I have an 87 300SDL I bought about a year and a half ago, and have rebuilt the front suspension, redone the brakes (pads, rotors, rebuilt calipers), put new tires and new springs and shocks on it, new vaccum pump, om606 fan, new belt tensioner, etc. Right now it needs a windshield (got cracked right after I replaced it), and the A/C needs to be fixed. Otherwise I have driven it daily for about 10k miles and it has been fine.

Just recently I noticed some drips of coolant on the front of the engine, and it looks like the head gasket has started to fail and over pressurize the cooling system and push coolant out of the seam where the upper radiator tank is crimped on. The cooling system stays pressurized after sitting overnight too. Whatever happened is very recent, because it didn't do this when I got it and I have never overheated it. It does still drive fine and doesn't get hot but I expect the radiator to eventually totally fail so I don't really want to take it on any long trips.

The problem is, I only have a place to work on it outside, and while I am pretty sure I could get it done eventually, at my skill level I figure I am looking at 12-18 months minimum to get it repaired and on the road again. I do have a used #22 head and used replacement radiator from Pick-n-Pull and have pulled several heads by myself but that's about it. I can afford the parts it would take to repair the car with no problem, but I can't afford what it would cost to have someone else fix it for me.

If I get rid of this car I probably wouldn't get another OM603 Mercedes (just because they are all likely to do this), and I know I don't want an OM617 just because I need to merge onto the freeway faster than they are capable of sometimes. I'm not sure whether to get rid of this car and get either an OM606 Mercedes or something completely different, or if I am overestimating the time it would take to replace the head, gasket and timing chain. I have another car to drive so I don't have to worry about it right away, but having a car that's of limited use is a waste of space and insurance and registration money, etc so I will have to decide eventually.

If the chain isn't stretched, leave it be. If you prep the new head before you pull the old one, you should be able to swap the head and get it back on the engine in a weekend if you're working by yourself and unfamiliar with the job. If you've done head work before, or if you have a helper, you can do the job in a day. I was terrified to do this job on my SDL since I'd never pulled a head before. After the job was done, I didn't see what all the moaning was about, it wasn't that bad.

Take the time to prepare what you need before you start. Have all the gaskets, nuts, studs, etc in hand before you start. Print off or obtain the sections of the service manual for cam removal, head removal, and any other related parts. It'll make the job go a LOT easier to have it already in hand.

If the radiator is blowing coolant out of the top tank, it's time for a radiator. Pressurizing the system should pop the radiator cap long before it blows coolant out of a radiator seal.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

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

I don't know if the chain is stretched or not, although I could check without much trouble. The car has about 290k on it, and I have no idea at all of the history of it other than that it appears to have had the injection pump replaced at some point. It runs fine other than smoking a lot at high RPM and although it starts easily even when its cold out it obviously doesn't start as fast as a recently rebuilt one did in a car for sale that I looked at.

Where could I find the information from the service manual? I have tried and couldn't find anything OM603 specific. Is there any place I could find information on how the exhaust manifold comes apart? I have pulled heads in Pick-n-Pull and even having it off the car in my hand I can't understand it.

Also, is there any decent list of what parts to order from someone else doing this job? Part of the reason for estimating 12-18 months is that it seems like parts for this car are 2-3 weeks out for almost everything, even longer for dealer stuff coming from Germany.

Where are you buying parts that takes 2-3 weeks? Try ordering parts from our sponsor - they can get you most parts for your car in a matter of a few days.

For the speciality items, the Classic Center in Irvine can get you things very quickly - they are used to dealing with shops that need stuff ASAP, so even stuff from overseas doesn't take long. I'm talking 3-4 business days from Germany. Anything in the US will be at my house by Thursday if I order it on Monday.

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1983 300D Midnight Blue
4 speed, W115 intake mani, non-EGR exhaust mani, KKK K26, 3 pc Euro bumpers, Lo-spec Euro headlights, AL129X, hubcaps, custom A/C

1987 300TD Smoke Silver
Euro headlights, thermostat relocation, coolant bypass mod, rebuilt Becker + Jehnert + Helix audio, OEM Oris roof boxes and surfboard racks, Euro towbar

1983 300TD Reed (Moss) Green / Dark Olive MB Tex Euro spec

1983 300TD Silver Blue / Blue cloth Euro spec, OM648 and 722.6, 15" hubcaps, W126 S2 brakes

Pulling the pins for the chain guide can take a bit of time if you aren't prepared. The rest is not bad. Have a look at the recient posts Squiggle Dog posted on GregMN's 1991 W126 350SDL Has A New Home, he just finished the job. Keep it repair it you will impress yourself.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

This site isn't competitive on pricing and I don't agree with their return policy for dealer parts. If I am working on the car on a weekend and go to the dealer Monday the parts show up the following Wednesday if they are coming from Atlanta, so that means skipping a weekend before I can work on the car again, or if I order parts from the place with the lifetime guarantee that has better prices it takes a few days longer than that. Stuff from Germany takes another week, plus usually ends up spending a few days to a week in customs in the last 3 years or so.

As far as the timing chain pins I have done that a couple times on junkyard heads without too much trouble. I'm more worried about how to get the exhaust manifold loose from the head, swapping the injectors into the new head, changing the timing chain if it's stretched too much, etc.

Then use one of the other two big parts sites that are more competitive. All three can get you most parts for your car in under a week, unless you aren't wiling to pay for expedited shipping, of course.

As I mentioned, the Classic Center has lightning fast fulfillment and shipping. They will accept returns on unused parts within 30 days. Professional, knowledgable, and a pleasure to work with. I highly recommend giving them a call next time you need things.

