dunno specifically about the XJ but most engines are similar in these facts.
-you shouldnt beat on the car until the oil temp gets to min of 180F (which takes wayyyyyyyyyyyyyyyy longer than getting your coolant temp up)
-max you want to get with dino before you must back out of it is 250F
- 280F w/ synthetic you want to think about easing off the beast. 300-310F you need to back out and let the temps get back down.
In general most cars under normal driving (once you've been driving 30 minutes+) are running 170-215F ideal oil temp is around 200F
if i was you i'd skip the oil temp gauge and get a good oil pressure aftermarket gauge...factory one is slow to react and you can't trust. with an oil pressure gauge you can basically tell when the oil temp is hot enough to beat on it, as for knowing when you oil temp is getting too hot w/ an oil pressure gauge... it varies some cars will drop below the normal 'fully hot' oil pressure, and you will know its really getting up there. but other cars...most that i've seen....even if too hot the oil pressure will still read the fully hot normal oil pressure at idle.
basically if you already have an aftermarket oil press gauge, get the oil temp for the engine. if you dont get the oil pressure first... its far more important. also oil temp is more dependent on RPM while coolant temp is more dependent on LOAD of the engine. so if you are flooring it but keeping the revs at 3200rpm or below your coolant temp is gonna get up there whereas your oil will get a bit hotter but not crazy at all. whereas if you were to drive in first gear at redline holding that steady state...you'd be very light on the gas to do that....coolant temps would be fine...but that high rpm would really drive the oil temp up pretty fast.
oil temp for the automatic trans i do not know the ideal temps for those, i always run 5 or 6 speed in all my cars, i dont have very much knowledge of auto's.
