low oil pressure

when i start my 1950 for tractor 8n, it reads about 40lbs pressure, half hour later while running it goes down to about 12 or 13 lbs on the oil pressure, i did a compression check on the cylinders, cold engine 90,,,,warm engine 92,,,,,on all cylinders,,,no oil on any of the spark plugs, what do suppose it is?

I would suspect a stuck pressure relief valve on the oil pump.

That is not really bad on that engine.

I wouldn't be too fussed. The N's are pretty low pressure machines - your numbers aren't too out of line. That's assuming 12 is read at a lower idle and it's a thin or multiweight oil. If you're running thicker oil and that's read at full RPM it maybe a bit more concerning. If it's the original gauge, they can also be a trifle inaccurate, and any tiny leaks in the line (i.e. threads/flanges not sealing) can make a difference on reading.

My father still uses a 2N as a daily put-about tractor and I actually use the same one to log some red pine plantations where its small size can get around in the bush. It reads just like yours: 40 or so when started, 10-20 once warm. That's running 15w40 in it. Has been running like that for years and years with no trouble.

They're a really easy engine to pop the pan off and roll a set of new main and rod bearings into
without having to drop the crank - if you get really worried you could try that first and see if it tightens
things up a little. Don't think I would bother myself, however.

I'd suggest asking this on the N board below because folks there will be more likely to read it (though you have to be a little careful on the N board: Some of those folks get a pretty picky about their N's: They'll get into vicious arguments over trifles like 30 wt. vs. 40 wt oil, or what style or rad cap is historically accurate).

This post was edited by DanielW on 10/24/2023 at 09:27 am.

(quoted from post at 12:48:25 10/24/23) when i start my 1950 for tractor 8n, it reads about 40lbs pressure, half hour later while running it goes down to about 12 or 13 lbs on the oil pressure, i did a compression check on the cylinders, cold engine 90,,,,warm engine 92,,,,,on all cylinders,,,no oil on any of the spark plugs, what do suppose it is?

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you've got a worn 70 year old engine. it's fine, people operate Ns with worse numbers than that every day. use it and enjoy it.

(quoted from post at 11:23:08 10/24/23)


Some of those folks get a pretty picky about their N's: They'll get into vicious arguments over trifles like 30 wt. vs. 40 wt oil, or what style or rad cap is historically accurate).

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You mean it's not just John Deere people who do that???

I have a 8N on that I use on some property away from the house. Smokes like h-ll when it first starts, always starts even in zero weather on
a 6 volt system yet. Has about 15lbs of oil pressure when cold and goes down to maybe 5lbs hot. I ran it that way for at least five years
already. Haven't changed oil in it for them five years because I have to keep adding oil. One of these days I should clean the battery cables
though. It never let me down!

If you are nervous use a 15-40 oil it might improve a few pounds/sq in. But pretty normal. Jim

For sure it's not the compression. Compression has nothing to do with oil pressure. The engine could have 150PSI compression or 35PSI compression, wouldn't matter.

Oil pressure is most affected by clearance in engine bearings. Mains, rods, and cam. Very rarely is it the oil pump. Hardly ever is it the regulator. It's almost always worn bearings.

Is the 12PSI at idle or wide open?

Those oil pumps also wear and there are kits that can rebuild the oil pump

Old time mechanic once told me that 10 psi per 1000rpm is just fine for any engine.

Experiment with straight weight sae 40 oil .

That warm pressure is not all that bad on many such older tractors and if lower than
normal or when new may well be worn bearings. Keep good oil in her maybe try
different grades but there's a good chance it will be okay

John T NOT a Ford man see if they agree ??

The old Chevy splashers just had about 10-15 PSI with s dipper cup on the rod cap. The reason I call then splashers. And they never had more than about that oil pressure for the life ovf the engine . Run it and don't worry if it bothers you that much put a piece of tape over it so you can't see it. Since the gauge changes it is not stuck.

I heard that too. Additionally there are at least two types of pressurized lube of which I know. One is high pressure and low volume
and the other low pressure high volume. My Dodge 361 ran up to 30 psi initially and stayed there. My Chevy 350s would follow
engine rpms....I initially worried about it until I found out what I told you.

Or chunk the gauge and install an idiot light and pressure switch for the sending unit....usually at or near the output of the oil pump, probably where your gauge sending device (a pipe) is located. I have grown to like them because you aren't constantly watching your oil pressure and worrying about something that doesn't require your worrying!

(reply to post at 10:38:03 10/27/23)

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Then you worry about the light not burnt out.

I think I would prefer a green light that is on confirming oil pressure.