I came across something at the MG Owners Club's Virtual Octagon (http://
users.ccnet.com/~jensten/) that may be of some help. Joseph
Oil Pressure Lag
By Marty Ray
Oil pressure should come essentially instantly on startup. If not, in short
order your engine could be ruined. Possible causes of delay in an otherwise
sound engine are: oil level in sump too low, oil pump loss of prime, pressure
relief valve stuck open, oil filter drainage or siphon back to sump. The latter
problem occurred in my car recently. This MGB has an upside down mounted
filter,
which relies on a rubber valve-like seal to keep oil from draining back to the
sump. When removed, the filter was empty! A new (and better quality!) filter
has
apparently cured the problem, though at first it seemed not to. I am not sure
why the lag still occurred a couple of times after fitting the new filter. It
hasn't happened since, but I'm still wary.
_______________________________________________________________________________
Subject: Oil pressure problem.
From: "Jacques Dupuis" <JDMG@msn.com> at Internet
Date: 3/6/97 2:10 AM
I would very much appreciate if someone could give me some clues towards the
resulution of my problem.
THE CAR: 1974 MGB. The engine was totally rebuilt about 6000 mi.ago (3
years).All internal parts were replaced with new parts and assembly was done
according to the book. Engine was balanced, all clearances were set to specs
and assembly was done by an old British Layland pro. (unfortunately, he died a
few months later). The car is not a daily driver but is only used under ideal
conditions in the summer time, has never seen any "brutal" driving and the car
is a 98 points. Total mileage on the car is 36,000 mi.since new.
THE PROBLEM: When the engine is started from cold after being stopped for
several hours, the oil pressure takes up to 10 to 15 seconds to buil-up to
normal. During that time taht looks eternity to me, I can hear some knocking
and chatter coming from some oil starved parts inside the engine. Once
pressure is up, everything returns to normal with oil pressure between 55 and
60 psi, whatever the temperature is. The engine runs perfectly with no signs
of distress. I know I am preparing myself for a pretty hefty bill but I don"t
know what to look for anymore.
To try and identify and correct this problem, the following has been done:
New oil pump installed (gaskets are positionned right)
Oil lines to the oil cooler replaced and oil cooler cleaned. Oil presure
checked with an outside oil pressure gauge (confirming the problem)
3 different brands of oil filter tested ( (top loading) . Oil changed from
the regular 20/50 to 5/50 (syntetic), 15/40,10/30,5/40 and 5/30. (Have you
ever heard someone changing oil and filter 5 times in a week end?) I"ve done
it. Used oil has been tested by a lab and no abnormal traces of metal or other
substances were found. Oil pressure relief valve has been replaced and spring
tension checked according to specs.
The engine will be coming out next week-end and I'll have a look at the
internal.
WHAT SHOULD I BE LOOKING FOR?
Thank you for your help.
Jacques Dupuis
Magog, Quebec, Canada
BRG 74B
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