Yeah... but you do that on your Chevy like I do my Chevy right? Never on a BENZ!!!

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'87 300SDL, intensely modified Greasecar setup, with nickle plated heat exchanger, 3 valve setup, 312,000 miles
'95 Suburban diesel, Greasecar basics, 16 plate heat exchanger, mercedes fuel lines, Racor filter
'85 Renault Alliance converted full electric vehicle

The beating of the dash is a pure frustration outlet. The fact it works occasionally is just icing on the cake!

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1983 300D-Turbo - Deep Blue w Palomino MB Tex (total loss in fire 1/5/09 RIP)
1995 E320 W124 Polar White/Grey Mushroom MB Tex
2005 F150 Supercrew - Arizona Beige - Lear topper
1985 Piaggio Vespa T5 - Black and Chrome

www.cphilip.com

On the W126 you can get it from the top, easy as can be...

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

D'oh, I forgot this wasn't a 124. Near impossible to change that thing from the top on a 124... the cooler lines, steering box, and washer reservoir are all in the way. Just imagine what a 602 in a 201 must be like!

If I hook my manual pressure gauge up to this... Does anyone know what the PSI should be?

Bill

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'87 300SDL, intensely modified Greasecar setup, with nickle plated heat exchanger, 3 valve setup, 312,000 miles
'95 Suburban diesel, Greasecar basics, 16 plate heat exchanger, mercedes fuel lines, Racor filter
'85 Renault Alliance converted full electric vehicle

3 bar works out to roughly 45 psi, so it should be well above that whenever the car is not idling.

Now starting ten minute countdown by the end of which someone will have proved that it's in fact 43.5113213psi instead of 45.

However, as you're staring at your gauge, you'll see the needle hovering somewhere over "45" and be happy

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~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

Well a new sending unit arrived before I could find a metric machine thread fitting to hook a manual gauge into...

Results with the new sending unit are the same. When I started it up she was pegged at 3 right away... as it warmed she dropped to 2 and just slowly kept dropping over the next few minutes to almost 1. I turned off the engine at this point. I've never seen the pressure so low.

I'm still going to see if I can hook up a manual tester if I can find a fitting that is M12 x 1.5 into something I can hook a hose to.

Going back to something Sixto said... I will admit I have thought my engine to be knocking loud for quite some time. You had stated that it could be a crankshaft bearing or a rod bearing... Probably this stuff is over my head... because I don't think you can replace them simply by taking off the oil pan... How would these bearings affect oil pressure?

As Ipicture it there's a gear on the end of the crank with a chain around it that turns the oil pump. Shouldn't I test my oil pump first some how?

Also on another thread on this topic it talks about a check valve being open or even the O rings in the oil filter housing... Now I'm a thousand or so miles since my last change and this happened fast so it wasn't like I was just in the housing... I took off the lift pump, cleaned it up, put it back... and now low oil pressure.

I appreciate additional input on this.

Thanks,
Bill

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'87 300SDL, intensely modified Greasecar setup, with nickle plated heat exchanger, 3 valve setup, 312,000 miles
'95 Suburban diesel, Greasecar basics, 16 plate heat exchanger, mercedes fuel lines, Racor filter
'85 Renault Alliance converted full electric vehicle

Just getting the oil pan off is a lot of work. The engine doesn't have to come out of the car but it has to be lifted off its mounts for enough room to remove the pan. With the pan off, you can remove the main and rod caps to check the bearings. I think you can get to all of them.

Something to consider is oil analysis. There might be enough clues to determine what's causing low oil pressure. How long has the current fill been in the engine?

Folks on this forum have used Blackstone Laboratories and Performance Analysis (run by George Murphy).

Sixto
87 300D

I have about 1,000 miles on the oil right now. But considering this is supposed to be my daily driver I just might take it into the shop to get it done faster. Inside of the engine would be new territory for me.

She's got over 300,000 miles so wear on these bearings wouldn't surprise me, but it just happened so fast! I'm still not convinced I haven't over looked something simple...

I think I'll call the shop on Monday.

