Partial flow oil cooler

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Aug 6, 2026
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Hi all
On an om642 which has a reputation for high oil temps I am fitting an oil cooler. Rather than aftermarket solutions I thought would use the factory option used on the pickup truck.
A partial flow oil cooler. The size I have chosen is basically the same as the aftermarket full flow option and a bit bigger than the factory partial flow solution.
The question is really related to do I need a thermostat, aftermarket and merc version don’t use them.
And the other is does a partial flow cooler have the same effect as a full flow if it uses the same size cooler. Obviously it only cools half the oil perhaps a bit cooler than full flow, then mixes it back into hotter oil, where a full flow cools the whole lot.
Anyway interested in thoughts.
Thanks.
 
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Since diesels are said to be cooler running and/or take a long time to heat up, whatever you decide to do MAY REQUIRE a thermostat be included.

Where you live and how you drive might be factors.

An M-B site might have more members with specified knowledge and experiences. I had to look up om642.

If you can benefit from an oil cooler, maybe adding a transmission cooler is smart?
 
Hi all
On an om642 which has a reputation for high oil temps I am fitting an oil cooler. Rather than aftermarket solutions I thought would use the factory option used on the pickup truck.
A partial flow oil cooler. The size I have chosen is basically the same as the aftermarket full flow option and a bit bigger than the factory partial flow solution.
The question is really related to do I need a thermostat, aftermarket and merc version don’t use them.
And the other is does a partial flow cooler have the same effect as a full flow if it uses the same size cooler. Obviously it only cools half the oil perhaps a bit cooler than full flow, then mixes it back into hotter oil, where a full flow cools the whole lot.
Anyway interested in thoughts.
Thanks.
Why not run a oil to coolant type oil cooler/warmer?
I have Kubota diesels that are up to 27 years old they typically run 140 to 160f and are fine. Don't worry about "over cooling the oil.
 
I do have one, oil/coolant,that would do nicely, but the cooling system is adequate at the moment, but does show strain up hills so adding more heat into the coolant seems counter productive. Although would keep the oil at the right temp. The factory one is not big enough but is in the v so you cannot actually do much with it.
I wanted a bigger cooler but got a good deal on one that is big enough…..
 
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