This week I have been doing one of those charity runs where you tow a trailer decked out as Santas Sleigh with lights and music, bringing Santa to see children in the neighbourhood. Basically 2 hours of slow tickover driving an idling.

Last night I felt it smelt a bit warm and when I checked the oil it was very low, off the bottom of the dip stick My own fault I 've meant to do an oil change for ages. For now I topped up the oil to a healthy level but tonight the oil warning light came on. It would only come on when idling and would go off when revved slightly, presumably pumping the oil a bit harder. I checked the oil level and it was still good, (hadn't leaked out!) so I was happyish to keep going rather than cancel the outing. After 20mins the light pretty much went out, though it did flash on for a couple of seconds a couple of hours later when I was reversing on to my drive.

Any idea what would cause this? I haven't seen the warning behave like that before. Is it something to do with having run the car so low on oil? I have a 3.3L 1997 Voyager. Naturally I'm a bit concerned about taking it out again for tomorrow night's run...

 

Try servicing with new oil and filter as it needs doing anyway then re check if warning light comes on.
Dan

 

I'm with Dan
Years ago I had a big old Volvo 240 and had about the same. I was late with oil change and running low on oil and got some warning lights. Topping oil up didn't work. Changing the oil filter only worked for a very short while, but changing the oil + a new filter solved all.
I guesstimate the old oil clogged the new filter immediately but new clean oil + new filter made the old Volvo run without warning lights for another 50K km

 

Your old oil would have thinned slightly over time due to the temperature and therefore easier to pump around your engine but with less lubrication properties. Now you have added new oil that will have a higher viscosity it is going need more effort from the oil pump to move it through what I believe to be an almost clogged filter. Hence why you get the oil pressure light at idle but when Revs increase the pump produces more effort and the light goes out. When you do change the oil and filter consider using an engine oil flush before refilling new oil.

 

Great advice and explanation of what is going on. Thanks everyone.

Oil change is definitely on the job list for the weekend!

On the subject what is the recommended oil and quantity? To top up I used a 10/40W semi synthetic.

 

Oil is like a religious/politics discussion
After years of discussions, research and searching for expert advises I would go for an A-brand 5W30 full synth

 

I've never been on a car forum where that's not the case! It did cross my mind that the 10W40 might have been a bit too thick and hence not pumping efficiently when just idling.

 

Imho the viscosity is not the main problem as long as you give the engine some time to heat up before taking off, but indeed 5W30 lubricates the engine better/quicker in moderate to cold weather
The main advantage of synthetic oil is that it lasts a lot longer (much longer oil change interval) and is much better resistant to heavy circumstances and use.
In my 2.5 CRD my OCI using a good A-brand fully synth oil is 20-30.000km (12-18.000 miles)