2019 vs 2025 G550: What Changed (Engine, Tech, and Feel)
January 27, 2026
Single-digit temperatures. Snow on the ground. Perfect diesel weather.
This 1993 G350 turbo diesel arrived from the East Coast not running. The original OM603 engine had catastrophically failed—timing chain issues, valvetrain damage, internal components colliding in ways they absolutely shouldn’t. In short, it was beyond saving.
Instead of scrapping the truck or attempting a questionable rebuild, we gave it something better:
An OM606 turbo diesel swap—done properly.
Early OM603 engines have a reputation. When they’re healthy, they’re fine. But when they fail, they tend to fail in dramatic fashion. In this case, the camshaft seized, the timing chain let go, and the internal carnage made the decision easy.
Game over for the 603.
Rather than rebuild a problematic platform, we sourced a low-mileage OM606 from an E300 turbo diesel—one of the most respected Mercedes diesel engines of its era.
The OM606 is a 3.0L, dual overhead cam diesel known for:
Stronger design
Better reliability
Greater upgrade potential
Smoother operation
Improved breathing
The donor engine had under 80,000 miles and came from a rear-ended vehicle. Before installation, it was fully refreshed with:
New gaskets and seals
Water pump
Glow plugs
Injector inspection
Full reseal and inspection process
We don’t just drop used engines in. We prep them properly so they start their second life correctly.
This isn’t a wild, smoke-everything build. It’s intentionally mild.
Here’s what the truck received:
Full mechanical injection pump (6mm)
Turbocharger upgrade (modified internal housing)
Factory-style intercooler mounted behind a vented G500 bumper
Custom in-house intercooler mounts and piping
Cold air intake routed for fresh airflow
Stainless TIG-welded exhaust system
Suspension refresh with springs + Fox 2.0 shocks
Braided stainless brake lines
Full bushing refresh
The goal was simple:
Clean power, smooth drivability, and long-term reliability.
No oversized pump. No extreme fueling. Just a properly breathing turbo diesel that behaves.
It was five degrees out when we filmed this.
The engine was stone cold. Snow on the ground. No warm-up tricks.
Glow plugs cycled. Key turned.
It fired.
It sounds like a diesel. It behaves like a diesel. And most importantly—it runs. Which is a huge improvement over how it arrived.
Seat heaters? Working.
Cabin heat? Working.
Engine? Happy.
For a truck that previously couldn’t travel more than seven miles without breaking down, that’s a serious transformation.
Originally a 1993 G350 turbo diesel, this truck is now effectively a G300 turbo diesel configuration thanks to the OM606.
The chassis itself has over 342,000 kilometers, but the new engine has under 80,000 miles and has been fully refreshed. With proper setup and sensible tuning, these engines have a long future ahead of them.
And paired with permanent all-wheel drive (as found in 463 models), it’s exactly what you want on snowy, icy days like this.
The best way to describe it: calm until you ask for more.
Light throttle? Smooth and easy.
Floor it? It wakes up and moves with authority.
Cruising? Stable, clean, no weird behavior.
We’ve put roughly 150 miles on it since completion, and it’s doing exactly what it should—starting, driving, and behaving like a proper Mercedes diesel should.
No drama. No smoke clouds. No overheating. Just reliable torque.
Phase two includes:
Minor interior refinements
Lighting upgrades
Final detailing
Transport back to its owner
This truck went from non-running and written off by multiple shops to fully functional, winter-ready, and genuinely enjoyable to drive.
Older G-Wagons with blown motors aren’t dead—they just need the right plan.
Sometimes the solution isn’t rebuilding what failed. It’s upgrading to something better engineered. In this case, the OM606 provided exactly that: modernized reliability while keeping the mechanical diesel character intact.
If you’ve got a G-Wagon that’s been sitting, misdiagnosed, or written off as “too far gone,” there’s almost always a path forward.
This one is proof.
Get in touch with Joe Gocher and the team at Alliance Auto Care—we’ll get your truck squared away the right way.