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Old 10-08-2004, 10:57 AM
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UPDATE - 560SEL Oil Pressure - SUCCESS!!

I posted earlier this year that when I took my 1988 560sel out of winter storage and took it for a 30 mile or so drive the oil pressure guage slowly started to fall while I was on the highway until, by the time I got home, it was at 1 bar. I shut the engine off and immediately restarted it and it climbed to 2.5 bar then slowly started to fall to 1 bar again within a couple of minutes. If the car was left to sit overnight and started again in the morning it would read 3 bar until the engine was at operating temp and then the same thing happened all over again. Having other priorities I let the car sit until August when I changed the oil pressure sensor and took the wire to it and disassembled the connector and cleaned it real good with fine sandpaper until it was good and clean and then re-assembled the connector and put it on the sensor. Took the car for a ride and after the engine got to temp - the same thing happened again. Now I started to panic. There was a thread in August (or early Sept. ) that was from a 560 owner in Alberta who said that he cured his oil pressure guage problem by changing the brush pak in the alternator. I took my brush pak out and it was like new with 1/2" long brushes. The voltage from the alternator was 13.76 at fast idle and the battery is good. That solution did not cure my problem. Now thinking that I had an internal engine problem I was getting panicy. Last fall I had the oil changed at the Mercedes dealership here and they said that with this old engine Quaker State 10w-30 is what they always use. So I told them OK do it and they changed the filter at the same time. Out of shear desperation I decided to change the oil and filter - even though the car had only travelled about 250 miles since the oil change. This time I switched to Syntech 5w-50 synthetic. I pulled the oil filter and they had installed a Mercedes Benz labelled filter. I had bought Mann filters and threw one of these in with the synthetic oil. When I started the car, the oil guage did not move for a few seconds then BANG - it shot up to over 3 bar and stayed there. SUCCESS! - NOT. The car was taken on a 100 mile trip and the guage stayed pegged. I was happy UNTIL - I read a thread on this board about the "DREADED pegged oil pressure guage". Apparently, the guage would peg at 3 bar as soon as the key was turned on for this poster - even with the engine off. No Solution found. So I went home and turned the key on without starting the engine - and POW - the oil pressure guage pegged at over 3 bar. Now I am really ticked - I switched one problem for another. So-o-o I went under the car and took the connector off of the oil pressure sending unit, and with it off turned the key on without starting the engine. The guage was still pegged. Trying to figure out what was going on, I took a test wire with alligator clips on both ends and put one on the disconnected terminal and the other end of the wire to ground. I turned the key on without starting the car and guage was reading "0". So with no oil pressure the sensor had to put out a short reading for the guage to read "0". Something in the guage still caused the guage to peg with the engine not running even with the senser disconnected. Shorting the wire to the guage (disconnected from the sensor of course) allowed the guage to return to "0". So, then, I took my ohmeter and checked the terminal of the new sensor to ground - without the engine running I had determined that the sensor should be in a "0" ohms mode. It wasn't. It was extremely high ohmage. Getting pretty ticked off by this time, I took a big screwdriver and whacked the sensor from underneath - totally out of frustration. I read the terminal of the sensor with the ohmeter again and IT WAS "0"!!! Hey things are looking up. Re-attached the connector to the sensor and turned the key on - "0"!!! YES. Started the engine and the guage quickly swung up to over 3 bar. Saints be praised! Tried turning the car on and off a few times - SUCCESS AT LAST!! Have driven the car for about a week now and put a few hundred miles on it and the guage works perfectly!! With the engine hot at idle the guage reads about 2 bar but snaps to over 3 bar as soon as the engine is revved. It works!! So it appears that two things were in play here:
1) Original problem was somehow caused by the Quaker State oil and Mercedes oil filter - may be the filter was blocked ? - who knows but with a new filter and synthetic oil - my original problem is cured. Hope this helps someone else with oil guage pressure drop problems.
2) The "dreaded pegged oil pressure guage syndrome" - Near as I can figure out - when I changed the oil and filter and started the engine it took a few seconds for the guage to read and the needle shot up like a bullet when the oil pressure kicked in. Somehow the sudden burst of oil pressure caused the new sensor and guage to stick in high pressure over 3 bar reading even with the engine off. By whacking the sensor with the screwdriver - it unjammed it inside and by shorting the lead disconnected from the sensor to the guage to ground with the ignition on but engine not running, it reset the guage somehow and now all is well. So anyone else with the same "dreaded pegged guage" - it could have happened at oil change from the sudden shot of initial oil pressure and whacking the sensor with the engine off and shorting the wire to the oil guage to ground with the ignition on may also work for you.
It has been a trying year for a stupid little problem but thanks to all on this site that offered their suggestions - while they did not work in my case - they were very enlightening.
Hope this helps others

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Old 10-08-2004, 08:29 PM
Hatterasguy's Avatar
Join Date: Nov 2002
Location: Milford, CT
Posts: 19,318
Glad to see you finally got it sorted out!
1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200
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Old 09-30-2008, 01:33 AM
Abadjay's Avatar
Join Date: Jun 2008
Location: North Hills
Posts: 256
Is there a possibility that this same procedure can be used on an '87 300SDL? My Oil Pressure reads 3 all the livelong day and it's annoying because it's not normal.
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Old 10-05-2008, 04:17 AM
hey_allen's Avatar
greasy fingered tinkerer
Join Date: May 2006
Location: Tacoma, WA
Posts: 728
Is the 300SDL reading 3 when warmed and idling, or even when the engine is off?
If so, it couldn't hurt to rap the sender a few times with a screwdriver handle.

If it's just running that high when you're driving, it's normal. Heck, mine doesn't stop at 3, it pegs off scale on the top end when the engine is above 1000 rpm!
Testing the cheap Mercedes axiom, one bolt at a time...
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Old 10-06-2008, 02:53 PM
Registered User
Join Date: Sep 2008
Posts: 80
oil pressure

I read somewhere on here that this type of problem is properly fixed by doing the following: after an oil change, the car needs to be cranked with the main distributor coil disconnected to reestablish the oil pressure. Once oil pressure is re-established, re-connect the coil and start the engine.
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Old 10-06-2008, 06:48 PM
Johnhef's Avatar
Senior Member
Join Date: Feb 2005
Location: Frederick, Md
Posts: 4,540
Thats usually to prevent chain snap and guide rail breakage.


1980 500SE/AMG Euro
1981 500SEL Euro
1982 380SEL
1983 300TD
1983 500SEC/AMG Euro
1984 500SEC
1984 300TD Euro
1986 190E 2.3-16
1986 190E 2.3
1987 300D
1997 C36 AMG
2003 C320T 4matic

past: 1969 280SE 4.5 | 1978 240D | 1978 300D | 1981 300SD | 1981 300SD | 1982 300CD | 1983 300CD | 1983 300SD | 1983 380SEC | 1984 300D | 1984 300D | 1984 300TD | 1984 500SEL | 1984 300SD | 1985 300D | 1986 300E | 1986 560SEL | 1986 560SEL/Carat | 1987 560SEC | 1991 300D 2.5 | 2006 R350
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