Your 617.950 oil pump or fuel pump never drops below 31psi?

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1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42

Oil pressure....It is always 30 psi hot, at idle in gear and never drops below that figure. The oil jets in the block open around 15 psi, IIRC.

My Dad's 617.952 drops down to around 10-15 psi at hot idle. Since the 617 oil pump is chain driven, as opposed to gear driven, there isn't a wear issue using higher oil pressure. When I rebuilt the engine, I used a new MBZ oil pump and added a custom made, .060" stainless steel shim under the pressure regulator spring. We will be doing the same thing on Dad's 617.952.

I did this on EVERY 617 I worked on at the dealership and have many still in service with good results...Robert

So what your saying is that the oil pressure reg. is failing at idle, allowing oil to leak out, and is causing low oil pressure at idle.

I was always under the impression that a reg. set at 8bar would be sealed until the pressure was ~ 8bar, not beginning to leak from < 1bar.

I was always under the impression that the reason for lower oil pressure at idle, was from worn bearings and a worn oil pump itself.

I guess I better pull the pan off and add a shim to my oil press. reg to up my oil pressure at idle, its only around 1.9bar.

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1998 Mercedes E300TD

1983 Mercedes 240D Turbo, 131bar injectors, Cosworth intercooler and 63' Ford Falcon radiator, Ardic Parking heater, Headlight wipers, Best 38.6mpg.

1973 Saab 96 Rally Car, 1.8l V4 with all the race bits

I don`t see how shimming the oil pressure relief valve helps raising the hot oil pressure at idle ..unless the spring is reeeeally tired or broken.

Graminal,

Here is the long version....

My 617.950, as with everyone that I do a major overhaul on, was set to the 'low side' (minimum) specifications on bearing clearances. I also use a new pump and new spring everytime and I check the clearances in the pumps to be certain they are within specification. I have seen a few that were out of specification and required hand-fitting the cover to the pump body. I also add a .060" shim to the spring, as previously mentioned. I also polish and enlarge (slightly) the tube from the oil pump into the block to ensure a smooth fluid transition.

Idle oil pressure is more a virtue of everything being 'right' (or tight if you prefer) and high rpm pressure a virtue of relief spring tension.

The reason that I prefer higher oil pressure at idle (20 psi would suit me fine) is to ensure that the piston crown cooling jets, which open at roughly 15 psi, are open at idle and contributing to temperature reduction during the cool-down period.

An engine with worn bearings/journals isn't going to have high oil pressure at lower rpm, neither will an engine with a badly worn oil pump. Shimming the relief spring will raise your pressure relief limit, but it won't show you much of a change at idle.

What I have seen here recently is a drop in hot idle oil pressure with the 'brand x' oil filter elements. Dad used a Fram in his 617.952 and began to notice lower hot idle oil pressure; an overall loss of roughly 5 psi and this with 15/40 Shell Rotella, his favorite lube.

Changing back to a Mann filter brought the pressure right back up.

Hope this helps...Robert

vox_incognita it can't help the oil pressure at idle.

I was just making a statement that might have come from someone who read about shimming the oil press reg. and idle oil pressure statement. The shim should have no relation to idle oil pressure, which is due to bearing clearence, oil pump wear, oil viscosity, and restriction in the oil filter. I guess its hard to be sarcastic when typing.

On a side note does anyone know the dimensional difference between the 616, and 617 NA oil pump? I would like to have a little higher pressure at idle (maybe use the 617 pump), since my turbo sucks a bit of flow I see lower pressure at idle.

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1998 Mercedes E300TD

1983 Mercedes 240D Turbo, 131bar injectors, Cosworth intercooler and 63' Ford Falcon radiator, Ardic Parking heater, Headlight wipers, Best 38.6mpg.

1973 Saab 96 Rally Car, 1.8l V4 with all the race bits

Graminal,

I hope my clarification was helpful to one and all.

May I ask what axle ratio you are using in your 37 mpg 240???...Robert

I have had a fuel pressure gauge on my 616 for two years now and also have replaced the lift pump with a new one. Gauge is between the filter and the IP.

I have a ball valve in the return line and have it closed, dead heading the Pump. (it is not recommended to do this)

My pressure readings dance between 18-20 psi at idle, if I rev the engine up it steadies out at 15 psi and during hard acceleration it drops to 10 to 12 psi.

At an idle if I open the valve the pressure goes to 0 psi and the idle drops!, so that tells me that the lift pump pressure affects the amount of fuel that is injected.

I would like to see my fuel pressure at 20 psi all the time with return fuel flow. I am ordering a spring that is better sized for the pressure requirement and speed of the cam.

>>At an idle if I open the valve the pressure goes to 0 psi

That suggests a faulty IP relief valve to me.

I can well imagine that the pressure dropping to 0 affects the amount of fuel being injected!

Yes, that is very low pressure. The pump should be able to make well over 30psi at idle.

