? Low oil pressure

[Gottlieb]

I have a '91 190 E 2.6 with 152k miles.On cold starting the oil pressure gauge shoots up and gradually decreases as the engine warms . Once @ operating temperature,and especially after highway driving the oil pressure gauge reads almost zero when the car is stopped and in drive. With the trans in park oil pressure reads normal per MB manual. Upon accelerating ,even slight, the pressure shoots up immediately and stays up as long as RPM's are above idle in drive.Is this drop to zero while stopped in drive a concern ?

[yvrbenz]

Is this drop to zero while stopped in drive a concern ?


How long has the oil pressure been that low? Did it start suddenly or gradually work its way down?

This is definitely a concern. With the transmission in gear and the car held to a stop with the service brakes the oil pressure should be in the .9-1.5 bar range.

But before you panic and figure you have to rebuild the engine check the oil pressure monitoring system first. Check the oil pressure sending unit and the gauge for faults. The rest of the behaviour that you have described sounds normal.

[Tim in N FL]

Absolutely, indeed...check your oil pressure monitoring system. Mine has been acting odd only at idle...bounces all over the place but whenever it goes above idle, it behaves appropriately. I have pin-pointed the issue to a poor (oxydized) connection at the oil pressure sender. Since cleaning that connection it behaves much better...less bouncing at idle. I used a product called "DeOxit" by Kaig Laboratories... :cool:

[Gottlieb]

This oil pressure drop started 1 or 2 days after an oil change.I will troubleshoot the sensing equipment and greatly appreciate the rapid assistance.

[yvrbenz]

Did you by any chance switch to a synthetic oil?

Or perhaps switch to a different grade?

[Gottlieb]

Did not change grade or to synthetic.The engine consumes approx. 1 quart/800 miles and I can't justify spending $$ on synthetic oil.My work requires that I drive approx. 60-90 miles/day.Upon inspection the oil pressure sensing unit appears to have a damp spot along a seal,I'm hoping this weak spot is preventing the sensor from reading properly @ low pressure .I'll be replacing it within 1-2 days.

[Gottlieb]

I replaced the OP sending unit to the tune of $73 and the operating temperature reading with the brakes applied in drive is 1.4 bar.Happy motoring and thanks.