'81 H36 colling water temperature question

[tmjb]

I posted a related question about this not long after purchasing my H36 in late 2014 and got great info and advice from a number of people describing the Sen-Dure fresh-water cooling conversion installed on my Yanmar 2QM20.

One of the responses I received, from Rardi36, stated that his experience was that the Sen-Dure 2550 heat exchanger installed as standard for this boat/engine was undersized and that he had experienced the cooling water high temp alarm sounding when running at 80% + power for a sustained period. He went on to say that he has a water temperature gauge installed and since he could see that his temperature stayed well below the 170 degrees that factory fresh water cooled engines run at he was not alarmed.

I had not experienced this until this last weekend when I pushed my engine to about 2500 rpm for 20-30 mins. Typically I have run at about 2000 rpm when cruising with no alarm.

My questions are as follows:

Have others had similar experiences with the alarm?

For anyone with a water temperature gauge, how have you installed it/what have you used?

Has anyone considered purchasing the larger Sen-Dure 2553 (same diameter but longer), part of the equivalent conversion for the 3QM30 engine?

Any and all thoughts, experiences, advice would be much appreciated?

 

[Alctel]

I THINK you are not supposed to run at 'redline' (2500) for more than 20 mins anyway, according to the manual - I could be wrong. I tend to stick around 2000/2100

 

[tmjb]

Oh oh! I don't think my rev counter has a redline. Stupidly I didn't check the manual. Part of my reason for running at higher revs was that I had read that the engine needs to be run at higher revs which I typically have not because I generally do little motoring.

 

[rardiH36]

Give me a day or so and I will post some info about my experiences and about my temp sender installation ...

 

[Tally Ho]

Wow. My 2GM20 is supposed to run at 3400 RPMs. 2400 seems low.

I can run my engine at 3000 RPMs without any issues, but if I push her to 3400, I start to get black stuff out the exhaust, and eventually, she will overheat.

I will be inspecting my exhaust elbow over the long Chicago winter. A diesel mechanic also suggested I add some fuel injector cleaner to the fuel. May also need to take the HE apart to make sure it is not clogged.

Greg

 

[tmjb]

Many thanks. Much appreciate it.

 

[tmjb]

I'm sure different engines have different characteristics.

 

[Jim Legere]

I'm sure different engines have different characteristics.

You are quite right. The QM series are raw water-cooled designs (hence the Sendure conversions) that are quite a bit heavier and slower turning than the GM series that replaced them. With my 3QM20 I seldom run above 2500 RPM except for short bursts. It seems happiest in the 2200 to 2400 RPM range. And the manual supports this approach.

 

[tmjb]

Thanks Jim. I take it you don't have a water temp gauge and haven't experienced the high water temp alarm using your engine as you describe?

Does your 3QM20 have the larger Sen-Dure 2553?

 

[RoyS]

I run my 2qm15 at 2800 all day with the temperature never exceeding 160F which is my thermostat setting. The engine is rated for 3000 RPM. You should check your alarm sending unit on the engine. The factory supplies two: One for fresh water cooled engines and one for salt water cooled engines. With fresh water cooling you should have the green colored sender which goes off at 203F. The salt water cooled sender goes off at 140F. Perhaps you have the wrong sender for a (now) fresh water cooled engine.

 

[kloudie1]

The QM shop manual says 2600 RPM continuous max and 2800 RPM "one hour" rating.. Have you verified the tachometer with an accurate tachometer? The Yanmar tacho is notoriously inaccurate..
Something like this is sufficient:
https://www.amazon.com/Digital-Phot...1475069273&sr=8-2&keywords=optical+tachometer

 

[tmjb]

Thanks again. I replaced the sender right after I purchased the boat - beginning of 2015. I asked at the time whether the new sender I was purchasing was good for the fresh water cooled version and was told there was one tstat. My guess is I got bad info and have the one for the raw water cooled version.

I just called my regional Yanmar distributor who tells me there are actually three versions of tstat available rated for 60, 65 & 95 centigrade (140, 149 & 203 F) the latter being for the fresh water cooled engine. They told me that the part # for the latter is 127610-91350. Does this correspond with what what others have.

Re rpm, I am just going by the gauge so much appreciate the input re verifying the actaul revs.

Thanks again for all input.

