Oil pressure in most engines drops at idle. Engine oil pump is turning very
low rpm and can't pump much oil at 800rpm. The engine also doesn't need
much oil pressure to run at that RPM so not to worry. The light coming on
with 25 psi shouldn't be happening, though. Think the light is switched at
something around 10psi. Sounds like your gauge or light sensor is out of
whack.
It would be nice if pressure at speed was over 40psi but that's still enough
pressure. Behavior of the pressure, over time, is something that you should
have real concern about. If its holding steady in a range and not dropping
as engine is worked, its probably okay. If pressure starts off high and
then drops as oil warms, it could be the pressure relief in the pump, stuck
full open. BTDT. Of the four 2 1/4 engines I've become intimate with, none
ran pressure over 50psi at speed. Two of those engines were completely
rebuilt so should have been running optimal pressure.
FWIW Oil pressure is only a rough indication of an engines condition. When
I bought my 109, it was undrivable because of the hydraulics. Engine
started up fine and held good oil pressure, around 50 psi, after warming up.
Thought the engine was okay until I decided to check the bearings for the
hell of it while I had the transmission out. Bearings were worn down to the
shell with almost no bearing material remaining. The crank had worn oval
and needed to be ground. Engine was about ready to blow but the oil
pressure sure didn't let me know that. If you really want to be sure about
the bearings, you can pull the pan and check all but the rear main bearing
with 'plastigauge'. You could throw in an oil pump rebuild kit while your
in there, just to add a little insurance.
I wouldn't worry about the oil pressure unless you have secondary
indications like rod knock or other lower end thumps before the oil pressure
builds up when starting up from cold.
Aloha
Peter O.
>From: "RON WARD" <ronward@synovustrust.com>
>Reply-To: lro@works.team.net
>To: <lro@Works.Team.Net>
>Subject: LRO: Re: Oil pressure question.
>Date: Fri, 15 Jun 2001 14:09:03 -0400
>
>Wow. My stock IIa set up runs 40psi at idle and 65 at 3000rpm.
>
> >>> Marin.Faure@PSS.Boeing.com 06/15/01 11:46AM >>>
>Date: Thu, 14 Jun 2001 17:44:46 -0400
>From: Keith Tanner <keith@miata.net>
>Subject: LRO: Oil pressure question.
>
> >Since I installed a spin-on oil filter adaptor, I've been getting only 25
>psi of pressure at idle (according to my gauge) and the warning light comes
>on. Running pressure is about 40. Oil weight is 10W40 as it was before the
>installation. Should I be concerned?
>
>That sounds awfully low, especially at idle. My SIII has always had a
>minimum
>of 40 psi (12:00 position on the dial, which I think is 40 psi), and the
>pressure difference between idle and cruising rpm is negligible UNLESS I
>let
>the oil get a bit low. Then the pressure drops to a needle's width or so
>below
>the midpoint on the dial at idle, and climbs back to a needle's width above
>the
>midpoint when the revs go back up. Returning the oil level to the correct
>level
>fixes this, and there is virtually no difference between idle psi and 3,000
>rpm
>psi. If you're getting only 25 psi at idle plus the
>light comes on, I'd say you have a problem. I have always used Castrol
>20-40
>in my SIII, so I wouldn't say the cause of your low pressure is the wrong
>weight
>oil. My engine has the original filter system on it, but I have heard that
>it's possible
>to install a spin-on adapter in such a way that the oil pressure is
>negatively affected.
>___________________________
>C. Marin Faure
> (original owner)
> 1973 Land Rover Series III-88
> 1991 Range Rover Vogue SE
> Seattle
>
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