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simonjudge
simonjudge

Posted: Mon Apr 16, 2012 12:00pm

Post Subject: Engine running cold

I have a 1994 mitsubishi 4 cyl diesel on my narrow boat. Since an episode of mild overheating last year (the fan belt snapped) the engine has been running a little cool - as measured by the temp guage and also the temperature of the hot water stored in the calorifier. Especially on canal running (lots of idling in locks) it rarely gets above 70 degC. I suspect the thermostat is sticking open, or partly open, and so plan to replace that (and the gaskets). But before I do so does anyone have any other suggestions? Many thanks

Tony-B
Tony-B

Posted: Mon Apr 16, 2012 2:25pm

Post Subject: Engine running cold

If it takes a similar time to get to 70 now as it did before the overheat then I suspect that the rectification work would have resulted in ridding the skin tank of air/gas that had built up over the previous years. If so then the cooling would have been compromised so what you thought of as normal may have been a slight overheat. It is far from unknown for a 74 degree thermostat to be fitted to marine engines in an attempt to limit the calorifier temperature. I mention this is case when you take the stat out you find it is OK. Earlier waxstat type thermostat had a clip mechanism so if they overheated (which often causes them to loose wax) they would clip in the open position so if it takes a lot longer to reach 70 than it did before I would go with your diagnosis. Tony Brooks

simonjudge
simonjudge

Posted: Mon Apr 16, 2012 2:46pm

Post Subject: Engine running cold

Thanks - very helpful. It is a few years since the system was drained so air buildup is a possibility. But I sense the engine is taking longer to warm up even to 70 than it did before. The manual suggests an 82 thermo, which is what I intend to fit. I am relaxed about the calorifier water getting hot as it only feeds the galley tap. The hot taps shower and sink in the loo are really only warm, as they fed via a hidden mixer valve which mixes hot and cold water to produce a safe temperature.

simonjudge
simonjudge

Posted: Sun Apr 22, 2012 11:01pm

Post Subject: Engine running cold

Dear Tony Thanks again for your advice. This procedure went very smoothly yesterday - no leaks at all- and the hot water is now properly hot again. Of course my guage does not read the same as the thermo setting (165 deg F vs 82 deg C respectively, a 8 deg C difference!) but I am not too worried about that. If anyone is interested in my system for producing warm water for the bathroom from a very hot calorifier, see the schematic on page 15 of the boat's manual: http://scholargypsy.judgefamily.o rg.uk/instructions.pdf

Tony-B
Tony-B

Posted: Mon Apr 23, 2012 8:43am

Post Subject: Engine running cold

It is perfectly normal for the running temperature to be up to 10 degrees higher or so than that marked on the thermostat. The marked temperature is that at which it starts to open not at which it is fully open. I am pleased this is resolved and went well. Thanks for the feedback. Tony Brooks

simonjudge
simonjudge

Posted: Thu Apr 26, 2012 6:03am

Post Subject: Engine running cold

Thanks again, Tony. I have the opposite issue, namely the gauge is reading 165 deg F which is 74 deg C. I don't think I really want to change the entre guage system, so I think I will continue my current approach of taking action if the guage is not at its habitual reading!

Tony-B
Tony-B

Posted: Fri Apr 27, 2012 2:26pm

Post Subject: Engine running cold

To be honest I did not bother to convert F to C because I feel that if the questioner wants help it is for them to do. I am afraid that gauges and senders are not much more than indicators - especially if they have temperatures on them so your engine could well be running at a higher temperate than you think. An infrared laser type thermometer pointing at the thermostat housing would tell you. If you have a large calorifier that would slow the warm up period considerably. Temperature senders are available separately as long as you know what type and make of gauge you have. Personally I would not give the temperature any more thought. Tony Brooks

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