Oil pressure guage problem 1988 560sel - PeachParts Mercedes-Benz Forum

#1 06-30-2004, 10:29 AM

Need some advice here. Just took the baby out of winter storage and took it for a 30 miles drive - worked perfectly- the oil guage was pegged at 3 all the time except at idle when it dropped to about 1.5 at idle - all normal. Started the car to go home and noticed the oil guage was only at 2.5 not 3. As I drove the 30 miles home the pressure slowly kept falling to about 1.5 when I started to panic and tried coming to a stop to let the motor idle. The guage showed 0 but the engine sounded good so I revved it up and she when to 2. I continued driving at about 40 mph and by the time I got home the oil guage was only showing about 1.25 at 3000 rpm. I shut the engine off and started it again. The oil guage went to 2 at 2000 rpm. Shut it off and started it again - it went to 2.5. Shut it off and started it again - it went to almost 3 . Held the revs at 2000 rpm for about 3 minutes and it started to drop again. I sincerely hope it is a bad oil pressure sensor. Before I dash out to buy one - any one else have an idea? Sure is scarey when your oil pressure doesn't read right!

Hatterasguy · #2 06-30-2004, 12:42 PM

On my SDL it won't peg all of the way sometimes. The guage needle will also bounce up and down a little, If I wiggle the wire on the sensor it will act normal for awhile. I'm betting your sensor is bad, I ordered one for mine and am waiting for it now. When I change mine I'll let you know.

MikeTangas · #3 06-30-2004, 01:48 PM

Morris, It could be the sending unit or the connection. Start by cleaning the connection, then see what the gauge does. You can also check the condition of the sender with an Ohm meter, but I don't know the specific values off the top of my head...they are in the manual though. A new sender is about $65 US.

#4 06-30-2004, 02:10 PM

Thanks Mike and Hadderasguy. I checked the Mercedes dealer up here and they are nuts-- $138CDN plus 15% tax for the sensor. I found a supplier in Ontario that has a new one - exact same part number-0065429417 - for $56 CDN- it should be here Friday. Will let you know what I find. Thanks again for the replies - and thanks Mike for the tip on the connector - sometimes a guy just needs that extra assurance from forum members like you guys.

MikeTangas · #5 06-30-2004, 03:20 PM

Hey, I keep a wallet full of Canuck Bucks now a days, maybe I should buy a bunch of senders from your source in Ontario since they work out to about $41.00 US, bring them bacl across the border and sell them for $60 US....hmmmm...free enterprise

Hatterasguy · #6 06-30-2004, 05:00 PM

I just installed my new sender, and all is normal once again. My connection was very dirty, so I cleaned it real well with some electrical contact cleaner. Made by CRC, this stuff seemed to work well. I paid $65US for mine.

#7 07-05-2004, 09:32 AM

Hi Mike and others - OK now I am starting to get a little nervous. I changed the sensor, took the connector cover apart and used emery paper to make sure the brass inside the connector was nice and clean and the solder connection looked good, then I crimped the connection tube a little for a nice tight fit, reassembled the connector cover and pushed it on to the sensor. When I started the car the engine oil pressure guage shot up to 3 bar pegged. Success. NOT. As soon as the engine reached operating temperature the guage slowly started to fall to under 2 again. Brought the car to a stop and revved the engine a few times - the needle literally jumped to about 2 and a half mark then slowly started falling again. Revving the engine caused the needle of the oil guage to jump a little a couple of times keeping the reading at about 2-2 and a half - then it just slowly started to sink again to about 1 and a half regardless of if the engine was held at an idle of about 1200 rpm or at 3000 rpm. . I shut the engine off and left it until I got back to this forum. I know the guage works on resistance which is provided by the sensor. Common sense tells me that if it was a broken wire or a loose connection the guage would read and then not read depending on if the wire was making or breaking connection. This guage does not ever drop to "0" it just slowly reads low and occasionally jumps up to a higher reading but when the engine is hot it NEVER pegs the needle - it only pegs the needle when the engine oil is cold. I am running Pennsoil 10w30 in it as recommended by the Mercedes dealership up here. I really hope that is not an engine problem with low oil pressure when hot but I do not tend to think that that is the case because of the way the needle jumps up every now and then. There is no difference in reading with the old sensor or the new one. Could the wire to the sensor have internal resistance? The car ran great last year. I started it up and moved it a few feet every week for the entire storage time until I took it on the 30 mile jaunt. The guage worked good on the first leg of the jaunt and acted up on the way home. The only other abnormality that I am noticing is that there is a slight miss at idle that is random and not rhythmic that you can hear in the exhaust if you listen. But - hey - these 560's are known for this problem. Anyone with some advice??? Just grasping at straws - but could a bad oil filter (just changed with oil when I stored it) cause the problem? THanks for any ideas in advance.
Morris

