Question about oilpressure trouble

[Fred Munro]

Hi Bjorn;

If you have verified the idle oil pressure is correct, the cause of your low
pressure at idle is the oil is running out of the crankshaft or camshaft
bearings almost as fast as the oil pump supplies it. This can be caused by a
restriction in the oil supply system, a worn oil pump, or worn bearings. One
common cause is worn crankshaft main bearings, although worn rod bearings
can also be a cause. When the oil heats up and gets thin, it runs out of the
bearings almost as fast as the oil pump can supply it at idle, resulting in
low oil pressure. As the engine speed increases, the oil pump puts out more
volume, supplies more oil than is running out of the bearings, and the oil
pressure increases. When the engine is cold, the oil is thicker and doesn't
flow out of the bearings as fast, and the oil pressure at idle is higher.
A worn oil pump that is not supplying the design volume at idle can also
cause low oil pressure at idle, as will a restriction in the supply system
that reduces the volume of oil delivered. Such a restriction would have to
be between the oil pump and the pressure gauge or in the oil pickup to give
the symptoms you are seeing.
You can compensate by using an oil with a higher hot temperature viscosity
(such as 25W50 or 30W30 instead of 5W40 or 10W40) but if worn bearings are
the cause, eventually you may have to replace them.
If you or your mechanic feels the engine bearings and oil feed system is OK,
you could look for an oil pressure sender that trips at a lower pressure
(say 0.7 bar instead of 0.9 bar).

Good luck!

Fred Munro
'94 S4

----- Original Message -----
From: "Tore Sollibråten" <skipsreder73 at hotmail.com>
To: <quattro at audifans.com>
Sent: Tuesday, April 23, 2002 11:08 AM
Subject: Question about oilpressure trouble



Hei guys!
I realy hope there is someone that can help me with this:

I have some problem with my 95 A6, 2,5 Tdi. I have owned it for about two
and a half year now, and I have runned it from around 70 000 km to 145 000
km.

Before it passed 80 000 km, after going up hills and the engine was warm the
the oilpressure light came on when the engine was idling under 1000 rpm.

In that time the car was running with mobil 1 oil-5-50. I changed to Castrol
GTX3 and later Castrol Performans (it should to be a 10(or 15?)-40 oil). I
change oil and filter every 10 000km. I have always used the original audi
filter so the trouble should not be connected to the use of wrong filter?.

After a while the light comes up every time the engine is warm and ideling
under 1000 rpm. Sometimes it goes away by it self when engine ideling. Or
most normal it goes away if I lift the ideling to over 1000 rpm, but comes
back if the ideling again goes under 1 rpm. It is no not normal noise from
the engine when ideling even if the lamp is on - just the beautiful sound of
a diesel running.

After it first happend I had it to the dealer and he told me to have the
sender unit for oil pressure replaced with a new one. It was a quite easy
operation, but unfourtenatly it didnt helped. The dealer told me if it
didn`t helped probably I should have got the oil pressure pump changed.
Since it would take a lot of money to have the job done and the car was
acting quite OK I didn`t do it.

But now after more than 60 000 km!!!! I still have the light coming on when
the engine is ideling down under 1000 rpm when it`s warm. But it is not
getting any worse and no bad sounds from the engine have occured.

In the meantime I have changed the sender unit once more, to be sure that i
hadn`t got two of them bad. I have also drived a period with an oil pressure
gauge to check the pressure. So far as I now it acting quite normal, with a
pressure up to 4-5 bar when it is speeding and when ideling when it`s warm
it goes a litle under 1 bar. The orginaly sender unit is called to be a 0,9
bar sender- and it`s written on it that it should function between 0,75-1,05
bar.

I live in Norway and here it is big changes in temperature through the year.
It looks to be a litle better when the temperature is down to -15 degreeds,
but still the light comes on when ideling after going up hills.

I have also thaught of only adjusting the ideling level to a litle over 1000
rpm but the dealer told me that it wasn`t possible to adjust it!

Does anyone of you have any advices or experiens about likely problems?
Is there any other type of filter or other types of oil I should try?

I`m getting tired of this lamp now and want to do something with it-I`m
greatful for all advices that may help me solve this problem.

Bjørn


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