Hi all!

Quick question (and hoping for a quick answer and a peace of mind):

I checked my oil level yesterday and to my shock, it was just on the red MIN mark. I mean it was barely on it. What prompted me to check was the oil indicator light (yellow)that went on while I was driving. My oil pressure gauge behaved normally when this happened--3 when moving and 1.5-2 at idle or a stop. Should I worry about that I was driving my car while the oil level was on the MIN mark? Or the fact that my oil pressure gauge gave me a positive pressure reading is reason enough that I should NOT worry? Car is a 1990 190E. Thanks!

Oh, one more question. The place that I get my oil changed does this to my car while (or after) oil is being poured into my engine: The mechanic revs my engine; he says that is to create a vacuum for the oil filter or something. Hmmm, I think he also said it is to see if there are any leaks coming from the oil filter. Is this a normal procedure?

You should be able to go down to the "minimum" mark without the risk of engine damage, although it is better to keep it near "full". You will have a greater safety margin that way. Checking ones fluids is a good thing to be a little compulsive about. Once a week should be the minimum. More often if your car consumes oil or fluids. Make sure it is level; even a slight tilt or incline can make a significant difference in the reading on the dipstick. Can't think of any particular reason to high rev an engine after changing the oil. The "vacumn in the oil filter" sounds like BS. I suppose revving it to a fast idle might bring the pressure up a little and help check for leaks, although if it has a leak it should show up at idle speed also.

There is no way that there can be vacuum in an oil filter. The oil is PRESSURED into the filter.

Good luck,

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Larry Bible
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles

I would start getting my oil changed somewhere else if the guy is running your engine while pouring oil in. Like Larry said there is no vacuum, oil is pressured through the filter. You should be fine if you drove and your oil was at the min. level. This thing to learn from this is to check your oil more frequently, like everytime you fill up, or every Saturday morning. Also, long hard trips can burn condensation and contaminents from your oil and that will lower your level. So check it after long trips or hard driving where the engine was hotter than usual. I always keep a full gallon of oil in the trunk in case I ever need it. 7 bucks is cheap insurance.

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Jason Priest
1986 420SEL

My understanding of oil, in any engine:

PRESSURE forms the hydraulic wedge on "plain bearing" surfaces, such as crankhafts. This prevents metal-to-metal contact. These bearings need very little pressure to keep the metal pieces apart. Too little, like "0" on the gauge, will produce the dreaded metal-to-metal contact and damage in a very short time.

That's why cars have an oil pressure warning device, either a gauge or a light that comes on when the pressure gets too low.

Oil pressure also pushes oil through the filter and then it circulates through the engine, picking up heat on contact from the internal parts. [Some diesels engines spray oil under the pistons to add to the cooling effect.] So, oil also COOLS the engine. Newer BMW motorycles look air cooled but are mostly cooled internally by oil flow and oil coolers.

Oil LEVEL measures oil VOLUME. Too little oil means there is a smaller volume to remove the same amount of heat, which means hotter oil temperatures and quicker oil breakdown, which means even less oil, and so on in a "death spiral." Severely overheated oil gets very thick and sludgy, and sludge doesn't pump well or make good hydraulic bearings (see above.)

This oil breakdown takes time, which is why [most]cars don't have an oil level warning device, but a manual dipstick. It's also why the oil is changed at time/distance intervals.

Add too much oil and it goes squirting in places you'd rather it didn't. 'Way-way-way too much' and you could put the engine into hydraulic lock, I guess...

Oil level just needs to be between MIN and MAX. Don't panic! Check it at reasonable intervals and add a quart when it will fit. That's why the Min and MAX marks are about a quart [litre?] apart

BCingU, Jim


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'96 E300D 60k mi (wife's daily ride)
'95 Audi 90 120k mi
'92 GMC Suburban 139k mi
'85 300SD 234k mi (my daily ride)

I would definately not rev an engine above idle until the oil pressure comes up. After an oil change, this could be a couple of seconds, depending on how long it takes to fill the filter and oil gallery, etc. After that reving the motor does nothing except attract attention

From my days of flying piston aircraft, when starting an engine, the ONLY gauge you looked at was the oil pressure. If it didn't come up within a couple seconds, you shutdown, no questions.