Increasing oil level in diesel engines is a known phenomenon. It is the result of overfuelling allowing diesel fuel to get into the crankcase. A couple of potential causes. Worn, faulty or leaky injectors allowing too much fuel in is one. If the car has a Diesel Particulate Filter (DPF), the engine management unit (EMU) will undertake regular DPF regenerations to rid the DPF of deposits. These require additional fuel to be injected on the exhaust stroke which is burned off in the DPF to clean the deposits. Cars with DPFs require regular long runs for the DPF to get up to temperature so the regenerations work properly. If the vehicle has regular short runs the EMU will keep trying to run a DPF regeneration cycle, leading to excessive fuel injection. You say your car has mostly highway use, so that seems unlikely. I suspect your car is possibly undertaking DPF regens rather frequently. It's a while since I ran a diesel, but 500km/300 miles seems quite a short interval between regens, but I could be wrong on that. The 'sniff' test may allow you to decide if the engine oil has diesel fuel contamination.

 

I have just remembered that shortly after the service I added a fuel system cleaning additive. I personally do not believe in additives, but went for it, because the engine is knocking and there's a slight vibration in the car, which my mechanic believes is a faulty injector, while I think it's one of the tappets. We figured it might improve things, or make things worse, thus either way proving it's the injectors. So it could be the injectors leaking now, although that refurb job was planned for a warmer time like spring because good luck removing 18 year old injectors in winter, but I guess the cleaning additive sped things up.

Mechanic told me to come by later in the day. I will also do a quick DiagBox run to see the oil level, because those 106% was back then, it must be higher now.

I suspect your car is possibly undertaking DPF regens rather frequently. It's a while since I ran a diesel, but 500km/300 miles seems quite a short interval between regens, but I could be wrong on that.

I googled it and 300 miles seems to be the average regen interval for the average car. It also couldn't be the regen attempts causing dilution, because the oil level was fine after the car had done the regen 26km back.

 

The mechanic drained the excess and said if the level keeps rising, then will have to take it seriously.

DiagBox is still showing 106% so I guess the oil level sensor (pressure sensor?) is shot and to be ignored.

Still no explanation how they overfilled it and how the level came back.

 

PEUGEOT 308 1.6 HDiF DV6TED4 (9HZ) 2007 - 2010

 

Thanks! Looking up online it says 3.5L, a downloaded manual says 3.75L, and the German manual in my car says 3.85L for the 9HZ.

 

100 km later did a diag run. DiagBox showing 100% oil level.

Measured the oil level myself and again, the entire dipstick was in oil.

I don't know what to think of this... Fuel consumption is at 4.6L/100km, high but it's winter after all. I see oil dilution through fuel as the only suspect. Where to go from here?

 

You've surely answered your question yourself. Oil dilution is from excessive fuel input (as I've already suggested above) and you've already stated there is a problem with how the engine is running and fuel consumption is high. Your mechanic has indicated that he believes there is an injector problem. I'm sorry but 'Where to go from here?' has a straightforward answer. Just get on with fixing the obvious, known, problems.

 

Well, personally I think if the injector(s) started to leak that badly, there would be a noticeable change in the behavior of the car.
I have brought the car to the shop. Will keep this thread updated.

 

Mechanic brought the car into the shop today, said the oil level is at max. I suppose the curve in the tube covered the dipstick in oil and gave me a false reading last time. Him saying the oil is at max matches with the reported 100% level in DiagBox.
Told him to do the injector refurbishment job anyway.

 

Got the car today. Three injectors were cleaned and one replaced, no more vibration in the car. Mechanic said the oil level has remained the same while in the shop. Will see how it goes. Now the problem is that the boot won't open, the switch got damp in the winter and would randomly open, looks like it gave out completely.

 

Thanks for the update on the injector problem and that the car is now driving properly. Hopefully the work will see the end of the oil contamination.