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      10-01-2013, 04:43 PM   #1
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Ethanol + Tstat Delete not good for oxygen sensors?

I started getting some codes (p29e0, p29e1 and p0171) and SES light suggesting my oxygen sensors may need to be replaced. This started after installing the BMS Tstat delete, which reduced my oil temps 30 deg F, with my E40 tune. I did some internet searching to see if there is a correlation between ethanol and oxygen sensors, and came across this bit at a website called "Fuel School":

Oxygen sensors (O2) used in most of today's automotive gasoline engines are failing at an ever increasing rate.

There can be one to five sensors per vehicles and having them replaced can cost a consumer $100.00 to over $300.00 each.

Also, they rarely fail together, which means a customer can have one replaced and be back next month or even next week to have another done. This can go on and on until the customer takes their business elsewhere.

This can happen in brand new vehicles with low mileage or older high mileage ones.

Vehicles such as ambulances, police cars, and service equipment that have long idle periods and or a high percentage of idle time; and vehicles used for short trips are most susceptible to these problems.

Interestingly, most of these "failed" sensors are not actually defective or even worn out. What has happened, is that a small amount Ethanol in the gasoline (gasohol) will get past the piston rings and into the motor oil.

The Ethanol with agitation and heat liberates some of the phosphorus from the motor oil. This phosphorus is vaporized and sucked into the Positive Crankcase Ventilation (PCV) system and burned in the combustion chamber. This burned phosphorus on its way out the exhaust coats the O2 sensor(s) building up in layers.

This phosphorus coating acts as a insulation causing the sensor to react slower than normal. The engine computer reads this slow reaction time as a failure of the sensor forcing its replacement.

Note: This is the same material that coats catalytic converters causing them to go "cold" or cease to function.

Replacement of the sensor(s) is not the only option. It is possible to with a properly formulated chemical additive to clean up and remove this coating (both from O2 Sensors and Catalytic Converters) with a service procedure or with a tank additive.


Any thoughts?
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      10-01-2013, 04:47 PM   #2
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I don't know but Im curious about this as Im interested in the tstat delete as well
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      10-01-2013, 04:55 PM   #3
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Hmmm.....hmmm. I do get occasional fuel mixture codes, and I think on two occasions a lean condition limp mode from just cruising around/partial throttle that went away when the car was re-started.

I have the thermo delete and run E30 more or less always. Blew a lambda o2 last fall.

Who knows if there is any causal link here though, i'm just speculating.
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      10-01-2013, 06:28 PM   #4
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Here's the link to that article.

http://fuelschool.blogspot.com/2009/...catalytic.html

I'm going to investigate the phosphorus + ethanol = coating on O2 sensor chemistry a bit. Gonna put on my chemical engineering hat for this one!

If in fact ethanol consumes the phosphorus additive (ZDDP - Zinc Dialkyldithiophosphate (*)), then this could also explain why E85 users suggest more frequent oil changes.

(*) From the BITOG website:
Zinc Dialkyldithiophosphate: Affectionately known as “ZDDP”, this miracle multi-purpose chemical and has been the chief anti-wear (AW), extreme pressure (EP), and anti-oxidant (AO) additive for decades. It is so effective and low cost that it is virtually irreplaceable, which is why it survives all efforts to remove phosphorus (P) from oils to protect the catalyst. With modern oils putting caps on the maximum P allowed, other additives are now being used to supplement this old standard, such as Molybdenum anti-wear compounds and ashless anti-oxidants. There are different types of ZDDPs including primaries, secondaries, and aryls, each with its own strengths & weaknesses, and the mix is balanced to the type of service the oil will see.
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      10-01-2013, 06:45 PM   #5
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why would you delete the thermostat? You're probably running open loop.
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      10-01-2013, 06:55 PM   #6
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Quote:
Originally Posted by N8N View Post
why would you delete the thermostat? You're probably running open loop.
I thought I wanted my oil temp to be lower than 240F. But this may not be ideal for me. I'm thinking it may be contributing to my sudden code issues, so I plan to reinstall my oil Tstat.
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      10-01-2013, 06:58 PM   #7
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Quote:
Originally Posted by N8N View Post
why would you delete the thermostat? You're probably running open loop.
It bypasses the thermo so oil is flowing through the cooler at all times, calling it a "delete" is probably a bit misleading. Just what it goes by I guess. Car still runs closed loop.

