Ever since I bought my '81 380 SL a couple of months ago, the oil pressure behavior has bothered me. Whenever I apply the gas, accelerating or merely maintaining speed, it really pegs the needle. Only when applying brakes or idling does it drop to just over "1". Is this normal? It seems to run fine, except for low gas mileage of 11MPG. It has 116,000 miles, but was recently tuned-up w/ oil change.
Chip
Normal.
Don't know about gas engines but that oil pressure behavior is normal for diesels. At speed, the needle pegs. Hot and idling, somewhere between one and two.
You can also get a situation with low oil level where the needle will fluctuate as the oil sloshes around on acceleration and deceleration. Needles to say, this should be promptly attended to.
Normal.
Starts after the oil has cooled usually peg the oil pressure gauge until the car warms up as well. When you have to worry is when the needle does not peg under load. For example, I knew the engine bottom end in my old 250c was worn when the oil pressure needle would not peg after an hour or two on the highway. Idle speed will affect the reading at idle, so make sure the idle is correct. Over 1 bar seems to be pretty good to me.
11 Mpg seems low. It seems to me it should be more like 18.Normal.
My first suspect would be the sending unit or a grounded wire to the sending unit.
I have a '79 mb 240d w 200k miles.
the oil pressure pegs when I start and stays that there when driving.
after warms up, at stop, idling, will drop about 1/2.
j.
If you haven't looked at the back of the instrument cluster, then you might think this is the problem. However, most MB use an actual line (with pressurized oil in it) connected to the oil gauge. Its the actual oil pressure from the pump being shown on the gauge. Thats why it is so fast to rise up, and moves so much when you accelerate, etc. If it doesn't move, then its probably a problem with the oil. Mine didn't move at all (didn't drop back down at idle) for the first couple of weeks that I had the car, once I drove it some more, it starting moving and doing the same thing. I would have thought it was a problem had my uncle not informed me already that it would do that.
If you're interested, the guys on CarTalk (on NPR) had a question about this a few weeks ago. You can download the episodes for free now as a podcast (I get mine from iTunes). They said the same thing, Normal.
You are correct! My apologies. I was not paying attention to the model. Newer MBs don't even have an oil pressure gauge.
I think the minimum pressure MB recommends is .7 BAR (10.15 PSI), below that indicates (hopefully) low idle or a (bummer) worn low end (bearings)
I also think there is a sending unit, but as I remember now it was oil level not pressure.
Karl asks:
Sure does.
Well, there we go. I'll put that on the list for the next time the car goes into the shop. Thanks!
Geoff
-- "Have you ever noticed that whenever you sneeze on your dashboard or computer monitor, it smells like pussy?" -- bandy
my '79 mb 240d has an oil line going to the oil pressure guage. No electric sensor to go bad.
j.
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