Oil sending unit- Question??

Have a 91 XJ, The oil pressure gauge was operating fine, then it went wacko and starting getting stuck on high, but would go back down. Eventually it just stayed on high and would never move. So I changed the OSU today, after starting the XJ the gauge jumps back to high. When the motor is off the needle moves back down. Before I changed it the gauge the gauge was stuck on high. What could cause this???

Sounds like you might have a short in the wiring to the sending unit. The most likely area is in the engine bay itself where the wiring passes close to the block. Check the state of the insulation and make sure it isn't chafed or peeled away.

ON the 91, I believe it will default to high when the connection is broken, so check not for a short but an open condition. Make sure the plug is making good contact.

i have a similar problem mine is xj 90 bbut the problem is when yopu first start it the needle is pointing 3/4 and when it gets warm mark 1/4 and when you acelerate goes up is this normal or there is a problem with it

herreraxto said:

i have a similar problem mine is xj 90 bbut the problem is when yopu first start it the needle is pointing 3/4 and when it gets warm mark 1/4 and when you acelerate goes up is this normal or there is a problem with it

Click to expand...

This is normal. The oil is thicker when it is cold and therefore the pressure is always higher.

When the engine is warm, if the pressure when the engine is idling is approximately 1/4 and if it is approximately 1/2 when driving above 50 MPH (+/- 80 KPH), that is normal.

thank you, i was starting to worry about it i think it was the oil pump or other problem

Oil filters can also produce variances in oil pressure. My 98 is almost at 200,000mi and last winter I swapped out my idiot light cluster for a gauge cluster and have only done 2 oil changes. When I first did the change the K&N oil filter and Mobil-1 10w30 ran pretty high all the time ~70 when cruising. Did an oil and filter change using a Mopar filter and the oil pressure dropped to ~50 when cruising. It is about time for another one and this time I have restocked with Mobil-1 filters so I am curious what that will produce. Will probably find that out next week, right now I'm busy cleaning carbs on my mower, tractor, brushcutter and chainsaw in an attempt to cut back and reduce the jungle thats grown from all the freakin rain we've had...

Thanks all! I will first check to make sure there are no breaks or shorts. And herreraxto, yes thats exactly what mine used to do before it just get stuck at full. I was worrying that it might be the oil pump or other problem also. Although changing some gaskets, ie. (oil pan) is on my list to do. So if I'm down there might as well replace the oil pump.

So I guess it's off to check the wiring. I'll let you know how it goes.
Thanks!