Here in the Southwest the desert is really dusty, with lots of cakey-silt. Last year I noticed the bottom inch of my overflow bottle was all mud from this silt getting into the vent on the overflow bottle, which mixed into my radiator and made it pretty nasty.

So I decided to add an "air filter" to it. Had to trim a little plastic on the spout of the overflow vent and I slipped some hose over it with a hose clamp. Can't remember the size, probably 5/8". Then after a foot or so I used 3/8" hose and a hose clamp as a reducer to go down to a generic fuel filter. Plenty of flow through this, I can blow through it easily. I tuck it behind the battery.

I figured id share Incase anyone else gets a filthy coolant bottle too

 

Hm, I like it!

 

Neat trick, but I'd bet the gunk is from inside the radiator and not the outside air........when was the last time you flushed your cooling system out real good ?