Bill

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'87 300SDL, intensely modified Greasecar setup, with nickle plated heat exchanger, 3 valve setup, 312,000 miles
'95 Suburban diesel, Greasecar basics, 16 plate heat exchanger, mercedes fuel lines, Racor filter
'85 Renault Alliance converted full electric vehicle

I know someone with an 86-87 SDL. Records show a failed vacuum pump was repaired before he got the car. After years of second ownership the oil pump somehow sucked a ball bearing. At least that's what a post-mortem suggests - ball bearing size hole in the mesh, deformed ball bearing in the impellers, oil pump sprocket sheared off the pump (that's some chain!). Oil pump seized causing a main bearing to seize so the engine seized. Everything else looked fine.

For kicks, does the vacuum pump on your engine have 4 visible screw heads?

Should it turn out to be a lower end problem, consider a good used engine or short block vs having your engine rebuilt. I don't necessarily advocate it, just providing food for thought.

Sixto
87 300D

Throw in a new oil filter and see if that helps. Cut open the old filter to see if there's anything in it besides bugs and twigs

Sixto
87 300D

The '86 performs in an identical manner.

I've got a suspicion that the oil cooler plays some part in the illumination of the light. The light won't illuminate when the engine is cold...........it's got to be fully warm after a decent run on the highway. Once illuminated, it cycle depending on grade, engine temperature, or curves.

The only way to keep the light off is to keep the oil level at, or near, the full mark.

OK... I finally found a M12x1.5 to NPT male adapter so that I can hookup a cheap water pressure guage that I had lying around. Here's the scoop...

My first question is why when I turn on the ignition was the car's oil pressure gauge pegged at 3 without the engine even running. Seems short sited to me to have the gauge default to 3. So I started up and got 70psi, almost 5 bar. It took a while to warm up and at moderate revs (2000rpm) I could still hit 70 psi, but once warm it idled around 20psi or just under 2 bar.

Even when I release from 2000 rpm oil pressure did not drop below 1.5 bar while it rebounded to 1.8 bar.

So far so good... The interesting news is that my Benz's oil pressure gauge gradually dropped the whole time... It ended just under 2 bar by the time I decided I tested enough. I'm betting it would have kept dropping just like when I was test driving. So it appears to me I have a faulty dash gauge... or maybe something is shorting it out.

What I find as odd is that when I had the stock gauge hooked up it would fall and rise with the rpms... but always gradually falling overall. So maybe it did respond somewhat to what the sender was putting out, but has some other problem as well.

I have a spot open that I could put in an aftermarket oil pressure gauge. I might feel more comfortable with that then replacing the stock and possibly still have a wiring problem.

The only real downer is I'm now burning oil for some reason. I think this goes back to my original project where I took off the lift pump and cleaned it out. I guess something's not right there and perhaps oil is seeping in thru the fuel? But I'm not sure that would give me the same smokey results for why most people see a lot of smoke.

Thoughts overall anyone?

Bill

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'87 300SDL, intensely modified Greasecar setup, with nickle plated heat exchanger, 3 valve setup, 312,000 miles
'95 Suburban diesel, Greasecar basics, 16 plate heat exchanger, mercedes fuel lines, Racor filter
'85 Renault Alliance converted full electric vehicle

I'm not sure exactly where it is but check the ground.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

If your dash gauge pegs at 3, with engine off, something is amiss, however your mechanical gauge should level off when the engine is hot at idle, and should be a min of say 15 psi, and if it does keep dropping, then you have a problem.

70 psi cold is ok, no problems there.

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1984 Euro 300SDC, (4spd standard)
1986 Toyota Landcruiser Diesel HJ60 5spd X2

Gone but not forgotten (some sold, some stripped)
1983 300 SD, 1985 300 SD, 1983 240D, 1986 300 SDL, 1985 300 SDL, 1983 300 D, 1984 300 D, 1985 300SD, 1987 300 SDL, 1983 300 SD, 1985 300 TD Euro, 1983 380SEC, 1990 300 D, 1987 300D, 1982 300D, 1982 300D, 1994 E420, 1987 300 TD, 1987 300 D, 1984 300 D