Last Thursday, I get in my 05 GT, and the oil pressure is maxed out. I crank it up a few minutes later, and it's high but barely in the normal zone. The next morning, it's maxed out again. I stop, turn it off, and crank it back up, and it goes back to normal. I changed the oil thinking it might be the filter. It hasn't maxed out since, but the gauge fluctuates from 50% to 90% in the normal zone. The service light has yet to come on. Do you think it's the sending unit?
It's hard to say. Was it maxed out when the engine was cold? I have a true mechanical Autometer oil pressure gauge and at a cold start it's near 70 lbs, then when warmed up it's at 55-60 lbs cruising and close to 40 at idle.
It is probably the gauge cluster, or possibly a bad ground or voltage fluctuation caused by a bad battery or alternator. I have had the speedometer get stuck or be WAY off before. One time I was driving down the highway with traffic, but when I looked at the speedometer it said that I was doing 120 The stepper motor that drives the speedo is known to have issues, especially in cold weather. I have also heard of sticking or way off guage readings when the battery or alternator is going bad. Usually it affects the fuel guage, but I'm sure that it could affect the others as well. Typically an excessivly high oil pressure reading would be a false reading, especially if it seems to stick, and change when you turn off/restart the car.
