Heres one for the gurus,

When at idle, the guage drops flat to 0. Then when I give it peddle, it basically pegs, then when im cruisin at 50, it's stays around 2.5 - 3.

Does anyone know what the issue could be here?

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1983 300SD 296K+
1984 300SD parts car

Those are not good numbers. It should be pegged at 50mph and higher than 0 at idle. Classic symptom of bad rod and/or main bearings but maybe something else. Is there adequate oil in the engine? What kind and viscosity?

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Electric oil pressure sender I believe. One of the differences between the W126 617 and the W123 617. Sorry I can't be more specific but I lack experience with the W126.

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Seth

1984 300D 225K
1985 300D Donor body
1985 300D Turbo 165K. Totaled. Donor Engine. It runs!!!
1980 300SD 311K My New Baby.
1979 BMW 633csi 62K+++? Dead odo

Bingo, and a bad ground for the cluster could be the culprit. I doubt any engine can live at 0 psi for long, unless you run non-detergent Quaker State. Just kidding....

Confirm the veracity of your numbers with a manual oil pressure gauge before proceeding.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

The first step is to get a external gauge hooked up to double check what the true oil pressure readings are. True zero at idle with engine warm is going to mean you will be going into the engine. Perhaps only as far as the oil pump. These engines are not to be used at less than 1/2 bar minumin at idle I believe. Your reading of 2 1/2 bar at 50 is a little low as welll. Your gauge or sender might be defective and that could be the easiest cause of your difficulty that I can think of.

Ditto on using a mechanical guage before anything else, a bent lower oil pan will hinder the pickup from pulling oil and starve the oil pump.

The oil pressure sending units reads changes in ohms of resistance as the pressure goes up and down, there should be a spec you can look up to check with a volt/ohm meter to see if the sensor is good. They aren't cheap nowadays.

When the oil senders start going bad they read low, mine reads between .5 and 1 bar at operating temp idle, a year ago it read 2 bar in the same conditions. I am expecting mine will die soon, I'll replace it when it truly begins reading some crazy levels. It also skitters when I go around corners, been doing it a long while...engine is fine.

If your engine is running fine when the gauge is showing those readings, replace the electronic sender on the oil filter housing, thats all that needs to be done. The only other step you could do is to check the condition of the wire attached to the sender, it may be in bad shape.

I'd not bother with trying to check it with a manual gauge.

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
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'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

If the sender is not too difficult to remove. You could rig up an air pressure set up to check it off the car but still wired to the dash gauge. Duplicate the ground of course in the process. Another quick test might be to warm up your engine till zero is indicated and loosen the sender. If oil squirts out around it under pressure you know it is not the engine.
I forgot most guys do not have a mechanical oil pressure test gauge around. The main thing is do not to assume you have oil pressure and a bad sender. It just might be doing its job. There might be a better point to loosen something on the engine to check for the presence of oil pressure. If so I just cannot think of it at the moment. .
If I was in the desert for example and had to check it out. One could remove it from the block. Make a ground up for it and blow hard on the end. Should be good for almost 1/2 bar indicated on the dash.

With the engine running, you could remove the oil fill cap and check if you can see oil squirting on the valve train.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

It is shoting oil onto the valve train, and the engine runs smooth. My levels are fine.

It must be the sending unit, I will investigate the condition of this later on tonight and possibly replace it.

I just brought a "parts car" home today. '84 300SD Turbo, $200 bucks! Shes in rough shape but once we got her started and burned some carbon buildup out, the thing ran like a top!

Anyway I am getting off topic here, but thanks for all the suggestions. But I am 99.9% sure the oil pressure guage must be wrong as I drive the car daily and is always smooth running and temps are good. I will post again once I have checked out the sender/cluster ground.

Thanks again

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1983 300SD 296K+
1984 300SD parts car

Have you checked your oil level? If the oil level is really low your gauge will do funny things.

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Then you have good pressure. What Kerry was saying earlier about the bad main bearings is true, as that is one of the first places that gets oiled. Any slop there lets more oil out so the system can't pressurize enough to oil the rest of the moving parts.

__________________
RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K