low oil pressure reading

[pett3227b]

Hello, New to the site. Have 48 farmall cub. I am wondering if it is normal for the oil pressure reading to get very low after about 30 minutes of driving. When I first crank the motor the gauge needle is in the middle of the gauge. After the tractor warms up hot the gauge always reads only at about 1/4 of the gauge amount. Is this normal? and if there is a problem what might it be?

[Matt Kirsch]

Hi, first thing is you need to get a known good gauge with numbers to get actual oil pressure readings. Occasionally, the 70 year old gauge will not read accurately.

Most likely the cause of the dropping oil pressure is worn bearings on the crankshaft. Very rarely is it the oil pump or the pressure regulator, and I mean VERY rarely, as in, almost never. The real question is, is it bad enough to warrant performing expensive work on the engine. That is where actual oil pressure readings will be helpful. You need about 1PSI for every 10 cubic inches of engine displacement at idle. For a 60 CI engine, that means 6lbs of oil pressure at idle.

Thicker oil does nothing to help, in my experience. I went from 10W30 to 20W50 on a tractor with iffy oil pressure. It had the same oil pressure afterward.

[TallCoolOne58]

What Matt said, and this:

Is it the original oil pressure gauge, or aftermarket? Often an aftermarket reads too high, i.e. 80 psi max, and this reduces sensitivity to lower pressures. 'Halfway' on an aftermarket 80 psi gauge cold, and 1/4 at idle after thorough warm-up wouldn't be bad. According to Service Manual GSS-1411, high idle (full throttle) oil pressure is 30-35 psi @ 1800 rpm on a Cub, max oil pressure allowed by the oil pressure regulator valve and spring. In my operator's manual #1 014 462 R2 Rev. 1 8-75 (82) the only other help offered is with my stock 0-40 gauge, the oil pressure needle should read past the first mark @ 100 rpm above idle speed, with idle speed specified @ 475 rpm plus or minus 25 rpm.

It is normal for the oil pressure to drop a bit after the engine and oil thoroughly warms up, and the oil thins, particularly after working the tractor.

It's been discussed here before, but dropping the oil pan and taking a peek at and cleaning the oil pump intake screen if necessary is sometimes worth a shot.

[staninlowerAL]

It won't help your oil pressure but a tuneup including valve adjustment and compression test will give you some idea of how worn the engine is and to help you determine if other work is needed if you decide to replace the rod/main bearings.

[Glen]

Hi,
If you need a new oil pressure gauge, TM Tractor, at the bottom of the page, has some that they say they had made to look like the originals.
A Cub oil pressure system is 35 lbs at 1800 RPM, the Cub service manual says, like was said above.
If you use a high pressure gauge on it, the pointer only goes up part way on the dial.

This gauge below is the 2nd one used, it shows in TM Tractor's listings.

http://www.tmtractor.com/new/en/5732fp.htm

This gauge below was used beginning in the mid 1950's, and has numbers.

http://www.tmtractor.com/new/en/3291fp.htm

[outdoors4evr]

As the engine warms up, the oil gets thinner which drops the oil pressure.
The behavior you are seeing is normal, and the behavior gets worse as the engine wears.
You then have to ask when it is appropriate to rebuild the engine. Rod and Main bearings would help increase oil pressure. Unfortunately, then you get into the "since you are there" you should probably do the piston rings and that means measuring and cleaning up (or boring) the cylinder walls.

[pett3227b]

Thanks to those who responded to my questions. It looks like I should get a new gauge and drop the oil pan to look at the oil pump. I am wondering what the oil pump intake screen will look like and where it is. If these two simple things still show that I have oil pressure that is below an acceptable level I must then think about replacing the crankshaft bearings. I can only Imagine what needs to be done to the rest of the engine while I'm in there. Thank you again.

[Slim140]

Thanks to those who responded to my questions. It looks like I should get a new gauge and drop the oil pan to look at the oil pump. I am wondering what the oil pump intake screen will look like and where it is. If these two simple things still show that I have oil pressure that is below an acceptable level I must then think about replacing the crankshaft bearings. I can only Imagine what needs to be done to the rest of the engine while I'm in there. Thank you again.

The oil pump isn't in the pan like a normal engine. It's on the back, it's just 2 gears under a cover, you have to split the tractor to get to it. The pick up tube does have a screen on it inside the oil pan though. There is a pressure regulator accessible from the side of the engine. Do some searching on here and you can find out more info about it.

Try a new gauge, do a compression test, etc. and go from there. All that will tell you if you need to rebuild it or not.

Here's a picture of the screen and tube.

[Matt Kirsch]

I would recommend a diagnostic style oil pressure gauge that's "calibrated" and graduated, such as this one from Harbor Freight:

https://www.harborfreight.com/engine-oi ... 62621.html

[Crimson Tim]

Have you checked your oil level lately? Mine burns about a quart of oil over the course of a month with regular usage. I’ve noticed that when the oil level is right at the High mark, my oil pressure tends to ride right in the middle of the gauge. As the oil level drops, so does the pressure. By the time the oil level gets to the Low mark, the pressure gauge is barely registering anything. Obviously, I try to stay on top of it so it doesn’t get that low.
I’m not sure if this is normal behavior, or if this is indicative of some issue, but it’s what mine does.

[BigBill]

My fcub oil pressure is about 1/16” below the max reading on the needle with 15/40 wt delvac Mobil oil. (Summer Time oil)

[pett3227b]

Well putting the heavier weight oil worked to increase my oil pressure! My only concern now is that I had to use detergent oil. I have been running non-detergent oil in it for at least 9 years and have regularly changed oil filter once a year. I am wondering if I am now in danger using detergent oil? Advice will be appreciated. thank-you

[inairam]

detergent oil is used with systems with filters which the cub has. I only run detergent oil.

Change the filter ( not the oil unless you want to) more frequently for the next few months until the insides are cleaned out.