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Old 02-08-2020, 17:03   #1
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Yanmar 2gm20f temp creeping up

Hi all. My 2gm20 operating temp is a little on the high side, nearing 150F at 2500 RPM (normal cruising for me). Heats further if I go to 2800 RPM. Typically I run around 140F. Not a critical problem however I don't think I should be seeing an increase. Maybe I am wrong, need some outside input.

FW flow at exhaust looks OK but precise flow rate is hard to gauge without measurement which I have not done.

I have verified FW intake is clear as is seacock and strainer, hose to water pump">raw water pump clear, impeller replaced, no leaks at RW pump. Tested flow into bucket, post FW pump, looks fine.

Hose from FW pump to HE is clear with good flow. Checked HE tubes I could see through the FW hose opening. No build up noted (when I bought boat 20 years ago I was overheating due to near closure of HE core tubes so I have an idea what bad looks like). I did find chunk of old impeller lodged in intake port of HE and removed that thinking, bingo I got it, but this did not resolve.

About 8 years ago I had complete blockage of elbow. Replaced with Yanmar OEM parts at that time. Have done about 1000 hours since then and a lot of charging at sea while under sail. I am wondering if I ought to just proactively replace elbow with the thought that it may be slowly gunking up and restricting flow.

But, before I do that I need to say that I sail and motor a lot on the California Delta where water temps go up 10 to 15 degrees in summer (like now) so I am wondering if the cooling system may be fully operational and I am just seeing the result of warmer FW?? The question is, how sensitive is the 2GM2F to warmer FW? Seems like it should be minimal but I would like someone with experience water temps vs cooling performance to provide some feedback on this.
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Old 02-08-2020, 17:11   #2
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Re: Yanmar 2gm20f temp creeping up

Can't you inspect the elbow rather than just replacing it on a speculation?

Excuse my ignorance but what does FW mean?
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Old 02-08-2020, 17:39   #3
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Re: Yanmar 2gm20f temp creeping up

Whilst I cant comment on fresh water cooled 2GM20 in fresh water I can tell you our oil temp on our raw water cooled ysm8 does go up around 10oC in summer water/air temps in the sea.
I would guess that the water up in the delta would go up about 25oF actually, least it did around Bethel island IIRC.
Do you go back to the bay often? be easy to see then.
If you replace elbow my recommendation is to get an ss aftermarket one rather than Yanmars for longer life
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Old 02-08-2020, 18:09   #4
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Re: Yanmar 2gm20f temp creeping up

FW, free water? Usually fresh water though, but here it seems to be raw water?
What id the thermostat temp rating? My 4JHE is 165 and it runs 165, but higher throttle and higher raw water temp usually means temp will creep up, but 150 is actually pretty low I think, almost sounds like you have a stuck thermostat.

Ideally an engine should run the same water temp regardless, but some motors seem to have smallish heat exchangers and for them it’s normal to run warmer at higher throttle settings as you exceed the heat exchangers capacity, but as temp difference between raw and fresh goes up, so does heat flow so they can still cool just at a slightly higher temp.
I’d verify thermostat temp setting by placing in a pan of water and heating it with a thermometer.

A 150 rated thermostat should begin to open at 150 plus or minus 3 degrees F, but won’t be fully open until 15 or 20 degrees above rated temp, so temps up to 20 higher than thermostat rating are normal. More than 20 degrees though is too high because at that point your at full water flow and engine temp should be controlled at less than full flow, there should be some cushion, usually a lot of cushion actually.
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Old 02-08-2020, 18:19   #5
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Re: Yanmar 2gm20f temp creeping up

My 3GM30F running temp does vary about 10 deg F between Summer and Winter. I have found all the trouble removing the mixing elbow just replace rather than clean. 4 years into a 316 SS I bought off ebay (so far so good).

For the heat exchanger tubes I use a 32 cal brass rifle cleaning brush, extension, and battery powered drill. Just remove the fwd cap and clean the tube interior. The tube baffling arrangement is configured for 3 pass if you get confused. First time I removed both caps but now just the front.

Above kept the temp under control for 25 years on my 2GM, and 15 years on my 3GM.


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Old 03-08-2020, 10:34   #6
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Re: Yanmar 2gm20f temp creeping up

after 8yrs and 1000 hrs runtime [maybe 50% at charging rpm which is usually low rpm], i'd go for the mixing elbow replacement. will likely be partially plugged and the casting will likely be compromised by the seawater.

is this temp rise new recent behavior?

post edit: "recent" meant to mean this year or last... not usual.....
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Old 04-08-2020, 09:00   #7
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Re: Yanmar 2gm20f temp creeping up

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Originally Posted by Wotname View Post
Can't you inspect the elbow rather than just replacing it on a speculation?

Excuse my ignorance but what does FW mean?
My bad, I should have written Raw Water RW instead of Fresh Water FW. I am on the Cali Delta so I got hung up on the Fresh Water which is what we have out here.

