Hello,

I'm a newbie to this forum, and following your advice, I searched for an anser to my question. However, I dont know much about cars, so my simple query of oil pressure lead to over 2000 hits. I figure I'd just ask the question:

I have a '94 S420 andI seem to notice a direct correlation between the Engine Temperrature and the oil pressure when the car idles and when it drives. Starting the car in the morning, the oil pressure gague jumps to the max 3 and stays that way whenever/however I drive it. However, as the engine warms up, the idle oil pessure is lowered. Eventually, the engine will heat up tCo above 100 C (is that normal too? because it cools off ( about 90C) when you drive it, heats up when you idle in traffic). When past 100 C , the oil pressure is at 0 at idle and moves barely to the 1 when doing city traffic (35 mph). Is this something I need to concern myself with?

Thanks for your help!

No need to concern yourself with the correlation of oil pressure at idle and engine temp. That's just physics. I'd be concerned that the gauge is reading below 1 at any time. Certainly if it doesn't peg quickly as the revs climb.

What oil are you using? What's your change interval?

Sixto
95 S420
87 300SDL

I believe its 10W40 (its 2AM and im not inclined to go out and check, but ill verify tomorrow), and Its changed every 3000 miles, give or take. The oil was changed within the past 2 months.

I suppose it's worth a professional opinion because it could be low oil pressure or a faulty reading. If it's warm where you are, switching to 20W-50 or Mobil 1 15W-50 might improve oil pressure.

Sixto
95 S420
87 300SDL

You have a defective visco clutch -- engine shouldn't be getting much above 85C in traffic unless it's REALLY hot.

You also have a defective pressure relief valve in the oil filter housing -- I've heard of this before. You MUST have 3 bar oil pressure by 1500 rpm or you risk bearing damage (read $$$$$$). The seat for the relief valve is bad, and won't hold proper pressure with the oil hot.

Normal oil pressure is about 1 bar at idle hot, maybe as low as 0.5 bar, rising immediately as the engine speeds up. On turbodiesels, it must not drop below 2 bar idleing hot (this is the opening pressure for the piston spray jets).

Before getting hysterical, though, you need to get a mechanical gauge on there and verify that the oil pressure gauge is correct! If so, replace the oil filter housing (relief valve is not available separately) and see what happens. Cheaper than a new engine!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Gee, Peter, this is the second time I disagree with you today. Per JimF's website and SteveB's comments, later engines run a lot hotter. The S420 engine temp hits 100C anytime I'm creeping in traffic with AC. Freaked the heck out of me until I checked the archives. JimF sells resistors to trick the fans into coming on sooner but there's some debate over which models have a separate fan sensor and which models share a sensor between fan and ECU (ergo don't mess with it).

Sixto
95 S420
87 300SDL

Sixto:

So far as I know (and I'm not claiming omnipotence here!) most the later (post 88 or so) MB temp sensors are dual duty. Save a buck or two, eh?

The temp senorr on my sister's 92 Volvo was a wierd one too -- looked just like the earlier ones I snagged from the u-pullit when I did her head replacement a couple years back, but has TWO thermistors instead of one. Needless to say, the replacement caused a error code. All the temp senors were fried by the loss of coolant (along with the head -- badly warped -- and the plastic parts and thermostat). Sis never does things by halves!

I don't suppose there is any real reason to get upset by higher temps -- the greater the difference in temp between the rad and the air, the greater the heat transfer, but I'm surprised.

Then again, I don't have anything that new.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!