low oil prssure

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UpstateSC
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low oil prssure

Unread post by UpstateSC » April 9th, 2017, 10:54 pm

restoring an a2, I have it running and have been driving it around a bit seeing about the engine before I take everything apart.

I have low oil pressure, 5psi at idle, and 25psi driving at 40 mph

What needs to be done to improve pressure. are oversize main bearing avail, can you get them out and in from the pan side?

what else is main cause of low pressure?

Fil Bonica
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Re: low oil prssure

Unread post by Fil Bonica » April 9th, 2017, 11:17 pm

Check oil pressure with a known good mechanical gauge not the existing unit.
After doing that test and there is still a problem start looking further.
You could have a clogged or failing oil pump:


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Mark
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Re: low oil prssure

Unread post by Mark » April 9th, 2017, 11:35 pm

I had very low oil pressure in my 151, found the oil screen/tube plugged up, before that I pulled the engine, plastigauged the bearings, took oil pump out, checked that out with a drill(shot oil out very good).
mark


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kmam
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Re: low oil prssure

Unread post by kmam » April 10th, 2017, 7:36 am

Wher/what is the oil screen/tube? How do I check and clean it? I am about to pull the power plant as I have 0psi at idle and 25psi at operating revs measired with a quality oil pressure guage.

Howard
Mark wrote:I had very low oil pressure in my 151, found the oil screen/tube plugged up, before that I pulled the engine, plastigauged the bearings, took oil pump out, checked that out with a drill(shot oil out very good).
Howard

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rickf
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Re: low oil prssure

Unread post by rickf » April 10th, 2017, 8:31 am

You will have to pull the oil pan to get at the pump and the pick up. If the pick up is not clogged then the bearings might be bad, as Mark said check them with plastigauge. If they are bad then you will have to take a real good look at the crankshaft because the bearings do not just wear out without some sort of abrasive action. That in turn is going to damage the crankshaft and it will need to be turned down in a machine shop. Yes there are oversize bearings available but the crank has to be machined for them to fit. Another thing to check, if the bearings are good then it is possible that the oil pressure relief valve spring in the oil pump went out. The chances of finding a correct spring are very slim so a new pump would be in order. And remember the cam bearings, if the rod and main bearings are bad the cam bearings will also be bad.
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Re: low oil prssure

Unread post by UpstateSC » April 11th, 2017, 9:37 am

excellent advise.


I drained the oil, Filled the crankcase with Diesel fuel, and ran it for a few minutes. While running, I had 3PSI at idle and 10PSI at fast idle, and the PSI improved by a few PSI during the process (i think the screen was restricted by goo) . Drained the Diesel, changed the oil filter, loaded new straight weight 40 .

Drove it about 15 miles this morning, I now have 35psi at 40mph, 13 at idle. I'll let you know what it looks like for a longer run at warmer temps this afternoon.

When I pull the PU later this season, I'll have a chance to check the crankcase over more carefully. From this little test, it looks like the engine bearing clearances are OK>

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Re: low oil prssure

Unread post by UpstateSC » April 11th, 2017, 9:39 am

BTW, SAE 40. I live in South Carolina, never that cold here. I use 40 weight a lot in MV's .

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Re: low oil prssure

Unread post by rickf » April 11th, 2017, 2:17 pm

You are aware that modern diesel fuel is a solvent more than a lubricant so you pretty much washed the bearings and rings of any and all oil the whole time you ran it that way. Diesel fuel today is not like it was 20 years ago, now it is ultra low sulfur fuel and even the older injection pumps are having lubrication issues with it. If you ever want to do that type of test again I strongly suggest Marvel Mystery oil. It is made for that.
1964 M151A1
1984 M1008
1967 M416
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12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

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Re: low oil prssure

Unread post by Hambone » April 11th, 2017, 7:39 pm

UpstateSC wrote:excellent advise.


I drained the oil, Filled the crankcase with Diesel fuel, and ran it for a few minutes. While running, I had 3PSI at idle and 10PSI at fast idle, and the PSI improved by a few PSI during the process (i think the screen was restricted by goo) . Drained the Diesel, changed the oil filter, loaded new straight weight 40 .

Drove it about 15 miles this morning, I now have 35psi at 40mph, 13 at idle. I'll let you know what it looks like for a longer run at warmer temps this afternoon.

When I pull the PU later this season, I'll have a chance to check the crankcase over more carefully. From this little test, it looks like the engine bearing clearances are OK>
Wow, you are lucky to get by with that, as Rick said, modern diesel isn't a lubricator but has good cleaning properties, I remember my grandpa would drain a quart of oil, mix a quart of diesel/kerosene to flush old tractor engines, I would replace the oil again real soon, you didn't get it all out when you drained it.

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