As l drive the gauge rises and stays at hot.What could cause it, what should l do to fix it?

is your fan working if not check the fuses for the fan you will probably have 2 or 3 fuses for the fans so check them all

A blown head gasket or cracked head can cause this. To check it look in the expansion or overflow tank and see if there are bubbles in it when it is hot. Also a stuck thermostat can cause it to over heat. If you get it too hot that can cause the head to crack, get it fixed soon before there is more damage. Good luck.

There r a number of possible causes.

Your thermostat might be stuck partially shut, preventing the coolant from flowing through ur radiator fast enough to effectively cool the car.

Your waterpump might be failing & not circulating coolant through ur cooling system.

You fan might not be working properly & not blowing air across ur radiator.

If the gauge gets too high, stop driving & let the car cool down. If the car overheats u could warp ur cylinder heads, which will require a top-end engine rebuild or a new engine - very expensive.

Besides the things mentioned by others, it could be that then engine is running lean. This can be caused by timing error, or fuel mixture.
If the fans are coming on, then try running some systems cleaner in one tank of gas, and also replace fuel filter.
If the engine has one temp sensor for the gage and another for the computer, replace the one for the computer.

If u actually had to add coolant, then u have a leak in the system somewhere. If it is external (i.e. water pump, radiator, hose, etc.) there will be evidence of this on the underside of the car, either by a streak of liquid coolant, puddles on the ground under the car, or a whitish stain from where it has dried. It is also possible ur thermostat has stuck closed, or the electric fans have stopped working, which will cause the engine to run hot, & boil the coolant out through the overflow tank. If there r no signs of an external leak, but you're still adding coolant/ running hot, then it is likely a headgasket failure. 1996-2004 Legacies with the 2.5 engine were prone to this, due to a poor gasket design. My 98 Outback manifested itself in much the same way. First thing to do, is to stop driving the car, & get it looked at as soon as possible. The longer u drive it with the temp high, the more u risk damaging the engine further (warping cylinder heads).

This same thing happened to me.

l am willing to bet $20 (!!) that it is a blown head gasket, especially if the gauge fluctuates between normal and hot.

My repair cost ~ $1200, as they had to drop the engine and grind the engine block.

Good luck!

Other than this issue, my 97 subie was incredibly reliable up until last month when someone hit me and the car was totalled. l am now the proud owner of a used 07 Outback.

OK. It is the driver is side head gasket leaking externally at the back corner. They all do it. Check with your local Subaru dealer to see if it is under warranty. They are still fixing some of these for free. If not, you are looking at about $600 to fix it. I've done hundreds of them.