These days it is more like Green Water though.

With regard to inspection. I replaced the elbow about 8 years ago. It is almost impossible to inspect while it is installed (at least on my boat). I decided to just purchase a new elbow so when the old came out I would not be stuck awaiting a part. Turns out when the old came off I found it impossible to see the area where water is injected. It is around the elbow curve, just out of sight. If I had had a small endoscope camera I could probably have inspected it. Actually I have just such a camera queued up in my Amazon "save for later" list so maybe I'll buy it. Lots of uses aboard the boat, including elbow inspection.
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Old 04-08-2020, 09:12   #8
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Re: Yanmar 2gm20f temp creeping up

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Originally Posted by Compass790 View Post
Whilst I cant comment on fresh water cooled 2GM20 in fresh water I can tell you our oil temp on our raw water cooled ysm8 does go up around 10oC in summer water/air temps in the sea.
I would guess that the water up in the delta would go up about 25oF actually, least it did around Bethel island IIRC.
Do you go back to the bay often? be easy to see then.
If you replace elbow my recommendation is to get an ss aftermarket one rather than Yanmars for longer life
Yes, I do go up to the Bay frequently, at least until Covid came along. I was thinking the same thing. Raw Water is much colder up there so I would certainly be able to confirm the relationship between water and engine temps. But I am a little surprised there would be that much difference in a properly functioning engine cooling system.

I am in Discovery Bay, about ten miles south of Bethel. I don't think we see as much as 25 degrees F water temp change but could be. I know it gets a lot colder in winter. I imagine SF Bay water temps would be close to Delta winter temps though.
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Old 04-08-2020, 09:21   #9
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Re: Yanmar 2gm20f temp creeping up

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Originally Posted by a64pilot View Post
FW, free water? Usually fresh water though, but here it seems to be raw water?
What id the thermostat temp rating? My 4JHE is 165 and it runs 165, but higher throttle and higher raw water temp usually means temp will creep up, but 150 is actually pretty low I think, almost sounds like you have a stuck thermostat.

Ideally an engine should run the same water temp regardless, but some motors seem to have smallish heat exchangers and for them it’s normal to run warmer at higher throttle settings as you exceed the heat exchangers capacity, but as temp difference between raw and fresh goes up, so does heat flow so they can still cool just at a slightly higher temp.
I’d verify thermostat temp setting by placing in a pan of water and heating it with a thermometer.

A 150 rated thermostat should begin to open at 150 plus or minus 3 degrees F, but won’t be fully open until 15 or 20 degrees above rated temp, so temps up to 20 higher than thermostat rating are normal. More than 20 degrees though is too high because at that point your at full water flow and engine temp should be controlled at less than full flow, there should be some cushion, usually a lot of cushion actually.
Very helpful info, thanks. I am embarrassed to say I donlt know what the thermostat opening temp is off hand, I do have the Yanmar maint manual and have seen the pages describing thermostat testing. I will need to take a look at the test description for the rating. I can say I definitely have a Yanmar OEM thermostat in there because I replaced it a number of years ago.

The important part of your response for me was the description of gradual opening of the thermostat based on engine temp. Somehow I had it in my mind it was an on/off situation. If the thermostat is, for lack of a better word, regulated then some variation in engine temp is probably to be expected.

The GM manual indicates 140 degrees F is the "nominal" operating temp. I have an IR heat gun aboard and I see about 148 F at the block at 2500 RPM and around 155 F at 2800 RPM so maybe I am just being overly paranoid??
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Old 04-08-2020, 09:33   #10
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Re: Yanmar 2gm20f temp creeping up

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Originally Posted by Frankly View Post
My 3GM30F running temp does vary about 10 deg F between Summer and Winter. I have found all the trouble removing the mixing elbow just replace rather than clean. 4 years into a 316 SS I bought off ebay (so far so good).

For the heat exchanger tubes I use a 32 cal brass rifle cleaning brush, extension, and battery powered drill. Just remove the fwd cap and clean the tube interior. The tube baffling arrangement is configured for 3 pass if you get confused. First time I removed both caps but now just the front.

Above kept the temp under control for 25 years on my 2GM, and 15 years on my 3GM.


Frankly
This is why this forum is great! Excellent suggestion re cleaning the HE tubes. When I bought the boat 20 years ago the HE tubes were almost completely blocked. I pulled both caps and removed the core out the front. I cleaned with a 1/4 inch very long drill bit which fit perfectly into the tubes. To this day that bit is in my tool box aboard. But, as you can imagine, this is a big hassle. I much prefer the technique you described. I also like the brush idea, I'll google the item for a source.

