I am constantly having to add coolant to my 1998 Grand Cherokee (318 V8); about 1L every couple of months or few thousand km. Exhaust is clear, consistently passes emissions tests, no puddles where parked or indications of drips. It's been like this for years. I have the car serviced by a Chrysler dealership about once or twice a year (I do relatively low mileage), never remember to mention it to the service tech, and no mention has ever come up on inspections.
My question: Where could the coolant be going? Do catalytic converters consume the "white smoke" that I always thought was the symptom of a coolant leak into the cylinders? Is a liter per few months/few thousand kms slow enough that drips/puddles/white smoke would not be noticeable? More importantly, is this a "time bomb" waiting to go off, or is a consumption pattern like this inconsequential to the car as long as I keep the reservoir topped up?
One other observation which may be unrelated: the engine knocks under high throttle on mid-grade fuel (despite owner's manual recommendation for regular grade), which suggests to me some sort of build up in the cylinders / on spark plugs; could it be residue from coolant being burned in the cylinders?