603 low oil pressure?

[LJetronic]

I've got an 86 sdl with nearly 300k miles on the original engine. The car runs quite well and has very minimal blowby, consuming one quart every 2-3k miles. The issue i am having is with the oil pressure. Immediately after startup cold, the gauge pegs. As the engine warms, and i drive it a bit the oil pressure falls sometimes the gauge reads 0 or very very close at idle, like .1 or .2. This occurs with intown driving or highway driving. Also, when warm the gauge does not reach 3 bar unless the engine rpm is greater than 2500. The lifters are all making noise too. I changed the pressure sensor on the oil filter housing thinking it might be wrong, but the new one reads the exact same.

What regulates oil pressure in the 603 motor? Is there a relief valve that could be stuck? Is it common for the oil pump to wear out and make less pressure in these engines?

I did forget to mention that the oil level is correct, the o rings are good on the filter housing, and i use straight 30 weight oil as i have in many mercedes diesels. I have never seen oil pressure this low in a 617 diesel, but this is my first 603...

Any ideas?

[babymog]

Time to pull the side-sump from the oil pan and have a look inside.

One of our members who had this recently found that two of his oil squirters had come loose and were crushed and in the pan, I had one do the same. Both of these engines were 3.5L but the same oil squirters.

It's not good.

[Jeremy5848]

30 weight is too low; 15W-40 is recommended and it must be diesel-rated. Nonetheless, the pressure should not be that low. First you should confirm the low pressure with another gauge. The oil pump has a relief valve but it is supposed to open at about 50 psi. If your pressure stays low with correct oil then you have an oil pump problem or some bad bearings. Others may add more possible causes.

[Skippy]

Originally Posted by Jeremy5848

30 weight is too low; 15W-40 is recommended and it must be diesel-rated. Nonetheless, the pressure should not be that low. First you should confirm the low pressure with another gauge. The oil pump has a relief valve but it is supposed to open at about 50 psi. If your pressure stays low with correct oil then you have an oil pump problem or some bad bearings. Others may add more possible causes.

This.

[LJetronic]

thanks for the great replies. I have another 603 engine laying around and was just planning to swap the oil pump and see if that makes a difference. I never considered the oil squirter trouble. Are they replaceable with the engine together, or is that something crazy to replace requiring the head off/sleeves out or something like that?

[vstech]

there is no 30 weight oil that's diesel rated anymore. if you've been using 30 weight for several oil changes, likely damage has occured, and the soot has washed your bearings, and the sleeves. I'd certainly dump that oil, install some rotella 15W40 dino oil in the white bottle, run it 100 miles, dump it, and put in some 15W40 diesel rated oil of choice! get good filters for both oil changes.
don't waste money on synthetic unless the oil pressure comes back.
if the lifters quiet up, with the second oil change, then you might be OK.
good luck!

[barry123400]

Straight 30 is too low in viscosity for older diesel indirect injection engines. You also reside in a fairly warm climatic zone that worsens the problem.

Your swapping the oil pump does not sound like too bad of an ideal. Thats if the higher viscosity oil does not solve the issue.

There is a chance the relief valve in the oil pump is less than ideal as well. I think your hot idle oil pressure is below factory recomendations at this time.

[winmutt]

Before you do anything test/replace the pressure sender.

[vstech]

Originally Posted by winmutt

Before you do anything test/replace the pressure sender.

he says he changed that in the first post.
that 30weight scares me!

[winmutt]

Originally Posted by vstech

he says he changed that in the first post.
that 30weight scares me!

He sure did. Yes 30wt is bad. He certainly should verify the gauge as well.

[Jeremy5848]

I agree. The factory electric gauge is not to be trusted in a potentially critical situation like this one. It's more of a "serving suggestion" than a true reading of oil pressure. I have a mechanical gauge tapped into the lid of the oil filter housing; when the engine is cold and just started, the pressure is up around 50-60 psi (5+ bar, where the limiter on the oil pump opens). When the engine is hot and idling, pressure can drop to as low as 15 psi (~1 bar). [YMMV]

[babymog]

Originally Posted by LJetronic

thanks for the great replies. I have another 603 engine laying around and was just planning to swap the oil pump and see if that makes a difference. I never considered the oil squirter trouble. Are they replaceable with the engine together, or is that something crazy to replace requiring the head off/sleeves out or something like that?

The piston oil squrters are attached to the block at the bottom of the cylinder sleeves and are easy to access with the pan off.

[86-300sdl]

I'v been running rotella (white bottle) 30 wt with a quart of Lucas Oil treatment as advised by a reportedly great MB diesel shop. Really quited things down. Now with 318k. Am I killing it. I'm on a road trip now and will get it changed in the morning if 30 wt is a disaster.

Thanks

[barry123400]

All experiences with the viscosity improver have not been good. Or at least it is not worth the chance if there is any truth in the stories.

Something about a mass being found in some of the oil pans comes to mind. May be an old wives tale by the way as well. This was on non mercedes vehicles.

The most important factor of using the straight thirty is the lack of certain additives to keep the soot in suspension as well as the inadaquate viscosity when used alone.

[winmutt]

Yes. Lucas causes frothing.