Engine Temperature Gauge Help Please.

[Wotname]

Originally Posted by GILow

PM me your details and I will post it to you. If it works, I will send the other one. I was only keeping them on the boat for emergencies, better they do someone some good. If they work, you could send me your old higher temperature gauge as a trade then I'll have useful backup.
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Hmm… I don't actually have any gauge to send in return - none are fitted to the standard 2GM20 ; hence the difficulty and this thread.

At this stage I going off the idea of fitting a NTC style temp. sensor because as others have said, it is quite a task to fit one. This is no spare bung just to stick it into. There is space to drill and tap into the head casting part of the water jacket but unless I had the perfect gauge and sender, it is too much work for a mediocre return.

Unless I find something better, I am leaning to Snowpetrel's suggestion back in post 3 and fit an Engine Watchdog TM2 or TM4. These are thermocouple devices and the sensor is bolted on externally. There is even a suitable tapped hole in the head directly above existing thermostat and sensor. See photo below.

Originally Posted by GrahamHO

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I also looked for a suitable gauge and gave up on the idea as not worth pursuing, but if you find one I suggest you still do the checks I've suggested.

Yep, those checks are good practice, I currently (occasionally) shoot the IR thermometer over the head and exhaust

Check the TM2 mentioned above, you might find it suitable.

Originally Posted by GrahamHO

Yanmar 2GM20 seawater thermostats are a consumable just like the engine oil.
Change the thermostat every couple of years and check a few times between and you won't need a temperature gauge.

Maybe you could have 2 gauges in case one is faulty. But then you wouldn't know which one is faulty so you should really have 3 temperature gauges and if 2 read the same those will most likely be correct.

The temperature reading gun someone suggested sounds a good idea. You could direct it at different parts of the engine occasionally.

This whole thread has allowed me to really think though all the issues so a big thanks to each and every contributor

Fitting a gauge allows for for monitoring:
1 Too low a temperature as when the thermostat sticks fully open.
2 A partially stuck open thermostat which was the genesis of the thread
3 Too high a temperature and a failed temperature switch. The temperature switch is never checked during normal operation and unless one removes it and tests externally, one is unaware of a failure until way too late . FWIW, my temp switch operates at 62 C (145 F).

If the temp switch has failed, there is no indication at all (without a gauge) until the water starts boiling in the head - not good.

Engine temp monitoring is a critical engine parameter. I erroneously thought that water flow out the exhaust was suitable fallback indicator for a failed temp switch but of course, this is wrong (at least in a 2GM20). So there is no fallback for a failed temp switch unless a gauge is fitted (or two temp switches )

Note the nice tapped hole (actually two holes) just above and behind the thermostat and temp switch. Perfect place to bolt on a thermocouple

There is a big pile of water directly underneath these blind holes and it is the probably the hottest part of the water circuit.

[GrahamHO]

Originally Posted by Wotname

Allow me to correct this statement

A 2GM20 will almost certainly run hot if the thermostat is removed and in tropical waters can seriously overheat with the thermostat removed.

The reason is that most of the cooling water bypasses the block and head when the thermostat is removed. The moving disc of the theromstat actually closes off the water bypass circuit when the thermostat is fully open. Without that disc, most of the water goes straight into the exhaust, not into the block / head.

Thanks, yes I believe you are correct as its a bypass. A car engine will run too cool without a thermostat. But the advice still remains to not to run the engine without the thermostat.

Slightly off topic; I once had a terrible Ruggerini engine and it cracked its head a month out of warranty. The reason was a thin web of cast iron partially blocking the water hole in the head passage to the cast iron exhaust bend. The head casting hadn't been properly fettled. There was an argument, the agency had changed but they grudgingly paid but I did all the labor. I had rigged a suitable temperature gauge on that engine but it didn't indicate overheating as the sensor was in a part of the engine away from the problem. As new cooling salt water is coming in all the time some can be the correct temperature and some can be too hot. The cooling water doesn't circulate as in a car or heat exchanger marine diesel.

[Snowpetrel]

Just got my TM 4 in the post. It's a compact little thing. Hopefully I'll get it fitted in the weekend if you want to see it wotname.

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[Snowpetrel]

Here's a pic...

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[Snowpetrel]

Just installed and tested the TM4 albeit in my normal crude way... It works well. Got 62 degrees on the block, and 18 degrees on the raw Water cooled exhaust elbow. Didn't test the alarm, and haven't hooked up the oil pressure.

I checked it against my handheld remote thermometer thingamy. It was about 5 degrees lower, but I am not sure which one is correct, and anyway I don't need exact temps, just relative ones. Very pleased.


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[Wotname]

[GrahamHO]

Originally Posted by Snowpetrel

Just installed and tested the TM4 albeit in my normal crude way... It works well. Got 62 degrees on the block, and 18 degrees on the raw Water cooled exhaust elbow. Didn't test the alarm, and haven't hooked up the oil pressure.

I checked it against my handheld remote thermometer thingamy. It was about 5 degrees lower, but I am not sure which one is correct, and anyway I don't need exact temps, just relative ones. Very pleased.


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Sounds good. Though 18*c sounds cool for the exhaust elbow. That's about a cool sea temperature around here depending on season. Not that I think that matters as its really the head temperature that's most important.

If your thermometer reads over 100*c you could check its calibration by boiling some water at sea level to see if it reads 100. I suppose your boat is at sea level unless you're sailing on Lake Titicaca. It's not the exact temperature that matters; just any big change that occurs.

[Snowpetrel]

Ha, good idea, I'll try boiling something and then testing it with the Ray gun. Sea temp here is about 12 degrees I guess, a ways up the derwent river at POW bay, and a fair bit of snow melt at the moment.. but I'm just guessing because the hull is at 12degrees according to the magic Ray gun!

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