Too lean means the air-fuel ratio is incorrect-not enough fuel for the mass of air.
The water jacket is the path inside the engine block that the coolant flows through.
You can try and kill 2 birds with one stone by performing a power flush on the cooling system. Remove the thermostat, replace the housing, and use pressurized water through the cooling system. Just make sure you collect the old coolant, since in many places it is a crime to allow it to run into the sewers.
As fixitmr mentioned, do you have any white smoke coming out the exhaust? The best way to locate a leak is to pressure test the cooling system. You should be able to rent or borrow a tester from a parts store.
Tuesday, December 13th, 2011 AT 1:24 AM