Siitting at 275,000 miles.

No issues, but thinking of changing the headgasket.
Most of the threads I've read here are after a blow out.

Compression is between 365-390 across cylinders, though oil burning at highway speed is about half a quart every 600miles –I have changed valve stem seals.

Curious if anyone here has done such a thing and a.) found no reason to do anything else to the head ie, simple swap b.) performed any other pre-emptive maintenance while the head was off eg timing chain/rails/ tensioner.

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1981 240D 4sp manual. Ivory White.

What are you looking to gain by replacing a head gasket that isn't bad? If you aren't solving a problem, you're going to exert a lot of work (and some expense) for no gain in the end. Unless your head gasket is blown out between an oil passageway and cylinder, it won't do anything for your oil consumption either. There would be other signs of oil passage being blown into the cylinder like a bouncing oil pressure gauge or oil starvation symptoms to the valvetrain. If the valve stem seals have been replaced, about the only other place oil consumption takes place is from worn cylinder walls or worn out/clogged rings, neither of which a new HG will address.

Sometimes things are better left alone.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]

He would be looking to gain a lot of unwanted trouble.

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84 300D, 82 Volvo 244Gl Diesel

Thanks for the data point. I've read in a few places the oil consumption might be tied to the sustained higher rpms seen at cruising speed.

I appreciate it. Makes perfect sense.

This is a hobby, not a hostage situation.

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1981 240D 4sp manual. Ivory White.

I mentioned the oil consumption in relation to valve guides, apropos of people sending their heads off to a shop. In addition to rings, my understanding is that play in the valve guides can also be a source of oil consumption.

I’m with you re: sleeping dogs, but I’m getting up there mileage-wise on a 45 year old gasket. Seems like the sort of thing that’s coming up soon enough. My intention was to do it in my own time rather than out of necessity.

Wasn’t thinking performance gains, just defusing a bomb whose fuse length is unknown to me.

Thoughts?

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1981 240D 4sp manual. Ivory White.

That oil consumption is pretty normal, with new seals it won't change a lot even with new guides. I did the gasket because it leaked on my M103 at 280K. The head needed no work other a very minor skim cut and new seals.

I'd focus more on the timing chain and if the car is a long term keeper get the parts to do a valve job if one is needed later as parts could get difficult to find. A head gasket, new bolts, valve seals and guides and store them. Valves are pricey to buy them for an unknown IMO.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Head gaskets can last a very, very long time, especially if the engine is taken care of. 616's are pretty low stress all things considered and the short length of the block and similar metals of both head and block are good things for longevity of the head gasket in general.

Barring a catastrophic overheat or something bad, they rarely just "let go" they give warning and plenty of time to plan for the job. Your most common tattletale is residual pressure in the cooling system or a mystery coolant consumption that can't be traced and all external sources are ruled out. I wouldn't lose sleep over it.

If the head comes off, it's a good idea to do valve guides and get a complete valve job done along with a skim to give a good flat surface. Again, not something worth doing until it's needed.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]

FWIW, my experience agrees with higher RPM increasing oil consumption a little. Noticed you are in a warm climate that will thin the oil also causing a little more consumption. In that climate I'd run at least a 15W-40 and if doing frequent longer trips a straight 30W. For short trips a multi-viscosity.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Hey Shern,

You’re crazy.

Ok, now that we have that out of the way let’s think about where your oil could be going. My 240D used a quart every thousand miles. It mostly leaked out. But my recollection of your car is that it is sealed up pretty well.

Is your oil filling up your separator at that rate? Does the car have the puff of smoke under hard acceleration?

If you are burning it I’d try a leak down test before pulling the head. I was able to macgyver a leak down tester with some glow plug fittings from my compression tester and my pancake compressor. Get the cylinder up to TDC and start filling the cylinder with air slowly. Hold the crank with a wrench and do NOT let it fly around and hit you in the face (I like a helper to hold the wrench…it takes surprisingly little force to hold the engine from spinning when it’s at TDC but if it gets off TDC the wrench will really fly).