 

[rardiH36]

Hi TMJB: My comments/observations/alternatives embedded in blue below (hit the "click to expand" to expose the full message):

I had not experienced this until this last weekend when I pushed my engine to about 2500 rpm for 20-30 mins. Typically I have run at about 2000 rpm when cruising with no alarm. Our 2QM20 models are rated at 2600 rpm. See nameplate photo attached. My understanding is that continuous running of about 80% of max is ideal.

My questions are as follows:

Have others had similar experiences with the alarm? As we have threaded together in the past and which you referenced, yes.

For anyone with a water temperature gauge, how have you installed it/what have you used? Please see the attached pictures which I took yesterday. I mounted generic temp sender in the rubber coolant hose leading from the engine block to the thermostat housing. It is fitted into the threads of a common galvanized T-fitting available in the plumbing sections of most hardware stores. When I bought my boat, the PO had mounted a nice gauge set in the nav station area. But had not installed/connected from the engine. Nor did the PO buy a sender for it. I bought a generic temp sender off of eBay to get it working.

Has anyone considered purchasing the larger Sen-Dure 2553 (same diameter but longer), part of the equivalent conversion for the 3QM30 engine? The summer-time sea water temperature in your sailing area is much warmer than mine. I don't need a larger heat exchanger. Considering that Hunter designed our odd cooling systems in Florida, I expect that they and Yanmar considered the original part sufficient. Several thoughts/observations:

1) My alarm would generally go off after I had motored at say 2200 rpm for a while then shut off the engine for several minutes. When restarting, the alarm would sound for several minutes then stop. I think I have previously posted my theory about why this was happening: The difference between the thermostat maintenance temp and the "alarm on" temp is very small. When the engine is run and shut off, the high residual temperature around the cylinder head and block transfers to the now non-circulating coolant. The coolant temp rises above the temp alarm trigger point. Then after several minutes of motoring again, as the coolant is circulated through heat exchanger, the temp drops down below the alarm-on temp. My solution to this issue was to install a different spec alarm switch. I also have a GM series Yanmar manual. I noticed (accidentally) from comparing the two that the seawater cooled alarm switch of the GM's had a somewhat higher activation level, than the QM series seawater cooled switch. GM "on" = 65c +/-2 QM "on" = 60c +/-2. I bought/installed the 65c version which solved the problem. The higher threshold GM seawater alarm switch has a White indication dot and the original part number was 128275-91340. (Your Yanmar dealer will be able to provide you with the same unit but now has a different part number.) Note on this: Do not install a Yanmar contained system alarm switch. This has a trigger temp of 95c = well above our operating temperature.

2) If your existing heat exchanger hasn't been cleaned/restored in a while, consider taking to a radiator shop that also does heat exchangers. Aside from the end cap that is easily removed with the bolt, the shop can de-solder the other end-cap as well. They can descale/clean out all the tubes. Also inspect for pitting/corrosion of the tubes and the baffles and restore to as new condition.


Any and all thoughts, experiences, advice would be much appreciated?

 

[RoyS]

Regarding where to install an additional sending unit: Your original salt water cooled engine has a zinc on a plug near the alarm sending unit. If your engine is now fresh water (coolant) cooled you no longer need the zinc. I drilled and tapped that plug to accept a gauge sending unit. That puts the gauge sender and the alarm sender in the same location. Not that this would apply to most people, but my hearing is not what it used to be and I sometimes cannot hear that alarm sound. As a precaution, I added a boat horn to the alarm sender to ensure that if it ever went off I would hear it. That alarm will wake the dead.

 

[tmjb]

Apologies for such a late reply and many thanks for the detailed and thoughtful responses. I much appreciate it.

It has taken me a few days to assimilate the input I have received, to analyze it and to check out things on my boat in the context of what I have learned. In particular this weekend I went to my boat to take a more careful look and to perform a test. I found that the new temp switch that I was sold and installed on the engine last year is a yellow dot (60c/140F?) switch. I ran the engine at about 2,000rpm for about 45 mins under power and got no alarms.

I have not yet, but intend to perform a a thorough clean, and refurbishment if necessary, of the heat exchanger over the winter (it's almost the end of the season here). I also plan on installing the white dot (65c/150F) temp switch and am hopeful that this will be appropriate to run the engine at about 2,100rpm (80% of 2,600rpm) for sustained periods.

I also think that the ideas about where to install a sender for a temp gauge are great and pretty easy to accomplish so may well try tat over the winter too.

Many thanks again.