I had problems purging the air from the IP, so I removed the ball and spring to allow the fuel to free flow when the ball valve is open. I have not had any problems with air since.

When I get the new spring in, I am going to put an adjustable fuel pressure regulator in the return line, with the valve for a bypass option.

Glad to see there are still a few gentleman around this thread. Decided to mull over and design a very simple test for that contensious first bearing issue today. It had to be simple so it will get done at some point by someone.

I have struggled with the ideal of the number one rod bearing being at the end of the oiling line. At the time decided mercedes would not leave an oiling issue problem alone for a long time usually. At that time I thought the company from the engineering standpoint at least was still well run. They wanted their engines to stand up to wide open running and designed an abnormally effective oiling system to enable this.

Yet from introduction to end of production I think there where no changes implemented for this bearing feed. In Europe these engines may have been pushed substantially harder than over here. So it should have been even a worse issue over there.

I will not go into the merits or lack of them regarding applications etc. of the milli volt test. Although it should be quite adaquate for our purposes as a general indicator easily enough to utilise in this situation in my opinion.

Now anyone with a pressure gauge installed. If they temporarily install a valve anywhere between the lift pump and the injection pump. Let the car run until warmed up.

Then read the mill volts present on the first cylinders glow plug. Next read the milli volts present on the fourth fifth or six cylinders glow plug. Start closing the valve next watching the pressure drop away to say three pounds.

Read the same glow plugs milli volts again. Now if an increasing spread in milli volts has occured and by mathamatics the first cylinders actual miili volts are higher by ratio. To me it might indicate The number ones cylinder temperature has increased somewhat in relationship to the other cylinder.

Idealy the number one glow plug would be producing a higher voltage and your refference cylinder a lower or perhaps simular to the initial reading if the idle speed has crept up a little. This should only occur if the idle has not changed much between the two senarios.

This is very indicative more loading has been shifted to the number one cylinder under low base pump pressure. In my opinion if any positive indicators arise from this test I think the effort can be made to refine the proccedure further.

Even an increase of .2 milli volts or a little more in the spread is a signifigant number in my opinion. Especially if the idle has remained fairly constant between measuring attempts.

For the testers amusement you can decrease the pressure a little further I fully expect the idle quality not idle speed at idle to deteriorate from past observations. Reading the milli volts at that point as well might also reveal something.

Actually since I am a slow thinker it just occured to me that the posting gentleman with the valve on the return line is already fully equiped to preform this test. Thats if he has a digital voltmeter.Or perhaps a friend with one.

With his presently installed valve he can modify the idle pressure enough I believe to see if there is a signifigant voltage change between the number one plug and another refference plug. Although the reference plug should be further away than cylinders number 2&3.
the reasons for this I will leave alone till later. We hopefully will be able to decode his information easily enough if posted.

For his information if he is not aware of the milli volt test. With engine warmed up you set a digital volmeter to the 200 milli volt range. The vast majority of all digital meters have either a 200 or 300 milli volt range.either range is usable . Ground the negative or black probe to the cylinder head or other part of the engine. Only use some point on the engine never the negaive terminal of the battery or body for ground.

Then take the positive lead and touch a glow plug terminal. I have to hope your car has plugs that do not have squiggly wires between the glow plugs. If so the test is not practical. If the engine does not have the series plugs. Used before 1980 I believe. We are good.

On the glow plug relay is a removable harness plug. You can very easily read the voltages on that plug when you unplug it.

Let us know if you are interested in attempting this. It will start to put some things to rest I believe. As well as opening up this thread somewhat to more opinion and speculation.

You probably aleady knew all this but just in case and to perhaps save you time figuring out how to milli volt test the glow plugs.

Do I have to additionaly qualify this by stating we have never met before or corresponded to my knowledge. Certain posted results just might start people wondering.

Do I have some fairly easy tests lined up in my head for you if you want to do them. The information derived from them will be possibly good for many.

I have posted an outline of a first test already if you are interested. It would really help start to clear things up.

I would not exceed 20 lbs base pressure that is your current maximum without a little thought. Since you are obviously a believer as well that base pressure does have some effect. The tests should be enjoyable to do for you as well.

The spring that came in the new lift pump generated about 13 lbs of force just before coil bind which is @.900".

The free length of the spring is 2.450" and the installed height of the spring is 1.425"+-. The witness marks on my old pump suggests a piston travel of .250"+-.

The piston dia is .865 (measured quickly with calipers) and has an area of about .587 sqin.

If we were to say the area was .500 sqin for simplicity, and if the spring was at coil bind, the most pressure the pump could make would be 26 psi.

The spring I am getting has a free length of 2.5" and a rate of 25Lb per inch rate. It will be able to generate the pressures I want and will be able to keep better contact with the cam at high speeds.

Tell that to my lift pump as it peggs my 30psi gauge.