What's the most likely failure that could cause this lamp to be lit?
I noticed it driving last night, turned off the engine immediately and checked the oil level, which was fine. Restarting the engine (risky move..?) caused the light to go out, and it stayed out for the rest of the way home (another 5 miiles or so). I tried a quick run out in it today, it seemed fine until then the light came back on after about 4 miles. Again it went back out upon restarting the engine.
Does this sound like an oil pump could be on the way out - or could it be a faulty oil pressure sensor? Car is a 96 N and has about 110,000 miles on it. Oil last changed about 4 months/4000 miles ago.
Incorrect grade oil in the engine during your last change. Incorrect type of oil, thinning under use once warmed up. Worn oil pump. Oil pump over pressure valve sticking open (gummed or knackered). Oil filter partially wound loose, or faulty. Intermittant oil pressure sensor fault. Oil seal failure somewhere on the engine. Damaged oil line. Loose oil line to turbocharger. Turbocharger failure. Loose engine oil filler cap.
My personal feeling, considering the milage, is that your oil pump is worn. As oil warms up it gets harder to pump because it thins out when it is warm. If you have an oil pump that is worn, it will just not be able to keep up with the demand and the pressure will fall off. The wrong grade of oil or oil that is life expired will also cause the same problem. As an example, I have to maintain a very large 600hp marine diesel (the size of a Zafira), the oil is due for a change, and when it is hot the oil is literally as fluid as water. Although this has not flagged the oil warning light (in this case it would just shut down) it makes for poor starting characteristics from hot with the engine having to be excessivly cranked in order to build up pressure to enable a start.
If you have a combination of poor oil with a worn pump, then once the oil reaches operational heat, you will get warning lights. The same also applies on the wrong grade of oil. I suggest that you first change the oil for something like Castrol GTD, fit a new filter, then run her as normal. If the oil pressure light comes back on then next look for obvious signs of leakage before investigating the oil pump (which is a pig to change).
Thanks for the suggestions. I took it in today, the problem turned out to be with the oil pressure sensor/switch which was replaced. All seems good again now.
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