Sudden Oil Pressure Loss

[mespe]

Ok,

I know this sounds like a blocked oil pickup screen, but maybe there might be something else.

Start a 1983 300SD, after about 20-30 seconds, oil pressure on the gauge drops to ZERO.

Any other suggestions?

Marty

[leathermang]

So it goes to a normal reading THEN drops ?

[aklim]

I had that problem before. Turned out to be a bad sensor. Let me ask you this, do you hear rattling? If not, I would think either gauge or sensor. Probably sensor. Try that first, if not hook up a gauge to the port. Had that problem and panicked and asked Gilly. He said it was probably ok. I was paranoid and brought it to him and he said it was the sensor, most likely since he could hear no rattling which would be present if the pressure was really zero. Changed oil sensor and life was good.

[mespe]

The gauge drops all the way to Zero. I also noticed that it seems the oil in the pan is low when car is immediately shut off, but after sitting awhile, the oil level is back to normal.

Could this oil be going somewhere it's not supposed to be going to? then drain back into the pan?

Yeah I thought sensor too, but when I immediately restart the vehicle, it doesn't take as long for the needle to drop. The needle goes from 3 to 2.8 (for about 1-2 seconds) , then drops as if I shut the car off.

I haven't let it run when it showed no oil pressure, but I do notice alot of oil opn the Cam.

Could it be the oil draining back into the oil pan from the oil filter housing, then it gets pumped to where it's supposed to be, and then I'm really running out of oil???


Marty

[aklim]

When you shut it off and let it sit, the oil drains back from the heads, springs, etc, etc back to the pan, Immediately after shutoff, the internals are soaking with oil from the splashing around and the spraying of the pump. Which is why when I check the oil, I let it sit for a bit. I pump gas and all that before I check the oil level. If it were really getting zero psi, your engine would run bad because the hydraulic lifters would be dry and so would everything and it would rattle and make a lot of noise.

[tangofox007]

It is quite normal for oil to drain back into the oil pan after the engine is shut down.

To confirm that you have oil pressure, remove the oil filler cap. With the engine running, you should be able to see oil being sprayed onto one or two of the cam lobes. (All of the cam lobes should be so lubricated, but you can only see a couple of them through the oil filler.) That will not happen with an oil pressure of zero.

[aklim]

Originally Posted by tangofox007

It is quite normal for oil to drain back into the oil pan after the engine is shut down.

What he said. If it doesn't, I would be worried.

In fact one of my engines had some special paint put onto the lifter valley to facilitate oil going back into the pan.

Is your engine making a hell of a lot of noise? You'd know if it was. If so, it has a bad oil pump. If it, I'll bet the problem goes away with a sensor or gauge.

[tangofox007]

Originally Posted by aklim

If it were really getting zero psi, your engine would run bad because the hydraulic lifters would be dry and so would everything and it would rattle and make a lot of noise.

And exactly how many hydraulic lifters does a 617 engine have?

[aklim]

Originally Posted by tangofox007

And exactly how many hydraulic lifters does a 617 engine have?

Whoops, thinking of my gas engines. Anyways, there is oil all over the engine internals and that will lower the oil level till it drips back into the pan.

[Rick Miley]

What is the condition of the two rubber rings on the oil filter stem? I'm thinking they are petrified, allowing the oil from the filter housing to drain back to the pan. Then you start the engine, it pumps the filter housing full, and there isn't enough oil left in the pan.

[djugurba]

Originally Posted by Rick Miley

What is the condition of the two rubber rings on the oil filter stem? I'm thinking they are petrified, allowing the oil from the filter housing to drain back to the pan. Then you start the engine, it pumps the filter housing full, and there isn't enough oil left in the pan.

beat me to it. good possibility Rick.

[mespe]

I drained some oil out and mixed some diesel in with the motor oil. Ran it a few times (to clean any potential gunk) Then I drained the oil, took the oil pressure sending unit off and replaced it with one I pulled form a 190e. (Yes a gasser has the same oil pressure sending unit, it amazed me too) TY Aklim for the point to the pressure sending unit.
Well problem resolved, now to deal with the slowness off the line. When the turbo spools up, the acceleration is pretty decent, it's just off the line that it really sucks. I also noticed when I hit the accelerator pedal, the engine slowly increases in RPM.

Now a question about the fuel pump. If teh fuel pump was sucking in air, would I have decent performance at higher RPM's?

[tangofox007]

Originally Posted by mespe

now to deal with the slowness off the line. When the turbo spools up, the acceleration is pretty decent, it's just off the line that it really sucks. I also noticed when I hit the accelerator pedal, the engine slowly increases in RPM.

Symptoms described are consistent with a clogged pressure line from intake manifold to switchover valve. Adjusting the ALDA might also be in order. Adjusted the valves lately?

I would think tangofox is correct, however occasionally the rubber line into the ID rots out and will take in air. You will not have any performance then.
Easy to check, Just pull it off and plug the end and blow on it. If any leaks replace it.
Check the switchover lines and valve though. The line comes out of the extreme rear of the intake manifold through a small banjo bolt. That line and the banjo bolt get plugged up with gunk. The line should be clear all the way to the ALDA, through the valve mounted on the cowl. It serves to carry a pressure signal to the ALDA that in turn opens the fuel flow to the injectors to match the increase in air flow coming in when the turbo spools up.

[mespe]

After I pulled the top can off the ALDA, I adjusted it about 2 and a half turns counter clockwise. I immediatley noticed quicker RPM increase when I gave it throttle. Used to be (before ALDA adjustment) with the car in park, the RPM would increase slowly even when the accelrator peda mashed to teh floor.

Now when the mashingh occurs the RPMs increase very much like my other 300SD.

This engine has got alot of life left to it, unfortanetly the body is SO rusted out that The car is UNSAFE at any speed, with this in mind, I'm not going to tweek the ALDA any further. (The Driver side tire looks like it's about to fall off) The sway bar is broke andthe tire tlts in about 5 degrees. Not to mention the severe pull to the left when braking.

Now to pull the engine and find me a buyer.

http://www.benzbonz.biz

Marty