nearly 80psi difference in cold to hot oil pressure at idle

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clm
Posts: 278
Joined: Mon Dec 26, 2011 11:17

nearly 80psi difference in cold to hot oil pressure at idle

Post by clm » Sun Jun 23, 2013 7:33

Hey all, I am about to pull the 1100 out of the moke, I am really not pleased at the oil pressure. At start up the guage is pegged at 100psi, well once the pump primes which it takes an inordinately long time to do, and then hot after a 7 mile jaunt down the highway at 55-60mph the oil pressure at idle is maybe 20psi but it still goes up to 50-75 psi when I rev the engine.

I understand my bearings could be toast by now... but starting at so high of a pressure, I can't understand quite why the difference would be so great hot and cold. If everything in the engine was toast shouldn't the cold pressure be mediocre at best? My oil pressure does not pump up quickly on the starter alone either... when I was testing oil pressure on the bench I even had to bleed the oil pressure take off to get it to read on the test gauge every time.

Judging by the initial oil pressure readings and the difficulty it has priming I am inclined to guess the oil pump is not in the best state but due to the high initial pressure the bearings might have more life left in them. It does have the cooper "s" ball and appropriate spring as a oil pressure relief valve and is currently using fairly recent Valvoline VR1 20w50 oil with maybe 300 miles of run time on it and 500 miles flat towing behind my pickup. It doesn't smoke or burn oil, there is no noticeable blow by, and oil level has been pretty stable since I filled it last month not even varying from the full mark.

Chris
1965 Austin Moke - Rust was not free, I paid dearly for it
1961 Morris Traveller - Bent but repairable
1960 Morris saloon.. err wagon.. err Pickup, yeah that's it! - My first car
1980 Mini 95 Van shell - pickup load floor donor

Nigel(no top)Sykes
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Re: nearly 80psi difference in cold to hot oil pressure at i

Post by Nigel(no top)Sykes » Sun Jun 23, 2013 8:29

Oil pressure always drops when the engine is idling, I seem to remember reading an article at one time by one of the engine experts in which he said that 20psi or so on idle is pretty much normal, as long as you are getting 60 - 70 psi when running at revs.
The delay in getting pressure? I'm not sure about that one, only thing I can say is the engine that I was running in mine took a while to show pressure on the gauge pretty much every time I started it and it ran for 14 years or so like that (it still does run BTW). In my head I put it down to the connection pipe between engine and gauge
California dreaming

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fistral fig
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Joined: Thu May 26, 2011 17:42
Location: Chipping Ongar, Essex

Re: nearly 80psi difference in cold to hot oil pressure at i

Post by fistral fig » Sun Jun 30, 2013 8:17

Hi Chris,
I have been pondering on your question and tend to agree with Nigel, as 20 psi is OK for idle hot, and 50-70 psi when in general use is normal, you don't mention whether you have an oil pressure light connected up? if so is this going out as soon as you start up or upon cranking (with the coil disconnected) and also when you turn off and switch the ign back on straight away how long the light takes to come back on. With most minis (but not all of course) they never had an oil pressure gauge only the light, and if that is going out on start up you would be looking no further as you are.
Not forgetting of course oil pressure readings will always be slightly higher when the oil is cold and thicker.
I have just compared my pressure on the mini I have just finished rebuilding and I have an oil gauge in that one, on start up from cold it took about 2 seconds to read 75psi and gradually dropped to about 40psi when warmed up but not full warm after a run as I was only on the drive, and under revs it still reached 70psi,
With your suspected delay issue if it is? I wonder if the oil pick up strainer could be restricting initial priming in any way on first start up?.......FF

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clm
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Joined: Mon Dec 26, 2011 11:17

Re: nearly 80psi difference in cold to hot oil pressure at i

Post by clm » Sun Jun 30, 2013 8:53

It's a possibility, however the engine did the same thing on both of the transmissions I have had it on. I still can't imagine the bearings are totally toast as it would never have high oil pressure. All I can think of is the oil pump is worn to the point that when cold the clearances are allowing decent oil pressure but as it heats up the clearances are going to pot... we will find out when I get the replacement oil filter for the 850 and swap the engines

Chris
1965 Austin Moke - Rust was not free, I paid dearly for it
1961 Morris Traveller - Bent but repairable
1960 Morris saloon.. err wagon.. err Pickup, yeah that's it! - My first car
1980 Mini 95 Van shell - pickup load floor donor

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