Idiot lights

OT: My sons Kubota's oil light is coming on and staying on until the tractor is speeded up cnsiderably.  According to him this is a change and he was wondering if it could be the oil pump or the sensor or the light.  I said yes.  He said the tractor sounds fine as always and has never used any oil.  It's a 3 cy diesel.  Is there any testing I can do before he just changes the sensor and or light.  Hate to drop the pan but if we  need to we can haul it to my shop and tackle the job. Any suggestions before we do that.  THX, Jim 

I'd get a pressure guage and check the pressure.  I don't know the spec's but your dealer should.  There is a chance that the sending unit is bad and needs more pressure to turn the light out (hopefully).  Also does it take more RPM to turn out the light when the engine is warm, if so that is and indication of low oil pressure due to something out of clearance .  I don't know much about kobuta, but get a pressure check done.  If low, then you got a project to figure out where.  Good Luck.  

Thanks to all.  I hope to get over there and check it out Saturday.  The T idea is a good one if I can find a metric T.  Darn metric stuff is still hard to find around here.  Jim 

I had a kubota, that would act like you describe, I would put a mechanical gauge on it, as the other poster said. If that confirms drop in pressure, try dropping the oil pan, and take the suction tube off of the pump at the joint. There is an o-ring that got hard, and cracked, when the oil got thin enough it would suck air.  That model was a 2 cyl, L185, if I remember the # right.