Correlation between E85 and premature O2 sensor failures

[LowPSI]

I'm debating on a set of headers and unfortunately I've found myself down a rabbit hole torn between trying to understand anecdotal internet tales and a logical understanding of the relationship between E85 and how it may contribute to damaged O2 sensors. The reccomended fix here, when switching to headers and E85 is to rotate the O2 sensor bungs 45 degrees up from horizontal to allow condensation to drip from the sensors and prevent damage. This does not make sense to me based on the fact that at operating temperature water would be in vapor form and not collecting on the sensor. After shutoff, the sensor would only be exposed to ambient humidity. Ignoring short trips that do not allow the vehicle to get to operating temperature, how would any extra moisture content find its way onto the O2 sensors?

My first thought is confounding variables like incorrect tuning when switching to E85 has caused the perception that E85 causes O2 sensor damage and the need to rotate the sensors. My second thought is that there is a contamination/sensor poisoning effect occurring that has not been well documented. The only discussion on this I could find was buried on a bmw forum where they discussed ethanol causing increased phosphorus vaporization (ZDDP) from the oil which then contaminates the O2 sensors.

Long story short, I'm curious by what mechanism E85 would cause an increase in O2 sensor failure rates.

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[WildHorse]

FORD recommends filling up with gas, once a month when running pump E85.
IF you run E85 from the barrel, you'll never have a condensation problem.

 

[LowPSI]

FORD recommends filling up with gas, once a month when running pump E85.
IF you run E85 from the barrel, you'll never have a condensation problem.

There's lots of other issues with water being absorbed by E85 in the tank. I'm specifically looking to understand how E85 (varying levels of water contamination or not) could damage an O2 sensor. What mechanism allows condensation to form on the sensor?

 

[WildHorse]

There's lots of other issues with water being absorbed by E85 in the tank. I'm specifically looking to understand how E85 (varying levels of water contamination or not) could damage an O2 sensor. What mechanism allows condensation to form on the sensor?

Same reason you get condensation on your car from a hot day to a cool night.
The ceramic element in the O2 sensor heats up too quickly while wet, it can crack due to thermal shock. This is why most modern sensors are heated gradually (via internal heater circuits) to reduce risk.

 

[LowPSI]

Same reason you get condensation on your car from a hot day to a cool night.
The ceramic element in the O2 sensor heats up too quickly while wet, it can crack due to thermal shock. This is why most modern sensors are heated gradually (via internal heater circuits) to reduce risk.

After engine shutdown would the exhaust not be subjected to atmospheric humidity? How would E85 change anything with regards to ambient humidity?

Also, if that statement were true and rapid heating of condensation caused stress fractures in the o2 ceramic, then anyone starting their car on a cold morning in Florida would damage their o2 sensors.

 

[WildHorse]

Cause the 02 is heated gradually.
water vapor byproduct from e85 is around 1.5x that of regular gasoline, so around 12%.
Anyways, it's all moot anyways. Factory flex fuel cars don't have that problem.
Aftermarket thin wall headers definitely collect condensation with any amount of humidity in the air.

 

[RNM]

I am coming up to 2 years with kooks longtubes here in Florida and I have never had any o2 issues.

 

[engineermike]

@LowPSI I like your thought process.

Combustion of any hydrocarbon produces chiefly water vapor and co2. Ethanol brings 1/3 more hydrogen with it so it produces 1/3 more water vapor. However, gasoline combustion produces a lot of water vapor as well. Technically, all o2 sensors are supposed to be installed at least 10 deg above horizontal and the Bosch datasheet says so, regardless of fuel.

Regarding alternating fuels, ever since coyote was introduced in 2011, and probably before then, ford has recommended running a tank of gasoline through it once per oil change interval.

 

[LowPSI]

@LowPSI I like your thought process.

Combustion of any hydrocarbon produces chiefly water vapor and co2. Ethanol brings 1/3 more hydrogen with it so it produces 1/3 more water vapor. However, gasoline combustion produces a lot of water vapor as well. Technically, all o2 sensors are supposed to be installed at least 10 deg above horizontal and the Bosch datasheet says so, regardless of fuel.

Regarding alternating fuels, ever since coyote was introduced in 2011, and probably before then, ford has recommended running a tank of gasoline through it once per oil change interval.

Thank you for the info on the Bosch data sheet. Based on that 10 degree requirement, I think it's reasonable to assume that might help mitigate normal condensation and potentially any debris regardless of fuel type.

My assertion is that, post engine shutoff (engine up to full temp), regardless of fuel type, only atmospheric moisture will remain. The combustion byproducts will be largely out of the exhaust and only small residual will remain. E85 should not relevantly impact the amount of condensation on an O2 sensor post operation (full engine temp achieved).

Now during engine operation the O2 sensor should see increased water vapor in the exhaust stream with a switch to E85. However, again, I would argue that additional water vapor would not have any more meaningful of an impact than say driving in a low humidity environment (ie desert) vs a high humidity environment (ie a swamp).

 

[2morrow]

Yes lol.

im surprised I still have functioning cats

 

[GregO]

E85 combustion produce formaldehyde and acetaldehyde. Those two compounds react with H2O.
Just a laymen’s guess. Way out of my wheelhouse here.

 

[robvas]

Sounds like another 'e85 myth'

Installing widebands in the upper portion of the exhaust pipe has always been suggested by the companies that supply them, nothing to do with e85

Kooks has them at 9 and 3 and they are just fine

 

[engineermike]

Am I crazy or have at least 3 posts vanished from this thread?

 

[Duece McCracken]

So I've absolutely smoked O2 sensors by running defoulers and having them angled wrong. Allowing condensation to enter the sensor and short it out. Quite a few. On 93 oct.

On E30 and E85 on various vehicles, never had a failure with a properly angled O2 sensor.

I don't believe an E85 thing, its a general shorting out thing from improperly installed parts getting a cocktail of various exhaust/combustion byproducts entering the sensor with water as a carrier.

 

[WildHorse]

Impact of Water Vapor on O₂ Sensors – E10 vs E85

(OEM vs Aftermarket, Wideband vs Narrowband)

Sensor Type	Fuel	Water Vapor Output (per mile)	Condensation Risk	Corrosion / Acid Risk	Heater Load	Typical Lifespan*
OEM Wideband	E10	Baseline	Moderate	Low	Normal	80–120k mi
OEM Wideband	E85	~25–30% higher	High	Higher (ethanol acids)	Higher duty	50–80k mi
Aftermarket Wideband	E10	Baseline	Moderate	Low–Med (materials vary)	Normal	40–80k mi
Aftermarket Wideband	E85	~25–30% higher	High	High	Higher duty	20–50k mi
OEM Narrowband	E10	Baseline	Moderate	Low	Normal	80–120k mi
OEM Narrowband	E85	~25–30% higher	High	Higher	Higher duty	50–80k mi
Aftermarket Narrowband	E10	Baseline	Moderate	Low–Med	Normal	40–80k mi
Aftermarket Narrowband	E85	~25–30% higher	High	High	Higher duty	20–50k mi

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