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  #1  
Old 02-26-2004, 05:13 AM
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Exclamation 87 300D loss of oil pressure

OM603 owners take note,

Purchased 300D about two years ago with great enthusiam since the car was the smoothest running diesel I've owned. During the test drive I noticed excellent oil pressure, better than I had ever seen. After purchase, I became aware that the oil pressure gauge would go to 3 bar with the just the key turned on, engine not running. Purchased new oil pressure sender and installed. Oil pressure indication was now where it should be at idle and rose to max pressure accordling with higher rpm. However, at idle the needle would jump around and fluctuate erradically. A couple of weeks later the gauge started doing the same thing, going to 3 bar with the key on, engine off. I assumed another bad sender and knowing I had good oil pressure, ignored the gauge problem.
On Thanksgiving day, my son and I were cruising around 70 showing about 3000 rpm, when there was loud knock from the engine and immediate loss of power! After getting towed home, I drained oil with chunks of metal and ball bearings coming out. Removed oil pan reservior and found oil pump chain and sprocket jammed up between the crankshaft and timing chain cover. Found oil pump chain tensioner in half with broken piece still in oil pan. Failure of the oil pump chain tensioner ($4 part) determined to be the culprit. Without tensioner, chain was sloppy causing the oil pump to pump erradic oil pressure, hence the erradic indication. The sloppy chain eventually caused the sprocket bolt to shear, with the resulting catastrophic failure. I assume the sender failed the second time from being pulsated beyond its normal range. I failed to sense the problem (I had oil pressure, who cared about the indication, these diesels last for ever, right), now I have an engine upside down on the engine stand getting ready for rebuild. Cam appears OK but the crank rod journals are groved and will hopefully be suitable for regrind. I will update condition of components and progress of rebuild with associated costs. Moral of the story:Oil pressure indication must be smooth from idle to max pressure. Donot ignore oil pressure indication problems.

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Old 02-26-2004, 07:46 AM
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Add a mechanical gauge with T. Re: 87 300D loss of oil pressure

Hello skleutz
My condolences on your loss.

I work on some of the most expensive cars in the world.
This is why I suggest adding a mechanical gauge with a T fitting off the oil pressure sender.
If both gauges show issues; shut it down.
I do not want to rebuild a Rolls-Royce, Ferrari, Mercedes Benz or any other engine after oil pressure loss.
The co$t is huge to the owner and can be avoided in 99% of ca$e$ by having a mechanical gauge installed permanently to cross check.
Some owners have asked me to add an oil pressure loss engine kill circuit, logical, when the engines in their cars are $50,000.00+ for a rebuild.
Have a great day.
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Old 02-26-2004, 10:58 AM
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Skleutz -

How many miles on the om603? Do you know the cars maintenance history? Just curious.

- JimY
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Old 02-26-2004, 02:27 PM
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OM603 oil pressure loss

whunter,

Thanks for the info on the mechanical oil gauge, I will definitely try a retrofit.

jimy,

I bought the car with 209,000 miles on the odometer. The seller told me the transmission was rebuilt, however, never saw any
papers. The history of the engine was unknown yet after several
test drives of other potenetial purchases, this engine was by far the smoothest and used less than a quart of oil between changes. It was very possible the engine was rebuilt at sometime. CarFax was clean.
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Old 02-26-2004, 05:16 PM
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I've never heard of an om603 failing in such a manner. Of course, I've only been hanging around MB diesels for about 10 years, so I'm a relative newbie.

I'd recommend you check the vacuum pump while it's apart. The ball bearings in the oil pan are generally associated with failure of the vacuum pump. If unlucky, the disintegrating vacuum pump jams the cam chain. Perhaps you've found another failure mode?

Conventional wisdom is to replace the vacuum pump at about 150K miles as preventative maintenance.

I wasn't aware there was a tensioner on the oil pump chain. I've occasionally heard of changing the pump chain on the old 123 diesels, but don't believe they used a tensioner.

- JimY
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Old 02-26-2004, 06:07 PM
mb123mercedes
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Jim Y.

Same for the w123.
There is a tensioner.

Louis.
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  #7  
Old 02-26-2004, 08:48 PM
VeeDubTDI
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skleutz, sorry to hear about your oil pump failure.

Regarding the bouncing oil pressure gauge, mine will bounce a bit when it's between 2 and 3 Bar, but I think that's due to an old oil pressure sender, or perhaps it's because the gauge is old... who knows. Otherwise, pressure is good at idle (1.5 Bar), and rises quickly to 3 Bar at or about 1,000 RPMs. If I hold the engine at 850 RPMs or so, it will bounce between 2 and 2.5 Bar.

At this point, I'm not really worried about it, since the pressure is always good. I will have to give some serious consideration to a mechanical gauge though, since the engine has 270,000 miles on it.
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  #8  
Old 02-26-2004, 10:40 PM
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300SDL bouncing oil gauge

Veedubtdi

The tensioner, chain, oil pump and oil pump sprocket are very easy to check. Drain oil, remove extra capacity oil reservior on right hand side of oil pan, look inside with very bright light. Test chain tension with finger, it may also be helpful to use an inspection mirror. You may also find some unusual substances in your oil pan if it has never been removed. As usual prepare for the dreaded diesel oil mess, as you may get a little on the floor. I use old cardboard, it soaks up the oil very well.

I think the mechanical oil gauge is an excellent idea that I will install while my engine is out. I will post when I come up with a retrofit.

Do not ignore any unusual indications. The check can be completed easily in a couple of hours. Be careful not to overtighten the bolts when installing the reservior.

Let me know if you find a problem.

skleutz
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Old 02-26-2004, 11:41 PM
VeeDubTDI
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Thumbs up

skleutz,

Thanks for the advice! I need to pull off my oil pan anyway because the gasket is leaking a bit. I will do this as soon as the weather warms up.
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  #10  
Old 02-27-2004, 01:02 PM
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Great Idea, I am planning to add a gauge on a single pod to my 300D turbo.
Does anyone know a source for a suitable Tee? I am having a hard time finding Metric pipe stuff.
Dieseldiehard
1971 220 (gas) 4-spd manual 104041
1979 300TD w/ 85 turbo engine 289560
1983 300D 237490
1985 300TD 206150
1975 300D (looking for an engine)
1987 300D 250K newest addition
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  #11  
Old 02-27-2004, 01:11 PM
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NAPA

NAPA has them.

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