I'm the original owner of a 1991 350 SDL with 177K miles on it now. I would like to keep it.

Engine has been relatively trouble free but head gasket now has a small external leak in the rear on the passenger side. No indication of leaking into the motor. Motor runs fine otherwise.

Indie shop I deal with is not thrilled with replacing the gasket and suggested I try K&W Block Sealer to fix it.

I have a good relationship with the MB dealer where I originally bought the car and they will replace the head gasket for $1,800-$2,200 including a new timing chain (my idea). I have confidence in them and their senior diesel mechanic and I have gotten along great over the years. This mechanic said we could be opening up a can of worms but is happy to do the head gasket job. He wil also do a compression test.

I'm wondering if we should do a valve job while we have the head off and neglected to ask what that might cost? Would appreciate opinions on whether or not to do the valve job? The engine uses about a quart of oil every 1200 miles, mechanic says this is typical.

This car is in otherwise excellent condition, looks great and everything still works.

Am I missing anything else that I should consider here?

Thank you.

Yep, you are opening a can of worms........alright.

But, if you insist on pulling the head, then I'd certainly have the valves done. The guides should also be replaced at the same time.

I wouldn't trust the job to any local machine shop. I've had great success with Metric Motors who knows the engine thoroughly. The cost should be less than $1K........depending on what's required. In the case of the SD, I succumbed to the "while we are in there" syndrome and replaced all the prechambers. All the shafts for the balls were loose and Metric was fairly sure that they would not go more than another 100K or so. The total cost for the 617 was about $1K..........the 603 will be more if you go the whole route.

I'd have the dealer check the height of the pistons against the deck.......just out of curiosity.

I'd not waste a lot of $$ on the head if the rods are the next thing to go?!
Out of curiosity, ask the mechanic if he knows what a set of upgraded rods would run you.

__________________
'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!

............you just had to say it........didn't you?

I have no indication of the rod problem so that does not bother me. Mechanic says these are 400K motors if they get past the first 100K and are maintained.

Most if not all of the rod problems I've seen discussed happen before 100K miles and tend to be in cold climates. This car has lived in Florida all it's life.

I'm trying to be optimistic, I am aware of the risks. Trying to figure out if I'm overlooking anything other than the potential rod problem?

Thank you.

if any mechanic told me that 1 gt oil is normal for a 3.5 diesel to use in 1200 miles i would avoid him for sure.
you are at the stage of bent rods and it will get worse pretty fast.
you dont have to believe anything that has been written about these engines here in the forum, but please go read the threads.
its a money pit now, make some wise choices.
larry perkins lou ky
86 old cars(3 are 1991 350 sdl)

My oil consumption has been about the same for the last approximately 100K miles, it's not something that is progressing so I'm not focused on that issue now. I have been reading the 350SDL posts here for a number of years now. Is it possible that bad valve guide/seals are contributing to the oil consumption? I can and have lived with the oil consumption for about 10 years now. Engine runs fine with no abnormal noises and plenty of power.

The head gasket is my main issue now.

I'm trying to be optimistic, I am aware of the risks and I'm willing to take the gamble at this point. Trying to figure out if I'm overlooking anything other than the potential rod problem?

Thank you.

Definitely.

If the oil consumption is remaining the same over 10,000 miles, you can bet that it's not caused by a bent rod.

The turbo can also be a source of oil consumption on these engines. Ask me how I know.

Brian,

Funny you should bring that up. If I remember correctly I had a rebuilt turbo installed (turbo bearing was failing) around the time my oil consumption increased. How can you tell if the oil is going thru the turbo?

I have never checked, but my car is a late 1991 version. Is it possible I have the beefed up rods already installed?

Thank you.

If it's leaking into the intake side (most likely), then you can pull the crossover tube and the riser from the turbo. It will be wet with oil. With consumption at 1 quart per 1000, the oil won't be that obvious.......maybe a light coating. It's difficult to separate oil consumption by the turbo and normal blowby oil from the crankcase on the 603 because they both originate from the same place. But, if you have very low blowby, and you have oil residue in the crossover and the turbo outlet, I'd bet a dollar that the turbo seals are the culprit. My '86 has this issue right now........consumption at about 1 quart every 2K. This one shows signs of oil residue on the turbo and the external tube from the turbo.

The engine originated in 1990 and had problems right through '93 IIRC. So, it's not possible that the engine came from the factory with updated rods.

I have no indication of blow-by when I remove the oil filler cap with the engine running. If my oil consumption is going thru the turbo is it ok to just leave it alone? It hasn't bothered me for 10 years.

Thank you.

ok we are trying to get to the bottom of the problem.
what is the possibility that a head gasket fails without anything else being wrong,i say slim to none.
turbo passes oil,carbon builds up on top of piston and on head,raises compression, blows gasket, the rods just arent strong enough to handle the force applied and there fore bend.
so is it smart to go replace the head gasket and do the required maintenance,spend the 2k,and leave the possibility open that there are loose bolts and washers in the oil pan???
larry perkins lou ky
have to end this early ,got to go to a meeting

Larry,

I have to trust the MB dealer master diesel mechanic on this one.

Not an issue. The engine can live happily at a consumption of 1 quart per 1000.

Normally, if it's the turbo seals, however, the problem increases with time. They don't remain at a steady leakage indefinitely.

The engine consumed this level of oil at low mileage as well........less than 50K??

Oil cosumption started at around 75K miles sometime around when turbo was replaced (noisy bearings). The independent who replaced the turbo later said the oil consumption was typical in these cars (good CYA), I didn't know any better. The turbo is showing a good bit of oil wetness around both joints on the plumbing leading to the intake manifold but not enough to drip to the ground. When the turbo was replaced the mechanic put a ball bearing in the vacuum connection hose (EGR?).

1/1200th of a quart per mile does not seem like a lot to cause problems?