Oil Pressure at idle Inconsistent 500E

[Deebo]

Have noticed this for a while now but paid close attention on a long drive through the mountains this morning.
500E serviced recently with genuine 229.1 10w40 13x,000 kms

In the course of the same 4 hour drive oil pressure at 600 rpm idle varied widely and would like to get an idea what others have experienced to be normal--

When stopping at a red light pressure would at times sit just below 2 bar , 1.4 bar at another point and got down to just under 1 bar at one point after a good run through the hills.- Always @3 bar and above when under load.

I'm aware the FSM says as long as its not 0 bar that 1-3 bar is considered normal but in comparing to my E320 which is super consistent wanted to get some insight from other's experience .

 

[gsxr]

Pressure at idle will vary based on oil temp, which can be vastly different than coolant temp. What you describe sound normal, although just under 1 bar after running for the hills is a bit lower than I'd prefer.

Has the oil pressure sending unit ever been replaced? These are mechanical units and tend to get weak, and read lower than actual pressure, when they get old. A new sending unit may show higher pressures, especially at hot idle. Make sure to only buy Genuine MB / OE dealer sending unit, almost all the aftermarket ones now are SuperChina and you do not want one of those.

 

[gerryvz]

Agree, what you are describing is 100% normal. Even a needle at or just under 1 bar at idle is OK, with a hot engine at idle. The needle should ALWAYS be pegged at 3 when underway, especially at say 1,200 RPM or higher. It will increase from idle up to 3 when you begin to step on the gas.

Oil pressure senders can get lazy over the years, so it’s not a bad idea to replace it at some point. Easy DIY job, with a HOW-TO here on the forum. Not a super expensive part, but get a quality part, not a cheap Chinese one.

Thread 'HOW-TO: Replacing M119 oil pressure sensor'

Jun 1, 2013

The oil pressure switch** sensor on the M119, thankfully, is a rather easy job to replace.

Symptoms of a failing oil pressure sensor are low or no pressure indicated on the gauge (below 0.5-0.75 bar when the engine oil is hot); not jumping to the 3-bar mark when the gas pedal is pressed, and other types of lazy oil pressure behavior. Do note that it is POTENTIALLY possible for the oil pressure gauge or wiring to be defective (electrical fault), so this should thoroughly be checked out before diagnosing the oil pressure switch as the culprit for poor oil pressure behavior.

Also note...

• gerryvz
• Replies: 19
• Forum: "HOW-TO" Tutorial Articles

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[Deebo]

Thanks very much for the insight Gerry and Dave, definitely had the oil properly hot when it was reading under 1 Bar@ idle
It looks to be the factory sender in place and I have a steadfast rule of only Genuine parts where still available- would never dream of replacing any part on this car with a chineseium replacement

I will order a replacement just to have for my spares pile- A0065429417 *C49 though still available to order* and also think i will drop the sump cover and give the pickup a bath in brake cleaner for good measure.

 

[gerryvz]

You shouldn’t need to do anything with the pickup in the oil pan. But if you do, order a new rubber boot and wire screen. And the two new o-rings for the oil level sender and reseal it. Those are “while you’re in there” jobs with very low parts costs, but good preventative maintenance.

The oil level sender in particular will leak sooner or later. Replacing the two o-rings just makes sense.

Thread 'HOW-TO: Replacing M119 Oil Level Sensor'

May 25, 2015

Introduction & Background

The culprit for a fairly common motor oil leak on M119s with more than 100K on the clock can often be the oil level sensor. (Note that this is very different from the oil pressure sender, which is located nearby. A HOW-TO on replacing the oil pressure sender is located here).

The function of the oil level sender is to indicate whether the level of motor oil in the lower oilpan is too low, and thereby opening an electrical circuit that results in a lamp on the dashboard of the car being illuminated. The electrical circuit status is...

• gerryvz
• Replies: 50
• Forum: "HOW-TO" Tutorial Articles

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[Deebo]

Good call ! Definitely will change those whilst i'm there - Cheers!

 

[TerryA]

@Deebo,
I hope you have tiny hands to change the O-Rings on the “Oil Level Sender”. I did this job and found it a real PITA. Long skinny fingers would be a real plus due to limited access.

 

[emerydc8]

There is a retaining clip for the oil level sender and I was able to install it easily with this long-reach plier from Harbor Freight. It allows you to pre-position the clip on the pliers and install it on the sender tip from below. The clip goes on the outside of the sump. The pliers made that step much easier than trying to install with fingers alone.

Post in thread 'Heater Hoses both drivers and pasangers sides'

Jul 22, 2026

What Dave said. I removed the firewall plastic but I didn’t have to remove the throttle linkage. Harbor Freight makes a 16” long-reach hose plier but sometimes they are hard to find in their catalogue. The last one I bought in the last year came in a set with two other long-reach pliers. Looking at their catalogue now I see the 11” but not 16”.

https://www.harborfreight.com/3-piece-long-reach-hose-grip-pliers-37909.html

• emerydc8

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