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  #1  
Old 04-04-2002, 10:23 AM
pmizell's Avatar
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Low oil pressure ....

Hello everyone:

My M103 with 20w/50 dino oil drops just below 1 bar after running for awhile. This is with car in D at a stop light. In N, it will raise to about 1 1/2 bars.

Does this seem low with this high of viscosity oil? What other factors affect oil pressure besides oil viscosity?

Thanks for any insight on the matter.

~Paul

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  #2  
Old 04-04-2002, 12:24 PM
Jackd
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208K miles certainly has an effect on oil pressure.
Tired oil pump, increased clearance on crankshaft/camshaft journals from wear amongst other things could have an negative effect on oil pressure.
If oil pressure goes over 2bars at running speed, I would not woorry too much.
jackD
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  #3  
Old 04-04-2002, 12:50 PM
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Thank you Jack

The needle immediately pins at 3 upon acceleration so I guess everything's OK. I can only imagine how low my oil pressure would be with low viscosity synthetic

Thanks for the response!

~Paul

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  #4  
Old 04-04-2002, 10:45 PM
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Paul,
You may actually be impressed with a pressure RISE with the right synthetic. My oil pressure has ALWAYS gone down to as low as 0.5 bar in drive, at idle, in hot weather (and I got the car at 25,000 miles and it did it back then). As you know from your owner's manual, anything above 0.3 bar at idle (at least for my car) is considered OK by MB.

Since I switched to Mobil 1 15W-50, it never drops below 1 bar. Even when I use 5W-30 Mobil 1 in the winter, the pressure stays above 1 bar (but of course the ambient temp is lower then too).

Try it, you'll like it!
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'93 400E
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  #5  
Old 04-05-2002, 01:05 AM
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Paul:

While your car has a 124 body and mine a 126, they both have M103 motors. I see 1 bar at idle fully warmed up using either dino 10W-40 or 20W-50. Also see 3 bar as soon as it gets to about 1500 rpm.
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  #6  
Old 04-05-2002, 01:47 AM
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Thanks all for the replies...

I guess it's time to switch to synthetic then since my engine is finally sealed tight. Apparently, contrary to what I thought, oil viscosity doesn't play a major role in affecting oil pressure .. so it's time to do some experimenting.

Thanks again!

~Paul

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  #7  
Old 04-05-2002, 02:07 AM
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oil viscosity does affect oil pressure.

in the winter, my (M103) engine temp is always low, and the oil pressure is always high at idle, because the oil is more viscous when cold. In the summer, the engine temp is higher (brings on the fan) and the oil pressure drops at idle, because it becomes less viscous; however the pressure is still above 1bar.

synthetic oil is more resistant to viscosity change with temperature than dino oil, and that's one of the things it buys you (it is also more resistant to oil breakdown)
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Old 04-05-2002, 08:29 AM
Matt Crooke
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My 190 always sits at between 2&3 bar on tickover, and goes straight to 3 on acceleration. A while back, it started to drop to 1 on tickover once it was warmed up. It turns out that when the car was last serviced, the idiot who serviced it (the previous owner!) had done the oil filter up with a pair of grips...hence it was pretty crushed. Over time where the paint had cracked off the filter it had rusted....and eventually split...causing the leak, which made the pressure drop.
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  #9  
Old 04-10-2002, 06:15 AM
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OIl Pressure 89 420 SEL

I've read numerous posts on appropriate oil pressure and they seem to conflict. Whats the bottom line? My 420 with 104k seems to indicate about .3 on the gauge. Is this ok? If not, what should I check? Sorry if these are newbie questions, but this is my first (not last) Benz.
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Old 04-10-2002, 08:09 AM
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spwilliams,
I know someone else will probably have a different opinion but I would suspect it's probably normal as long as the pressure rises promptly when you hit the throttle. At least that's what my owner's manual says -- this might be covered in yours, too.

It is very unlikely to represent something serious like bad bearings since the "bottom end" of MB engines are incredibly robust (assuming oil has been changed at appropriate intervals).
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  #11  
Old 04-10-2002, 06:20 PM
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Talking oil pressure

Hi guys ! This is cristi from romania , owner of a '77 w123 240D with 135000km.....
back here i'm using 20w50 pennzoil gt performance plus , mineral oil at 2,5$/l , and my pressure gauge stays at 3 no matter what ...I would consider my engine "tired" if it drops under 2 .
Still , even if it was already discussed , how do you measure oil level , engine cold or warm ?
Thanks all...
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  #12  
Old 04-10-2002, 06:26 PM
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I think the MB spec is 'no less than .7 bar' at idle. Typical is 1.25 to 1.75 bar at idle. Personally, I would not like to see it less that 1 bar.
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  #13  
Old 04-10-2002, 06:37 PM
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I have the m103 engine too and I have a lot of miles on it. Other than switching out the oil pump, I would reccomend changing to 20w50 oil as well as adding a quart of synthetic just to protect the engine at hot temperatures. I just changed the oil on my 300e with the topsider and added the Mobil 1 205 oil filter to some 20w50 mixed w/ Mobil 1 10w30 and my oil pressure stays at 2.5 at idle warmed up and then after intense driving of half an hour it'll drop down to 1.5. If you see it is dropping too low change the oil, I like Chevron 20w50 because I buy it from Costco for 11.xx for a 12pack. Don't be cheap, use a Mobil 1 Filter and you will be happy.

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  #14  
Old 04-10-2002, 08:59 PM
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As Micael LaFleur says:

"I think the MB spec is 'no less than .7 bar' at idle. Typical is 1.25 to 1.75 bar at idle. Personally, I would not like to see it less that 1 bar."



Michael,

Not to put too fine a point on it but I think it really depends on the engine, ambient temp, and choice of oil. My owner's manual says:

"The oil pressure at idle speed may drop to 4.4 psi (0.3 bar) if the engine is at operating temperature. This will not jeopardize its operational reliability.

Pressure must, however, rise immediately upon acceleration."

Mine always used to run pressures around 0.5 bar in summer in stop and go traffic (before I switched to Mobil 1), and I got the car with only 25,000 miles on the clock so I'm pretty sure it was in good mechanical condition then, and now, for that matter.

I think one of the reasons the engineers removed the oil pressure gauge in newer models was to prevent us obsessive types (and I include myself in that group) from getting too hung up on numbers . . .

Cristi-mic,
My manual says to check oil level 5 minutes after shutting down the engine, which implies it should be checked warm. In general, the ideal level is halfway between the two marks. If it's on the high side, my engine (at least) will tend to somehow use it up until it hits midpoint and then stay there. If I just fill it to the halfway mark from the getgo, it'll stay there for the entire oil change interval.
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  #15  
Old 04-10-2002, 09:26 PM
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OIl Pressure 89 420 SEL

After my post, I reread the owners manual (duhhhh ) and found the passage that Steve Wendel quotes. However, my oil presure does not rise dramatically when I accelerate.

My gut feeling is that everything is fine, because otherwise the engine runs like a top, and the rest of the car is really cherry. I am concerned that I am missing something here.

The point about oil level at halfway is similar to mine as well. I was concerned that it was using oil, but it seems stuck at halfway.

Thanks to everyone for their posts. This forum is really a terrific resource for a new W126 owner like me.

S
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