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Wife's new vehicle is a 2021 Colorado! Z71. Right now it has only 1,200 miles on it. So far, I haven't noticed anything out of the normal.

I don't even have my flapper operational.? I hose clamped it open when my truck was new!

Nice looking tire, but I'm very happy with my Defender LTX's!

Thanks for that info. Hopefully the possible problems encountered with E85 are hit and miss with different vehicles.

When I worked (retired now) and drove 70 miles a day, my average was 22mpg. Strictly 93 octane too. I couldn't have been happier. Now that I barely put 2,000 miles a year on my truck, I have opted for E85 for no other reason that price. MPG isn't all that critical to me anymore, plus the fact I can go across the border to Ohio and pay as little as 1.83 per gallon. With E85 my mpg is normally around 16. Big difference, but so what. I'm am not a lead foot either, but the noticeable power factor running E85 is pretty cool too. I have no doubt, if I go back to 93 octane, my mileage will go right back to what it used to be. I love the fact too, my truck is a bit over 4 years old now and at barely 40,000 miles, it's still barely broke in.

As whitestallion posted don't confuse "normal operation" concerning this, with some sort of leak. If there isn't a coolant smell don't worry about it. I asked this same question back in 2014, and pretty much got the same reply as whitestallion's. My truck has done this from day one when it's warm temp, damp and rainy, and cold temp and precipitating. I've actually got out and smelled it. Nothing but water vapor.

Could very well be something with exhaust. It does have that funky smell due to the converters.

If they in fact did that, and with what 15HDriver posted, I'd be getting something in writing pronto from the dealer/tech involved that did the work so you have something to fall back on if you encounter issues later because of that brain fart.

I'm wondering if the way the truck is driven and what it is subject too would be the determining factor of when or even if the fluid should be changed. Granted these are more advanced than the older 4L60-E's, but the principles are the same. My previous truck was a '98 5.7 Silverado. Just the fluid was changed at 70,000. Never touched it after that. For eight years of its sixteen year life, I hauled two trailer loads of hay every summer. Probably close to max weight for a sixteen foot tandem with brakes. It was used for lighter things here and there, but the hay was the heaviest. The fluid was never touched for the remaining 225,000 miles I put on it before it was traded in March of 2014. If it wasn't for what I had to add when I replaced a cooler line, I would have never had to add a drop. It was as red as the day it was put in.

Is this the one you are referring to? http://www.gm-trucks.com/forums/topic/145676-bbp-independent-intake-test-results/page-1 I searched for exhaust tests by BBP, but couldn't come up with any on the Ecotec.

Those numbers make me feel good that I've had my flapper clamped open since the thread about it's usefulness good or bad first appeared on these forums. Granted, it doesn't help with WOT, but I rarely ever do that anyway.

I used thread sealant on the threaded fittings and hose clamps for all the barbs. I think not a tight seal is all that's the problem on yours.

For sure, if there was gasoline in the mixture.

This just about exactly 1,000 miles. Not sure what it mainly consisted of, but it sure smelled like fuel. I don't let the truck idle more than a couple minutes tops when it's started outside after work. From home it's in a garage, so hardly any idle time. I would say average outside temp was in neighborhood of 30F.

Same here from day one. I tried 93 for a while, but didn't notice any change in mpg. Not sure if it (93) will make any other difference, but 91 seems just fine.