82 300SD engine diagnosis - PeachParts Mercedes-Benz Forum

anhydrous7 · #1 01-26-2006, 02:27 PM

I recently acquired a second 82 300SD. The disease has got me. The PO allowed this car to overheat due to possibly two reasons. The first is that he ran the car without the radiator overflow cap in place. He had it back on when I looked at the car, so I dont know how long he ran it like this. Secondly he lost the valve cover cap and ran with it off for a period of time. The car overheated, he said the temp gauge was pegged at 120°C (dont know for how long) so he pulled over and had it towed home. To make matters worse, he used a tube sock to cover the opening on the valve cover. As you may guess the sock got injested and was sent throught out the upper valve deck and down through the engine. Since I have had the car, I have dropped the lower oil pan and found the oil pickup screen to be completely clogged with sock material. I have cleaned this and placed fresh oil in the engine. I then started the car up and got it to run. Upon cold start up, the oil pressure pegs out at over three bar, and the engine temp looked good. As the engine warms up, say over a period of 10 to 15 minutes, I saw the engine temp move into the 100°C range. As this happened I slowly lost oil pressure. The oil pressure bottomed out at just around the 1 bar range. It should also be noted that as the car warms up, it loses power. Very slow acceleration, etc.

My question for those of you who have 617 engine is this:

I believe one of my next steps is to do a compression test to see what shape the rings are in. I believe the overtemp condition may have stressed the piston rings, I beleive this may be the reason for the loss of power when the engine becomes warm.

I have not dropped the oil pan a second time to see the condition of the inlet screen. Having said that, what else could be causing the drop in oil pressure as the engine warms up? Is it possible that the lack of oil caused damage that would result in low oil pressure over time and increased temperature.

The car is in pretty good shape otherwise, so I am looking for any advice or suggestions on what to do or look for to get this engine running correctly.

I think replacing the piston rings is in order, and would not mind doing that, but I am worried there are bigger problems with the dropping oil pressure.

Has anyone experienced a similar situation and brought one of these engines back to life after situations like this?

Thanks,

Rob

Brian Carlton · #2 01-26-2006, 02:51 PM

Quote:

Originally Posted by anhydrous7

As the engine warms up, say over a period of 10 to 15 minutes, I saw the engine temp move into the 100°C range. As this happened I slowly lost oil pressure. The oil pressure bottomed out at just around the 1 bar range.

I believe one of my next steps is to do a compression test to see what shape the rings are in. I believe the overtemp condition may have stressed the piston rings, I beleive this may be the reason for the loss of power when the engine becomes warm.

You don't mention whether the 1.0 oil pressure reading is at idle or at 2000 rpm.

I agree with the compresson test. I'd also do a leakdown test because some damage may have been done to the valves..............and..........it's not unheard of to crack one of these heads when they overheat.

I've got a suspicion that you are going to have to pull the head to see what you have there. But, the tests noted above may tell some tales.

Pete Burton · #3 01-26-2006, 03:38 PM

My 617 drops in idle oil pressure from over 3 bar to 1 bar when warmed up (85C). I rebuilt it 10K ago and it runs great. FSM allows idle oil pressure as low as 0.3 bar.

But if you saw how this engine is put together you would understand why.

Brian Carlton · #4 01-26-2006, 03:48 PM

Quote:

Originally Posted by Pete Burton

My 617 drops in idle oil pressure from over 3 bar to 1 bar when warmed up (85C). I rebuilt it 10K ago and it runs great. FSM allows idle oil pressure as low as 0.3 bar.

But if you saw how this engine is put together you would understand why.

Since I did the head replacement, the pressure at idle, fully warmed is now 2.1. I can't figure out what would cause it to rise??

Wonder if the gauge is in error?

Kebowers · #5 01-26-2006, 03:52 PM

#1 Compression test cold and hot
#2 Cylinder leak-down tset HOT and COLD
#3 Cooling system pressure test HOT and COLD
#4 Oil Pressure HOT with fresh 10W30
#5 Injector pump timing check/ set
#6 Ease of starting Cold &Hot
#7 Smoke at idle and under full load low & HighRPM
#8 Inspect turbo both sides for oil leaks past seal
THese simple tests will give any competent diesel mechanic a real good fix on the overall condition of the engine--head gasket, valves, piston/rings, cylinder wear, injection pump, injectors, bearings.

anhydrous7 · #6 01-26-2006, 04:52 PM

Quote:

You don't mention whether the 1.0 oil pressure reading is at idle or at 2000 rpm.

The oil pressure was at or slightly below 1 bar at ildle and 2000 rpm. Didn't seem to matter once the engine was heat soaked.

I have a compression tester, but the guauge only goes up to 300 psig. i believe I need to find a guage that goes up to 400 psig.

As far as the leak down test, what kind of pressures do you need to use to perform this test. I believe the idea here is to pressurize the cylinder with both valves closed and see how long it takes to bleed off the pressure that is introduced into the cylinder. Ideally, if everything is healthy, it will take longer to bleed off or leak down the pressure.

Having said all of this, these tests don't address the low oil pressure. Is it worth taking the head off if, the tests show a problem, if there is still a problem with the low oil pressure?

Pete Burton · #7 01-26-2006, 05:52 PM

although it's not too common, but because your oil pump has been "socked" (sorry

), I'd suspect a problem with the oil pump. At 2000 RPM, that gauge should be pegged over 3 bar, even at 100C engine temp.