I change my water hose on a Grand Prix 2006 3800. Then I change the thermostat but it still rising but never go in the red I don't have any leak anywhere but I have to out more water in it. This start
If its using coolant its likely a head gasket failure and its leaking into the engine and being sent out the exhaust as steam. It could also be ending up in the oil. Check it. If its a milky color then that's where the coolant is going, if its not, then its likely leaking into a cylinder. I'd start out with an application or two of Bar's Leak. It's available at any auto parts store, is safe for your cooling system and works very well. It may well save you having to pull the engine apart to replace gaskets which is a major job, and may not be worth it on a 10 yer old car. I've used Bar's Leak on my car and it pretty much solved the problem.
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