'85 300cd oil pressure - PeachParts Mercedes-Benz Forum

underp2 · #1 04-15-2004, 09:15 PM

I finally got the '85 300CD to start, but there is no oil pressure. It hadn't run in months when I got it. New starter, battery charging, fuel filter(s), vacuum line repair, oil drain & change, new primer pump, diesel kleen, etc. I have read through the many posts about oil pressure on the forum, but still have questions.

1. How long is reasonable to wait for pressure to build (oil was thouroughly drained- about 1 week between drain & refill)?
2. Some posts concern the pressure relief valve. This does not sound like an easy fix-is it? Please keep in mind that before sinking more money into this car it must run OK & be somewhat roadworthy.
3. The oil pan (lower) is stove in pretty badly. I think this could only affect leaks and oil capacity (which I understand is important, & I plan to replace the pan).

Thanks (still only 279k on it until we can cover some ground- not putting on many miles on the jackstands & ramps).

kerry · #2 04-15-2004, 09:28 PM

If the oil pan is stove in, it seems possible that the oil pick up is damaged. Are you sure it is not a gauge problem? Can you see oil on the cam thru the oil fill hole. Don't run it for more than a second or two to see if oil is flowing.
If you loosen the nuts on the oil filter housing cap, oil should pump out there right away.

underp2 · #3 04-15-2004, 10:15 PM

Is the pickup tube metal? plastic? other?

I am not sure if it is a guage problem, but I don't think so. The only way it could be guage related is if I haven't let it run long enough to build pressure. This is painful to do as you stare at an oil pressure guage that reads zero.

There is no oil on the cam, but I haven't tried looking through the fill hole while it is running. I also haven't tried loosening the filter bolts to see if there is pressure there. I'm not sure if these are possible at this point - it requires some accelerator pressure to keep running.

The oil filter & valve cover checks sound easy enough once I get someone over to help me out. This will keep me busy this weekend (so many projects, so little time).

Stevo · #4 04-15-2004, 11:09 PM

Not sure about the 617 oil pump but the o/p on the 616 (240D) comes "down " easy after you drop the lower pan. I would pull it and set it in a pan of oil and see if it pumps turning it by hand. A new one for my 240d was a little over $100.00. pumps usually last the life of the car but like Kerry said, it coulda got damaged.

underp2 · #5 04-19-2004, 09:43 AM

I am now in the market for an oil pump. I am not interested in fastlane's prices (over $300.).
Steveo- where did you get yours for $100? Or is that because the 240D has a different pump than the 300CD?

Stevo · #6 04-19-2004, 06:55 PM

"Steveo- where did you get yours for $100? Or is that because the 240D has a different pump than the 300CD"

Your o/p may just be more expensave than the 616 one. I get parts through a friend with a shop but usually Phils or Rustys prices are not that much more. Like I said you should be able to see if it pumps when you pull it before you spend your $.

adamb · #7 04-19-2004, 09:05 PM

The 240 pump is definitely a lot different and won't work on a 300. You could get a used pump, but I would first take the bottom pan off, replace with a new pan ( I think they are about 24 bucks) and check the condition of the pick-up and pump.
Good luck,
Adam Bush

underp2 · #8 04-23-2004, 08:35 AM

The pan has been removed. The pickup looks OK, but the pump is in horrible shape. I would be glad to get hold of a used one, or a rebuild (if available).
I haven't been able to find a used one on the internet (yet), I guess I will post in the parts forum. That is unless anyone would like to sell one from your parts car

I could sure use it if the price is right.

Rick Miley · #9 04-23-2004, 10:42 AM

http://www.silverstarrecycling.com

http://www.pgauto.com

underp2 · #10 07-29-2004, 02:41 PM

Actually the pump was OK, but it was the pickup that was smashed. I didn't realize this until the used oil pump arrived & I could see what it was supposed to look like (intact). Now the pressure pegs on startup, and levels off. Unfortunately, after ~ 10 minutes or more, the pressure goes to zero. This has me baffled. The pressure goes back up if I restart, but doesn't sound too good.any ideas on this?

Stevo · #11 07-29-2004, 07:58 PM

If the pick up portion of the pump was damaged, I would suspect the main part is damaged also. Did you pull it and see if it pumps when in a pan of oil?

underp2 · #12 07-30-2004, 10:05 AM

No I didn't pull it to test. The pickup easisly unbolted from the pump, so I just did a swap. The used pump looked identical to the pump underneath. No damage to the pump was visible. Any ideas on why I would have oil pressure for 10 minutes, then none? This makes me think that the pump works OK if it can maintain pressure for that long. I am also suspecting the pressure relief valve may get stuck open & rob me of valuable oil pressure. Any thoughts on this? Thanks.

reddog · #13 07-30-2004, 11:09 AM

My 82 sd did the same thing. Full pressure on start up, and gradually coming back to zero. It was the pressure sending unit, diaphram had a hole in it. Right before I replaced it, it started to leak out the vent hole.

underp2 · #14 09-24-2004, 11:00 AM

Quote:

Originally Posted by reddog

My 82 sd did the same thing. Full pressure on start up, and gradually coming back to zero. It was the pressure sending unit, diaphram had a hole in it. Right before I replaced it, it started to leak out the vent hole.

Where is the pressure sending unit located? When it develops a leak, are you actually losing oil pressure, or does teh guage just 'read' less pressure?

franklyspeaking · #15 09-24-2004, 01:59 PM

300D's don't have sending units; they have an oil pressure line to the gauge. SD's are electronic with sending units.

My guess would be your oil pump maybe giving up the ghost after it heats up....maybe slightly bent and locks up when the impeller heats up? Does the pressure return after restarting hot...or do you have wait until it cools off? Changing out the pump maybe a smart move?

Good luck!