Holden Commercial Range

It’s quite common for an oil pressure sensor to develop a fault where it sends the incorrect information to the car’s computer which then lights up the low oil pressure warning. But since you’ve already replaced this sensor, maybe that’s not the case here.

The big clue is that fresh oil and filters improved things a little, which makes me think it’s a genuine oil pressure problem. I also reckon you might be bang on the target by suggesting that it’s an oil pick-up problem. The oil pick-up lives in the sump of these engines and if the pick up inlet is blocked or partially blocked by sludge from the engine, it can fail to suck up enough oil to maintain the correct oil pressure. The higher the revs, the bigger the pressure shortfall. Failing that, sludge can block the various oilways around the engine that allow the oil to get to where it needs to be. Either way, you wind up with insufficient oil pressure and flow and risk destroying the engine.

I wouldn’t have thought 136,000km on an engine would have it showing signs of oil sludging, but that’s based on proper maintenance (not to mention that even modern diesels are filthy things inside). Have you owned the vehicle from new? Has it always been serviced correctly and promptly? If it’s been neglected (even one skipped oil change) it can develop the deadly sludge and it can be all downhill from there.

Possibly the best course of action would be to remove the sump and check the oil pick-up strainer for signs of gunk and build up. If that’s okay, then two or three quick oil changes (say, every 1000km) with an engine oil designed for trucks (which has lots of detergent as an additive) might clean things up internally enough to keep the oil pressure light at bay.

The other thing to try would be a new oil pump. Like any engine component, these can wear out over time and kilometres but, again, I wouldn’t expect to see significant wear on one that’s just 136,000km old. Other causes to consider would be excessive bearing clearance in the engine (due to wear or damage). In that case, a tear down and rebuild is the best option, because worn engine parts don’t repair themselves.

You might find that the ignition barrel has collapsed internally, jamming the whole thing up and refusing to start the car. But before you call in the locksmith, try this: The ignition barrel on this car also operates the steering lock mechanism. If the key has been removed and the steering locked at a particular angle, you can have these very symptoms next time you try to start the car.

What’s happening is that the steering lock is resting against the little mechanism that frees it when you turn the key, making the key feel like it’s jammed. The solution is to pull the steering wheel one way or the other until you feel it move a millimetre or two. At that point, you might find the key will now turn freely.

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.