Slight oil pressure drop when using A/C and engine is warmer... - PeachParts Mercedes-Benz Forum

Blevinsax · #1 05-30-2007, 12:52 PM

Now that it is HOT here in Las Vegas, I have begun to use my A/C and I have noticed that my oil pressure will drop to 1.3-1.4 instead of the normal 1.5 I always see when not using the A/C. The temp gauge does go up to about 90-95 when using the A/C, but never any higher than that. Does any of this seem unusual or anything about which I should be concerned?

300SD81 · #2 05-30-2007, 12:58 PM

How about your RPMs? I believe the AC will slightly lower your idle speed, causing a drop in oil pressure.

Blevinsax · #3 05-30-2007, 01:56 PM

Quote:

Originally Posted by 300SD81

How about your RPMs? I believe the AC will slightly lower your idle speed, causing a drop in oil pressure.

I haven't noticed a significant drop in idle rpm's - typically right around 500 - but I'll see if that is affected today while driving the car.

Kuhlrover · #4 05-30-2007, 04:11 PM

My 83-300D does the same thing. The A/C compressor is causing a slight decrease in engine RPM. You are still above 1 atm. Don't worry about it.

TimK

C Sean Watts · #5 05-30-2007, 07:29 PM

As long as you are changing the oil on time/mileage. You might see less of a drop with a fresh changed full synthetic over a 4000 mile mineral oil. IF you see rapid fluctuation of the needle, check the small O-rings on the metal tube that rides in the center of the oil filter (if yours has that.)

Cervan · #6 05-31-2007, 03:19 AM

at idle you must have atleast .5 bar of pressure but it must go to max when floored.

hectormario · #7 07-12-2007, 10:32 AM

I have a 1990 300D (2.5 liter turbodiesel) that will maintain oil pressure at 2 and then increase to 3 when I accelerate or making a passing manuever. My green 1995 E300D (155K miles) maintains a steady 3 for oil pressure. I just recently purchased a black E300D with 233K miles and it maintains a steady 1.5 for oil pressure and does not increase this reading when I accelerate or pass. Is this something to worry about?

vstech · #8 07-12-2007, 10:36 AM

Quote:

Originally Posted by hectormario

I have a 1990 300D (2.5 liter turbodiesel) that will maintain oil pressure at 2 and then increase to 3 when I accelerate or making a passing manuever. My green 1995 E300D (155K miles) maintains a steady 3 for oil pressure. I just recently purchased a black E300D with 233K miles and it maintains a steady 1.5 for oil pressure and does not increase this reading when I accelerate or pass. Is this something to worry about?

yup. have you changed the oil since you got the car? perhaps you have some loaded oil in there and the viscosity is too high from the soot and you have issues there. drain and fill with your favorite DIESEL rated oil and see if it improves.

babymog · #9 07-12-2007, 10:46 AM

Can also be sender, voltage, or ground.

ched454 · #10 07-12-2007, 02:39 PM

Quote:

Originally Posted by Blevinsax

Now that it is HOT here in Las Vegas, I have begun to use my A/C and I have noticed that my oil pressure will drop to 1.3-1.4 instead of the normal 1.5 I always see when not using the A/C. The temp gauge does go up to about 90-95 when using the A/C, but never any higher than that. Does any of this seem unusual or anything about which I should be concerned?

My car is about the same when the oil is approaching the need for the 3K change, the new oil may bump up the idle pressure. If the pressure immediately rebounds to 3.0 with RPMs and maintains, everything should be normal. The temp is exactly where you want it especially in hot weather under a load using the A/C.