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Old 08-29-2016, 09:16 PM
Registered User
Join Date: Aug 2016
Posts: 2
1992 300SD Engine Swap

Hi All,
I have a 1992 300SD with a troubled engine that has been deemed done.
The engine overheated on the freeway. Now I have a cracked head and oil leaks are starting to manifest themselves.
I am obviously having a hard time locating an engine. All I have been able to find is an older om603 (1987) out of a 300SDL. I know that the specs are not the same on the two engines, but is a swap a possibility?
I am not afraid of changing bits and pieces and re routing a few things here and there, but I am not looking to do a complete custom job that is going to take extensive modifications.
Any help and thoughts are greatly appreciated.


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Old 08-30-2016, 11:53 AM
babymog's Avatar
Loose Cannon - No Balls
Join Date: Jan 2006
Location: Northeast Indiana
Posts: 10,767
Where are you located?

In answer to your question regarding swap, it is possible, but you will have less torque from an earlier 603 3.0L engine (the 3.0L is OM603.960 (W124) or OM603.961 (W126), the 3.5L is OM603.970 (W126), and OM603.971 (W140)).

Your 3.5L engine and transmission are set up for more low-end power, and a lower shift point. You can rev the engine by manually shifting to use the higher RPM, I don't believe that running 3.0L RPMs in the 3.5L transmission will cause it any harm, but the torque converter and shift points are tuned for the 3.5L.

As far as the engine physically fitting, you will need the oil pan / sump from the 3.5L, the 3.5L exhaust manifold, if you want to use the turbo from the 3.5L you will benefit from the faster spool-up. If the 3.0 comes with a Garrett turbo I would use the (pressure-actuated) wastegate from the 3.0L.

Other items you would want from the 3.5L: if you want better performance would be the IP, re-tuned to the higher RPM, the timing chain cover for its stronger design, vacuum pump, engine mount arms.

I have a good running engine from my '92 300SD, started and ran great, leaks oil though and will need a seal somewhere (shouldn't be too tough, the engine is out), I haven't had the time to mess with it and could be persuaded to part with it, and possibly a spare '87 300TD short-block which also ran great when I removed it. LMK if you're interested/local and we can figure out what it's worth. Don't toss your old engine either, there are parts on the .971 that are worth saving/selling.

Gone to the dark side

- Jeff
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Old 08-30-2016, 01:03 PM
oldsinner111's Avatar
once a happy man
Join Date: Nov 2008
Location: bristol,tn
Posts: 5,826
look in europe at have the better 6 cylinder engine.And even the 4.2 v8 diesel.
plant, and animal life matter. human's had their chance.
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Old 08-30-2016, 03:10 PM
Registered User
Join Date: Aug 2016
Posts: 2
Thanks for the quick replies.
I am located in California and not too many of these cars made it to this side of the world.

Will the car suffer from extremely slow start much like a 617?
If that is the case I would have to look at some other option

I'll check in Europe but I would really like to find something in this country.

I was not aware of a v8 diesel. What is the engine code?

Thanks Again

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