Hey Scotty - coming at you from Calgary, Alberta.

Five plus years ago we bought a 2007 Mercedes ML320 CDI from a good friend who owned it since new and had taken incredible care of it both cosmetically and mechanically (all services done per schedule). It had 208,000 KM ( 129,000 miles) on it and as you predicted it has had a bit of work done every year. We have done some work on the turbo (first a controller and then replaced the entire unit this year) but thanks to a great mechanic have been able to keep it running for not too much due to low initial cost and using reasonable part options.

We are now at 360,000 km (224,000 miles) but have an ongoing issue that we cannot figure out. At low speeds it does not have the same smooth acceleration anymore and you really need to rely on the turbo to kick in. The diesel originally had a beautiful smooth power band but now it lags a lot until the turbo kicks in.  So from low speed until up to 35 miles per hour it hesitates a bit. No codes are coming up and my mechanic wonders if the compression has dropped on the engine, it does not burn any oil between changes (15000 km interval) and transmission is still very smooth.. My wife still likes the vehicle and it is an amazing highway vehicle but the lag/slow acceleration is a bit of a safety concern.

One of the great features of this model is the range, you can go up to 1100 km or 650 miles on a fill.

Any recommendation on where to start with identifying the problem? Does the compression diagnosis make sense to you? It came on slowly but has not gotten any worst.

Thanks and enjoy your videos.  The replacement will be an older RX350 once we decide to move on from the ML320.

Sincerely,

Tim