#7. BTDT. Pull the plugs.  The extremely clean one is the faulty cylinder.

#1 is the symptom
#2 will cause it to overheat at all times
#3 will cause it to overheat at high speeds, not low.
#4 the cooling system is pressurized.  It pushes, not pulls.
#5 maybe, but that doesn't explain #1
#6 once again, will exhibit overheating primarily at high speed.
#7 Bingo!

Jim

Colin Stanfield wrote:

>
> 1) Continued air in system
> 2) Faulty thermostat
> 3) Faulty water pump
> 4) Obstruction in coolant hose and or leak in hose connection allowing air
> into system
> 5) Faulty sensor for turning on coolant fan
> 6) Old and clogged radiator
> 7) Combustion gases getting into coolant system due to faulty head gasket