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Oil pressure question

Farmall Super A, AV, 100, 130, & 140 1939 - 1973
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treeman53
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Oil pressure question

Postby treeman53 » Tue Nov 12, 2019 10:27 am

First off, My Farmall A runs great, but it is obviously has some wear on it. It's a 1946, and I use it to mow, has a Woods L59 mower. Now, my question...
What kind of oil pressure do you normally see on these? I rebuilt a used pump, and installed it last summer. The old pump was showing low, very close to the red zone, when first started. After running for 20 minutes, or so, the gauge would not show any pressure. With the rebuilt pump, it shows over half gauge when cold, then stays just above red zone after heating up. I'm guessing 55 PSI cold, maybe 12 to 15 hot. I have been running 15/40 oil. Is this normal for thermal syphon set up? I thought the pressure would stay higher, since the oil is supposed to get heavier as it heats up...

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BullDAWG
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Re: Oil pressure question

Postby BullDAWG » Tue Nov 12, 2019 12:01 pm

That is low, most A-140's run slightly right of vertical cold and vertical when warm. And if I'm not mistaken the oil gauge is 50 psi max. So vertical would be 25 psi and just above red zone is 6-8psi. And most ppl run 10w-30. Though some do 15-40. But it sounds like you either need a new oil pressure relief spring, or the bearings are worn if you already replaced the pressure spring. Also did you resurface the oil pump housing? Take the cover off and see if it's flat, resurface it w/ sandpaper on a piece of glass to correct any warpage
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Eugene
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Re: Oil pressure question

Postby Eugene » Tue Nov 12, 2019 3:40 pm

Ol Timey Farming LLC wrote:But it sounds like you either need a new oil pressure relief spring, or the bearings are worn.
If you don't know the history of the tractor, last complete engine overhaul, my thought is worn main and rod bearings.

Weak oil pressure relief valve spring would be my very last oil pressure suspect.

Figure out some way to test the accuracy of the oil pressure gauge before doing anything else.
I have an excuse. CRS.

treeman53
Posts: 25
Joined: Sun Sep 15, 2019 11:02 am
Zip Code: 16417

Re: Oil pressure question

Postby treeman53 » Tue Nov 12, 2019 10:58 pm

My gauge is 75PSI max, and I did resurface oil pump housing. Gauge is accurate, as I replaced it, and it reads same as the other one did. When I had the pan off, I did try to check play in rod bearings, and they seemed tight. I did not pull caps to actually check rod or crank bearings. The engine has probably never been rebuilt, but it does run great, no smoke. I guess I can live with the pressure where it is, I was just curious about the major difference when it gets hot. As I mentioned, I thought pressure should increase, if the 15/40 oil really thickened as it got hot.

Jim Becker
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Re: Oil pressure question

Postby Jim Becker » Wed Nov 13, 2019 12:57 am

15/40 oil does not get thicker as it gets warmer. It just gets thinner less than a straight weight oil.

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Re: Oil pressure question

Postby Gary Dotson » Wed Nov 13, 2019 8:12 am

15 = cold 15wt. oil, 40 = hot 40wt. oil.

treeman53
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Zip Code: 16417

Re: Oil pressure question

Postby treeman53 » Wed Nov 13, 2019 2:44 pm

Wouldn't it seem that my oil pressure should be lowest when cold, and highest when warm, if the multi wt oil really acted as 15 cold, and 40 warm?

Jim Becker
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Re: Oil pressure question

Postby Jim Becker » Wed Nov 13, 2019 2:49 pm

As I thought I already stated, hot 40 is thinner than cold 15.

Eugene
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Re: Oil pressure question

Postby Eugene » Wed Nov 13, 2019 3:46 pm

Concur with Jim.

Plastigage rod and main bearings. Engine is probably due for an overhaul.
I have an excuse. CRS.

BullDAWG
10+ Years
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Posts: 855
Joined: Fri Dec 30, 2011 6:09 pm
Zip Code: 39401
Tractors Owned: 1950 Super A
1955 John Deere 60 (sold)
1950 Cub (sold) 1950 Cub l59 woods belly mower (sold)
1951 Cub (sold) 1950 Cub w/ 5' sicklebar (sold)
Tufline 6' disc (old heavy pull type)
1953+ A-295A 2 furrow SlatWing Plow Chief plow (SA)
1950 cub-193 1 furrow SWPC plow (cub) (sold)
6' home made bush hog. Mounts on drawbar
Circle of Safety: Y

Re: Oil pressure question

Postby BullDAWG » Wed Nov 13, 2019 5:37 pm

treeman53 wrote:Wouldn't it seem that my oil pressure should be lowest when cold, and highest when warm, if the multi wt oil really acted as 15 cold, and 40 warm?

oil rating is not saying what cold vs hot viscosities. Instead think of just HOT or COLD. a straight 40 weight oil would be thicker than 30 weight but when its cold then the 40 weight would be too thick and not flow, so thats why its 15W-40, so when its cold it flows like a 15 straight weight oil, but when hot it flows like a straight 40 weight. BUT again when its cold vs hot a straight weight 30 oil would be thicker when cold than a 15w-40 and also thinner when hot. But even 90 weight gear oil when heated hot enough it will flow like a 10 weight oil thats cold. So you can't compare hot vs cold except straight weights, if its a multi-viscosity oil like 10w-30 or 15w-40 then you JUST compare the hot # vs hot or straight weight and then the cold # to the cold # or if a straight weight then that #.
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