oil pressure gauge gone goofy, 420 SEL

[William]

The vehicle is a 420 SEL, W126 1986 version. The oil pressure gauge on the instrument panel has gone goofy.

The needle remains pegged out on 3, while the vehicle is sitting in the driveway and the ignition turned "off".

While still sitting, when the ignition key is once again turned "on", the needle drops down to between 1 and 2. It then immediately pegs out on 3 when the engine is cranked.

While driving the car, the needle never comes down from the 3, at idle or any other time.

With the engine shut down, and the ignition turned "on", I have detached the wire from the oil pressure sender switch and grounded it to the frame and then removed it. When grounded, the needle pegs out on 3 and then when I remove the ground the needle remains on 3, even though the wire is still unattached to the sender switch. At no time will the needle fall to "0".

Any thoughts would be appreciated.

William

[William]

The saga continues....................I just went out and took a look at the oil pressure gauge, with the car just sitting, and oops, the needle had fallen to zero. I'm more confused than ever.

[Harold in NC]

Sounds like an intermitent short to ground somewhere between the sender and the gauge. I just researched the pegged at 3 problem with the help of this board. My problem is a bad sender. If I remember correctly you should bypass the wiring and jumper from the sender to the input at the instrument cluster. If this clears the problem you would indeed have a short to ground that comes and goes, maybe a chaffed wire. Also, could be the sender is failing and is not completely dead yet. Seems to be a very common problem.
Harold

[braverichard]

I'm currently experiencing erratic and inaccurate readings from my coolant temperature gauge in my '84 300SD. Our problems probably point to the same thing - the sending unit. Afterall, these are 18+ year old cars. Since we are running on the original units, I wouldn't be surprised if they are all faulty. But who knows.

[William]

Thanks very much for the help.

To close the loop, I've reached the conclusion that I have a defective "oil pressure sender". I did maintenance on the connecting wire, but it didn't cure the problem. I then removed the "sender" for cleaning and also cleaned the oil passageway and the filter housing, all to no avail.

William

[El Maddog]

I have a '87 420SEL w/ 185k miles.
Oil reading was always staying up at 3 with no drop @ idle-so I suspected that the sender may bad. Replaced it and the reading did not change. Guess the motor is still tight.
Sender is about $56 & very easy to change.

Jeff