MY TEMP GAUGE IS REGISTERING HOT WHEN I AM RUNNING MY A/C AND WHEN I TURN OFF THE A/C IT WILL START TO GO DOWN TO THE HALF WAY POINT OR LESS. THIS IS A 2001 MAZDA 626 LX. I HAVE NOT HAD THIS PROBLEM UNTIL THE LAST PART OF JULY 08 AND IT WAS NOT AS BAD UNTIL JUST A WEEK AGO.

the usual suspects are:
stuck shut thermostat
clogged raiator
dead water pump
low coolant level
it's sunday, rovers don't work on sunday.
Then again, maybe its wednesday, rovers take half a day then.

to me the temp gauge running at the half way point is correct. why was the t-stat changed?

fans came late on those car,like 212 and second fan comes on at 224,you reprogram it to come a lot sooner,,other thing is there might be gunk inside the block,and coolant has hard time to pass through,and staying longer than enough in block temp goes high,even tough the radiator is doing it's job,it is just coming out block lot hotter than it suppose to be,and gauge read the block not the radiator

I would supect you actually have two problems going on here. First off it sounds like your guage is reading inaccuratly. When it is reading at one quarter it probably should be at the half way point. This is the normal operating range. The most likely cause is the temp sensor for the guage. When you pull a trailer and engine gets under a load the tempature sounds like its going up too high. Your engine light comes on because it uses a different sensor and is registering accurate tempature. I would start by comparing actual tempature of engine with what the guage reads, this can be done with a scanner or a heat gun pointed at the thermostat housing. I believe you will find a faulty sensor or possibly an outside chance of a bad guage.(but doubt it!)Once that is straightned out you will have to look at why is the engine getting too warm under load. I would start with radiator flow,A ristricted radiator either internally or externally will cause this. Good luck!

During the winter time the engine may not produce enough heat to go half way. You can modify this by installing a hotter thermostat. But I would not go more that 20 degrees F though, or you could create issues for summer driving.

the gauge or temp sender is bad. i would try replacing the sender first. good luck.

may be you gauge nedd to be calibrated

try changing the temp sending unit

First when vehicle is cold like in the morning check and make sure that the vehicle has enough coolant/ antifreeze in radiator and reservoir. If coolant is need use a 50/50 mixture of water and antifreeze. You will need some time to do this let car run at idle until the temp guage is in the middle NOT+ normal operating temperature. At this point if the thermostat should be in the open position. Let vehicle run and check to make sure that radiator fan comes on. This should come on when guage is about midway/half way. If temperature rises above half going to h/hot and fan doesn't come on, you either have a BAD FAN BAD FAN SWITCH BAD FAN RELAY OR BLOWN FAN SWITCH FUSE. You will need to check all of the following I will help if its needed. If fan comes on and doesn't go off and vehicle continues to get hot even with fan running. Feel radiator hoses and see if the lower radiator hose is cool/cold. If it is you have thermostat that stuck closed. Replace thermostat and fix problem. If all the above is good and vehicle continues to over heat. THE BAD NEW IS THAT YOU MAY HAVE A BLOWN HEAD GASKET /CRACKED HEAD /BROKEN WATER JACKET. Basically you will need a HEAD JOB at least a head gasket. ONe tell tail sign of this is oil looking like milkshake/chocolate milk-a creamish while residue in oil or antifreeze. Contact if you need hel0p. Good Luck and thanks for using FIX YA