything was ok again Have you had the thermostat out I beleve it is possible to fit this in reverse. is your strainer /skin fitting clean ?
hope this helps
Pete

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[LadyInBed]

I take it that you check your raw water strainer regularly.
No mention of the thermostat!
Have you had that out and tested it yet?
I would think that 9 years is too short a time for the water way to the head to get blocked, if that's any consolation!


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[Evadne]

Another place to look is the hose from the impeller to the engine block. On my 1GM7 (same layout as 1GM10) this is adjacent to the anode and it can get blocked with zinc salts, especially just above the impeller outlet, restricting water flow. Remove the hose to check it is clear and also check the metal pipes it fits to. I guess the antifreeze advice is to clear salts elsewhere in the system, I will have to try that one myself.

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[poggy]

Hi,

I have the same engine and mine pumps out black water at full revs, I think it is just the carbon from diesel which has not been fully burned.

With regard to the overheat, if it takes an hour at full revs before it overheats there can't be a lot wrong with it. If there was a major problem with the cooling etc, then surely this would happen a lot quicker. I assume that it is the temperature alarm which leads you to believe it is overheating. These can go wrong and often do. I would check all the wiring to this and make sure that all connections are clean.

I am not expert but I hope this helps.

Poggy

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[LadyInBed]

Another thought, how hot is the exaust water, is it boiling - steaming and too hot to touch or what?

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[Alerion172]

Hi. I have a 1994 Yanmar 1GM10 that has recently started overheating. I have replaced the impeller and gasket. I have been advised to run the engine with anti-freeze and leave it in the engine for about 30mins followed by flushing with fresh water, (the engine is saltwater cooled).

Can anyone suggest anything else?

I don't know whether this may have anything to do with it, however, when running at high speeds I sometimes get a black liquid (not oil) coming out of the exhaust.

<hr width=100% size=1>Scott.

I have a similar problem with a 2001 1 GN 10. At 2500 RPM after about 20 minutes run time in 70 degree water (savannah), the alarm sounded. I assume hot water alarm. throttled back and alarm quieted. Later at the dock, I ran the boat in gear and could only get 2500 rpms in forward, and bit more in reverse. There was soot at high rpm in the exhaust. I could put my finger in the exhaust without burning. It was hot but not that hot. In neutral, I can get 3000 rpms. Water flow out exhaust seems to be normal volume. Bottom and prop are clean. Prop has been on the boat for 19 years. Put in new fuel filters, new thermostat, new impeller. Problem persists. A week or so before this happened, I tightened the stuffing box (graphite) so that the stuffing box does not drip at the dock but does under power. Could it be this? Could it be oil pump? (As most know, the 1 GM 10 has one alarm for both oil pressure and heat.) Other ideas? Thank you. John