Fuel / oil gage...

[n1265]

Here is one for you,

On a 1977 W200 when I turn the key on the oil gage moves at the same pace as the Gas gage, It stops in about the same place too
( 1/4 tank of gas and about 20 lbs of oil pressure ) This is without the motor running.....

Any Ideas ?

Many thanks,

[712edf]

Short in the circuit board (or wiring). The oil gauge wire is receiving a partial ground from the gas gauge wire. It should not. The gas gauge wire is lightblue with black tracer (18 ga) that goes to pin B on the circuit board connector...The oil gauge wire is white (18 ga) and goes to pin E on the same connector. On Dodge gauges of that era the gauges receive a constant reduced voltage. What makes them move is a change in GROUND continuity. The stronger the ground the fuller the gauge will show. No ground equals no reading. On the back of the circuit board in your instrument panel these things are located close together, easy to get a short.

[OLD DODGE]

Or a bad sending unit?

[712edf]

Or a bad sending unit?

Yep, check and see if unhooking it does anything.

[yogibare143]

There is a lamp socket on back of cluster between to nuts that hold oil pressure gauge in. Make sure there is no lamp in socket. Socket is for oil low pressure light. If lamp is in socket it can cause false reading on oil gauge.

Mark

[n1265]

Here is the deal.

I checked the lamp socket on the back of the gage by reaching up behind there and found there was no bulb in the hole. I then unhooked the sending unit and sure enough, no pressure at the gage when running.

I then plugged the sending unit back in and tapped it a few times with an 3/8 ths. extension and got it to work somewhat normal.

Right now I am kinda wondering if these things can be cleaned with any success...

[712edf]

Right now I am kinda wondering if these things can be cleaned with any success...

Maybe, but would you trust it to be accurate?

[n1265]

I'm not sure...

[n1265]

Engineer #1 : Hey, I got an idea ! how about we put the oil sending unit in an accessible place, That way if some fat smuck has to change it 30-40 years from now it wont be a hassle.

Engineer # 2 : Dammit ! How many times I gotta tell you to stick with what you do best, Drinking coffee.... You just leave the real engineering decisions to me!



Well you guessed it, I went ahead and changed the sending unit today , It reads quite a bit higher than the old one and now I am wondering just how accurate It is. The old one would normally run around the first line on the gage, the new one runs at "40 " on the gage.

Is 40 psi of oil pressure " normal " for a 30 year old 318 with 75 - 100 K miles ? ( not exactly sure of the mileage )

Just wondering...

[712edf]

40 psi is feasible. On the vehicles I've encountered with seasoned engines, oil pressure is highest at startup, drops when the engine temp rises..May rise and fall with rpm's......If you've got clean oil/filter on an engine that's not tapping, knocking, clanging or otherwise making noise or hemorraging then you are in good shape regardless of whether it shows 30 psi or 55 psi. Its made it this far. You have one of the most trustworthy engines ever put in an American vehicle!