Hatterasguy · #8 07-05-2004, 10:07 AM

If the 560's oil filter is like the one in my SDL, their is a rod going threw the filter with 2 o-rings on it. These become hard and I am told can cause a drop in oil pressure. Also 10w-30 seems too light, I don't know how cold it is up their but Mobil 1 0w-40 or 5w-40 would probably be a better choice. I sudjest changing the oil and filter with Mobil 1 and a German filter. For the oil pressure to drop that quickly makes me think it is electrical, but it might not be, maybe having the old oil that comes out tested could tell you if anything major went wrong.

Or you could take it to a shop and have them put a mechanical guage on it. I wouldn't run it any more until you find out what is causing this.

MikeTangas · #9 07-05-2004, 10:59 AM

I think it is time to verify the oil pressur using a mechanical gauge. I think you need a 12 mm nipple to tap into the the orifice the sender is in (double check the size, I couldn't locate the correct size in Port Huron). Run the mechanical gauge and see if you get the same results at the filter housing. If the pressure remains good throughout the temp ranges you know your problem is in the dash gauge or wiring.

#10 07-05-2004, 11:12 AM

Thanks Mike - I have an aftermarket oil pressure guage with feed tube that reads in lbs per sq inch which I could tap into the sensor opening temporarily - what does 2 and 3 bar convert to in lbs per sq inch? I will be able to try it tomorrow and let you know the results. I am also going to try the different engine oil and put in a new Mann filter - (that is all I have been using) and check those two O rings at the same time - I believe that they are original and might be a good idea to check. Are corroded connections at the instrument cluster a problem? Only other thing I can think of for electrical problem - and again I don't know - does the wire from the sensor have another under the hood connection that could have corrosion or does it go directly to the guage?
Thanks again
Morris

bhatt · #11 07-05-2004, 01:47 PM

Moedip,

One Bar is equal to atmospheric pressure (14.7psi).

1 BAR - 14.7PSI
2 BAR - 29.4PSI
3 BAR - 44.1PSI

Hope this helps!

PS. What supplier did you find that part from in Ontario? I purchase my parts from the US because they are so expensive here.. Altrom is the only one I know of and they're usually *way* overpriced.

Neal

#12 07-05-2004, 01:59 PM

Altrom is the one. Sometimes they are more expensive sometimes they are cheaper. I know they want about $48 for a VW block heater and VW has them for $32. But at the same token - check them for prices and compare to the dealership before you order. I have been using their stuff for over 4 years now and other than one defective FAG wheel bearing which they replaced under warranty - all the rest has been good quality stuff. I have 4 adult kids and 5 VW Diesels under 1991 in the family and all are kept in excellent running shape by me using Altrom parts from piston rings, head gaskets, rotors brakes etc. Their alternator, cv joints and starter prices are out to lunch though - there I use an after market supplier. So far - totally satisfied - but compare prices before ordering from them - some of their prices are a bit(?) ridiculous.
Morris