1949 Ford 8N low oil pressure, what is the thickest oil I should be using

[Astroguy]

my 1949 Ford 8N new to me starts and runs apparently very well. I did some brush hogging today just under an acre of medium load brush hogging.
at the end I noticed that even it over 3/4 throttle the oil pressure was only at about 10 and drops to zero at idle.
I have put in 10w40 diesel grade motor oil last december.
I am planning on running a heavier oil, any recommendations and do you think it'll even make any difference?

 

[Fritz Maurer]

Put some 50W in it for the summer and some lighter oil in the winter.

Those pumps weren't high-output to begin with...its probably getting a little loose.

10psi is not the end of the world, that's all a WD-45 has brand new.

When the pump gets really bad it will start loosing it's prime after a few days, then it will have to come out.

 

[560Dennis]

Verify the gauge.
Suggest clean the gauge ,
Check the sump , make sure there isn’t mouse nest blockage .

 

[NY 986]

Put some 50W in it for the summer and some lighter oil in the winter.

Those pumps weren't high-output to begin with...its probably getting a little loose.

10psi is not the end of the world, that's all a WD-45 has brand new.

When the pump gets really bad it will start loosing it's prime after a few days, then it will have to come out.

I've heard of guys putting in 50W or 20W50 oil in an 8N. They never said if they had a problem so it must have been OK. As Dennis said verify the reading on the gauge and know that oil flow is good or not.

 

[560Dennis]

helpful video

 

[soaked]

my 1949 Ford 8N new to me starts and runs apparently very well. I did some brush hogging today just under an acre of medium load brush hogging.
at the end I noticed that even it over 3/4 throttle the oil pressure was only at about 10 and drops to zero at idle.
I have put in 10w40 diesel grade motor oil last december.
I am planning on running a heavier oil, any recommendations and do you think it'll even make any difference?

Hi Astroguy,
10psi hot, throttled up, 99.9% of the time means it's time to rebuild. Oil pump, and often grind the crank.
Heavier oil may make a person feel better, but wont add much psi.
I run 20-50, but only use mowing.

There is, however, a real way outside chance something is up with the relief plunger/spring. Its worth unscrewing the 15/16 cover nut, and pull em out to inspect. Plunger is supposed to have the little notch. It directs some oil psi to lube the timing gears.

These are some of what I've found on 8ns over the years:
Top one had a rubber garden hose washer on the face of the block, that moved the cover nut back, lowering the spring pressure so more psi leaked out into the timing cover. Is also mising a spiral so the spring is shorter. Taking it out, and putting the new aftermarket spring at the bottom did boost psi on the gauge.

The little nut went with the next spring down, prolly cause spring was too short.

3rd one down a PO must have stretched it, attempting to get more push (just guessing.)

Plungers show spirals dig in and wear on the plungers.
Its way more likely than not its time to rebuild,

But Hope you get lucky

 

[KCTractors]

my 1949 Ford 8N new to me starts and runs apparently very well. I did some brush hogging today just under an acre of medium load brush hogging.
at the end I noticed that even it over 3/4 throttle the oil pressure was only at about 10 and drops to zero at idle.
I have put in 10w40 diesel grade motor oil last december.
I am planning on running a heavier oil, any recommendations and do you think it'll even make any difference?

I have a 8N that has been running like that for years with no oil pressure at idle and very little at wide open. It's not worth a rebuilt engine but when I need it, it never lets me down. I paid $700 for it about ten years ago. I never have to change oil in it because I have to add so much.

 

[Mad Farmer]

I got my 9N in the 1980s and it has always had low oil pressure when hot , a little more than 10psi, cold it is ~30-35psi. This concerned me at first but it never knocked and by the time it needs to add oil it's time to change it.

I've attributed it to the gauge.

 

[petertay]

Our Jubilee showed so little pressure it was alarming. We changed the pressure gauge and that solved the problem.

 

[Blackhole49]

my 1949 Ford 8N new to me starts and runs apparently very well. I did some brush hogging today just under an acre of medium load brush hogging.
at the end I noticed that even it over 3/4 throttle the oil pressure was only at about 10 and drops to zero at idle.
I have put in 10w40 diesel grade motor oil last december.
I am planning on running a heavier oil, any recommendations and do you think it'll even make any difference?

My tired old 8n burns about a qt every 5 hrs. It has better oil pressure than yours, but not much. I have been running it with 20w50 for 25 years cutting with a 6' finish mower. My personal opinion is: thicker oil isn't going to gain you much in oil pressure. Like KC, I just keep adding oil and mowing.

 

[Astroguy]

Thankyou, a great bunch of responses !
The darn tractor runs so well I don't want to fool with it... it's 76 years old... I think I'll do as some mentioned and just keep running.
It might outlive me!

 

[miangus]

I would run a straight 40W with a quart of Lucus oil stablizer.

 

[INCase]

father in law had a nice little 8N and all of a sudden it had low/no oil pressure. found out the float in the carb stuck and filled the crankcase with gas thus diluting the oil.

may not be your problem but worth a look at the condition of your oil. turn off the gas when done

 

[Non-farmer]

I got my 9N in the 1980s and it has always had low oil pressure when hot , a little more than 10psi, cold it is ~30-35psi. This concerned me at first but it never knocked and by the time it needs to add oil it's time to change it.

I've attributed it to the gauge.

Mine has behaved similarly since the day I got it. 38 psi cold, 20 when hot. I was told by my local auto parts store owner (out here in tractor country, he truly seems to know his stuff) that this was indicative of some bearing wear in the mains, but not enough to be a cause for concern. When I rebuilt it (it was blowing oil out of both ends), he told me in-frame would be fine, keeping the crank in place and retaining the same main bearings. Sure enough, ~20 years after purchase, the numbers remain unchanged.

I've had straight 30W in it since I got it, but if I were the OP with the lower numbers I'd follow the suggestions of something with a 50 in it. No cornhead grease tho