Citroen DS Oil Pressure light

I’ve noticed the oil pressure light would come on at odd times in my Citroen DS.  Mostly when I would rev the engine, for example going up a hill.   It would go out if I would back off.  The way the light would come on at odd times made me think that the fault was probably more with the sender unit than actually low oil pressure.

I bought a new sender and had it on my todo list for the next oil change, assuming that removing the sender would require the engine to be free of oil.   However, my mechanic stopped by recently and told me that it can be changed at any time, and even changed it for me quickly.

I assumed that would be the end of it, however the light continued to come on randomly, and even sometimes came on at idle.  Coming on at idle made me think that maybe there could be more to this, so I decided that I wouldn’t drive the car until I tested the oil pressure properly.

Of course, Citroen didn’t use a common sized oil pressure sender, so none of the adaptors in my mechanical oil pressure gauge would work.    I still had the gauge from the saga with my 300SE a few years ago.

I looked online for adaptors.  They were not expensive, but most of them seemed to come from the UK with shipping higher than the actual adaptor.   I eventually found a local one.   The sender unit is a male M10x1.5 thread.   I found one that provided two ports, one a more standard size and the other for the original sender.  I purchased it.

When it arrived it looked pretty good, but there was a problem.  There isn’t a lot of clearance to get this larger adaptor in, and while I could get the adaptor in, I couldn’t then get the fitting for the mechanical gauge in.   I tried a few times, both from the top and the bottom.  Since the gauge was out of the car, I couldn’t start it, so I used a jack to lift the car to try from the bottom.  In my ineptitude I managed to let the car fall off it and put a scratch on the side.  Luckily its not that visible from the side and mostly hit the bottom.

That left a sour taste in my mouth, so I decided to just order one of the smaller adaptors from the UK.   It took a few weeks to arrive.  It was much smaller and doesn’t have provision for the current sender.  That wasn’t an issue for me as this is a troubleshooting step and not a permanent install.

After all the time wasted with the old adaptor, I had the new one installed quickly.   Its smaller size making it much easier.   I soon had the gauge installed as well.   Starting the car, I had good news.   about 4.5 bar of oil pressure, or 65psi.   It would rev to about 70psi.

I let the car warm up a bit and the pressure stayed good.  A I then took it for a drive around the industrial estate where I keep my cars. I was never able to get the pressure to lower even at 4,000rpm.   I then let the car idle for a while until the electric fan came on and the oil was good and hot.   The lowest pressure I saw was about 2.5 bar or 35psi at idle. I consulted the workshop manual, and the specification for the oil pressure is that it must be at least 3.8 bar (54psi) at 3,000rpm with the oil at 60 degrees. (assuming 20/50 oil, which I use).

At this point I was pretty confident I didn’t have an oil pressure problem. I took the car for a drive again with a warmer engine and hot oil pressure was still good.   I also noticed something else that really sealed the deal.   At one point, the oil pressure light came on when revving the engine.   This should not be possible as the sender is not plugged in.

Its possible that this is related to the circuit board in the instrument cluster.  I know mine already has an issue as I had to bridge the connection for the illumination.    It may also be to do with excessive voltage at high RPM.   I’ll put a voltage gauge on the car at the same time so I can check.

This test, has given me much more peace of mind that there is nothing actually wrong with my car.   Citroen DS engines are very tough.