I have a 99 Civic and at random times, mainly when still, the temperature needle will move from half way or less than half into the 3/4ths range. I have it looked at, but they tell me it's fine. The problem is I get either "it's fine" or "don't let it get too hot". So what exactly is a point that I should be concerned about?

 

Look into upgrading your thermostat.

 

It should NOT be that high. Mine barely gets close to the halfway point and I'm boosted.

 

I had this same issue with my 98, engine would show overheated within a minute, but wasn't even warmed up, needle would bounce all over the place, replaced the sender, but that wasnt the issue, I had seen something about a voltage regulator built into the cluster circuit board, thats the only explanation I could ever come up with made the gauge act crazy

 

You engine is severely overheating or your temp gauge circuit is faulty. Assume the former for safety's sake.

 

you need a reference temp gauge to compare against your gauge in the cluster

 

That's what I was thinking considering that most of the time it is at half/less than half. I figured something must be going wrong if it the temp can increase by 1/4 or more. I'm no expert though so I figured I would go to a Honda forum.

 

I dunno, looks fine from where I'm sitting...........

 

thermostat only sets the minimum temp the engine will run, not the maximum, and you cant take it out, the engine has to reach a certain temp for the oil to boil off condensation, and for the computer to go into closed loop. it's also designed as a restriction to give the coolant enough time to transfer heat in the radiator. once it opens fully, it pretty much stays open, unless you are in a blizzard in the middle of south dakota for example

 

The sender could be bad. The radiator could be clogged. The fan could be coming on too late. The water pump may be old and damaged. Etc. Etc. Etc.