I have owned this Cherokee 140 since 1994. I have logged over 1000 hours
in it through the original and the now installed overhauled engine. Oil
temps were usually at 180 degrees (both engines)when OATs were between
50-80 degrees or so. It would read 1 needle mark higher when it got to
be 95+ outside. In the last 150 hours or so, it has been drifting up and
is now reading about 2 needle marks above 180 degrees (200 degrees or
so?). I replaced the oil cooler because of age. It was cheaper to
replace it with a new PMA'd unit than to have it checked/cleaned. I
swapped the Vernatherm. No difference. Do the gauges/senders drift off
with age. I am going to test the sender/gauge with hot water and a
thermometer.

Once it gets to that mark, it seems to stabilize.

Baffles are all in good shape.

What else causes temps to drift high? I know that shifting main bearings
can cause this, but I doubt the engine would continue to operate for
this long if this were the case. I do wonder though because the cold oil
pressure is right at redline on takeoff. After 5 minutes it goes back
down into the middle of the green.

Thoughts/theories?

Thanks,
Mike