93 Accord temperature gauge reading cold

[craig21]

I have a 93 accord ex sedan, 4 cylinder, automatic that I bought in August. I live in South Dakota & it's starting to get cold here. When I first bought the car the temp gauge was working fine in that it would move to the middle of hot/cold range. Recently, I've noticed the interior doesn't get warm for awhile, even after driving 20 miles. It blows warm air but it seems like it should be warmer. I've also noticed the temperature gauge barely moves, if it does at all. Most of the time it doesn't move or just stays on cold. I did some research on here & thought I would try to change the thermostat, upper & lower hose and the antifreeze. I'm hoping this will heat up the interior better because it's starting to get cold here & fix the temp gauge.
Previously, I had a 91 accord & that would warm up great, even when it was bitterly cold here.
Would anybody have any other suggestions on what would cause the temp gauge to do this?
I'm even thinking about changing the transmission control module because I read on here that could cause the gauges to have wrong readings.
The speedo & rpm gauges also seem to have wrong readings, especially in the mornings or when I first drive it. I used my gps & found the speedo to be off by as much as 10 mph. The other item I've noticed is that I only get around 23-25 mpg highway & on my other accord I was averaging 28-30 mpg highway. Not sure if this is related or not but thought the more info the better
I have done all the basic maintenance-oil & filter, plugs & wires, valve cover gasket, air filter, tranny fluid but have never done anything with the heating/cooling system.
Sorry about the long post.
Awesome forum & full of useful info but I'm not sure where to start with this problem.

[jgr7]

Is the fluid level good? Do the radiator hoses get hot after driving for awhile? You may need a new thermostat.
I'm sure others will check in with more help soon.

[jeffcoslacker]

Your gauge seems to be reflecting what you notice in the temp coming from the system, so regardless of what else you have going on, it IS running too cold. So that would kind of eliminate heater control valve, dash control, in-dash plenum door problems, etc. You need to change the thermostat first. I think that will be your answer.

Running too cold also forces the fuel injection into a richer mode, which will show up as lower fuel mileage. My guess is you'll see some correction there as well.

Tach AND speedo misbehaving together makes me feel there is some kind of problem in the dash cluster itself, not computer or other causes. If one or the other was doing it, there might be external answers. I don't know what the cause might be, but I'd check the wiring couplers and grounds to the cluster and go from there...

[craig21]

I will change out the thermostat & see what happens. Hopefully, the gas mileage will increase as well. Thanks for the advice.