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Old 30-05-2012, 07:07   #1
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Engine running too cool

It seems I go from one extreme to another. Used my engine (isuzu C240 4-cyl diesel) for many hours on a recent trip from Annapolis area to Newport RI and back. It ran at about 170d -- too cool, as I understand.

My water pump">raw water pump works very well - perhaps too well. It spurts rather than gurgles water out the exhaust. I am wondering if putting a larger pulley on the pump, thus slowing down its rotation a bit, might be the answer.
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Old 30-05-2012, 07:13   #2
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Re: Engine running too cool

My first guess would be the thermostat in the block. Have you replaced that any time recently?

If it is corroded or frozen open it will allow too much water flow through the block and you will run too cool. They are also available with different temperature ratings if you want to run hotter or colder.

Also are you certain of the accuracy of the temp gauge?
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Old 30-05-2012, 07:14   #3
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Re: Engine running too cool

Can you restrict the raw water flow thru the heat exchanger, allowing the coolant to run hotter.
Did this on a Morris Marine engine once.
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Old 30-05-2012, 07:19   #4
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Re: Engine running too cool

I changed the thermostat recently and it has the same rating, but unlike the one I had before (could not find an exact replacement), this one has a blow through hole.
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Old 30-05-2012, 07:21   #5
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Re: Engine running too cool

I have a kubota 2 cylinder, and my engine runs between 165 and 180 depending on RPMs. I have to be pushing it at full throttle to get it to hit 180, then once the thermostat opens, it stays there.

I know that in performance cars, we'd often put lower temperature thermostats in our gas engines to increase the performance. What's the harm of the diesel running a little cool?
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Old 30-05-2012, 07:23   #6
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Re: Engine running too cool

No, that is not the answer, because you will impose wear on the cam, the can shaft and probably prematurely fail the seals.

The same principle would apply putting a hulking 300 A alternator on the engine. It would work...for a while.

The solution is to ask Isuzu what thermostat they use (it's probably common) and getting one rated for a higher temperature.

At least, that WOULD be the solution if you were running in fresh water on the Great Lakes. I customarily run between 165-175F because I have a Holley 180F thermostat on my Atomic 4.

In sea or brackish water, salts precipate out of hot water at around 150-155F, or so I recall. By running at 170F, you are in fact running too hot for salt water with a raw water cooling circuit. You are correct in that the engine is happier at 180-190F, however. But if you are precipitating salts, that gurgling won't be a problem for long. Like Pringles consumption and arteries...

So here's the solution, pardon the pun:

1) Get a higher temperature thermostat, AND do fresh water rinses at dock of the circuit.

2) Get a lower temperature thermostat suited for salt water.

3) Get a heat exchanger and go "fresh water cooling". The Dex or whatever that is being cooled can take whatever thermostat you want, and the raw water side can run much cooler (meaning less chance of salts depositing). The system increases in complexity, but the cooling is isolated from the seawater side of the equation, and you can run the diesel near kettle temps.

That C240 is a decent diesel and worth modding to keep it happy. Good luck.
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Old 30-05-2012, 07:49   #7
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Re: Engine running too cool

my yanmar runs at 120-130 degrees F. i was advised that is ok. the advisor who sed it was the yanmar dealer/distributor in sd.
the yanmar we used in sailing gulf of mexico ran at 130. was perfect.
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Old 07-06-2012, 17:13   #8
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Re: Engine running too cool

My westerbeke is also running cooler. It should operate at 185 degrees. It is operating at 120 degrees. A certified westerbeke diesel mechanic said the mileage for a gallon of diesel fuel will decrease. There will be more wear on the engine. CaptForce suggested I slowly close the saltwater intake seacock. This will be another scarey moment trying this fix. It only took me 6 months to change the thermostat. Fear of breaking off bolts.
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Old 07-06-2012, 18:21   #9
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Re: Engine running too cool

"slowly closing the intake", for a test, but that is not for all the time.
Zee, Sounds like you have the thermostat removed.
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Old 07-06-2012, 18:30   #10
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Re: Engine running too cool

Actually for a raw water cooled engine 130 degrees F would be correct. For a fresh water cooled diesel engine its ~170-180 degrees F. Sounds like the OP's engine is working fine too me. Mine btw runs 170-175 ish about all the time, after its warmed up.

OH don't forget that the gauge and or sender could be off a bit too
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Old 07-06-2012, 18:33   #11
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Re: Engine running too cool

170 F is a warmed up engine. I don't don't think there is a problem. My engine thermostats while under a full load run the engine at 175 F.
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Old 07-06-2012, 18:37   #12
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Re: Engine running too cool

D 'Ya have one of those laser thermometer thingys?
Twenty bucks at harbor freight, thirty at Ace.
Point n shoot, digital readout of any part of yer mill!
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Old 07-06-2012, 18:38   #13
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Re: Engine running too cool

Very good advice here. I assume the OP's motor has a fresh water loop & heat exchanger. It is always possible that the heat exchanger has failed and let raw water to the engine. This could also cause colder running.

I have to modulate our prop pitch and rpms to keep the temp under 190. I am hoping the exchanger cleaning I bought over the winter helps. THere was a lot of calcium & critter residue on pass 4 of the tube bundle. Boat was in Lauderdale but now Lake Michigan.
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Old 07-06-2012, 19:55   #14
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Re: Engine running too cool

Quote:
Originally Posted by David M View Post
170 F is a warmed up engine. I don't don't think there is a problem. My engine thermostats while under a full load run the engine at 175 F.

My new Yanmar (20 hp, 3gm, fresh water cooled) never goes above 150. The dealership and the certified mechanic who installed it both tell me this is fine and not to worry about it
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Old 07-06-2012, 20:32   #15
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Re: Engine running too cool

all motors will have a specific/design temperature to operate... the engineers will determine that and it will be a factor/function of how it is used, where it is used, along with location of the sensors/sending units...

if the sending unit is in a 'remote' location where the water doesnt circulate well, or is further from the combustion chamber, the temperature will be different/lower then if the sending unit is placed closer...

but as stated above, a RAW water cooled motor in a salt water location will need to operate in a lower temperature range... due to the desalination of the salt solution....

check with the engine manufacturer mechanics to determine the temperature the motor should operate in, and find out the operating temperature of the thermostat....

on my Yanmar 2qm15, the thermostat starts to open at 120, and is fully open at 125...

the alarm sending unit will open, (zero resistance) at 140 degrees... this is lower then the temperature that the salt water will desalinate, (and where/when the salt will crystalize onto the inside of the water jacket componenants of the motor block)...

If you have overheated in the past, you will need to acid flush and run de-salting solutions thru the cooling system to remove the salt scale and any other build up from the 'water jacket' surfaces to allow better cooling abilities...

I wanted to install a temperature guage along with an alarm sensor, but my motor only has one port to use... so i can have 'either or' but not both... unless I drill and tap a new port....

Some have suggested I could use a TEE fitting to screw into the solo port, but that wont be accurate as the water will not 'circulate' thru the tee.. only allow the water to pressurize inside the tee fitting...

I could 'calibrate' the guage but that would be a guesstimate... and maybe 'close enuf' but it is not ideal...

btw, I used an infra-red thermometer, purchased from Home Depot for about $30 to determine the temperature... I shot the temperature at the base of the water sensor, and now that I have acid flushed the motor, I can see (by way of the temperature climbing and dropping at the 120-125 degrees) how and when the thermostat opens and closes...

I am unable to determine if the over heating sensor will operate at the appropriate temperature... any suggestions on how I can check/verify that it will function per specifications???

thanks and good luck
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