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Discussion Starter #1
HH 2008 136k miles with original spark plugs. Been getting poor gas mileage here 20 Mpg. Mixed driving with cold temps / hills and snow tires. Regular gas used and I wonder if plugs are to blame although cars runs fine no bad idle or hesitation. Hybrid Battery was tested when I bought car last OCTOBER 2019 and wa told it was OK as was everything else. Synthetic oil, clean fluids.

On the highway before it got cold best I saw was 23.9 mpg on long highway trip. Car seems to hardly ever be in EV mode less 25mph only. Display shows battery green and hybrid system appears to be doing its thing.

A friend gets 28mpg in a gen one HH but of course it’s lighter. Makes me want to sell the HH it and get a LX 460!!
 

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Looks like you have done some research....you could pull a front spark plug to make sure they are the correct plug, double tipped iridium's don't really exhibit a lot of wear, but are replaced at 120K normally and as a mechanic stated they influence fuel mileage. Depends on if you were going to keep it a while. Definitely replace front and rear drive component fluids, and check engine air filter if it hasn't been done. Otherwise tire, temp. and hilly conditions have a huge influence on MPG. Seems the problem started earlier though. I also replaced the t-stat on mine, warms up faster so mileage is better, OEM stat only. I can get 28 on a hwy run, fresh fill-up. Warm engine out of Econ mode then activate econ, EV is only under certain conditions and below 25 mph.
 

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Yes I though of checking the front plugs just in case. Probably end up keeping it for a few years now it's all set up for winter so perhaps I need too bite the bullet and do the plugs - $400 ouch. It has the tow package but fluids looked clean. Engine sounds a little throaty so not sure if a exhaust seal is shot just noisy but might be the 3.3 v6- I often ride in a old 2003 Avalon that's got 195k on it and it's a lot smoother / quieter. Engine does get a lot of short trips in week, about 5 miles so may not be the best for gas milage but would think some of the longer highway trips we do on weekends, up and down hills though, would average out the mileage a little higher. Sits outside here in Colorado so starts are a bit brutal when it's down to 10F or so but on average we've been around 25-30F I guess. Love to get a 2017 q7 but need to wait for used prices to his 20k :)
 

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Definitely check t-stat function, it would influence mileage big-time. Exhaust leaks would also throw off cylinder back pressure balance. Think mine is a 3.5 so may be a different animal. Used to like Audi but stepped back from them when my son had an A4 turbo, fast car but it was a nightmare to work on. I'm sure the new ones are very reliable. ( and Fast ) Seems the very short trips can really be hard on the hybrids, they don't even get warmed up because of fuel conservation. Too much engine moisture can be a disaster. My take on it.
 
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