2005 Toyota Tundra v8

This truck overheats with no radiator fluid loss. Also had power loss. Motor shake. Codes came back with a voltage high/low and both oxygen sensors upstream needed replacement.

Replaced O2 sensors precat and now she runs stronger but overheats still. Shake stopped.

Now downstream O2 codes triggered.

1) can faulty O2 sensors cause overheating by running too lean or rich?

  • What evidence do you have that it is overheating?
    – HandyHowie
    Commented Feb 16, 2016 at 17:40
  • Temp gauge.... Both rad hoses hard n hot....
    – Dee
    Commented Feb 16, 2016 at 18:57
  • Side note... Switched out spark plugs... Bank 1 white bank 2 brown.... This was pre O2 sensor switch out...
    – Dee
    Commented Feb 16, 2016 at 18:59
  • Dee, could you get us the exact codes? P0xxx, preferably with a description.
    – Zaid
    Commented Feb 16, 2016 at 19:23
  • Will do after work @zaid
    – Dee
    Commented Feb 16, 2016 at 19:49

1 Answer 1


Bad O2 sensors can contribute extra heat to the system, but usually they have the opposite effect. When the ECU detects that the sensors are faulty, the engine will default to open-loop mode, which should cause a properly functioning engine to run a rich A/F ratio. This actually has the effect of cooling the combustion charge and removing more heat from the exhaust.

The fact that bank 1's plugs are white confirms your overheat condition and/or indicates a lean A/F ratio. The fact that you are getting voltage high/low error codes leads me to believe that you may not be able to trust your electronics until the source of that error is corrected, as the ECU may be having problems reading the correct/expected input from the sensors. I would suspect the alternator's voltage regulator. If overvoltage is occurring, it may actually be causing your O2 sensors to fail.

EDIT: When an engine is hot, the radiator hoses will always be "hard and hot." The system gets pressurized (by design) as water under added pressure boils at a hotter temperature than water at atmospheric pressure.

EDIT #2: Even an engine that is running lean will not usually cause the engine to overheat (on the coolant temp. gauge) if the cooling system is functioning correctly.

  • That does answer my question and sheds light on direction needed. Thx!💯🍻
    – Dee
    Commented Feb 17, 2016 at 1:20
  • Sure thing - happy to help! Commented Feb 29, 2016 at 18:45

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