Mercedes V6 diesel

Old Crows wrote:

funtogo1 wrote:
Looking at used Mercedes diesels,what is the best way to check whether bio diesel fuel has been used enough to damage the engine?Newby question..

I'm not sure that question is easily answered. There's just too many variables. I think (it's a guess) that if the previous owner didn't convert it to veggie oil or use high concentrations of bio-diesel (not generally available as a road fuel) you've not much to worry about.

The older Merc diesels (5 cylinder) are likely more forgiving of fuel and oil quality. The V-6s, not so much.

If it is a V-6 and you are really concerned, I'd check the maintenance records to see what has been serviced on the engine. Might be available from Mercedes dealer... or from the owner. The key items would be oil changes about every 10K and fuel filter about every 20K. Since it is an RV, I'd not get too concerned about time intervals... they tend to 'time out' before 'distancing out' when it comes to oil changes.

I'm of the mind that 'cleanliness is next to Godliness' when it comes to fueling my Sprinters. Open the filler flap by the driver's door and look closely at the filler neck and cap. If it's nice and tidy, I'd think that the owner took some care in fueling and was using ULSD. If it's funky and filthy.... I'd be a little skeptical and start asking questions.... (Doesn't tell us squat about what's inside the tank... but it could be an indicator...)


Inspection of the fuel filter element should tell a lot about the status of the fuel system before the injection system. (Changing the fuel filter is not a DIY service item until you have some experience with the V-6. It's buried in the V of the engine block and has some fiddley plastic clamps that are easily broken. Best let one of Mother's trained mechanics break them...)

A records check should tell you what oil has been used. If a V-6, it should meet MB BEVO Specification 229.51, or now, .51 or .52. It is a LOW SAPS oil to protect the diesel particulate filter (DPF), EGR, intake manifold, etc.. In my '09, it was 5W40. That was true in my '14 up till early 2015 where it's now 5W30 but always 229.51/52 spec.

Honestly, I'd be a bit more concerned about the oil used than the fuel since it's an RV, as it is more a more likely place for the previous owner to have taken short cuts. If it was changed by Mother Benz, you can have confidence that it was the correct, LOW SAPS, oil. If the previous owner DIY'd or took it to someone ...??? Be skeptical unless they can show you a oil can or invoice.

You could also take an oil sample and send it to Blackstone Labs and ask for a TBN in addition to the regular data dump. That will tell you the quality of the oil in the machine right now as well as any wear in the engine. Both my OM-642 V-6 CRD turbo diesels return good results with Mobil Formula "M" but do show elevated iron. Normal for the engine with 10,000 miles.

I hope this is helpful.