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1983 300D Midnight Blue
4 speed, W115 intake mani, non-EGR exhaust mani, KKK K26, 3 pc Euro bumpers, Lo-spec Euro headlights, AL129X, hubcaps, custom A/C

1987 300TD Smoke Silver
Euro headlights, thermostat relocation, coolant bypass mod, rebuilt Becker + Jehnert + Helix audio, OEM Oris roof boxes and surfboard racks, Euro towbar

1983 300TD Reed (Moss) Green / Dark Olive MB Tex Euro spec

1983 300TD Silver Blue / Blue cloth Euro spec, OM648 and 722.6, 15" hubcaps, W126 S2 brakes

Your rad cap should open at about 20 psi.

You can run a T fitting to a small hose that goes from the tank to the top of the radiator and check it with a pressure gauge.

The sure way to check for a blown head gasket/cracked head is to do a leak down test

OM603 manuals:

Mercedes Benz Model 124 - OM602, OM603 Maintenance Manuals

https://www.startekinfo.com/StarTek/outside/12253/?requestedDocId=12253

He has far more skill that I will ever have no matter how hard I tried, just from the pictures of how he took the exhaust apart I have had those parts in my hands and I don't see how that is possible to do that way lol. The only way I could do it when I pulled the junkyard heads was pull the head, manifold and turbo all together then separate it from the head out of the car.

How big a compressor do you need to do a leakdown test? I only have a small harbor freight pancake compressor that's just enough to inflate tires and that's it. If the cooling system has suddenly started holding pressure overnight enough to spray coolant everywhere when taking the cap off when it didn't used to do that a few months ago I am pretty sure that something is broken either way though.

It should be good enough.

I went through it in detail in this post:

OM603 #14 cracked head or head gasket leak?

Step back. Sounds like removing the head likely won't fix the problem and you will likely wind up with a broken car you never fix. As stated, the radiator should be able to hold pressure beyond where the radiator cap will vent (~16 psig). Never jump to the conclusion "head gasket" for an overheat. My sister was told that by a yokel shop on a long drive with her 1967 Mustang straight six ("my cousin Billy-Bob's 56 Chevy overheated and it was the head gasket, so ..."). I was only 17 but knew enough to tell her to keep adding water and find another shop. A busy shop 10 miles later quickly found a pinhole leak in a heater hose. Many other signs of a bad head gasket, like getting oil in the coolant. I don't know your car, but I just bought a new Spectra Tech radiator for my 1985 300D for $135. Aluminum, so lighter than the OE copper and gives better cooling.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

I would chime in here on getting it diagnosed before worrying about what it might be. BTW, the exhaust manifold isn't too bad to work on if you remove the heat shield entirely. It takes a bit of fiddling about but makes work on that side of the engine a lot easier. Soak those manifold bolts with penetrating oil and wait. Then do it again. Then work them back and forth a bit tight/loose/tight and they will come.
But the leak down test is first. Understand what's happening with that head. I don't read much on here nor have I experienced a failed head gasket on a 603. It is usually a cracked head. That said, you have a #22. Get it prepped and pop that baby on.
I would add, that if the car is in good shape otherwise, no rust etc., and you like it. Fix it. You didn't mention anything about oil usage or other issues. If those items are within normal parameters it is probably worth fixing (spoken by a 124/603 fan).

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DS
2010 CL550 - Heaven help me but it's beautiful
87 300D a labor of love
11 GLK 350 So far, so good
08 E350 4matic, Love it.
99 E320 too rusted, sold
87 260E Donated to Newgate School
www.Newgateschool.org - check it out.
12 Ford Escape, sold, forgotten
87 300D, sold, what a mistake
06 Passat 2.0T, PITA, sold

Las Vegas NV

It doesn't have any rust, the paint is pretty bad and I think it has been hit in the back and repaired (nicely), but otherwise the only thing wrong with it that probably can't be fixed is the sunroof.

I will try a leakdown test before taking anything apart to make it not run, but I am certain that something is wrong.

A few months ago if it sat overnight there would be no pressure in the cooling system, now the upper hose is still hard sitting overnight and I just checked now (Thursday night) when I have not driven it since Sunday afternoon and there is still pressure.

There is also oil leaking from the passenger side front corner of the engine between the head and block that was not there before. I can still drive it without the temperature going above the normal range though. The whole time I have had it the gauge has never gone over 3/4 of the way between the middle two marks.

I tested the coolant reservoir cap and it holds exactly 20 lbs, so is that correct?

Take it from me, you can repair the sunroof. Unfortunately, I know a little too much about that thing. But as for the head, you most likely have a crack given the symptom of the hard rad hose when the engine is cool. Check your rad reservoir for oil in the coolant. And let us know what happens with the leak down test. I concur with the other comments on the thread about the difficulty of swapping the head. They aren't too bad if you've got everything ready to go and you carefully document the process with photos and keeping bolts in labeled plastic bags and the like. The unknown is timing chain stretch which you should document before tearing it down. Have you done a compression test on all six and how is the blow by?
I would add that you can drive on a cracked head for a long time - I drove mine for about two years, just kept an eye on it. And the crack wasn't that bad and didn't seem to make the running temp higher at all. I don't know if the cracked head can lead to catastrophic failure at some point or not. Others on this forum have more experience than I with these #14 heads.

__________________
DS
2010 CL550 - Heaven help me but it's beautiful
87 300D a labor of love
11 GLK 350 So far, so good
08 E350 4matic, Love it.
99 E320 too rusted, sold
87 260E Donated to Newgate School
www.Newgateschool.org - check it out.
12 Ford Escape, sold, forgotten
87 300D, sold, what a mistake
06 Passat 2.0T, PITA, sold

Las Vegas NV