300sdl oil pressure problem!! - PeachParts Mercedes-Benz Forum

LJetronic · #1 03-11-2009, 07:52 PM

Guys, i really need help here. I have searched for hours on the forum looking for clues to help with my 86 300sdl. The motor has low oil pressure. I bought the car last summer and have since changed the oil to straight sae 30 and also changed the pressure sensor. Upon starting cold, the guage usually pegs and graudally comes down during the drive like normal but it will get very low at idle sometimes (scary). The lowest point i have seen is about .4-.5 bar after a run on the highway at 75. Before i changed the pressure sensor, the needle would be resting on the 0 pin!!! I kind of knew the motor had some pressure as it sounded and ran ok. This is my first 603 car, and all of the 617's ive had will maintain 1.5bar or so after a highway trip regardless. Yesterday morning when i started up cold (its getting warmer here in new orleans now... it was probably 75 degrees), it would only muster about a 2.5 or so. Also, i am getting some lifter tapping (sounds like 1 or mabye 2) at any time, but usually worse when cold. Its not horribly loud, but certainly identifyable. The motor has probably 300k miles, but makes great power, doesnt overheat at all, and consumes no more than one quart per month and this is a daily driver with lots of highway. My questions are: is there a pressure relief valve in the block or the pump that could be stuck? Does it sound like the pump's worn and in need of replacement? Is it the bearings in the motor that are the problem (i really doubt this one as it runs so good). I have found an NOS MB pump for about 300... is this a good deal? Should i do the lifters at the same time? Any help would be appreciated very much. I just dont know!!!
Patrick

79Mercy · #2 03-11-2009, 07:54 PM

what kind of filter did you use?

LJetronic · #3 03-11-2009, 08:00 PM

wix, and i even changed both of the little o-rings on the shaft in the filter housing.

NJ300sdl · #4 03-12-2009, 04:39 PM

Temporary mechanical oil guage on engine will give best pressure readings. Maybe your dash guage is not correct. Head gasket failure at forward oil passage can leak oil into timing chain area causing lifter noise.

Brian Carlton · #5 03-12-2009, 04:53 PM

Quote:

Originally Posted by LJetronic

I bought the car last summer and have since changed the oil to straight sae 30 and also changed the pressure sensor. Upon starting cold, the guage usually pegs and graudally comes down during the drive like normal but it will get very low at idle sometimes (scary). The lowest point i have seen is about .4-.5 bar after a run on the highway at 75.

The first issue is the weight of the oil. For the diesel, the weight should be 15W40 if you're using Dino oil (Rotella, Delo 400, or Delvac 1500 are preferred), or 5W40 if you're using synthetic (Mobil 1 or Rotella are preferred). All of these oils are diesel rated oil and designed to hold the soot in suspension.

If the oil pressure is .3 bar or above at idle, the engine is fine.

If the oil pressure is above 3 bar with the engine at 3000 rpm, the engine is fine.

LJetronic · #6 03-12-2009, 10:49 PM

thanks for the reassurance! the motor seems to run really well, consumes very little oil, makes great power, and has no blowby with only the mild lifter noise. Ill change the oil this weekend to a heavier weight and hopefully that will bring the pressure up a bit. I have always used either sae 30 or 40 and never a variable weight oil... i suppose its time to come out of the dark ages!

bustedbenz · #7 03-13-2009, 01:00 AM

I'm used to seeing .5 or a tad under after a long hot hard interstate run on a hot summer day. As long as it pops back up again immediately when you accelerate, and doesn't actually bottom out at idle, you're good.

leathermang · #8 03-13-2009, 01:06 AM

I agree with a couple of the above posts...
on old cars I use straight 40 weight to help fill the extra space at the worn bearings.
I don't use the mulitviscosity because the instructions on air cooled lawn mower engines always says ' straight 30 wt' ... and those are the most severe operating conditions I know of....so what they add to make it multiweight must decrease its lubrication ability some... but I am in a hot climate all the time.

Diesel911 · #9 03-13-2009, 01:15 AM

Quote:

Originally Posted by LJetronic

Guys, i really need help here. I have searched for hours on the forum looking for clues to help with my 86 300sdl. The motor has low oil pressure. I bought the car last summer and have since changed the oil to straight sae 30 and also changed the pressure sensor. Upon starting cold, the guage usually pegs and graudally comes down during the drive like normal but it will get very low at idle sometimes (scary). The lowest point i have seen is about .4-.5 bar after a run on the highway at 75. Before i changed the pressure sensor, the needle would be resting on the 0 pin!!! I kind of knew the motor had some pressure as it sounded and ran ok. This is my first 603 car, and all of the 617's ive had will maintain 1.5bar or so after a highway trip regardless. Yesterday morning when i started up cold (its getting warmer here in new orleans now... it was probably 75 degrees), it would only muster about a 2.5 or so. Also, i am getting some lifter tapping (sounds like 1 or mabye 2) at any time, but usually worse when cold. Its not horribly loud, but certainly identifyable. The motor has probably 300k miles, but makes great power, doesnt overheat at all, and consumes no more than one quart per month and this is a daily driver with lots of highway. My questions are: is there a pressure relief valve in the block or the pump that could be stuck? Does it sound like the pump's worn and in need of replacement? Is it the bearings in the motor that are the problem (i really doubt this one as it runs so good). I have found an NOS MB pump for about 300... is this a good deal? Should i do the lifters at the same time? Any help would be appreciated very much. I just dont know!!!
Patrick

How many miles are you getting before that 1 Quart of oil is consumed; or do you have some Oil leaks?

LJetronic · #10 03-13-2009, 07:20 PM

well, the odometer stopped working, but i would say that i am an avarage driver. so perhaps 1 quart for 1000-1300 miles, and there is quite a bit of highway driving at 75-80 in there. The engine consumes far less than most 617's that ive owned in the past and has very little to no blowby and no leaks. Other than the low (ish) oil pressure and the small lifter noise, it really seems like the motor is quite healthy!

LUVMBDiesels · #11 03-13-2009, 09:18 PM

I don't think you have a problem. Just go with the 15W40 or 5W40 Diesel oil and you should be OK. Check back with the oil pressure after you change the oil