Hello. Hope you can shed some light on my ongoing problem.
I have purchased a Mercedes sprinter 318 2007 plate approx 3 month ago.
So far I have had an injector renewed, new heater plugs with control unit, had dpf regenerated, had diesel cleaner through tank. New fuel filter and air filters.
My problems are
- bad starting in morning in cold weather and warm weather (engine will turn over for 5 seconds before firing).
- under normal driving conditions the van is powerfull and responsive all of a sudden the engine note will go lower and the engine will be so much quicker and too responsive if that makes sense! When this happens there is medium amounts of blue / dark smoke coming out of exhaust.
-my average mileage per tank is only 320 miles where as the estimated mileage starts off at 460 on the trip display. don't know if this has anything to do with problems above?

I travel about 10 - 15 miles per day. With a longer journey once a week to help get dpf to temp. I use shell optimax diesel which is supposedly cleanest diesel in my local area.
Hope my information is ok and any help or advice would be highly appreciated.
Many thanks.

Blue smoke is often associated with burning Oil.

I would be thinking where could I suddenly; after driving a while get Oil into the Combustion Chamber.
Is there any Oil consumption issue?

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84 300D, 82 Volvo 244Gl Diesel

Mopar Magazine | Diesel Engine Diagnostics
"Blue smoke is often caused by a turbocharger issue. These include a restricted turbo intake duct, an air leak in the boost system between the turbo compressor outlet and intake manifold, and obstructions in the exhaust. Problems in the valvetrain can also cause blue smoke. Worn and brittle valve seals and worn valve stems and guides are 
leading culprits."

Restricted Turbo Duct intake can also mean a plugged Air Filter. Low pressure caused by a plugged Air Filter can cause Oil to be pushed/pulled past the Compressor side Seals.
If that happens the inside of the Turbo Compressor Housing will be oily.

Anther site listed a Worn Engine as a cause of Blue Smoke. How may miles are on your Engine?

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84 300D, 82 Volvo 244Gl Diesel

Thanks for your input. The van has 129,000 miles on it now.
Last time it was in Mercedes they downloaded all new software.
I am not losing or using any oil. 2 month ago I had a full service and the oil level hasn't dropped at all since then. Thank you again