137,695 miles
I have had to add small amounts of water to the reservoir at least twice now in the past 2 months whenever the dash light came on with no discernible/visible leakage. When I first start the car, it runs rough as I depress the accelerator 3 or 4 times with white/blue smoke coming from the exhaust. After that, it levels out and runs smooth. There is no appreciable oil consumption. I'm due for an oil change now in 3K mile intervals and it's barely down a 1/2 quart. I went through a month or so this summer running hot (about 105-110C) until I had the replacement radiator replaced. I would say that the engine never technically overheated, i.e., never redlined during that period. I detect no water in the oil on the dipstick. The right front corner of the engine is wet with oil well below the valve cover but not at the valve cover. Could this be small amounts of water seeping into the first cylinder because of a warped head? Am I headed for hydraulic lock and a bent rod?

Get a coolant pressure tester and see how long it will hold 16psi. That will tell you if you are losing coolant or if it's just evaporating out the cap when the engine is fully warm.

I've read of 60x water pumps leaking without any indication in the weep hole visible from above. There is something of a drain tube at the bottom of the water pump. I don't know what it's for. I would have a 60x expert, they're few and far between, check the pump.

I'd love to have you pull the cylinder head to give the rest of us 3.5-ers a point of reference but I don't think your coolant loss warrants that as a first step.

Sixto
93 300SD

No but it might be the end of the begining. Just could not help it. Too obvious to miss. First do or have a pressure check done on your cooling system to see if any indications of a leak are there. That water pump for example may not seep with no pressure. After driving the car someday after it is good and warm park it and watch the ground for a drip with the engine running might help to locate a possible leak as well. I would not jump to any conclusions at this point with as little information and evidence as you have at this point.

love the sly winston churchill reference, barry.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Yes, trust someone from British North America to catch that one.

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Good one Barry.

Pressure test the cooling system, and check for leaks. Send a sample of the oil out to the lab to make sure there is not coolant in it. If they red flag it well then its probably the head gasket. These engines had the newer heads so cracking shouldn't be an issue.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200

If it were me, I would get that head gasket replaced at the very first opportunity that I could get the work done or I would not drive the car, unless it was absolutely necessary. The coolant loss is your warning and be thankful that it is not the 86 and 87 603s, which if it were and had the original #14 cylinder head; your symptoms would indicate, PROBABLY, that you were experiencing the symptoms of a cracked head, more so, than a blown head gasket or bent rod or anything else. I would especially get that carbon off of #1 and #6 exhaust valves and get the head gasket replaced now, if ONLY for insurance purposes or for preventive maintenance. But to answer your question, YES, would be my answer. But I think you have detected the problem in time to correct the issues before they become catastrophic oil consumption issues, like in my case.

BenzDiesel

My friend who has been working on MB's for over 35 years has the car now and we're planning our strategy. The threads on the injection ports were different from the pressure gauge fitting that he had so we aborted the 1st step compression step. Instead he took out all of the injectors and found the following: From front to back, the 1, 2, and 3 injector ends were black and greasy as might be expected. The 4, 5, and 6 injector ends were in varying degrees (steam?) clean with some rust up the collar to where the treads begin. At this point, still don't know if it's a cracked head or merely the head gasket so looks like he'll remove the head next. I will go back and photograph the injectors and each step of this process for further reporting.

Good Luck with your endeavor on the 350D. I will be following your progress and agonies, I hope they will be small, and that a Headgasket will remedy the situation.

COURAGE: the 350sdl is one of the most beautiful benzes ever. I take oil samples at every oil change (5,000 miles) and for the last 3 years no problems.

Then I hit a deer and the car was crumped pretty good driver side left. The engine wouldn't turn off with the key and I had to pry open the hood with the jack to get to the shut off. the temp gauge was at 120 when I shut it off. started up at body shop and ran fine. I get the car back next week and will see how the engine turned out. I have my fingers crossed....COURAGE

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71 220D 169K wrecked
83 240D 118K sweet 4 speed
91 350SDL (one of the 60% good engines) 156K
84 300d (loaner to my sister) 189K
79 300SD (partswagen)
86 420SEL partswagen
70 220d (partswagen)
68 280s GASSER!!! under construction now
85 300sd 310K miles winter beater car retired
93 300d 2.5 turbo 168K wife's car
83 280SL euro 5 speed 155K
69 250S newest project 54K

350SD for sale on eBay, the seller claims to have spent $16K on documented repairs hmmm, not good advertising
http://cgi.ebay.com/ebaymotors/Mercedes-Benz-S-Class-TURBO-DIESEL-91-350SD-OVER-16K-IN-DOCUMENTED-RECORDS-159K-MILES_W0QQitemZ190162368486QQihZ009QQcategoryZ6336QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

Thats excellent advertising if you know anything about these cars.

To me: "its always run perfect I have never had to do anything" Translation, I only changed the oil for the past 50k miles so $5k worth or parts are on edge and guess who gets to change them?

"$16k worth of recent repairs"
Some other sucka got stuck changing everything. Which means excellent buy!

Between say 150k and 250k miles a lot of parts are going to need to be replaced in order to keep the car running well, and well not a beater. Someone has got to do cough up the $$$$$, might as well be the PO.

__________________
2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200

the last one i rebuilt had about 150k miles and the rods were bent.
larry perkins

I've been moving slowly on this investigation too, but this is a collection of 350 symptoms I have heard of or seen on my car. Hope this helps you.

- increasing oil use, I'm still around 300 miles / qt even after the turbo rebuild. Mild blue smoke at idle or speed, but after idling for a minute a huge cloud comes out on acceleration
- see an oil leak at the head gasket / block interface, most often near the cylinder 1 exhaust going into the manifold. There is a lot of stuff going between the head and block at this point.
- compression is good on mine, 420 - 450 on all cylinders, runs quiet and smooth, no nailing
- a member on another forum + Sixto here pulled their heads and saw tilted pistons, pulling the head was the next suggestion by the dealer when I took it to them a year ago.
- the other guy took his lower end apart and found very slightly bent rods ( not visible but measurable), the pistons had tipped in the cylinder and worn a bevel on the top of the piston and at the opposite skirt area, this allowed oil by the rings
- the cylinder had ovalled only very slightly, .0005 if I remember ( 1/2 a thousandth). This was found later, as the guy installed a 606 engine instead.

Good luck in your investigation.

Chuck.