Hi, and welcome. My name is Marty. If there are no external coolant leaks and the coolant seems to be burning through the motor and out the tailpipe it indicates that the motor has a blown cylinder head gasket. This would be evident by a fair amount of white smoke coming out of the tailpipe when the motor is running. There is a pressure test that can be performed on the cylinders to determine exactly where the gasket is blown. In order to repair this problem the cylinder head will need to be removed to replace the gaskets and to check the head to see if it is warped or cracked. A machine shop can straighten a warped head and can usually repair most cracks in the head. There are sealants on the market that can be tried to see if you can stop the coolant loss without removing the cylinder head but this sounds like an awful lot of coolant loss. The sealants are not usually going to be successful with a leak this large. Click here for the sealant that I recommend.
Please let me know if you have any questions.
Can this kind of search/repair be done by a non-expert? It sounds very expensive to repair.
My husband said that the radiator fluid reservoir level does not go down. It remains constant even if he radiator needs fluid. If he adds too much fluid to the radiator, it then increases the reservoir fluid level. He changed the thermostat with a new one but it does not seem to be working. He replaced the upper radiator hose with a new one. He said that the oil filter had oil and water so he replaced that. He thinks there is an air pocket somewhere.
I purchased a bottle of Blue Devil head gasket sealer but the one the sales person recommended was the simpler one. We have not tried that yet.
Is it us just hoping that the problem is not an expensive head gasket repair or could it really be something else?