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Old 08-10-2011, 02:27 AM   #2 (permalink)
EcoModding Lurker
Join Date: Sep 2009
Location: Colorado
Posts: 28

'Stache Builder - '92 Honda Civic VX
90 day: 42.58 mpg (US)

White Dwarf - '09 Mazda 5
90 day: 28.87 mpg (US)
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Bubbling in an overflow tank has several causes: faulty radiator cap, stuck closed thermostat, faulty water pump, air pockets in the system (turn your heater on when bleeding it), blown head gasket.

I don't think that your P0118 would have anything to do with this, since it is an electrical circuit fault, and air bubbling in your overflow is a mechanical cooling system problem. The PCM uses the ECT sensor to determine fuel trims, closed loop, etc. If there is a problem with the ECT sensor, it may be staying in open loop, and you will notice a drop in fuel economy.

I fixed a car today that had a stuck closed thermostat, incidentally. Boiled a bunch of coolant out within minutes!
1992 Civic VX

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