15W40 in an old engine?

He claims it will blow a quart of oil from the back seal in about 8 hours of running, though it doesn't appear to burn any. Pressure starts at between 20 and 25 and by the end of the day is down to around 8, the wife tells me.

Should I replace the oil with regular 30 for summer and 10 in winter?

BTW: I ran it three hours home yesterday and the engine feels very strong. This model 1947/8 has a peculiar throttle, with three distinct levels: an idle, the running section, and another section "through the gate" where it really takes off. I assume that this is emergency power, because the whole tractor shakes and roars when I pull it into that setting. Needless to say after a couple of 1-second tries I left it alone until I hit the steep hill leading up to our driveway. A short burst of power plunked us into the driveway in 5th gear.

Higher viscosity oil would raise oil pressure which could put additional strain on the seal and cause increased loss.

Higher viscosity oil would be molecularly thicker with larger molecules which would tend to resist movement by the seal.

I haven't been able to tell any difference between straight 30 and the 15w-40 in use.

Oil's not that expensive.....try one and if it doesn't work try the other.

On 15w-40 I use it in all my tractors including a '50's TO-20 I gave to my son.

Mark

Generally, the engine oil pressure is NOT directly applied to the rear main seal.

Typically, there is an oil slinger on the crankshaft that throws any oil that flows out the back of the main bearing outward, into a large groove that is open to the crankcase, allowing the oil to freely return to the crankcase.

So, the "mechanical labyrinth seal" (the oil slinger) effectively separates the oil flow from the main bearing from the rear main seal, so increased oil pressure shouldn't be a factor in more leakage from the rear main seal.

Furthermore, thicker oil increases oil pressure because there is LESS flow of the higher viscosity oil through the bearings.

Therefore, with a given engine, with a certain oil clearance at the rear main bearing, increased viscosity = less flow through the bearing = less oil the slinger, and then the rear main seal have to deal with.

I suspect when the OH'd it, they did not get the rear seal in correctly, or didn't get the rear main cap or seal holder properly sealed to the engine.

The overhauler replaced the generator with a Delco alternator, so it's a 12v system with lots of juice.

In my experience this type of engine starts very well in cold weather. I never plugged in the decrepit model I used thirty years ago, yet it would start reliably after sitting for weeks in even the coldest weather. #10 oil, of course.

Would not want a dipstick heater. cooks the oil. Very little surface contact.

--->Paul