O.T. 15W40

I am an oil pressure nut. I have a worn out tractor that I just bought. I don't know what oil it had in it when purchased. But I do know this.

Start it up cold and the oil pressure is around 55 psig at idle. Mow with it for an hour and the pressure is 5 psig at idle.

I changed to Mobil 15W-40 C-4 oil. Pressure under same conditions held at 10 psig. Went to the store for more oil.

Changed again using HD 40 wt this time. Pressure held at 15 psig which is redline on the oil gauge.

So my question is this: If I only have 5 psig putting oil between two metal surfaces in the engine, how hard is it going to be for the engine to squish that oil out and attempt to put metal on metal.

I agree with film strength, but I'd bet modern oils have approximatly equal film strengths and molecular size..... ..... ....except synthetic. I have proven to myself that not only does it (syn)have a higher film strength, it also adheres to metal longer that paraffin....i.e. initial lubrication at start up indicated by noises the engines make or don't make including stopping piston slap in the winter time on cold starts of my diesel engines.

Residual oil film is what protects engines until new oil is circulated at engine start regardless of how long it takes to get there (due to viscosity). So if all non syn HD oils have approximate equal film strengths, the other consideration is the ability to retain this protective film under heavy loads and that is what viscous oils that produce high oil pressure do.

So, other than this tractor, I use Mobil 15w-40 in everything and Mobil 1 15w-50, 100% when I can afford it, 20% usually, and only on my oldest tractors, 0%.

The reason the oil companies recommend light oils is they have EPA mileage quotas to meet and it doesn't take a rocket scientist to realize that a crankshaft splashing around in thick oil takes more hp than one splashing around in thin oil.

Also, as others have learned, GM will not honor any warranty where the oil weight recommendation was violated and it caused a problem.

If you want your engine to last a long time, use synthetic oil in the proper weight range and change it and the filter per the manufacturers recommended intervals.

I agree about the oil clearance with a heavier weight oil. Along with that you will probably drop what little fuel mileage you get.

I stumbled onto another problem. I was a long time user, 40yrs, of Quakerstate oil. I bought a new Chevy 4cyl gasser and did the first two oil changes with Quakerstate 10w30 but notice my oil was extreamly black comparred to the factory oil at the same mileage change.

In the mean time I had been looking for a oil to use in my new F350 PSD and decided on Chevron Delo. no change in fuel mileage vs the factory oil.

So I thought I'd try Chevron Supreme 10w30 in my 4cyl. I picked up 2mpg the first tank. The first oil change went longer before the oil turned black and by the 2nd oil change, the oil was back to looking dark amber just like the factory oil but I now got another fuel mileage increase of 4mpg total vs using Quakerstate. No other changes were made.

Telling my son about my findings, so he trys CS 10w30 in his Ranger and got 2mpg increase the 2nd tank full.

T_Bone

2.how could putting heavier oil in a engine blow a head gasket when the oil is under low pressure there?a quad 4 is noted for head gasket trouble,i had 2 of them i learned after the second one too.
most new engines today use a break in oil to start with and once the engine has been run the oil never fully gets out of the bearings.
example-we had a 1066 that was getting tired so we parked it after last springs field work,we brought it into the shop in febuary without starting it tore it down and ordered parts for it. it sat in the shop that way for 2 weeks and it still dripped oil from the crankshaft when we installed the new bearings.