http://www.burgertuning.com/low_temp...W_135_335.html
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      10-01-2013, 06:59 PM   #8
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Here's another article on the effects of ethanol on engines. Same problem with ZDDP, but this article focuses on the phosphorus poisoning the cat precious metal.

http://www.ehow.com/info_12172217_ef...converter.html

If this is accurate info (I have no way to judge) then the high-ZDDP racing oils could increase these O2 sensor and cat problems.
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      10-01-2013, 07:00 PM   #9
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Quote:
Originally Posted by 135Pats View Post
It bypasses the thermo so oil is flowing through the cooler at all times, calling it a "delete" is probably a bit misleading. Just what it goes by I guess. Car still runs closed loop.

http://www.burgertuning.com/low_temp...W_135_335.html
Correct. It's not a delete, rather a diverter for free-flowing oil flow to the oil cooler and back.
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      10-01-2013, 08:03 PM   #10
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Been running e60 and bms thermostat for a few months now. I don't think there is any correlation imo.
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      10-01-2013, 08:13 PM   #11
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Quote:
Originally Posted by zeel View Post
Been running e60 and bms thermostat for a few months now. I don't think there is any correlation imo.
i'm inclined to agree
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      10-01-2013, 09:08 PM   #12
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We all know one thing for sure, eventually, regardless of what you run in your car, they will fail... Why you ask? Murphy's Law.
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      10-01-2013, 09:22 PM   #13
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Quote:
Originally Posted by Jeffman View Post
I started getting some codes (p29e0, p29e1 and p0171) and SES light suggesting my oxygen sensors may need to be replaced.
Those fault codes are actually for "mixture too lean", also known as fuel trim type codes. This can be caused by a number of things, but probably not your thermostat bypass. Could be that you're running close to the limits of the low-pressure fuel system.

Pretty much anything out there that boosts octane and performance is bad for 02 sensors and cats. MMT was in pump gas in the US for a long time, but it also causes metallic residue to coat the cats/sensors over time. MMT is what's in a lot of octane boosters, like Torco or NOS racing formula. ZDDP was eliminated from most engine oils because it can cause long term issues with cats. This is the first I've heard of ethanol causing this type of issue, but it's a fair trade for the performance in my opinion.

Anyway, I'd suspect if your issue really was related to ethanol as stated in that link, I'd think you would be getting codes related to slow 02 sensor response or "aging". My 2-cents, anyway.
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      10-02-2013, 12:34 AM   #14
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BMWM.D., you may be right it's not the O2 sensors as I'm not getting any lambda probe codes. My STFT values are spiking at 33% occasionally and I've seen LPFP pressures below 50 psi from time-to-time. However, ZDDP is still in the oil, more so in the racing oils. The total amount has been limited by EPA in non-racing oils. It's still present in the Castrol oil which is the stock OEM BMW oil.
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      10-02-2013, 02:47 AM   #15
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^ what he said
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      10-02-2013, 09:15 AM   #16
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Quote:
Originally Posted by Jeffman View Post
BMWM.D., you may be right it's not the O2 sensors as I'm not getting any lambda probe codes. My STFT values are spiking at 33% occasionally and I've seen LPFP pressures below 50 psi from time-to-time. However, ZDDP is still in the oil, more so in the racing oils. The total amount has been limited by EPA in non-racing oils. It's still present in the Castrol oil which is the stock OEM BMW oil.
Sorry, should have been more clear. I meant most off-the-shelf oils have very little any more. Usually the European formula oils have more of it.

You could have something going on with an injector/s. Might be an early sign of failure.
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      10-03-2013, 11:17 PM   #17
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UPDATE: just driving with Shell VPower 93 for two tank-fulls seems to have cleared up the codes. I think the adaptations for STFTs have modified themselves. Thanks to all who commented.
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      05-24-2014, 09:20 AM   #18
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UPDATE: the codes came back regularly as soon as it got cold out last winter, even on 93 Shell VPower. I just fixed a vacuum leak by the brake booster which helped somewhat with the codes (even on E30) and also fixed the low boost error. Now I got p29e0 and p0171 codes and SES light. As I just had the water pump replaced two days ago, I brought the car back to the shop to have them take a look and figure it out. I am keeping my fingers crossed that the O2 sensors need tightening (according to the BMW N54 diagnostics fault tree document that is circulating around here).
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