2018 Holden Rodeo twin-cab ute engine is 'making' oil

I’d say that you’re absolutely spot on that the rising level on your engine’s dipstick is caused by diesel getting into the sump. At this point, you have a problem because the diesel will be diluting the engine oil, meaning it won’t be lubricating the engine parts as well as it should. Leave it unchecked and eventually you’ll damage the engine internally.

There are a couple of major ways for this dilution to occur. Firstly, a worn, damaged or stuck fuel injector can dump excess fuel into the engine. At this point, the engine can’t burn it all, and some finds its way past the piston rings and into the engine’s sump.

The other common way for this to happen is when the vehicle’s Diesel Particulate Filter (DPF) becomes full of soot and needs to regenerate (clean itself). If you haven’t been driving at highway speeds for a while, the exhaust system may not have got hot enough to force this regeneration. At that point, the computer will inject extra fuel into the engine to make the exhaust run hotter. And, again, some of this excess fuel can find its way into the sump.

An oil change is your best plan of attack, and then keep a close eye on the level of the dipstick. Any increase in level should not be ignored.