Pulling the head on a 1991 350SDL
 

Plans are to do a compression test prior to pulling the head to try to determine what kind of condition the bottom end is in. Just rolled over ~260k miles and is getting oil in the coolant. I'm not so sure about going through the top end and doing nothing to the bottom end. It may be an opportunity for a rebuild:).

Good friend of mine that used to be a member here before he passed, had a 3L SDL with 440k on the stock bottom end. Head had been off twice.

Hell, I just did a valve job on my 300SEL with 287k on it... no scoring of the bores, full of crosshatching, compression was 160-170psi on all cylinders.

Basically, I would not waste the time. :)

Sounds good.Let us know how your headgasket job,turns out.

I was under the impression that this engine is considered a rod bender?

Some engines did bend rods.Most that messed up before a 100,000 miles were bad.Some went on to see many miles over that..They will never fess up to the problem.If I ever went as far as a head gasket with high miles,I might conseder a build.Thats if I wanted to keep it.

The owner has indicated he wants to keep the car going. I'll see what the numbers show.

How do you know for sure there is oil in the water?

A compression test ,while quick ,is less useful than a leak down test. A compression test tells you there is a compression leak, a leakdown test tells you there is a leak, how much and where the leak is.

For engines in general, the only way for oil to get in the coolant _THROUGH A HEAD GASKET_ is when there is a breach between the oil pressure feed and a coolant passage. This type of failure isn't very common but is possible depending on engine design. However, a broken head bolt can cause this type of failure.

A more common though still less likely point of failure is the head cracking between a oil passage and coolant.

More rare is a block crack that extends from a oil pressure passage and coolant. This was a common failure point on the 80's GM 2.8 V6 where they would crack in the lifter valley.

Does the car have a engine oil cooler that connects to the cooling system? This is a common source of failure. I'm not sure of the configuration on the 350 but it may be a laminated stack on the oil filter housing.

Another possible source is the turbo center housing if it is water cooled, though I don't have any data to say how likely it is the problem.

The 350SD is reported to be a rod bender due to much too thin rods. There was a factory fix though I do not know how to ID what motors have been upgraded.

The car actually runs out pretty good and the temp never gets higher than about 90dC. Here is a pic of the coolant reservoir.

What does the actual coolant look like? Looking through a aged brown plactic pressure tank does not tell much of a story.

If he coolant looks like coffee with cream, it is motor oil, if it looks like a strawberry milk shake if it auto trans fluid. In the case of trans fluid, the transfer would occur in the rad mounted cooler.

My 350 has 167,000, leaky #2 injector cup, when starting in cold weather without heat No 2 misses quite a bit, but once warmed up ok, idles good. run it til it goes...

That reservoir is not supposed to be brown:). It looks like some pretty nasty coffee with creamer in the reservoir. I'll drain it and get a better pic of it tomorrow. I suspect either way most of the rubber hoses are going to need to be replaced.

That looks like mine did and it had oil in the coolant. New gasket, new reservoir, no more coffee in the coolant...

Is there any sure-fire way to clean the [plastic? Mine is starting to age, even though the coolant looks clean.

I have trouble seeing the level.

Don't want to spend the cash for a new one when the other one is not broken.

I was planning on pulling the coolant reservoir, use Ivory dish detergent and water and try to clean it with that.

Let me know how that works, it's 6 degrees right now here, and I'm not going out to pull anything at this point.