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Car Forum / Mercedes-Benz Cars / November 2007Oil Pressure behavior
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. > 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, [quoted text clipped - 4 lines] > > Chip >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, [quoted text clipped - 4 lines] > >Chip 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. > 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, [quoted text clipped - 5 lines] > > Chip 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. >>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, [quoted text clipped - 17 lines] > > 11 Mpg seems low. It seems to me it should be more like 18. 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. Normal.  Signature© 2007 T.G.Lambach. Publication in any form requires prior written permission. The oil pressure needle in my '87 SDL hits the upper peg at engine start and stays there. One, the oil pressure can't possibly rise as quickly as the needle does (before the engine even reaches idle speed), and two, in my other three diesel Benzes, it dropped partway back down at idle once the engine had warmed up. Is that the result of a faulty pressure transmitter (or "sending unit," in auto-speak), or is something more subtle that might be the cause? Geoff -- "When his life was ruined, his family killed, his farm destroyed, Job knelt down on the ground and yelled up to the heavens, 'Why, God? Why me?' and the thundering voice of God answered, 'There's just something about you that pisses me off.'" -- Stephen King > The oil pressure needle in my '87 SDL hits the upper peg > at engine start and stays there. One, the oil pressure [quoted text clipped - 6 lines] > "sending unit," in auto-speak), or is something more > subtle that might be the cause? My first suspect would be the sending unit or a grounded wire to the sending unit. > "Geoff Miller" <geo...@lava.net> wrote in message > [quoted text clipped - 13 lines] > My first suspect would be the sending unit or a grounded wire to the > sending unit. 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. >> "Geoff Miller" <geo...@lava.net> wrote in message >> [quoted text clipped - 36 lines] > 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. Liquid transmits pressure almost immediately (that is why tsunami can go so fast). The instance the oil pump gear reaches certain speed, the pressure will be built up. When the oil is cold, the viscosity is high so is the pressure. Once warmed up the oil pressure should be at least 1 (bar) at idle. If you mean the needle stays at peg regardless cold or warm, run or idle, that seems too much pressure. What is the oil weight currently in the engine? Geoff Miller wrote: > The oil pressure needle in my '87 SDL hits the upper peg > at engine start and stays there. One, the oil pressure [quoted text clipped - 14 lines] > God? Why me?' and the thundering voice of God answered, 'There's > just something about you that pisses me off.'" -- Stephen King Does the oil pressure needle peg when you turn the key on and before you start the engine? If yes, either the wire is disconnected at the sender or the sender is bad. > The oil pressure needle in my '87 SDL hits the upper peg > at engine start and stays there. One, the oil pressure [quoted text clipped - 14 lines] > God? Why me?' and the thundering voice of God answered, 'There's > just something about you that pisses me off.'" -- Stephen King Karl <aufever@prodigy.net> asks: > Does the oil pressure needle peg when you turn the key on > and before you start the engine? Sure does. > If yes, either the wire is disconnected at the sender or > the sender is bad. 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 Geoff Miller wrote: > Karl <aufever@prodigy.net> asks: > [quoted text clipped - 13 lines] > "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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