Oil Pressure low?

Thu Dec 18, 2003 9:44 pm

Hi guys,
I've been running Miss Daisy '49 usually for a good stretch of 2 hrs. at a time pushing snow. It does a real nice job of levelling flat even after lots of traffic up and down the drive.
After the 2 hrs. is up I'll look down at the oil pressure and it looks to be on the low side even when working. There were no numbers on that gauge so I stole the one off of Frank '67. That gauge starts at 0 and goes to 75 with 15psi graduations on the gauge. When I fire up it sits right in the centre and will stay there for about 20min. then will begin to work it's way down, right down to 15 by the time I'm ready to put her away. My manual says 30-35psi at 100rpm above high idle, looks to me like I only have half that.
I'm thinking of putting in a different oil, say 10W/40 as a start to see if things will improve, remember I put fresh rod bearings in this one, the mains looked to be alright. I have been running straight 30 in it.

Should I see an increase in oil pressure, say if I'm really loading her?

What do you guys think about the 10W/40?

I've never done too much tinkering around with different oils, except running 5W/30 during winter for an Onan engine.

I'd hate to lose my little work-horse this early on, I've probably only got 10 tp 12 hrs. on it.
The engine sounds OK to me.

Fri Dec 19, 2003 12:00 am

EZ, did you plastigauge the mains when you did the rebuild? If not I'd drop the oil pan and check that out. After putting all that work into the tractor it'd be a shame to damage the crank!!!!

Fri Dec 19, 2003 7:49 am

The gauge only measures the pressure exerted to the main bearings. The connecting rod bearings do not recieve pressure from the oil pump. Rather when they plung into the oil bath oil flows up the tube on the bottom of the cap. So, to put it simply it is your main bearings.

Fri Dec 19, 2003 8:27 am

I'll have to ask George Willer about that?

Fri Dec 19, 2003 9:51 am

I think I'll have to take a little exception here. The main and rod bearings on a C-60 receive pressurized oil from the cross drilling in the crankshaft. (see pic in the above post). The rod bearings are not splash lubricated.

Next, I would not expect or recommend that you should go to 10W40 to get an increase in oil pressure. This oil presure subject has been discussed very thouroughly in previous posts. But if you didn't mic, or plastigage your mains, then that's something to consider. Worn oil pump gears and a weak pressure regulator spring are also places to look. At least pulling the oil pressure regulator apart is easy. I don't have the length or compression numbers for that spring, but I'm sure someone here does. Stay with the 30W if the temp doesn't get too cold.

Another thing to check, if you will examine the diagram above, you will see that the oil pressure gauge is connected to the oil filter housing on the outside of the element. The resistance of the filter element plays a part in oil pressure as well as the size of the orifice where the oil drains back to the oil pan. If someone has drilled out that orifice, then your oil pressure will be low. Just something else to check.

Fri Dec 19, 2003 10:14 am

Hey guys,

Thanks for the advice and pictures.
I know we have been over this before, the mains were not plasti-gauged as they looked fine to me. i.e. no scatches or scoring on them, my crank is slightly worn though. The new bearings measured .02 of extra clearance with the plasti-gauge, I was hoping that would not be too bad.

Seems to me as the oil heats up, of course it gets thinner and the pressure drops, I'll check the spring and valve and put 30W back in. I dropped the oil last nite, sure is black.

Question: Does anyone else have the 75PSI gauge? If so, where does your pressure generally sit at start-up? High side toward 75? Mid range?

I think my manual shows the reg. spring length. Maybe I'll end up stealing Franks'.