My D2 has the oil-cooler disconnected (bypassed with a 4" tube). Should I try and plumb it back in? Do I need to worry if I work the thing for hours on end when it's 90 degrees out? - Or, should I just put modern 15w40 multigrade oil in the beast, and not think about it?

I'm guessing, from reading the manual about adding kerosene to the oil when it was cold, and using thick oil when it was hot, that, in a world without multiviscosity oil, they didn't want the oil to change temperature very much, so they tried to keep it near ambient with an oil-cooler.


Cat D2 4U 4384

The old cat motors have about 2x if not more oil capacity than newer diesel engines.

I wouldn't worry about running then in 90 deg weather we have been running these cats in 110 - 115 deg weather around the clock for years with no problems.

The later model U series did not have an oil cooler, just a full width radiator.

A lot has changed in lube oils in the last 60 years when the old recomendations were made multigrade oils did not exist. There is really no temp control on the oil cooler for operating in cold weather than the bypass that might open with the thicker oil.

We use Delo 400 or Shell Rotella for the old cats.

Apparently some U series D2s had oil coolers and some did not. Those that did used a narrow radiator on the RH side of the water radiator. I have a D2 engine with OEM plugs in the cooler pipe holes. If you plug it off, there's a bypass valve in the bottom of the filter housing that should be removed. Or, you can leave the shunt pipe.

I have been told by Cat service people that the oil cooler was a big overkill on this lube system. The whole oil system on a D2 bordered on overkill--a huge pump with a pressure limiting valve controled by the pressure at the center main bearing. You can pretty much do whatever you want to do on this one.

On my 3J I bypassed the cooler a few years ago because the oil cooler was damaged by a board that was shuved into it while I was dozing an old chicken coop.

I talked some of my old timer friends that all told me the same thing, by pass it and forget about it, it wasn't needed anyway.

I have not had a problem with it since, and I've ran it in some really hot Hawaiian sun for hours at a time. Not everyday, but every so often.

Does not seem to bother anything that I can tell.

Aloha