How to check oil level?

[FGN59]

I apologize for raising such a trivial question: how does one determine the ‘right’ level of oil in the M130 engine?

While researching some data on 280SL cylinder heads, I came upon a set of (reproduction) stickers, in German (the meaning of which I can more or less decipher), one of which said (again more or less): ‘check oil level while engine is running’.

Until now, I’ve always checked the oil level in a car either before starting it (cold), or after letting the engine rest for a few minutes (if hot), so that the oil that’s been circulating around the engine flows back down in the pan.

First question: have I been wrong in the past (always happy to learn something)?

Second question: should the oil level when checked the Mercedes way (with engine running) reach the maximum level on the dipstick? Or should I (we) just verify that the oil level is safely above the minimum level on the dipstick when the engine is running, but not up to the maximum? Then what is the use of the maximum mark on the dipstick?

Third question, a bit less practical, almost philosophical (though not quite mystical): it doesn’t strike me as typical of the German engineering culture (for which I have immense admiration) to suggest a somewhat imprecise measurement method, which checking the (hot, therefore very fluid) oil in a running engine seems to be; so what am I missing (or mistranslating)?

I’m tempted to suggest a normalized way of checking the oil in any and all engines, but I could be making a lot of  enemies:

- the oil level in a Honda lawn mower (I have two different models, both to be treated the same way) should be measured with engine stopped, on the dipstick unscrewed from its housing, just resting on top of it
- the oil level on my ISEKI field mower (Kawasaki engine) should be checked with engine at rest, dipstick fully screwed in
- all my other cars (Audi, Toyota, Isuzu, Renault) should be checked with engine at rest
- now the Mercedes M130 way, with engine running

Why is the world so complicated? 😕🙃🤪

[mbzse]

.../... how does one determine the ‘right’ level of oil in the M130 engine?.../...

Do you not have an owners manual for your SL? I suggest you get one. All about measuring oil level is explained there.
It was published in French, even!
It is a vital documentation to read when you own a 50 yr old car.

PS. Oil level in aut gear box is measured with engine running at idle  DS.

[FGN59]

Thanks. I’ll do just that.

[MikeSimon]

I think Hans has the point here. The "while engine running" check refers to the automatic transmission, not the engine.

[FGN59]

Ok, that helps, thank you.

I was maybe a bit sarcastic in writing my original post, but this was still a genuine question for me.

I’ve just finished re-reading the reprint of the 250SL-280SL owner’s manual I purchased from MB Classic Store right after getting the car, and couldn’t find a specific procedure for checking the oil level. All it says is check the oil level frequently (doesn’t say how), use approved lubricants, change every 10.000 kms.

Now, if the sticker that got me puzzled was meant for the automatic gearbox and not the engine, that explains it.

[Benz Dr.]

I check with a cold engine - whatever that shows on the dip stick is how much oil you have available. As far as I know, the distance between full and add is one liter. On the transmission, the full and add lines are NOT one liter but more like maybe 250 ml. Always check your trans when hot with your engine running. Even a little bit low will cause shifting problems.

Another thing about engine oil: some engines will consume oil down to a certain level and then very slowly after that. This may not apply to our engines but is something to consider if you find your oil level is always a bit low after filling to the full level.
Oil is also a coolant so always check before anything more than a short drive. Low oil level will mean a hotter running engine.   

[FGN59]

Thank you Dan for taking the time to detail what may be obvious to most, but still represents a life-or-death issue for our engines.

Now, if I may take a bit more of your attention while on this subject, ever since I’ve had this car (all of 3 months) I have been wondering about the amount of oil ‘consumed’ or swallowed by the injection pump? I’ve traveled almost 2.000kms since buying the car, had the oil (and filter) changed after 1.300kms (the engine has been entirely rebuilt and had to be broken in), and I haven’t been able to detect the slightest dip in the oil level, either before or since the oil change?

[Cees Klumper]

On a '69 280, unless I am mistaken, there should be no dipstick or separate oil reservoir on the FI pump, it gets its lubrication from the engine?

[FGN59]

Indeed, the FIP has a small oil feed from the engine for internal lubrication, but then (unless I am mistaken), this oil is sent into the fuel flow to the injectors to be burned in the cylinders (there is no oil line from the FIP back into the engine for the oil). Hence my question: what is the ‘consumption’ of oil due to the FIP? It must be very small, but is it a matter for attention, or even noticeable?

[Cees Klumper]

I believe no oil gets burned in the pump, the line is there to ensure the pump has enough for itself. Although I suppose that if the pump would be really worn, maybe some oil could get past the plungers? It's a good question, don't recall it having been discussed before.

[Pawel66]

Indeed, the FIP has a small oil feed from the engine for internal lubrication, but then (unless I am mistaken), this oil is sent into the fuel flow to the injectors to be burned in the cylinders (there is no oil line from the FIP back into the engine for the oil). Hence my question: what is the ‘consumption’ of oil due to the FIP? It must be very small, but is it a matter for attention, or even noticeable?

If you are asking about noticeable "normal" or "scheduled" oil consumption by the FIP (Fuel Injection Pump) as oil goes to fuel - I do not think so (I am not a mechanic, but have not heard about it anywhere). There is a fuel chamber in the FIP up there under the area where fuel lines are attached. It is sealed from the oil area. One oil area is under the fuel chamber and we have there cam shaft and the plunger system, the other oil area is in the governor of the pump, which is the back of the pump. If oil gets from pump to fuel (or vice-versa) I suppose it is the result of the wear out and needs to be addressed if excessive.

To your question on how oil gets out of the pump, please follow this link: https://www.sl113.org/wiki/Fuel/Injection

It is explained on the third picture from the top. Oil goes through the shown opening back to engine.

I think exploring out Technical Manual is very useful - it contains a lot of information on how our cars are built and how they operate.

Have you observed an issue with engine oil level going up or down in your car? There may be some natural consumption, but not a lot. If too much oil is lost - you either see leaks or blue smoke at the tail pipe. if you have more and more oil in the engine - you may have too rich mixture for instance. Too rich mixture, I think, happens fairly often...

[FGN59]

Thank you Pawel for pointing me in the right direction again.

I read the section of the Technical Manual on the FIP early after joining the group, and must have misunderstood something. It is clearly said that in the later FIP with forced oil circulation there is a return channel for the oil to flow back to the engine oil pan.

So no oil consumption on account of the FIP.

And no, luckily, my car doesn’t consume any oil for the moment. The engine has been completely rebuilt by the PO (he didn’t do it himself, it was done by a small specialist shop near Paris), and seems more than fine. I bought the car in Paris last year and drove down to Provence on small country roads (800kms during the fall, a great experience) with no issues except cold starts. I was able (it took a while) to fix that cold start issue thanks to all the information in this forum. Next week the engine will get a complete tuneup by a specialist near Avignon (I live in the south of France) after being broken in since the renovation. Looking forward to spring soon!

[Pawel66]

Know what?

In the area where you live, I would not mind being stranded in a broken car and wait by the side of the road - I would have time to admire the landscape for some time....

 

[FGN59]

Always happy to share the view. But not necessary to get stranded, you can also enjoy it seated with a glass in hand 😊