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  #1  
Old 09-03-2004, 10:22 PM
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Location: Indianapolis,IN
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Oil Pressure Story

I have had my 1981 300SD for 2 weeks now and absolutely loke it. 98K miles and so far I have changed the following small things:
1. Primer pump.
2. Fuel hoses under tank.
3. Steering pump fluid.
4. Power windows white thingy to move it up and down.

Going home today, noticed oil pressure was not going above 2 bar. Idled there and flinched just a little when I stepped on it a little. Temp OK. stopped car looked under hood and under car, OK. Saw oil sprayed on cam then decided to take back roads and keep RPM close to idle. Got home, disconnected battery came to this forum, read for about 1 hour. Went back out, conneted battery, started car and now idled below 1 bar. Turned it off, looked under the hood, cleaned and replaced contacts on everything in the fusebox while I was trying to figure out where to start. Saw a loose vacuum to that black thingy on top of the valve cover (connected to throttle linkage - what is that thing - vacuum connection looked loose) and fixed it. Started the car and everything was OK. I have driven it around town for 10 miles since then and it still OK.

What was that all about? Is it a fuel pump failure warning, (100K miles now) or just an electric glitch. Previous owner changed oil at dealer the day I bought the car and I have the paperwork - I am changing oil again tomorrow and sticking with RotellaT like PO.

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  #2  
Old 09-04-2004, 10:52 AM
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If I understand your description correctly, the black "thingy" on top of the valve cover is for control of the EGR valve. It should have nothing to do with your oil pressure reading.

A couple of things to check for the problems you described. The oil pressure sending unit is on the side of the oil filter housing. Check the electrical connection. Also, check the main grounding strap from the chassis to the engine, including the bracket it attaches to. It is located on the passenger side near the starter. Finally, check your battery ground cable at both ends to ensure there is no corrosion.
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84 300SD 350K+ miles ( Blue Belle )
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  #3  
Old 09-04-2004, 02:35 PM
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Thanks for the suggestions, I will check them out today.

Update: Started the car this afternoon and oil pressure jumped all the way to max at idle? This in my opinion is a better problem than oil pressure not rising but it's still a problem. I will check electrical before going to mechanical. Tomorrow I might drop oil pan to see if there's anything fishy down there. Anyone know where I can get an oil pan gasket off the shelf? NAPA etc any good? Dealer is closed now.
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  #4  
Old 09-04-2004, 04:07 PM
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Don't drop the pan...

Aren't the oil pressure gauges on SDs mechanical? If so, then nothing with the electrical or vacuum systems is going to change that reading. Do an oil change ASAP and make sure you pull that oil filter and stab a new one in. Sounds like it's got either the wrong oil or filter in there.
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  #5  
Old 09-04-2004, 04:14 PM
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I think the SD oil pressure gauge is electric.

I agree with Randy. Put in a new oil filter, and make absolutely sure you have the right one. When you take the old filter out, look in the filter cavity and make sure there are no grommets from previous filters in there.
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  #6  
Old 09-04-2004, 04:48 PM
Brandon314159
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When my 300SD is cold (the gauge is electric on mine atleast) the gauge rockets up to the max at idle until it gets up to temp where it hovers between 1 and 2 (1 being no pressure...it never drops to zero)
I think the gauge is there to say "the oil pressure is fine, the oil pressure is on the low end, the oil pressure is zero"
just remember...atleast on mine...the 1 mark is zero....turn the car on before you start it see where the minimum is...it may freak you out at idle once it is warm but I wouldn't take notice unless you were doing 1500+ RPM
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Old 09-04-2004, 06:29 PM
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I always thought the guage was in bar. 3 bar being about 43.5psi.
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  #8  
Old 09-04-2004, 07:52 PM
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SD Blue, checked the electricals you recommended and they looked OK but leaned them up anyway.

Gauge is electric.

Brandon314159 you are correct. Once it warmed up, everything went back to normal. Drove 42 miles today and car is still OK. Can't expalin what happened but I am happy with it fo now.

I'll keep an eye on it and will let you all know. Thanks everyone for your input.
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  #9  
Old 09-05-2004, 02:59 PM
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Quote:
Originally Posted by Brandon314159
just remember...atleast on mine...the 1 mark is zero....
Now that is something. Would you believe that my SD does the exactly the same thing? The 1 mark is zero. I never spent the time to figure it out, but, clearly, the gauge is at 1 with no oil pressure. I find it difficult to believe, however, that when it idles at 1.6, it is really at .6. Something must be amiss with either the gauge or the sending unit.
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  #10  
Old 09-05-2004, 04:47 PM
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123 drivers, have you hugged your mechanical oil pressure gauge today?

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  #11  
Old 09-05-2004, 04:57 PM
Brandon314159
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Quote:
Originally Posted by wolf_walker
123 drivers, have you hugged your mechanical oil pressure gauge today?

I don't think they could...it was all oily...
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  #12  
Old 09-05-2004, 10:37 PM
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Electrical vs. Mechanical Oil Pressure Guage.

Disadvantages and advantages to both. The last time I changed a dash light, I did not have to worry about oil leaks on my floor mats.
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84 300SD 350K+ miles ( Blue Belle )
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  #13  
Old 09-05-2004, 10:54 PM
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Just returned from a 400 mile trip to MI to visit my brother. Car drove wonderful, oil pressure gauge BEHAVED! I am a happy camper.

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