would you define a ''bad head'' and how that would affect your GAS MILEAGE? I really am curious. The mechanic was hesitant to WASTE YOUR MONEY by doing an unnecessary test on your vehicle. A customer doesn't always get what they ask for if the dealership is on the up-and-up. Your mileage loss sounds like you are compensating for the loss of performance with your foot. The more dissatisfied over time with the lack of performance, the more gas you use. I wouldn't curse the mechanic too loudly, he's doing you a favor.

 

I'm running 35s and got about 17mpg after I lifted and went to 35's on my 2012 with 4.11's. In January, I saw my mileage drop to just over 15, then 14 and around 13.6. I'd had the tick since day 1 and taken it in several times but they wouldnt do anything. Then the MIL came on and I took it in, they flashed the computer but of course that did nothing. Then when I raised hell and threw a handful of printouts describing exactly what I'd already told them - they finally agreed to replace the head. Two days later, I had my jeep back, the tick was gone, and I was back to getting 17.5-19mpg and have been there since. I took a bit of a trip out of town yesterday and averaged 16.9, but I had a headwind most of the day so I expect a bit of a hit. In my case, my head was misfiring on cyl's 2 and 4 so I'd expect a drop in mileage. If it's bad, you will eventually throw a code, but the most obvious symptom will be the notorious tick. Do you have it?

 

bad valves in a head will cost you performance/mpg. Many articles have been done in performance mags (gm-high tech had one where a ls1 z28 picked back up 20+ rwhp by replacing heads that had bad valves) I have been into performance cars all my life and heads can make or break your car. Many ppl have already posted on this forum and many others about dealerships not doing there job. This was the second time my jeep as been there. The last time i dropped it off it was getting 13.6 mpg. In ard a month and a few hundred miles it dropped to 12.4 mpg. The service dept is use to dealing with ppl who know nothing about cars and can give them BS answers all day long and send them on their way. MY loss of mpg is over the same route with the same driving style as when it was getting 15+ mpg with mods. So your idea is way off.

 

At this point it just sounds like a loud valve train (similar to my z06 with cam/dual valve spings) so i know the dealership is just going to say its normal.