I would not be surprised that even though the tubes look on the clean side visually, they are actually coated with a nice layer of gunk. A cleaning is probably long overdue. That would be a way easier job than the elbow replacement.
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Old 04-08-2020, 09:43   #11
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Re: Yanmar 2gm20f temp creeping up

The mixing elbow/injection nozzle on that engine should be replaced at roughly 500 hours of operation per Yanmar's owner's manual. OTOH Mastry (Sp?) Marine mechanics suggest between 300 and 500. It would be wise to actually check your thermostat as the normal operating temp for that engine (2Gm20FW) is 180º. Low engine temps can result in inefficient fuel burn, soot and debris built up in the mixing elbow. BTDT...


FWIW...
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Old 04-08-2020, 09:44   #12
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Re: Yanmar 2gm20f temp creeping up

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Originally Posted by motretu View Post
after 8yrs and 1000 hrs runtime [maybe 50% at charging rpm which is usually low rpm], i'd go for the mixing elbow replacement. will likely be partially plugged and the casting will likely be compromised by the seawater.

is this temp rise new recent behavior?

post edit: "recent" meant to mean this year or last... not usual.....
Well, I wish I had logged engine temps over the years darn it. I am going to start doing so. All I can say is that I pulled some weed into the RW intake and got an overheat. Cleared that problem and inspected the cooling chain to ensure no junk got past strainer.

This event focused me on general engine temp and I noted I was running about 10 degrees F high to Yanmar spec. (140 F) Then I noted temp creep as I exceed 2500 RPM up to about 160 F at 2800 RPM and that does seem higher than I am used to. But it is summer, water is warm, etc. etc. so I posted here to sort of get a sanity check.

Given I have not cleaned the HE core in ages and the elbow has not been replaced in at least 8 years (1000 hours +/-) maybe I ought to just do both as a routine maintenance activity. I see aftermarket elbows + manifold flange kits out there for around $300 so the cost is not prohibitive. The only thing you need for the HE core work is a new gasket for the front cap (now that I have a simplified process thanks to this forum). I already have this gasket in my spares kit.
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Old 04-08-2020, 09:55   #13
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Re: Yanmar 2gm20f temp creeping up

This is a pretty good explaination of how a thermostat works
Stant

Ideally an engine under cruise operates just above the thermostat ‘cracking” temp. A well designed cooling system has a lot of excess cooling capacity, so that it takes a pretty degraded system to allow an overheat especially at cruise.

One good reason in my opinion to operate an engine occasionally at full throttle for 5 min or so is to test the cooling system, it may rise in temp as the thermostat fully opens, but it should stop rising. Thermostats are gradual devices, and it’s normal to see some temp variations based on load and raw water temp.

Normally a thermostat is never fully open, if it is then the engine will very close to overheating because any increase in engine heat production will result in an overheat as the cooling system is maxed out.

I would both clean the heat ex, can’t hurt and change the exhaust elbow. Even if clean it may be close to failure from corrosion, and often that failure results in water in the engine and a seized engine.
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Old 04-08-2020, 09:59   #14
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Re: Yanmar 2gm20f temp creeping up

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Originally Posted by svHyLyte View Post
The mixing elbow/injection nozzle on that engine should be replaced at roughly 500 hours of operation per Yanmar's owner's manual. OTOH Mastry (Sp?) Marine mechanics suggest between 300 and 500. It would be wise to actually check your thermostat as the normal operating temp for that engine (2Gm20FW) is 180º. Low engine temps can result in inefficient fuel burn, soot and debris built up in the mixing elbow. BTDT...


FWIW...
Yes, I am leaning toward just replacing the elbow as a preventative measure even if it is not severely restricted at this point.

Wow! I have never seen 180F on my engine except for overheat situations which have been very rare. The manual indicates 140 F as normal. At least I thought it did. I am going to go down there and recheck my manual. I'll report what I find for posterity. If 180 is correct then I have been running at low temp for years and years. I could imagine 180 being max temp but not normal??

I am pretty sure I have accurate readings because I have a temp gauge verified by IR measurements taken with a handheld unit.

Anyway, I'll recheck my spec. numbers.
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Old 04-08-2020, 10:12   #15
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Re: Yanmar 2gm20f temp creeping up

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This is a pretty good explaination of how a thermostat works
Stant

Ideally an engine under cruise operates just above the thermostat ‘cracking” temp. A well designed cooling system has a lot of excess cooling capacity, so that it takes a pretty degraded system to allow an overheat especially at cruise.

One good reason in my opinion to operate an engine occasionally at full throttle for 5 min or so is to test the cooling system, it may rise in temp as the thermostat fully opens, but it should stop rising. Thermostats are gradual devices, and it’s normal to see some temp variations based on load and raw water temp.

Normally a thermostat is never fully open, if it is then the engine will very close to overheating because any increase in engine heat production will result in an overheat as the cooling system is maxed out.

I would both clean the heat ex, can’t hurt and change the exhaust elbow. Even if clean it may be close to failure from corrosion, and often that failure results in water in the engine and a seized engine.
I read the article. Great info. Good God, how much is there to know about a little old diesel engine? I have been doing my own maintenance on the engine and fuel system for 20 years and continue to be shocked at how much I didn't know I didn't know. sheesh!
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