Hi there,
Well it could be a number to things..
The simplest thing I would do is get hold of an oil pressure gauge and fit it in place of or in tandem with the oil pressure switch. Then you can accuratly assess if your engine has a real oil pressure problem.
Maybe via a speed shop/car barn etc type place, buy a oil pressure gauge with some tube and crome mounting plate and fit it on or near your dash area so you can easily read it under different engine running conditions.
But the following basic troubleshooting principles apply.
1. change oil. Think you did that if I recall your post. If oil is wrong viscosity and is too thick at colder temps then that has bearing on the pressure from engine oil pump.
2. change oil filter. Think you also did that.
3. if one used a non genuine oil filter it may be not functioning correctly and letting oil bypass the element via an inbuilt relief valve. When that happens oil pressure from pump can drop a little and your sender light could come on.
(this is more a generic fault in lube systems)
4. the main oil pump has a pickup screen in the sump that could be partly clogged if the old oil had be in tooo long as was really gunky. This is sump off and is not simple job.
5. the engine is getting tied and bearings are worn so oil pressure is down with new clean oil.
Just looking in my service manual for a D750,850,950 kubota engines and the main oil pressure relief valve has a set range of 28 to 64psi (2 to 4.5 ). Not sure of model of engine in you machine. Maybe one other here can give you exact specs.
The oil pressure light switch is set to warn if oil pressure on that engine drops velow 7.1psi
so those numbers should be give you a clue to gauge purchase or borrow
hope that sheds some light on your prob.
I'd try gauge and if the oil pressure looks reasonable, then its likely the sender is becoming faulty.
regards
david
