This is caused by the car trying to regen itself and when this happens more fuel is used to raise the temp to help clear the DPF some of this fuel can end up in the sump which is not good as a diesel can run on its own oil which is very bad and would cause engine failure. If it is doing short journeys and idling a lot this will cause this.

I had a V60 with essentially the same VEA 2.0 litre twin-turbo diesel engine as in the S90, and had zero DPF issues in 3 years ownership despite my daily commute being 4 miles to work and 4 miles home again, with an occasional long run a couple of times per month.

Have a look at this post from Volvoforums.org.uk about the issue, it can apparently be caused by incorrect calibration of the electronic oil level gauge: www.volvoforums.org.uk/showthread.php?t=300797&...n

as previously mentioned each time it regens some diesel goes into the sump which over time raises the oil lever until it requires changing.

I had a diesel pick-up and it was regening every 80 or so miles, and the oil level was building up in the sump due to diesel dilution, it was back to the dealer numerous times but never resolved despite having the DPF filter cleaned, DPF filter pressure sensor changed, and new injectors,

Frequent cold starts and short trips are generally the cause and also not allowing the regen cycle to complete before stopping. This can cause the DPF filter to become partially blocked which in turn causes more frequent regens, a vicious cycle

In the end I sold my truck and bought a petrol engined Volvo

I dont have any experience of DPF or catalyst equipped vehicles, and dont much want any, but the usage pattern described seems like it should allow passive DPF regen.

Classically, oil dilution is down to excess fuelling (faulty injector) and/or excess blowby. possibly caused by bore wear or stuck piston rings.

Bore and/or ring wear would normally imply a high total mileage, which is not given

I dont have any experience with modern (OBD2 etc) cars either, but understand they should report fueling data to tell you if they are running rich, (Not sure if this applies to diesels) and/or you could get an emission test done.

Compression or leakdown test would tell you if excessive blowby is likely,

I dunno why the garage recommend a vacuum leak test, which "classically" wouldn't be relevant to a diesel, but I recall a "modern" VW diesel mentioned fairly recently had design features that rendered it subject to vacuum leaks, so perhaps this Volvo has been "enhaced" in the same way.

If you've got excessive blowby that's likely to require an engine strip, though unclogging rings (brake fluid or other solvent soak) and a catch can might help a bit

Edited by edlithgow on 23/07/2023 at 09:06