oil pressure

My 8-N has good pressure when first running, 40psi, but it slowly moves down toward 0 the longer I run it. I can keep it at 10psi if I keep the rpms up, but not at idel. I'm using 20-50 oil. Any ideas of what is going on? Thanks for any replies.

Maybe your gauge is faulty. However, it is quite common for the older engines to give the same results. Cold 50 psi, Hot sometimes 5 psi or so.

HTH John,PA

bethaney........would you believe that is NORMAL. Its called viscosity factor. COLD oil makes more oil pressure and as it gitts HOT, the oil leaks outta the pump gears and looses pressure. In 1939, Ford spec'd 30wt detergent and 40wt for HOT WEATHER. Ford also recommended a qt of kerosine in COLD weather. Modern multi-wt oil is so much better. Yer 20-50wt oil is really 20wt oil with temperature sensitive additives that makes it act like 50wt. But it is NOT 50wt oil. Yer 8N is supposed to be pressure relieved at about 35psi. (so 40psi is good) but as explained, HOT OIL is THIN and does NOT make alotta pressure. .......HTH, oily Dell

Worn bearings,oil pump and cam in the Ford.

(quoted from post at 17:41:08 10/03/13) My 8-N has good pressure when first running, 40psi, but it slowly moves down toward 0 the longer I run it. I can keep it at 10psi if I keep the rpms up, but not at idel. I'm using 20-50 oil. Any ideas of what is going on? Thanks for any replies.

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Yeah - your engine is badly worn and is asking for attention. It is NOT NORMAL to have 0 gauge pressure at hot idle - I don't care what oil you have in the sump. Your SAE 20W50 is has heavy as any oil Ford ever recommended and the low oil pressure when hot indicates you have EXCESSIVE oil clearances somewhere inside the engine. Time to tear into it and find out where the wear is and fix it. Or ignore the clear warnings and wait until it gets really bad and the fix more expensive....

TOH

Im with the TOH something may be amiss.Dose it go below 5lbs? If so you need to address it, less then 5lbs lbs with 20/50 would say something needs a look see.How long has it been this way? Now that said if I could see it at 10 lbs and how many RPM you have it may be nothing at all. I would at least put on a new gauge but nothing less then Stewart Warner gauge.

I looked for it in my Ford books and cant find any that say detergent oil or 40wt oil.What book is it in?

if you have not changed the gauge yet.. do so.. then re-evaluate

check the relief vale under the governer in the front cover area on right hand side of engine at the front. take the plug out and the spring and the plunger, and inspect all of them. check inside the housing also for junk that may hold plunger away from orifice allowing too much oil to by-pass and create low oil pressure. also pressure spring may be getting too weak to hold the pressure.

No, that isn't normal if those numbers are accurate. I would do as Soundguy suggested, but use a hydraulic pressure gauge to obtain pressure readings. It could be as simple as gauge replacement or an indicator of a more serious internal engine problem. Never trust a gauge. Gerard

A can of Motor Honey should increase the pressure about 10psi. If it does you have worn engine. This should get you through the summer.

(quoted from post at 22:43:05 10/03/13) check the relief vale under the governer in the front cover area on right hand side of engine at the front. take the plug out and the spring and the plunger, and inspect all of them. check inside the housing also for junk that may hold plunger away from orifice allowing too much oil to by-pass and create low oil pressure. also pressure spring may be getting too weak to hold the pressure.

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Let me start by saying that based on observation of my tractors my long held belief is that a properly functioning oil pressure relief does not bypass ANY oil until the pressure approaches 50 PSI. So just for giggles I did some measurements and calcs on what I believe to be a an original (1941) and properly functioning oil pressure relief valve assembly. Here is what I found:

[code:1:dd75232c03]
Spring free length: 1.75”
Wire diameter : .035”
OD of spring: .375
Spring rate: ~5.5 lb/in
Spring preload (.4” measured): ~2.2 lb
Surface area of poppet under pressure: ~.05 sq-in
Cracking pressure (2.2 lb/.05 sq-in): ~44 PSI
[/code:1:dd75232c03]

Those measurements are “crude” but close enough for a retired government worker ;-) So a properly operating oil pressure relief never opens until the oil pressure reaches ~45 PSI. And once open it can and will bypass a sufficient volume of the oil pump output to limit the pressure to 45-50 PSI (or very close to it) regardless of whether the oil is hot or cold. With that operation more or less "confirmed" I am going to repeat the assertion I have made several times before:

If you have elevated (40 PSI) oil pressure cold and near zero pressure hot it is [u:dd75232c03]extremely[/u:dd75232c03] unlikely the cause is the pressure relief valve bypassing too much oil. The lost pressure is almost surely caused by a defective/worn oil pump and/or excessive bearing clearances. By all means check the seat area for debris and the preload on the relief valve spring (proper preload is .4" of spring compression). Stretching it to increase the preload or installing a stronger spring will increase the relief valve cracking pressure but it will do NOTHING to increase hot oil pressure that is below the old cracking pressure.

TOH

Thanks for letting me to get back to finishing my PIONEER amp. I have been displace for my cellar-dweller office.

So, low oil pressure can be scarry.

I have to decide whether I should do a head job on my FORD escort or keep putt'N water/anti freeze in the radiator for this upcoming WINTER.
Tough season, here, for refrig. work.

John,PA

I tried, but I was disconnected.

A check-out on the CONNIE: Means how long will YOU require for oil dilution?

As much as necessary to start-em up in Thule, Greeenland, at 7:00 AM Local time.

Always worked for the FED's.

The Pioneer Amp[ works great. No 18 wheeler override during CELTIC musicians. PBS, Hershey PA.

John, PA

This meant....unscheduled maintenance stop....Duty FREE area, Shannon, Ireland. #4 engine. You know...this one we kept secured for our grand-baby.

Happy hour heres. Windsor/on the rocks.

John,PA

(quoted from post at 22:47:01 10/03/13) Maybe your gauge is faulty. However, it is quite common for the older engines to give the same results. Cold 50 psi, Hot sometimes 5 psi or so. HTH John,PA

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That's exactly what my '48 8N does. Guage is new. Low side is in the 5 -10 psi area after it gets heated up mowing for about 15 min. or so. Don't do anything harder than that with it, maybe plow some snow if it ever gets deep enough.