Oil pressure gauge

[UriahT]

So I just bought a great 1985 300CD. During the test drive (warm), the oil pressure read 1.75 then pegged as soon as the go pedal was hit.

A few weeks later when I picked it up, the oil pressure gauge stayed at 0. Only noticed on the highway doing about 70. Drove it 15 miles or so then parked it while I waited for registration to go through.

Seems like there's only 2 options for what happened here:
-Oil pressure sending unit is a no-go (either the unit itself or in the train of thought leading to the reading in the dash)

-Oil pump is gone. Seems unlikely considering I drove it 15 miles without blowing the engine. But what are the chances of that happening? Temp gauge stayed normal, didn't hear any exploding engine sounds.

Going to pick the thing up tomorrow (and driving home 100 miles). What should I check here to ensure I won't end up on the side of the highway with a cracked block?

[uberwasser]

There isn't a sending unit, or train of thought, involved in this gauge. There is a direct oil feed from the filter housing via an oil line to the gauge.

It is quite possible, though, that the gauge itself has failed. Or the oil line came off behind the cluster and you simply haven't noticed the big puddle of diesel oil on the floorboard??

I think you've reached a reasonable conclusion that with zero oil pressure you would have not made it 15 miles. More like 15 yards.

Check the oil level before driving it next of course. You could consider temporarily putting the oil/gas/temp gauge from your 1981 300TD in to this '85.

[oldsinner111]

verify your oil pressure by renting a guage.some causes guage or sender,and oil screen clogged

[UriahT]

Thanks! I did have a 84 300D that gave me a lapful of oil because of the cluster gauge. This didn't have any apparent oil in the driver footwell so I didn't think to check it.

Actually sold the 300TD so I can't pull the cluster from it. I'll check the oil level and for any obvious leaks.

I read about checking for the oil "squirters" when looking in the oil fill cap with engine running. I'll please ignorance and admit to having no idea what to look for here.

[cooljjay]

I think that this year had seen an electric oil gauge. I would look at the oil filter housing and see if there are wires or a pipe going from the back into the car.

[Mölyapina]

All W126 300SDs have electric oil gauges. The W123 was the last 'Benz with a mechanical oil gauge.

[cornemuse]

'83 300cd, high pressure when cold, when hot 'HOT', at idle, reads below 1atu. 1,000 rpms tho, it pegs the gauge, always. -c-

[uberwasser]

Originally Posted by cooljjay

I think that this year had seen an electric oil gauge. I would look at the oil filter housing and see if there are wires or a pipe going from the back into the car.

I have an '85 and just to confirm they do still have a mechanical oil gauge just like the rest of them. The thing that sets the '85 apart when it comes to the cluster is the tachometer is not run by a tach amp, instead it gets its reading from the EGR "computer". Otherwise everything there is same-old.

[mannys9130]

Originally Posted by Jooseppi Luna

All W126 300SDs have electric oil gauges. The W123 was the last 'Benz with a mechanical oil gauge.

The W201 was the last.

My early production 84 190D has a live pressure line and mechanical gauge. My late production 85 190D has an electric gauge.

[UriahT]

This car does have a mechanical gauge as uberwasser states.

Turns out the previous owner snipped the line for some reason in the week between purchase and pickup... guessing because it started leaking at the gauge.

The top of the cam was getting oil when it turned over and oil level was fine, so I drove ti home without a hitch. These 300CDs do handle a little more nimbly than the wagons, which I'm used to.

Thanks for the input!

[Mxfrank]

Originally Posted by Jooseppi Luna

All W126 300SDs have electric oil gauges. The W123 was the last 'Benz with a mechanical oil gauge.

Not the last...the early 201's had mechanical gauges.