Listen at the oil fill port for a hiss. Listen at your radiator for bubbling. Listen at your intake/exhaust for a hiss. If your head gasket has a problem you may be able to find it this way if your leak is to the oil galley. Shut down your compressor and watch the pressure leak down. This may help you actually diagnose a head gasket failure.

Maybe a bad oil control ring?

I wonder if you can pull your exhaust manifold and see if a runner has more oil in it than another. There must be some way to check for fouling. We have those prechambers that make it hard to inspect the bores.

A head gasket it still a decent amount of work. Try to come up with some diagnostics before getting into that.

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79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles
97 C280 147k miles

Ha, seems to be the general consensus.

Truth is, I wasn't really looking to solve for anything. Mentioned engine stats just for clarity. Was more so looking for another project and hoping to check off a box of preventative maintenance/learn something new along the way. Most of what I've done to this poor car had some second order reasoning, but that's always been my primary intention.

That said, Diseasel also makes a good point. These gaskets are tough and the om616 is a low stakes motor.

I have been curious about performing a leak down test, again, because it's something I've never done before. I still have the harbor freight compression tester fittings for the glow-plug holes and I can borrow an air compressor.

Re: keeping the engine immobile, I suppose I could also leave it in first gear?

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1981 240D 4sp manual. Ivory White.

You could. Chock the wheels and set the brake.

My old mentor taught me to hold the crank with a breaker bar at TDC. But he also warned me that leaning over the engine and listening at the intake, oil fill hole etc. risks getting the wrench launched into your teeth when the air pressure pushes the piston down.

It’s all in the physics. The crank has no torque at TDC. It’s like a balancing point. Once it slips past the piston will push down on the crank and generate increasingly larger amounts of torque. By the time the crank hits 90 degrees that wrench will be flying if you are using decent amounts of air pressure.

Just emphasizing this like my mentor did on me. It’s like being warned to use jackstands.

This is why I’d rather use a wrench than first gear. If you have any get lash in your transmission or differential the crank can move a little to an angle where it can create torque.

I’ve also noticed when rebuilding that bores in worn engines have the most wear at the tops where the piston tops out and the charge gets ignited. By holding the piston precisely at the top you get to check your piston to wall seal where it really counts.

Oh yeah and I found it was difficult to find TDC (compression) on our diesels because I cannot stick anything down a spark plug hole. I use a party balloon on the glow plug fitting to find TDC convenient. Relying on the balancer marks sometimes puts you at TDC exhaust where the valves are open.

I have a leak down tester someplace. It’s just a primitive flow meter (two pressure gauges with a constriction between them) and some fittings plus a regulator. It isn’t rocket science. After awhile I started ignoring the minimum and maximum flow and just listened to the hissing at various points on the engine. It’s helpful for isolating a leaking valve or head gasket leak. I just set upstream pressure with the regulator on the compressor and the leak becomes my flow restriction. Downstream pressure is atmospheric and upstream pressure is what you dial in on the compressor regulator. Easy.

This is what a professional one looks like.

__________________
79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles
97 C280 147k miles

There's a lot here. When I get around to it I'll circle back. Thanks Carl.

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1981 240D 4sp manual. Ivory White.

If you're looking for something to do on the W123 and haven't done it already instead of changing the head gasket,...
Change ALL fluids,
Replace brake hoses,
Clean under the battery tray,
Vent the battery with an extended tube out and under the car,
Thoroughly clean all body drains especially those in the hood hinge pockets,
Replace exhaust hangers with MBZ genuine...

IMHO, the oil consumption is normal for a new car yet yours is a high miler. Just run yours hard once it's hot to keep the rings clean and prevent sticking.

Post some pics, I bet you're car is really nice.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

My friend, we are well, well past that point.

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1981 240D 4sp manual. Ivory White.

That car is outstanding. Fanatic owned. The low res photos don’t do it justice. Unique woodwork and sound system.

Is that a 300D dash?

__________________
79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles
97 C280 147k miles