Oil Pressure Sending Unit? - PeachParts Mercedes-Benz Forum

spinedoc2304 · #1 02-06-2013, 09:28 AM

Hello to all!

I've got a 1991 300E with approx. 213K on it and have developed an oit pressure guage problem, I think.

There is no loss of oil in the vehicle as the dipstick measures correctly when cold. There is no ticking of the valves in the morning and upon cold startup the oil pressure guage pegs at 3. She runs like a top.

Once the car is warm the guage fluctuates with the RPMs upon acceleration but stays at 0 while coasting. It even drops and raises with the transmission shifts. It'll raise to 2-3 while accelerating but drop to 0 when not accelerating

Oil pressure sending unit?

Nick

anziani · #2 02-06-2013, 12:08 PM

It is your oil pressure sending unit. Mounted next to (?) the oil filter. Next oil change should you want to replace it. ($90?)
First time it happened to me, I thought I was going to have a heart attack!
Anziani
'97 C140
'95 E420

lorainfurniture · #3 02-06-2013, 01:36 PM

I would buy a mechanical oil pressure tester at harbor freight first. Its around $20. I thought the same thing one time, and it ended up being a mechanical problem.

macdoe · #4 03-08-2013, 12:21 AM

Quote:

Originally Posted by lorainfurniture

I would buy a mechanical oil pressure tester at harbor freight first. Its around $20. I thought the same thing one time, and it ended up being a mechanical problem.

Our 88' 420 SEL is doing the same thing.... goes according to rpm. Fine when idle but when the transmission is in gear it seems to drop to 0 when glidding?
Oil level good. What mechanical problem did you have that caused these symptoms?. How was it repaired? Thanks

lorainfurniture · #5 03-08-2013, 03:03 PM

Quote:

Originally Posted by macdoe

Our 88' 420 SEL is doing the same thing.... goes according to rpm. Fine when idle but when the transmission is in gear it seems to drop to 0 when glidding?
Oil level good. What mechanical problem did you have that caused these symptoms?. How was it repaired? Thanks

The timing chain guides disintegrated and fell to the bottom of the oil pan. All was well when cold, but once the oil warmed up, it started sucking in the plastic bits and clogging the oil pump screen.
Diagnosing low oil pressure symptoms for your mercedes

Buying the $20 gauge is cheaper than throwing the part at it.

macdoe · #6 03-08-2013, 05:18 PM

Great ... We actually just did the timing chain and guides and tensioner, so I hope it is'nt that. I seem to remember the thread you gave a link to and had gathered up some parts to do the oil pump pick up job, but was exploring additional possibilities when this thread came up. The op's desciption fit so well....I was about to get a sensor, but then you placed your alternative mechanical failure issue to match his symptoms and the older link. I guess either way it will be one or the other. I have looked at the oil pan and it has a substantial dent in the bottom, which originally had me leaning towards this pump pick up as the issue. I guess it's time to drop the oil pan. and find out for sure. (hates this job)

Thanks for your post of the alternate issue and for the follow up. We are not the only car to experience this...I am now encouraged that it may not be something major like I had thought. Been procrastinating due to the fear of something very bad....(too scared to look)

I have pulled the oil cap off the valve cover to stare at the cam oiler tubes which are supplying oil at idle but cannot replicate this o pressure guage phenomenon when in gear or moving the car ...obviously... at the same time as staring into v/c. Car has been parked since driving it from Dad's house when it was noticed.

Spinedoc, could you let us know if you fixed yours with a new sensor? If not.. there is this alternative from the link Lorainfurniture posted

lorainfurniture · #7 03-08-2013, 05:33 PM

unfortunately "droping the oil pan" requires engine removal, or at least partially.

Buy the oil gauge for 20 bucks. Thats the cheapest option.

macdoe · #8 03-08-2013, 05:43 PM

Wait a minute... Lorain...I have made a mistake...you have not posted the link for the oil pump pickup repair. I am Getting my open windows mixed up. Here is the link that I was thinking about earlier to go with the additional timing chain guide failure links from Lorainfurniture.

Oil pressure fluxuation

macdoe · #9 03-08-2013, 05:49 PM

Quote:

Originally Posted by lorainfurniture

unfortunately "droping the oil pan" requires engine removal, or at least partially.

Buy the oil gauge for 20 bucks. Thats the cheapest option.

Sorry I did'nt specify. We are working on a 420 sel, which is a 4.2 litre V8. I can take off the lower oil pan. If the upper pan has to come off then like you say...the engine has to come out. That sucks you have to pull the engine on the 6 cyl.

Where did you tie in to the oil supply for a pressure guage reading? Did you need an adapter? What size adapter was it.

lorainfurniture · #10 03-08-2013, 06:18 PM

Quote:

Originally Posted by macdoe

Sorry I did'nt specify. We are working on a 420 sel, which is a 4.2 litre V8. I can take off the lower oil pan. If the upper pan has to come off then like you say...the engine has to come out. That sucks you have to pull the engine on the 6 cyl.

Where did you tie in to the oil supply for a pressure guage reading? Did you need an adapter? What size adapter was it.

sorry, i thought we where talking about the m103 6. I plugged the gauge it right where the oil pressure sensor plugged in to . The "more complete" kit that they sell at harbor freight has all the fittings needed. just unscrew the sensor and screw in the gauge

macdoe · #11 03-08-2013, 06:43 PM

Quote:

Originally Posted by lorainfurniture

sorry, i thought we where talking about the m103 6. I plugged the gauge it right where the oil pressure sensor plugged in to . The "more complete" kit that they sell at harbor freight has all the fittings needed. just unscrew the sensor and screw in the gauge

Perfect, we have a similar store up here to your Harbour Freight. I will check it out. Thanks again.