912 overheating after maintenance

Some idle speculation:

Air pocket in oil/coolant systems, preventing efficient removal of heat ???

Or a loose ground or faulty sending unit or gauge?

It’s unlikely the tech would change the carb needle clip position.  And because the cylinder head temp and oil temp are now both higher than before the maintenance, a loose gauge/sender wire also seems unlikely.  So that leaves the new muffler as the most suspect.  A lot of the waste engine heat is normally removed through the exhaust system, and if restricted some of that heat will stay in the engine and exhaust headers. That’s where I would be looking.  

"It’s unlikely the tech would change the carb needle clip position."

It could have been an accident and at least be checked to rule it in or out. I've seen tech make mistakes in carbs before. "MIF" = mechanic induced failure. When something brand new and acute pop up after maint. it's time to look at that first to rule in or out possible mechanic induced issues whether done on purpose or accidentally done.

A poor installation and or incompatible exhaust could be a cause for odd and or different engine readings.

Food for thought;

I'm not a person that likes to throw money at problems, but I prefer to check and rule in or out the most common causes, easiest to check and cheapest. Good diagnostics like in a doctors office is your best avenue to take. Start at "A" then B then C and don't skip around to L or M because you may miss the easy fix which is what many issues are. A good diagnostics plan can not only save money, but weeks of trouble shooting. Thousands of people have replaced and spent money on fixes that weren't necessary and didn't fix the original issue if they had just looked at the most common and easy fixes and stayed the course on a could straight forward diagnostics.

Hi Roger,
Nick’s original post states that this overheating is happening at 75% power (map= 25.5) at 2000’ with an OAT of 75 degrees. That’s a density altitude of about 3700’, so I assume the throttle position in this configuration is greater than 3/4, where the needle position is no longer in play.  If it was the needles, then advancing the throttle past 3/4 should cool off the engine. I agree it’s a very easy thing to rule out, I just don’t think a needle position diagnosis fits the symptoms.