Yanmar 1GM10 overheating?

[KingOfComfort]

we have a '95 raw water cooled 1GM10 in a Seaward 25 sailboat. was originally in fresh water, then salt, now on Lake Champlain (fresh).

it has history of water temp alarm sounding. during survey alarm sounded (not sure about RPM) and surveyor aimed his temp sensing gun and claimed it was normal operating temp.

after multiple alarm events we had muriatic acid treatment and could then run under 1000 RPM w/out alarm sounding. after replacing water temp sending unit, exhaust elbow, and RydLyme flush we can typically run under 2000 RPM. last event was running 22-2400 RPM when alarm sounded after 1.5 hours. (these are rough estimates, hard to nail down or remember exactly what the numbers are/where)

basic questions: what is the normal high RPM rating? i've heard different numbers.

what is the proper sequence when alarm sounds? e.g. kill engine/or reduce RPM?

can this engine withstand additional muriatic acid treatments?

would appreciate any ideas or suggestions for how to address this....many thanks, David

 

[RichardS]

I think it it were my engine I would remove the thermostat and then blank off the bypass in such a way that all the cooling water is directed through the cylinder jacket all the time. Then run it up to speed and see if it's possible to get the alarm to sound. You could also use a cheap eBay remote temp reader (£2) clipped to the jacket or hose to give you a continuous digital temp readout so you can see exactly what is going on.

Richard

 

[KingOfComfort]

I think it it were my engine I would remove the thermostat and then blank off the bypass in such a way that all the cooling water is directed through the cylinder jacket all the time. Then run it up to speed and see if it's possible to get the alarm to sound. You could also use a cheap eBay remote temp reader (£2) clipped to the jacket or hose to give you a continuous digital temp readout so you can see exactly what is going on.

Richard

 

[KingOfComfort]

thanks Richard. we have run it with the t-stat out and with a new one in, same results. what do u mean by "blank off the bypass"?

 

[rotrax]

IIRC the 1GM10 thermostat is a bypass type.

Until it reaches operating temperature - for the thermostat not the engine - it allows cooling water to bypass the cylinder and head by blocking those passages.

When the wax pellet melts and opens the thermostat, removing the blocking, the water then flows around the cylinder and head, thus cooling the engine.

I have had several 1GM10's. None had an overheat alarm.

IMHO, if plenty of water is coming from the exhaust and the engine has plenty of oil and is working properly it is unlikely to overheat.

And, from direct experience, many alarm sensors give false readings.

And again from direct experience with 1GM10's, check for a blocked exhaust elbow.

Good luck.

 

[langstonelayabout]

I too had this problem with a previous boat's 1GM10.

Initially I changed the water pump impeller and thermostat, only to find the previous thermostat was still working correctly. No change.

I then flushed the engine's cooling gallery with Rydlyme which is assume is the equivalent of muriatic acid. That worked and the alarming stopped 99% of the time. I used it like that for a few seasons and sold the boat.

Had I wanted to retain it for a few years I would have taken the engine out over a winter and stripped, de-furred the cooling ways and reassembled after a few sessions in the dishwasher. I'd probably put in a new exhaust elbow and engine mounts too.

Bits for Yanmars are expensive, but the cleaning of the cooling ways is the cheapest job you can do, whether in the boat or on a bench in your garage. Try that first.

 

[KingOfComfort]

thanks, FYI muriatic acid is much more corrosive than RydLyme, which is fairly benign and claims to be biodegradable.

a friend suggested a compression check as a next step, anyone have an opinion on that? seems like that would only detect cracks between cooling channels and cylinder, not blockages in the cooling channels.

 

[RichardS]

a friend suggested a compression check as a next step, anyone have an opinion on that? seems like that would only detect cracks between cooling channels and cylinder, not blockages in the cooling channels.

If you have no water in your engine oil and are not burning oil and your engine starts OK and doesn't smoke or steam excessively out of the exhaust, I doubt whether compression will be your problem.

Richard

 

[vyv_cox]

thanks, FYI muriatic acid is much more corrosive than RydLyme, which is fairly benign and claims to be biodegradable.

a friend suggested a compression check as a next step, anyone have an opinion on that? seems like that would only detect cracks between cooling channels and cylinder, not blockages in the cooling channels.

The MSDS data sheet for rydlyme marine says it is 6-7% hydrochloric acid. It can happen that an older version is shown on internet but this one is dated November 2017.