w123 200 oil presure gauge, what is normal?

[skip rat]

hi first tech question,

my oil pressure needle just lives at the top of the gauge occasionally it drops to the middle when warm and coasting,

is this a sign of leaky gauge, if so that would or something like a blocked breather

thanks

 

[Ted]

It is designed to go hard against the stop when all is ok. They all do it.

 

[grober]

More than likely you have the M102 4 CYLINDER ENGINE.
TRY THIS INFO FOR CHASSIS
https://www.startekinfo.com/StarTek/outside/12265/program/matrix6.htm
UNFORTUNATELY THAT ENGINE WAS NOT IMPORTED TO THE STATES SO YOU NEED TO LOOK AT THE ENGINE DETAIL FOR THE LATER 190
https://www.startekinfo.com/StarTek/outside/11832/?requestedDocId=11832

 

[190]

It's normal for the oil pressure to be pegged against the stop in normal driving.

When hot it should fall at idle to approx. 1 bar. If it's any higher you might consider using a thinner oil.

What viscosity oil are you using ?

 

[PobodY]

On the Nissan the oil pressure only hits the top of the gauge if you're really hammering it, and when you're cruising it's about half way; idle is maybe a quarter.

If the oil pump is driven mechanically the pressure will always go up with engine revs (and drop with them too).

As above; it might be worth considering a different viscosity oil if the pressure is always at one extreme or the other.

 

[grober]

These cars normally run on a good 10w40 semi-synthetic changed with filter at 6,000 mile intervals.

see http://bevo.mercedes-benz.com/bevolistenmain.php?language_id=1
or
http://www.opieoils.co.uk/c-657-10w40-engine-oil.aspx

 

[190]

I ran 10W40 or 5W40 in my m102 engine for over 20 years and oil pressure was always more than adequate. Definitely doesn't need anything thicker. If I still had it I would use Shell Helix Ultra 5W40 which is 229.5 and at the thinner end of the 5W40 band.

 

[hotrodder]

As said they're designed to spend most of their time hard against the stop. Whether it's a mechanical gauge on a 123 or a leccy gauge on 124s etc they're more of a low pressure early warning system than a 'proper' oil gauge i.e. better than just a oil pressure light that tells you after something has gone wrong but not something that reports accurate oil pressure all the time

Granted it's a different engine (m104) but actual oil pressures at different rpm are listed here http://www.w124performance.com/service/w124CD1/Program/Engine/104/18-0070.pdf and aren't gonna be that different to an m103 or m102 etc
This one explains how the later leccy gauge works on various models http://www.w124performance.com/service/w124CD1/Program/Engine/104/18-0090.pdf
In practice the gauge in my 320 behaves exactly the same as mechanical gauges in 123s i've owned... pegged at 3 regardless of rpm until the engine warms up and once it's properly upto temp the gauge will drop some at idle. How much it drops depends on various things... on my 215k mile 320 it'll idle at a little over over 2 on the gauge if i've just been pootling about and just under 2 after getting the thing properly hot by pounding along m/ways. I've had a low mileage s123 that'd never drop below 2.5ish despite the engine using a chunk more oil than my current 320. All them were fed a relatively basic 10w40 oil that meets/exceeds 229.1 not much point in using a more expensive oil that meets a newer spec IMO as it's just a newer spec, not necessarily 'better'. Granted with a decent full synthetic oil change intervals can be extended which offsets the cost of more spendy oil but most of the newer oil specifications are about environmental tat (not killing dpfs or cats etc) that at best doesn't apply to older engines and at worst is bad for them... older engines/classics were often designed when oil had plenty of ZDDP in it which is a great anti wear additive that's absent from modern oils as it doesn't do catalytic converters any good. Doesn't apply so much to a 123 but older engines that are known for relativley weak (premature cam and/or lifter wear) valve trains benefit from a 'classic' oil rich in ZDDP

The scale on the gauge is fairly arbitrary and owners handbooks typically say anything as low as 0.3* at hot idle is OK provided the gauge immediatly rises as soon as the rpm increases. IIRC above 1300rpm the gauge should be pegged, that's a bigger deal than what it reads at idle IMO and time to check the actual oil pressure with a real gauge to confirm the dashboard is lying due to a dodgy sender or gunged up/leaking mechanical gauge

* not a typo, that's what it states in the owners handbook for mine