I occasionally pull a trailer with my stock JKU Rubicon. My mileage drops to ~12. I've always been curious if this causes more wear and tear than an aftermarket lift and larger tires that also result in 12 mpg. I understand the added tongue weight, but my reasoning is that if both cause 12 mpg, they're causing the engine and transmission to do the same amount of work. Any truth to this?

Also, I have a late build 2012 with 40k miles. Eventually I'll need the cylinder head replaced correct?

 

Pulling a trailer is done occasionally. Lift and tires are there all the time.

 

My 2012 was built in February 2012. It has 67,000 miles. It still runs like new. I've probably towed about the heaviest trailer of anyone on here. It was a box shaped toy hauler that weighed about 5000 pounds. I figured I towed that thing for a cumulative of 5-6000 miles in NJ, PA, VA, and NC. I can tell you that there is absolutely no sign of any increased wear as a result of this towing. I changed all fluids a few months ago and everything looked normal. I track every single gas fill up since new and put the data into a spreadsheet. The data shows no changes over the 67,000 miles. As for the head, it seems that the vast majority of failures were at lower miles. Having towed my heavy trailer in all kinds of conditions, and now having 67K on my jeep, I am fairly confident that the head won't go bad. If it does, the warranties have been extended to 150,000 miles.

 

I could be wrong but here is my understanding of the head issue: it was not a fundamental design flaw. It was a variability in manufactured quality. If it was made correctly the head is good. If it was out of nominal design it could go bad. The change in design that came later was a change that made it less likely that heads would be made in the "bad" condition. Being honest, I don't know what that "bad condition" is.
I work as an engineer in an aerospace company. We frequently make design tweaks so that parts are less likely to be made with design flaws. It's called Design For Manufacturing.

 

The engine might be operating at the same efficiency, but the overall wear is different. Lifting will cause things like u-joints to wear faster because of the increased axle drop, ball joints- higher center of gravity, etc. Towing affects weight distribution and would wear the rear axle and suspension components faster. Towing would wear friction surfaces like the clutch and brakes faster, it's generally harder on the trans to get a load moving, tow uphill, etc.

What I've heard it was an issue with the head not being fully cleaned of casting sands during the manufacturing process. Some but not all 2012's have the problem, and it seems like the issue makes itself known relatively early, although there are folks seeing the issue down the road at 20k, maybe even 30k miles or more.