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What do you guys think of using 15W40 in an old F134? I ran nothing but Castrol 15W40 in my M-37CDN (251 L6) for almost 20 years, and it is still going strong. I wonder if anyone has tried it in the Jeep engine? With the zinc being removed from most other oils now, I was thinking 15W40 might be the way to go.

I use 15-40 Rotella oil. Love it. John

I also am using Rotella 15W-40 along with 4oz of ZDDPlus. The ZDDPlus is supposed to increase engine oil concentrations of zinc and phosphorus to the levels needed by older engines especially those with flat tappets.

Shell Rotella is very good I have always used
It is available @ Walmart.
A high detergent oil, it will keep good clean engines clean & free from internal sludge & deposits.
Not sure I would be changing to this oil in a very old, tired engine though.

This engine is pretty good, doesn't smoke or anything and has lots of pep. One thing I used to do with my M-37, was add a quart of 2 cycle oil to every full tank of gas. It ran better on that than on straight gas. I might do the same with the M-38A1, but not as much oil. I never had any issues with fouled plugs or anything.

It's a good idea to pull the pan and side cover and clean up the old deposits. The higher detergent oil could unleash a load of crap. Once those items are cleaned, you won't have any problems. The pickup screen should also get cleaned up. John

My M38A1 was used by the Canadian military, and I assume they used 15W40 all through its service life as"15w40 engine oil" is stencilled onto the inside of the hood in the engine compartment. Also I have been running 15W40 since I got it, I have great oil pressure, and the engine runs quietly.

I use Petro Canada's 15/40 with Duron you can get it at Petro Canada's truck stops. They spent a ton of money developing it for their equipment up north it's a bit more money but this stuff does not break down. All the truckers up here swear by it. I have been running it in all my equipment for a few years now and it seems to stop engines from wearing out.

That settles it, 15W40 it is! By the looks of things, it has been running Chevron 15W40 since being rebuilt. Just found a piece of paper in the glove box today with that info on it.

is this what U are talking???

That is what is listed on the Walmart website as what the latest version container looks like.

For those in Canada I can confirm that both princess auto and Canadian Tire also carry this oil. Canadian tire also carries straight 40W in large quantities (confirmed at the Stoney Creek location this past Saturday)

Good to know! I will see if someone can get me some when they go to the mainland. Thanks!