'83 300SD Oil pressure - slow and low

I have an '83 300SD and when starting cold, it takes some time (5-10 seconds) to make oil pressure. I recently changed oil weight as winter is upon us. I'm using 5w40 now, and at a warm idle it makes just a little over 2 bars. I assume the gauge is measuring bars. When I was using 15w40 it made slightly under 3 bars when warm. The gauge is completely pegged when this engine has any throttle. According to the Mercedes manual this weight oil is appropriate for the temperature range in my area. It is ranging from about -5 at night to high 20's in the day.

I'm not certain if these problems are connected, or even that they are problems at all. Are the things I've mentioned normal for the circumstances or are they symptoms of problems I'll have to ferret out?

Forums

Diesel Engine Specific Aid

Chassis Model Number

W126

83 300SD Oil Pressure Slow and High

Hi Blneuman. I bought the Performance booklet that this site puts out. I forget what it cost but it wasn't much especially when you consider what you learn from it. And according to some criteria that Kent uses when he is analyzing a car, I would say that you don't have any problems at all. In fact I wish my warm idle numbers were as good as yours. They are not low they are high, which is a good thing. As for the slow gauge rise in pressure, I can't say for sure but my thoughts are that the oil is like molasses going up that little tube to the gauge. It is pretty cold were you are and every thing is a little stiff and sluggish in tempetures like that.

Thanks

I appreciate the vote of confidence. I've asked a few people I know whether they thought that was bad or not, but it's good to hear from someone with some Mercedes specific knowledge. Hopefully I'll be getting my hands on some of the books from Kent along with a few parts, but all in all I'm pretty impressed with how solid the car is.

Concur...at 22F below

It takes 10+ seconds to make pressure with 5w-40 and then there is a noticeable improvement in cranking speed and then it finally starts. It also takes 30+ seconds for the pressure to drain out. Sadly, with the thinner oil (and synthetic now), I leak like a sieve...the thinner synthetic stuff must make seals unhappy! 2 bar at warm idle is good. I have never gone below 1.8 and Mercedes factory says even 0.5 is ok. Idid manage to start at 22F below after plugin...but it wasn't easy and needed Diesel #1 (which I had filled up with four days before the cold spell...lucky....and expensive...my son wasn't so lucky...his fuel froze.)

A word to those who post...temp/pressure readings should be denoted by a unit...as the early US models had oil in PSI and water in Farenheit. The later have oil in bars and the water in Celcius. On this thread, all have units...thank you!

Also check this

If it is taking up to 10 seconds after cold start to build oil pressure it may indicate oil is draining out of your oil filter housing back into your oil pan over night. Start by replacing the o-ring seals at the end of the rod on the oil filter cap. CLICK HERE TO VIEW

I that does not help you will need to replace the oil filter housing assembly (has a built in check valve).

O-rings

I've been buying STP filters locally, and surprisingly enough, they come with new o-rings for both the shaft and cap of the assembly, along with the copper washers for the studs and oil plug. I've been replacing all of them at every oil change.

The cap isn't seeping oil, nor are the studs, so that can't be the source of the leak. The included o-rings fit tightly around the rod, but don't completely fill the recess lengthwise. They do however take the shape of the inside of the sending unit between oil changes and are flush with the outside of the shaft by the time they're replaced.

Possibly the supplied o-rings aren't thick enough to form a seal. I'll try some of yours and let you know how it goes. Thanks.

slow pressure

2 bar is fine but if i bothers you kent sells an oil pan warmer that sticks to the oil pan and is plugged in (put it on a timer so i will warm the oil about 2-3 hours before you go to work) that will build pressure sooner and reduce wear on start-up and warm-up. I'd rather heat my oil than coolant.