Originally Posted by JamesClarkIV
Could this be caused by faulty sensor? Could this be caused by vernathern that is opening and suddenly shunting hot oil away from oil cooler and dumping it onto the oil temp sensor (is this sensor at the output of the oil cooler return line?).
Yes. oil temp can't rise 35* in 30 seconds and vernatherms don't really fail like this. Likely a bad crimp at terminal on OT sensor. vibration patterns are changing as you pull the power back and is likely adding resistance at that bad crimp or loose connection.
Even if the VT was opening and closing erratically, I don't think the cooler can shed 35* in most cases. I thought is was closer to 20* or less, but not sure.
I would definitely start with OT sensor wiring.
Sensor is on the return side of the cooler, so when the VT is closed, it reads the temp of the oil returning from the cooler. However, VT's usually either stop working or fail to fully close the port. It would seem implausible to me to have a VT suddenly open and then magically close 10 minutes later. It is just a piston with with piece of wax that changes size with heat. Not very sophisticated. They typically fail by not closing or only partially closing. Having one suddenly open just isn't how they fail.