Not saying dirt and grime isn't a contributor to the problem, but this bolt is *IN THERE*. The torque spec is only 45nm which is not all that tight in the grand scheme of things, but this sucker laughed at a 24" cheater handle. I'm pretty sure this is the original water pump and original fan clutch, so if that's the case they've had 31+ years to become one with each other.

The lack of clearance is a serious hinderance too. I fail to understand why Mercedes couldn't have slipped a nut behind the clutch like - oh I don't know - EVERYONE ELSE. Putting an Allen (which I've learned to HATE since working on this car) in a high debris/heat/vibration area is just asking for trouble, especially when providing only about an inch of clearance to get to it. I'm on board with using XZN for replacement, I hate Allens with a passion.

__________________
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 doubt Diseasel300 made the novice mistake of not cleaning it out first.

Other novice mistakes:

1. Break loose a fastener by applying steady torque. Don't do that! You want to impact the breaker bar with your palm or a mallet.

2. Having the Allen bit off center.

I have stripped my share of Allen heads even taking all the precautions. They are just an old and inferior design. I got the stripped Allens out by hammering and forcing an XZN bit into the Allen and got them out every time. I think it works better than Easy Outs (I do not own any).

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I was almost there myself in my SDL. Someone had rounded out most of the Allen bolt in a prior attempt. Fortunately, I could get just enough of bite and was able to pop it loose.

When I inquired about a replacement bolt at a local McParts store they insisted I had to buy a water pump to get it...

The replacement bolt from the Mercedes dealer is a T55 Torx, if I recall correctly, and they had one on the shelf.

To answer the original question of this thread:

If the head rounds out, forget extracting it in the car. The water pump can be removed with the clutch/pulley/fan still attached. The bottom bolt is a pain to get to, but it's doable with a box end wrench.

I pulled the radiator, airbox, and rubber intake tube. To give access to the bolts on the water pump, I had to remove the belt tensioner. A 1/4" ratchet got out all but 2 of the water pump bolts.

The water pump itself appears to have been original. It's branded Lazo and says it was made in W. Germany. That kind of dates it! Bearings are most certainly done - when spun it makes the most horrible growling and squealing noises. Fan clutch is a newer Behr, the front of which has quite a lot of oil built up on it.

Getting that bolt of though. Sheesh. Tried hammering the Torx bit in, rounded out the head. Tried using an Easy-out, wound up rounding out the head more. I welded a 9/16 nut to the bolt head using the MIG welder and it broke off. Ground it down, welded it again, and it broke a 2nd time. Tired of that crap, I whipped out the stick welder and did a proper welding job. This time it held, but required the use of a bolt extractor, a breaker handle, and a 3' cheater handle to get it off. There is no way that bolt was ever coming out with the Allen bit, no possible chance.

__________________
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!)

Is that the Irwin bolt extractor kit?

__________________
Brian
87 300Dturbo 180K #14 head still running R-12 SOLD 12/2017
02 F350 Powerstroke 180K
05 Chevy Express 1 ton w/Royal Utility box 120K
08 Infiniti FX-35 40K
15 Golf Sportwagen TDI 35K
10 Sprinter 3500 chassis with a Class A Winnebago on it. 56K

Yes it is. Worked like a pro on this job. You can see how much it mangled the bolt I used it on, that's how tight that sucker was in there.

__________________
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!)

What a mess!

Well done getting it out, quite a job.

__________________
617 swapped Toyota Pickup, 22-24 MPG, 50k miles on swap

Good to know, I bought one a while back and have not used it yet.

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Brian
87 300Dturbo 180K #14 head still running R-12 SOLD 12/2017
02 F350 Powerstroke 180K
05 Chevy Express 1 ton w/Royal Utility box 120K
08 Infiniti FX-35 40K
15 Golf Sportwagen TDI 35K
10 Sprinter 3500 chassis with a Class A Winnebago on it. 56K

The Irwin in set is good... the snap on set is best.

Irwin has huge body sockets with external sides for a wrench.

Snap on set is very svelte but only has socket connectors, so it can be used in tight spaces.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

I have same set,and easy outs also.Never leave home without it.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

Just speaking from my personal experience with 2 different OM60x engines, if the bolt was in there that tight, it was not factory. Especially since you said the fan clutch looked recent (assuming before your time with the car).

Either someone cross threaded or massively overtorqued that bolt in the past.

Both of my OM60xs have had their fan clutch/fan replaced and the Allen bolt came out with just a L shaped 8 mm hex key with a 1/4 drive 8mm socket on the long end in a nut driver handle. I used a HF Pulley Tool to provide the counter hold.

In both cases the bolt was snug but nothing like what you found.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

The water pump is factory and certainly looks it inside. The fan clutch I'm not sure about. Looking at the Bimetal I pulled out of it yesterday, it's relatively clean and has a surprisingly clean Behr sticker on it. I am leaning towards the clutch being replaced at some point before the car was parked and Dope-O the Clown buzzing that sucker in there with a rattle gun. This is why I work on my own cars...

__________________
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!)

Mine was factory and was VERY tight. I had cheater bar on a high quality Allen key and bounced a hammer off the bar a bunch of times before it cracked loose....but I was sweating bullets the whole time that it would strip.

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RenaissanceMan Labs: where the future is being made today.

Garage:

2017 Chevy Colorado Diesel (nanny state emissions)
2005 Volvo S40 T5 AWD, 77k
1987 Mercedes-Benz 300D turbodiesel, 4 sp auto, 156k - 28.7 mpg
1996 Tracker 4x4, 2 door, 16v, 3 sp auto. 113k - 28.6 mpg

WARNING: this post may contain dangerous free thinking.

Mercedes also changed to a torx head T55 for the 606 engine in my '98 e300. I bought one from a Mercedes dealer when I changed my fan clutch a year or two ago. Either by design or accident, that bolt also accepts an 8mm hex socket. I used the 8mm stubby socket made by Stahlwille (a Mercedes tool part no. 103 01 98) which I bought from Samstag to put it in my car. (The Mercedes parts salesman told me I could use an 8mm socket when I bought the torx head bolt.) You have to use a stubby socket, because there is so little clearance between the radiator and the bolt.

May that forever continue to be the case.

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617 swapped Toyota Pickup, 22-24 MPG, 50k miles on swap