'Sudden' change in oil pressure

[Miguel]

I changed the oil in my S2 and made a 300 kilometre round trip. On the outward journey the oil pressure was ‘normal’, usually between 35 and 70. On the return journey I noticed that the pressure didn't even reach 35, including at 100 km/h and 3.500 RPM (photo). The engine runs beautifully. Any ideas what it could be? Thank you all PS: Could the gauge have been affected because many of the roads I drove on were very bumpy?..

[NeilS]

Perhaps check the wire on the oil pressure sender by the oil filter it may have come adrift or is loose, did you change the oil filter when you changed the oil? (I assume the correct oil quantity had been used, check the dipstick?)

[Miguel]

Neil, thanks for your reply! I did check the wire on the oil sender and the dipstick and everything was ok.

[Miguel]

I've just removed the relief valve and it was stuck in the open position. Shouldn't it be closed? Anyway, I took it apart, cleaned it and didn't see any damage. Could this have been the problem of the low pressure?

[Huib]

Oops. That is serious. The oil pressure was really low. Most of the time erratic behaviour of the oil pressure gauge is caused by bad contacts inside the sender. This can be fixed by prying it open, clean the contacts, bend the contact lip and close it.

[Miguel]

Huib, thank you very much for your very helpful reply. I'll then see if cleaning the sender contacts helps.

[Huib]

Before closing the sender again you can test it with compressed air. Make a set up with an interface, manometer and pressure regulator.

If your sender is the 0 - 6 bar version, the resistance is 300 ohm at 0 bar and 0 (close to 0) ohm at 6 bar.

If it is the 0 - 8 version it will be 0 ohm at 8 bar.

[Miguel]

Great, I certainly will also do it! Thanks again

[Miguel]

I took the relief valve apart, cleaned it and that seemed to solve the issue. Thank you all!