Low Oil Pressure M117

[hs500]

Good Morning Gents,

I am Timo, based in Germany and have just recently purchased a 450 SEL (US-Version). The car is in pretty good shape, lots of money has been invested by the PO. Part of the restoration process was an overhaul of the engine after which the car has just run roughly 10 k miles. Total mileage 100 k miles.

Anyway, we did an oil change after handing over the car. I was observing later that the oil pressure during idle (around 700 rpm) is dropping to roughly 0,5 bar (7 psi). Also during drive at 80 km/h or 50 mph the oil pressure is around 2 bar (30 psi)...so definitely not what you would expect from an overhauled engine, even though the manual gives 0.3 bar as lower limit.

Does anybody of you have any usual suspects in mind? Have checked the overpressure valve already, but there's no blockage and it moves freely (Maybe the spring has weakened?). Are there any other parts/devices in the engine that usually have a high oil consumption and might be suspicious? Chain tensioner? I am kind of confident that there's no main bearing/rod bearing issue as the engine was overhauled in a professional shop...but you never know.

I have already replaced the US (psi) gauge vs. a European (bar) gauge. Unfortunately no change in behavior.

Looking fwd to your experience.

Cheers,
hs500

[ramiro]

Hello,
What oil did you use ?
Normaly i only see below 1 bar on my cars when the engine is really really hot after stressing it , but they all have over 200k km  so so if you don't have super thin oil i would say something went wrong with the engine overhaul and i would speak with the one that overhauled the engine.

Did you really overhaul an us m117 to us spec in germany , i wouldve just gotten a used euro engine , normally the bottom end of the m117 is very durable ?

Ramiro

[UTn_boy]

During the overhaul, was the oil pump renewed? If not, then what was the point of a complete overhaul? And why was an M-117 overhauled at 90,000-100,000 miles?  That's a huge red flag.  Granted, it's not unusual to have to remove the cylinder heads to perform a valve job at 60,000-80,000 mile intervals.  If well taken care of, or even with slightly less care, the bottom ends tend to have a life span of 300,000-400,000 miles.  Did the previous owner give a reason as to why the whole engine had to be rebuilt?

[daantjie]

The gauge must peg hard to the max when you apply throttle coming off stationary and idling. 

Low pressure when idling and especially with thinner oil and after hard running is perfectly good but again the gauge must peg instantly when you pull off so something is for sure amiss.

[hs500]

Hi all,

many thanks for your replies. Good question why the engine was overhauled at that low mileage indeed. Looking at all the bills of the works that were carried out, the PO did not have a money problem and might wanted the car in a perfect condition. It appears the overhaul of the engine has been carried out based on the US specs as the PO did want to keep the car original (unfortunately).

We've put in 20W50 oil; in one of the restauration bills, it also states that the oil pump was replaced.

The engine is running pretty smoothly, so I am not really sure it is a major defect/failure/miss that we are facing. I am still hoping for just a little mistake somewhere in the supply system and was hoping anybody of you would have a hot hint where to look at i. e. like a missing orifice, some missing part on the oil pump (if possible?), a weak spring in the overpressure valve, a leaking chain tensioner etc....

Many thanks,
hs500

[daantjie]

20W-50 is good, nice and heavy so we know it's not too thin oil at least.

You can try and blow out the feed line to the gauge.  It'll be a bit messy and not sure if this is your problem but maybe worth checking.  You will need to pull the cluster and disconnect the line here, as well as at the back of the block.  I suppose a piece of dirt could restrict flow to the gauge.

[Randys01]

Get a proper reading from the oil supply line at the back of the motor............ie a separate oil pressure gauge screwed into the output line.
rule of thumb......never less than 1 bar....3plus when revving and hot.

[ptashek]

I have to disagree with 20W-50 being good for these engines. It's way too thick unless you're in a warm climate, like south of Europe.

In North European climate, 15W-40 is better, and personally I stick to 10W-40 in my M117. The manual for UK/Europe agrees it's the best all-round grade.

At hot idle (oil at 80°C) a pressure of 0.5 bar is considered to be within specification. But as others said, the moment you touch the throtle and go >1000rpm or so, the gauge should max out.

Maybe your sump pickup is clogged?
Was the filter changed with oil? Was it installed correctly? Maybe the media collapsed restricting flow?

These are things easy to check first.

[hs500]

Thanks all.

Yes, filter was replaced as well.

Will try to connect an external measuremente device to get the precise reading; however as I have already used two different gauges in the instrument cluster, I think those are measuring pretty reliably.

I think we will open the oil pan at next opportunity to check for any obvious blockages etc.

A question for the chain tensioner: Is the tensioner constantly leaking oil internally or is there no oil flow at all through that part? Just trying to understand potential ways where to lose pressure within the system...

Thanks all and a healthy start into 2024.

Cheers
hs500

[rumb]

Since you are hunting, check thst all the cam oilers are in place. A missing one might allow high oil flow up there?

If they have never been replacrd yet, it would be good maintensnce to do.

[hs500]

Thanks all.

Would somebody have the details for the connection/fitting for the oil tube at the cylinder head in mind? I would then look for proper gauges to measure the pressure externally.

Cheers,
hs500

[hs500]

And another questions to the professionals:
Is there also an overpressure valve inside the pump? (P/N: A 116 180 03 15)?

That would mean there're two valves installed? One in the pump and one in the front cover (P/N: A 114 180 02 15)? Does that make sense?

My source: https://nemigaparts.com/de/cat_spares/epc/mercedes/1/m/117986/67h/18/015/

Many thanks,
hs500

[ramiro]

There seems to be only 1 overpressure valve according to the official description :
https://handbook.w116.org/cd/Engine/107/M117_45/18-005.pdf

[Randys01]

From memory the oil pressure gauge is connected at the back of the block with a male threaded union which is static to  a female union which is a rubber flexible line.
The female union appears to be a 12mm nut. To get an oil pressure gauge to connect to the static male  union may be  case of suck it and see  ie might require a couple of fittings to adapt it to fit.

This is not a normal service item so I doubt there is a ready made solution. 
If this is all too hard, it might be just as easy to take a pressure reading with another gauge at the dashboard end..again I suspect there might be some jiggery pokery with adaptors as these are metric thread.

[UTn_boy]

From memory the oil pressure gauge is connected at the back of the block with a male threaded union which is static to  a female union which is a rubber flexible line.
The female union appears to be a 12mm nut. To get an oil pressure gauge to connect to the static male  union may be  case of suck it and see  ie might require a couple of fittings to adapt it to fit.

This is not a normal service item so I doubt there is a ready made solution. 
If this is all too hard, it might be just as easy to take a pressure reading with another gauge at the dashboard end..again I suspect there might be some jiggery pokery with adaptors as these are metric thread.

The connection is on the back of the left cylinder head, not the block.  Also, the outer hex size of the union nut on the hard plastic line is 14mm.  Saying as such, I'm assuming that you're not talking about the actual size of the threaded part(s).....which should be 10mm with a 1.25 or 1.50 thread pitch.