Cummins 5.9 330B Operating Temps

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Oct 11, 2007
Vessel Name
Circuit Breaker
Vessel Make
2021..22' Duffy Cuddy cabin
My 330B runs at 180 Degrees at 1800 RPM and 185 Degrees at 2600 RPM. Is this excessive? I see so many threads that are talking about 175 degree temps and that has me wondering about my own engine.
I would suspect running temperature would be a function of what thermostat is installed. 180 and 185 do not sound too high but I don't know the engine at all.
The old Ford Lehman 120 has a normal operating temperature range of 175-190 degrees f. Not knowing anything about the Cummins engine, I would agree with RTF that the temperatures you're seeing don't seem too high. But I would think the engine's operating manual would call out the proper temperature range. If you don't have access to a manual for this engine you should be able to get the information from a diesel shop that services these engines or from Cummins itself.

-- Edited by Marin at 21:35, 2007-11-23
My 330 B Series runs at 185 at 1800 and 188 at 2600. It has never varied in 3 years or 900 hours.
Thanks guys......This is what I love about this site......Simple question--real world feed back.

Doc:* Since your temps are the closest to what I'm experiencing, I'll ask you this. When running and the engine is heating the hot water tank, does the tap water (hot) spit, steam and pop out of the faucet? mine does but only with engine heated hot water. It's fine in the slip with shore power heating the tank.

No, mine is fine. I am surprised you are not blowing the safety valve if it's that hot. Since it is spitting and steaming I suspect an air leak somewhere in the system. You might check all your hose clamps. Sometimes an air leak won't drip water.

Are you using city water pressure at the dock and the 12 volt fresh water pump while underway?
Doc:* I quit using dock water several years ago. I left the boat unattended and had a bad experience. (Didn't sink, though.) I only use onboard water now with a 12 V pump. I must say that this 330 B is one of the best engines I've ever had and have had no trouble with it. BTW, What kind of speeds can you get with it in your boat?

1800 is 10 mph. More doesn't give much more. Maybe 14 wide open. I only have one.

I suspect the spitting and steaming*is due to the difference in hot water temperatures between the shore-power vs. engine-heated water.* If your Halvorsen has a Raritan water heater as mine does, you'll notice that there's a thermostat on the electric heating element that controls the water temp*at 120 degrees F.* When you're heating the water using the engine coolant, there's no temperature limitation.* Therefore, the hot water temperature will approach or equal that of the engine coolant (180+ degrees F).* Water that hot will steam and, if it comes into contact with water droplets remaining inside the faucet spout from the last use (now cooled to ambient temp), it will cause them to spit (a result of the rapid heating).

The lack of temperature limitation while underway is a safety hazard.* The Raritan manual states "Water temperature over 125F can cause severe burns instantly".** I 've considered adding a blending valve to my WH (to blend cold water in with the hot), but it seems this would also occur when using the shore power.** Guess I need an electrically (de)-activated blending valve.

BTW, my 5.9 (6BT5.9M, 210 HP) runs cooler (approx. 165F) and I don't have the steaming & spitting phenomenon.* The tap water is really hot, though.


-- Edited by jethrobd at 12:46, 2007-11-27
Jeff -

The blending (or anti-scald) valves are thermostatic, and you can set them for whatever temp you want - say 130 or so. They take hot & cold water input and vary the proportions to give you the desired temperature. If your electric temp is cooler than the set point (say 120 vs 130), you'll get pure "hot" water with no mixing.

Not extremely expensive (especially by boat standards) - under $50, I believe.

They're used with solar hot water installations, as you can easily get 150-160 degree hot water stored there, too.

Added benefit is that you stretch the hot water in the tank when you don't have access to AC power.
Nah, something's wrong there. 180 degree F water won't turn to steam... has to be over 212F (100 C). Under pressure that temperature rises. In any case, it's too hot or air is getting into the system. The tempering valves mentioned are good ideas... however I just warn people about the really hot water when we're underway.
If you search for "tempering valve," you'll come upon a 1/2" Watts 120-160 degree tempering valve for $27.49. You can probably get it from a local plumbing supply and get just the size & fittings you need.

If you have children aboard, it's a pretty good idea.

Whlie you're there, search for "infrared thermometer," and you'll find a bunch of non-contact thermometers for under $50. That would answer the question of how hot it's really getting - though you'll need to measure it under load.

Interesting that the gauge reads what it "should" (that is, I'd expect a 180 thermostat so that a 180 water temperature would make sense). I don't know how the Cummins is set up in terms of the relative locations of the thermostat, the "heater" outlets to the DHW tank, and the temperature sender. You'd think they would be in about the same location - as the coolant leaves the head and before it goes to the heat exchanger. Anybody know???
Thanks for the thermostatic tempering tip, Chris.* I notice, however, that the $27.49 Watts valve on Amazon is not an anti-scald valve; I assume that means that it can't react in time to prevent an initial slug of scalding water from coming out of the faucet.* I found some anti-scald tempering valves on; they seem to run about $95.

You're right about the super-hot water stretching the hot water supply.* We can take an amazing number of showers after a day's cruise.

Could be. I used one for quite a few years with solar hot water and never noticed a problem. I don't have one on my boat yet, but am planning to do it soon.

I think that by mounting it directly to the hot water outlet with a short metal nipple (can I say that??), it'll stay hot and you won't have any response lag.
Good point about it staying hot and thus active, Chris.* I think I'll see about adding one in this spring.

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