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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel
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  #1  
Old 08-05-2010
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Normal Operating Temperatures

I searched but didn't find any previous discussions related to this topic.

What do you guys normally see on your temp guages at normal cruise power? I know this will be engine specific, but I expect the operating temps will be similar in a fairly tight range.

At 2500-2800 RPM, I generally see temps of 170-175 and sometimes as high as 180 if its hot out, or I have some slime build up. I'm used to aircooled airplane engines where 180 is perfect. On an air cooled aircraft engine, temps below 180 indicate the oil is not hot enough to boil off any accumlated moisture, so I haven't worried about seeing 180 on the boat. However, I was recently told that 160 might be more reasonable for a marine diesel. If so, I'd need to give up at least a knot under power to keep the temps down.

What say ye'? Am I running my diesel too hard?
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Old 08-05-2010
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180 is a normal temp for me in my Yanmar 3QM30.
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Old 08-05-2010
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160 on Volvo MD17C in the sailboat.
185 in the work boat with a Volvo D-6.
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Old 08-05-2010
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Is your engine freshwater cooled or raw water cooled?

If it is raw water cooled, I'd point out that one reason to keep the temps a bit lower is to help prevent salts from precipitating out of the raw water side. This starts to happen around 150˚ and becomes a serious problem above 180˚ IIRC.

If it is fresh water cooled with a heat exchanger, then running it at 180˚ should be fine.
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Old 08-05-2010
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Hello,

As mentioned, the 'normal' operating temperature depends on if the boat is cooled with engine coolant or salt water.

I am going to assume that you have a heat exchanger and that the engine is cooled with engine coolant. If that is the case, the engine *should* run at whatever temperature the thermostat opens. I feel that 180 is best to provide complete combustion while not overheating the oil.

My boat has a Universal M25 - a 21HP engine with heat exchanger. The thermostat is a 180 and the engine runs at 180 almost all the time. The boat is in the Long Island sound and the water is close to 80 degrees now. I can motor at 80% of max RPM and the temperature stays at 180. If I push to 90% of max RPM the temp may go up to 185 or 190. In the spring and fall, when the water in the sound is cooler, I can never get the engine over 180.

IMHO, if your engine regularly exceeds the thermostat temperature, you either have a problem with your cooling system (clogged heat exchanger, bad raw water pump), the cooling system is undersized (like early M25 engines with 2" HX) or maybe the sea water is really warm. What temperatures do Florida boats run at?

Barry

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Last edited by BarryL; 08-05-2010 at 10:35 AM.
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Old 08-05-2010
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Quote:
On an air cooled aircraft engine, temps below 180 indicate the oil is not hot enough to boil off any accumlated moisture,
FWIW, I used a "point and shoot" infra red thermometer to take base readings on all the power train components on the boat this summer while it was up to operating temperature. While the head and cylinders were very close to the thermostat temperature (160'F), the block and oil pan were both higher, with the oil pan temperature around 250'F. I've not tried that with other engines but it surprised me somewhat that the oil got that hot.
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Old 08-05-2010
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Echoing Saildog...as I recall salt comes out in the 140's F range, so a raw water engine operating in salt water should not exceed 140F as operating temperature.

With fresh water or a closed cooling system, temps from 170-210F are normal, all depending on the engine. The hotter you run them, the more efficient they are, and the only question is "What is too hot" and will damage some part of the engine. So you get the manual, or check with a dealer, and find out what the correct thermostat is for your engine, and what operating tempearture the manufacturer recommends.

It is always possible that a PO needed a new thermostat, the store didn't have the right one, and they put in one that was 10-20 degrees hotter or cooler than optimum. Can't tell without the manual.
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Old 08-05-2010
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Our Pathfinder 55 coolant cooled diesel runs between 180-200, depending on how hard we push the engine.
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Old 08-06-2010
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Thanks, my engine is indeed a fresh water cooled Universal M35. Manual says 170-190 is the normal range, however there was a discussion among the owners group where an owner was concerned at seeing the temp around 180 when it was normally closer to 160 and several others offered suggested "fixes". Having had a cooling issue late last season and having gone through both the raw water and fresh water ciruits on my boat pretty well, I didn't think my boat needed any of the suggested fixes, but I knew my temps were regularly in the 180 range.

I know there were some lower HP Universals in earlier C36's and higher HP models in later boats. Perhaps one or the other is supposed to run cooler but between the responses here and the owners manual, I think my boat is "normal".

I am due for a coolant flush and refill at the end of this season so, we'll see if fresh coolant has any effect.
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Last edited by PalmettoSailor; 08-06-2010 at 11:31 AM.
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Old 08-07-2010
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Most of what there is to know has been posted, but I will add that I have a Universal 5432/M40 in my boat with freshwater cooling and she used to run cool at 160. After much research, and seeing the manual range, I changed my thermostat to 185 and she runs at that now. Big difference in the power of the engine and a lack of soot on the transom. More complete combustion. At temperatures somewhere below 170 there is a real concern of carbon build up. I also run a percentage of biodiesel for lubrication and eco reasons and this has a higher flash point than dino.

All being said, you should make sure your engine runs above 170 and anything below 200 is certainly fine for our Universals. Higher range is better. Cooler is bad. Nigel Calder has a nice description of the dangers of a cool (160) running diesel.
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