Oil pressure on new Benzes - WGB?

[s class]

Where is WGB these days?

A bloke here in the South African club who has numerous benzes, was complaining that his R129's oil pressure does not peg at 3 bar on hot idle. 

He claims he does get a 3 bar hot idle on his W126 560SEL and W116 350SE. 

Surely this is not right?

What did these cars do when new?

[TJ 450]

The 500SEC I once had would sit a 2 1/2 bar at 500RPM hot idle... they are electronic though and it was likely faulty.

I can't believe the claim of 3 bar on the 116 though. That's too high... FWIW, we have had Benzes in the family for years and I was always told what sort of pressures should be seen on the gauge.

I await WGB's response.

Tim

[wbrian63]

If he's seeing 3 bar at hot idle, I'd suspect he's also seeing 3 bar with the engine off (aka, the gauge is stuffed.)

3 bar is 42+ psi. I can't think of a single engine that would produce that kind of pressure at hot idle.

For the W116 M100, and the W140 M110 engine, "normal" hot idle is somewhere around 1 bar, maybe a little more, possibly a little less. I know at least on the M110, the hot idle pressure is greatly affected by the type of oil run. Running 20W-50 for our semi-tropical Houston heat is de-rigeur, and you'll see 1 bar at hot idle with outside temps around 100f. Hot idle pressure will be 1.5 bar in cooler temps. Using any oil thinner than 20W-50 will result in sub-1-bar pressures at hot idle.

I've not had a chance to verify the M100 #'s, but the values I quote are what I remember from the service manuals I have.

The gauge on M100's is a manual gauge. The gauge on a M110 is electric, so there's a sender that can cause issues. The R129 will also be an electric affair.

[s class]

The W140 engine you are referring to is surely not an M110.  M110 is the twincam six as in W116, 107, 126 etc. 

My M110 definately has a proper hydraulic pressure gauge.

When we rebuilt the engine nearly 250 000km ago, we just polished up the crank and fitted standard size bearings.  As a result, the bearing clearances were at the upper limit of what is acceptable, and oil pressure on hot idle a little lower than it might otherwise be. 

Over 250 000km it hasn't got any worse : 1.5 bar on hot idle in cold weather, 1.1 bar on hot idle in hot weather.  This is on 10W40.  On really hot days, if the A/C is on, and stuck in traffic, and coolant temp gets to 90 deg C, the oil pressure on my car can drop to 0.9 bar when idling in "D". 

[TJ 450]

I'm using a 10W40 in the 6.9. It will see a low of 1 bar at 500rpm idle after a long drive on a hot day. This seems typical for a well used car. FWIW, the only thing that changed when I switched from the 20W50 was the time it took for the gauge to peg itself at startup... it's much quicker.

Tim

[s class]

I would think that pegging quicker is a good thing. 

[wbrian63]

"The W140 engine you are referring to is surely not an M110.  M110 is the twincam six as in W116, 107, 126 etc.  "

Yes it is. 3.2L inline DOHC 6. 1992 300SE, aka S320. In the 116 car's it was 2.8L in displacement. In the 107, I think the same. In the 126 it was 3.0L displacement, generating (I think) about 175hp.

For the W140 300SE, they upped the displacement to 3.2L and added VVT to the intake camshaft. HP and Torque were identical at 228. "A little-bitty motor in a great-big car." (They actually offered a 2.8L variant of the W140 in Europe...).

My 5.5L W220 (S55 AMG) averages 18-19mpg in mixed driving around town. The W140 that was replaced by the AMG struggled to get 16 around town. Loaded down on the highway at 70mph, 18-20 was average. The S55 gets 22+ on a pretty consistent basis.

While the wonder of 6.9L motors in big MB sedans cannot be underrated, nor the unadulterated joy of the 355hp AMG mill in my daily driver, we must remember that early MB's had the focus of stability and durability - not high performance (at least in the stop-light-to-stoplight wars). Most hotrod American sedans of the 70's could out accelerate virtually all MB's of that same era. However, as speeds approached the century mark, the American iron was tapering off (and becoming quite a handful to control), while the MB was just settling in for a nice cruise. "You might out-run me to 60, but I'll pass you at 110..."

[Big_Richard]

Yes it is. 3.2L inline DOHC 6. 1992 300SE, aka S320. In the 116 car's it was 2.8L in displacement. In the 107, I think the same. In the 126 it was 3.0L displacement, generating (I think) about 175hp.

EARLY 6 cylinder w126, 2.8 litre M110
LATE 6 cylinder w126: M103
6 cylinder w140's M104

[TJ 450]

MT 6.9 has posted the facts.

Tim

[flutes]

Is there some arcane sort of naming convention going on with MB engines?  It always seems pretty arbitrary...

[TJ 450]

You raise an interesting point there Flutes. They certainly do seem to do as they please in that way.

Tim

[wbrian63]

TJ - you are completely right - I stand corrected. It was indeed an M104 motor...