00 izuzu rodeo 6cyl

Possible head gasket leak or cracked cylinder head maybe..Pull your spark plugs and see if any of them look real clean..also check exhaust when it’s running to see if you smell antifreeze..Both are good indications of antifreeze/water burning in one or more of your cylinders..Be a good place to start..

I had vehicle that use to loose antifreeze with no visual signs of where it was going put in some alum seal stop leak in cooling system and it took care of that problem.

Not saying it well take care of your problem but it is worth a try. I know a lot of people on this forum will suggest not using sealers saying it will clog up your cooling system and they are right if you use more then what is recommended so if it does not work after the first try it can clog up the system. Before adding to system read instructions some say you can try up to two times but definitely no more then that.