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Old 11-12-2011, 14:36   #1
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Yanmar 2qm20 Temperature Control Question

i've removed the thermostat because since fitting it the temp appears to be getting a little high on long ocean legs - when i got the boat 2 years ago there was no thermostat in situ. so i put one in - i can see the use of it for short runs but if the engine is over heating on long runs i suspect the thermostat is not opening properly, which may be why it was originally removed. Anyone got an 'its gonna blow up on you' opinion on running without a thermostat?
on my earlier question - theres a fitting on the front of head anode plate that i think may be the original temp warning alarm sensor but it seems to be wired to a temp gauge (which doesnt work) - were 2qm20s ever fitted with temp gauges?
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Old 11-12-2011, 18:01   #2
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Re: yanmar 2qm20 temp. control question

The thermostat is supposed to MODULATE the engine coolant temperature - i.e closed when cold, then opens to the heat exchanger (or to sea water if not fresh), and then closing when it drops again - repeat. If there is no thermostat installed, the engine will take much longer to heat up (not good in the long run) and then once at temp. it's actual operating temperature will be whatever the HX or sea water can take away - again, not optimal.
As far as gauges, no they were not standard, they only had idiot lights. Speaking of gauges - if you gauge doesn't work, how do you know you are overheating?
Seems to me the best way to start is to get the gauge working - pretty simple, a sender, one wire, the gauge itself.
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Old 11-12-2011, 18:10   #3
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In automobiles, and perhaps boats, removing the thermostat can cause circulation problems as the lack of restriction changes how the coolant flows. Better fix the actual problem. A thermostat can be easily tested in a pan on the stovetop.
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Old 11-12-2011, 19:22   #4
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Re: yanmar 2qm20 temp. control question

As I recall the 2QM was raw water cooled only. These thermostats were on the back side of the cooling system and slowed the water flow out of the engine before the exhaust manifold. You could leave the thermostat out and install a valve to regulate water flow and temp. This was common on older raw water cooled engines like the atomic 4. You want to keep the temp around 160, colder and the engine does not burn the fuel efficiently, hotter and the salt in the water starts to cause problems. If fresh water cooled 190 is a good temp. Make sure you do not have a thermostat set at 190. Like Mayday said get your gauges working first so you know what is really going on.
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Old 12-12-2011, 04:27   #5
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Re: Yanmar 2qm20 Temperature Control Question

hmmm, yeah think I'll put the thermostat back in, pull the temp sensor unit and test it. Thanks for the assisitance.
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Old 12-12-2011, 05:03   #6
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Re: Yanmar 2qm20 Temperature Control Question

Get yourself a hand held infrared temp tool. They are very handy for finding hot spots, to deterimine if injectors are working and check the efficiency of heat exchangers.

Also good for telling you if the water is warm enough to swim in.
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Old 12-12-2011, 06:05   #7
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Re: Yanmar 2qm20 Temperature Control Question

What mayday said and Greetings and welcome aboard the CF, mayday12.

See also Basic Engine Gauge Theory and Testing
Basic Engine Gauge Theory and Testing

Wiring Diagrams: ➥ Engine Gauge Wiring Diagram - See also Gauge Testing Diagrams Cruisers & Sailing Photo Gallery

Testing Instructions:
Testing Engine Gauges - See also Wiring Diagram & Sender Resistances Cruisers & Sailing Photo Gallery

Sender Resistance:
Testing Engine Gauges (2) - See also Wiring Diagram & Testing Instructions Cruisers & Sailing Photo Gallery
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