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I have a 1991 350 SDL with 140k miles on it...with leaking/blown head gasket. Pressure test show 20 psi. Repair cost is $2400 plus maybe cylinder(s) could be cracked taking cost to $5k. Repair could exceed value of car.
Advice would be helpful...
 

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Administratoris Emeritus
2021 SL770
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46,416 Posts
There's a fair chance you'll need to replace the head as well, part it out is right...
 

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Or, if you really like the car and the rest of it is in nice condition and well-sorted, you could spring for a new longblock from MB. They have the updated heads and connecting rods (obviously) so the previous issues that version of the 603 had are now gone. Weigh your options, either spend +/- $8K for a new engine and keep driving the car or figure out what you could replace it with for similar money. I vote that if the car is nice otherwise, fix it! But definitely go with a reman engine from either MB, Metric or Noels, as they are updated properly.
 

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500SE AMG, E350 4matic, GL 450
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If you have another car and you want to do it yourself:
1. Go on the w126 forum and get instructions for changing the head gasket. You might get lucky and pick up a copy of the w126 service manual, but they are hard to come by.
2. Remove head. Inspect cylinders if they are okay,send head out for reconditioning. If not, part out car.
3. Get new head gasket set and consider what else needs to be done "while you are in there".
4. Reinstall everything.

I would guess that that the total cost (assuming you have most of the tools) would about $1000 or less.
When I changed the head gasket on a w126, I needed to buy the head bolt tool. It was $30 or so I think. I also ended up getting a higher torque impact gun. Other than that, the regular tools-socket sets, pliers etc was all I needed.

Good luck. I hope it works out well. If you need the number of the place that did the machine work for me, pm me. He came with recommendations from other members of this forum.
 
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