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Old 02-14-2010, 12:42 PM   #1
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Proper Themostat for John Deer 6068

Inconnection with my 2000 hour maintenance procedures my John Deer mechanic changed to a new thermostat. The engines now run between 150 and 155 degrees at normal cruise (1500-1800RPM). This is about 30 degrees cooler than the old thermostats. The JD mechanic said it was cooler than he expected but no problem. Will the cooler temps harm the engines?

-- Edited by Ron Walton on Sunday 14th of February 2010 02:08:03 PM
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Old 02-14-2010, 03:52 PM   #2
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RE: Proper Themostat for John Deer 6068

Quote:
Ron Walton wrote:The JD mechanic said it was cooler than he expected but no problem. Will the cooler temps harm the engines?
Judging by Steve D's writings in the last year or two, I would say "yes."

Steve's a big advocate of getting the engine oil to between 180 & 200 degrees. Of course this is a function of how hot the engine runs. Newer diesels seem to run hotter than the older ones, the explanation being "to get a more complete fuel burn." If you have an IR gun, it would be interesting to see what the temp is on the oil filter. After coming up to engine operating temp, of course.

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Old 02-14-2010, 06:23 PM   #3
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RE: Proper Themostat for John Deer 6068

Thanks. I will check temp at oil filter next time out.
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Old 02-14-2010, 08:22 PM   #4
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RE: Proper Themostat for John Deer 6068

If they're raw water cooled (no fresh water cooling at all) the lower temp. thermostat is correct. If they're fresh water cooled (freshwater cooling in the engine and a heat exchanger) the higher temperature thermostat is appropriate.
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Old 02-15-2010, 03:53 AM   #5
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RE: Proper Themostat for John Deer 6068

"If they're raw water cooled (no fresh water cooling at all) the lower temp."

This is really rare on a modern engine converted to marine use.

On old heavy cast iron engines 140F thermostats were the norm , to cut down on salt buildups, and most would last 5-6 years in salt water.

I have only seen over cooling when using a keel cooler setup, not with sea water heat exchangers..

The solution there (OTS) is a thermostated return system.

Engine water will head to the keel cooler and a seperiate thermostat will divert enough hot water to the keel cooler return to keep the temperature up.

Usually there is only a 20F difference in the water leaving the engine , and the coolant return.

Personally I would be far happier with 180-190 at cruise than 155F on a Deere..
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Old 02-15-2010, 05:31 PM   #6
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RE: Proper Themostat for John Deer 6068

Quote:
Ron Walton wrote:

Will the cooler temps harm the engines?


Probably not in the short term but that seems awfully cool for those engines. I would expect the correct thermostat to be around 190 or 195* F
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Old 02-16-2010, 05:01 AM   #7
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RE: Proper Themostat for John Deer 6068

I would double or triple the oil changes , and work to cure the problem .
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Old 02-16-2010, 06:33 AM   #8
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RE: Proper Themostat for John Deer 6068

The fix ( if needed) is to change back to the original thermostats instead of the new ones recommended by the JD mechanic. Prior to the change the temps were 185.
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Old 02-16-2010, 09:47 AM   #9
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RE: Proper Themostat for John Deer 6068

Quote:
Ron Walton wrote:

The JD mechanic said it was cooler than he expected but no problem. Will the cooler temps harm the engines?

It sounds like your mechanic made a mistake and was trying to cover it up.* At no cost to you, he should install the proper thermostats.* You might check with the manufacturer to document the correct operating temp, in case the mechanic is unwilling to repair the problem at no cost. Currently, your running way too cold and engine life will suffer.......................Arctic Traveller

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Old 02-18-2010, 05:36 AM   #10
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RE: Proper Themostat for John Deer 6068

Thanks for all the input. The mechanic replaced the 180 thermostats with 160 because they work better when the engines are run at higher RPMs. Since I run primarily at low speeds he* will switch back to the original 180s.
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