How do I determine if oil level sender is bad? 87 300E

[dirtysocks]

yesterday I checked my oil and it seemed pretty low, below the red plastic min marker. I usually check it frequently, but I neglected to for a week or so, assuming that my low oil light would come on. Well, it never did. Is there a way to check if the sender is faulty? (multimeter or something?) I know the light itself works, b/c it comes on when I turn the key to position 2.

I already did a search on this, and surprisingly I could not find anything.

Thanks for your time.

[theairboy]

Yes it is just a switch controled by a float.

Remove wire plug and test for continuity. Oil level full should be open loop or very high ohm reading on the tester and low oil level or removed from pan and rite side up should show moderate ohm reading.

Yes, that would be a valid test, or simply turn on the key the next time you have the oil drained at oil change time and see if the light comes on. I guess it goes without saying that you should not turn the key to the start position, only to the ON position.

Good luck,

[nhdoc]

When I removed my level sensor to replace the gasket that was leaky I was surprised at how low the oil would have to go before it would "trip". Mine is an E300 diesel which holds almost 9 quarts of oil. When full, the oil level is about a pint above the sensor's mount (in other words, about a pint spills out when you remove the sensor. Then, it would appear that the level would have to drop at least another inch before the float would move and maybe another half inch to inch before the level sensor would trip. I would say that means on my car the oil would have to be down about 2-3 quarts from full or 1-2 below add on the dipstick before the level sensor would trip. I don't think that MB designed the level sensor in order to let you know when to add oil necessarily, but when the level is so critically low that you MUST attend to it. Apparently the diesels will shut down when the low oil level sensor trips. I don't know if that's true of the gas models but you wouldn't want it to do that if you were simply a quart low, I wouldn't think.

Today's modern cars without dipsticks would have a more refined electronic level sensor that actually tells you to add oil when it is just low...but the older warning systems seem to be just to prevent catastrophic damage...like the "belt and suspenders" approach.

[Ferdman]

dirtysocks, AFAIK and as mentioned by others the oil level needs to be dangerously low for the low oil level sensor to light. It certainly won't light if the engine is only a quart or so low. Larry Bible makes an excellent suggestion for testing that the level sensor is functioning. If you use an oil/liquid extractor when changing your oil you might check the function of the level sensor as you suction out 1 quart, 2 quarts, etc. so that you know at what specific level the sensor energizes the trouble light on the dash. Too bad this thread wasn't posted before late yesterday or I would have verified the sensor function when I changed the oil in our 1991 300CE the day before.

[richard28]

Thanks Marty for mentioning this part has a gasket which can leak. Yesterday. I noticed wet oil around the oil sender. Could someone post or describe removal instructions for a w124 ( 88 300ce). Thanks.

[nhdoc]

I was actually surprised to find the sender switch to be mounted below the oil level making the gasket critical to prevent leaks. I figured they would mount it above the oil level and let it dangle and therefore the seal would be much less critical only stopping splashed oil from escaping.

In my case the gasket was shot, but I have heard that sometimes the switch itself leaks. You should be able to tell if it is coming around the edge or from the center. On my car it was an easy fix...two bolts hold the switch to the side of the engine and the rubber seal is on the back. I replaced the gasket and put some sealer around the outside for extra measure too but I could see the defect in the gasket when I removed it.

[STORMINORMAN]

...if this is the same situation with the oil level sender on a 1991 420SEL?

My indy was saying he needed to drop the oil pan to replace the sender or the gasket (seal)?

Am I getting hosed?

Thanks in advance for any and all advice!

Cheers!

[STORMINORMAN]

...and it is now "Time to Fish or Cut Bait"! It's oil change time!


Before I go spending $200+ to have the oil level sender replaced at the indy I still have two or three questions:

1. I've seen the oil level sending unit (sensor?) described as a "$17 part" and as a "crazy expen$ive $130+" part, and as a $70 part: which is it ? Also, do they really leak through the electrical connection vs. around the O-ring?

2. Is removing the lower pan on a 420SEL swapping out the sensor (or just the O-ring) really that big of a deal? Gasket (P/N?) costs what?

3. How much oil is too much oil to be leaking from this puppy? I've added approximately 1/2 quart of Amsoil AME in 10K miles: am I just being just too anal-retentive? The light ONLY comes on when the oil is drained from the pan, so I believe the sensor is working as designed?

Thanks in advance for any and all replies!

Cheers!

[robert_stoever@]

Lets clarify something - on a prevoius post "When full, the oil level is about a pint above the sensor's mount (in other words, about a pint spills out when you remove the sensor. Then, it would appear that the level would have to drop at least another inch before the float would move and maybe another half inch to inch before the level sensor would trip. I would say that means on my car the oil would have to be down about 2-3 quarts from full or 1-2 below add on the dipstick before the level sensor would trip.".This oil is measured with engine off.
When the engine is running, the high flow pump has a couple of quarts circulating through the engine and the "static oil level" drops to a "Running oil level" condition.This is a testament to the MB engineers thinking: Design the oil sensor so it signals with 1 quart low with engine running and doesn't give false signals turning corners or during accel or stoping.
If the sensor was placed above this level it would flash at all times the engine is running OR when you turned a corner.
So if you think the oil sender is too low, consider all the thought which went into its placemtne to give an accurate signal at running condition without false signals.
RobEngineer

[STORMINORMAN]

Will some more experience & qualified (not a negative reference to RobEngineer!) MB W126 owners/mechanics PLEASE respond to my specific inquiry re: "am I just being just too anal-retentive?"???

I really am torn with the concept since make-up oil is really rather cheap when you just throw in a partial quart in a 10K interval, but if it something I really ought to repair then I want to do it.

Thanks!