I recently bought my Accord, it has 131k miles on it and seems to run quite well.
When I purchased it the temp. gauge was reading high. It would automatically go
straight to the red (even when I would just insert the key and turn the battery on but not the engine). When it
is cold, it takes a second for it to rise, but once the engine is warmed up it just stays red.
The guy I bought it from had just put in a new temp sending unit,
the one that screws into the head of the engine. He thought that would fix the problem, but it didn't.
The car does not seem to be actually over heating. The fans work. What is the next step?

 

Either the wire is grounded between sending unit and gauge, or the temp gauge itself is bad.

The DIY section has a thread called acc 5th gen... and that site has the shop manual split into pdfs so you can download them. There are some electrical tests that may be able to diagnose the problem.

Good luck.

 

Thanks! I will let you know what I figure out.
Those pdf's are very helpful!