Ok, my truck is a '00 Z71 that is approaching 100k miles now.

I got it last year with somewhere in the low 90's for mileage (got from my dad... I've been driving it since I was 16). When I first got it it wasn't getting very good gas mileage... like 12 or 13 average (some highway, some in town). I did all the maintenance on it like spark plugs, filters, oil, and seafoamed it. Well, it then jumped up to over 15mpg instantly and did that for quite a while.

Now for some reason it's back down to 12.xx average every time... I went from getting like 250 mi. per tank, to over 300 (close to 350 sometimes), and now I'm back down to 250-ish (barely going to make it this tank). Now, I know it isn't the type of driving that i do, because that is about 90% on the exact same path back and forth to home from school and back on weekends.... so that isn't it. I'm definitely not driving more aggressively.... And I don't see why a couple thousand miles on anything should be able to take away over 3mpg like that...

So I don't really even know what to check (it's not tire pressure either . lol)... Any ideas? What could it be?

Thanks for any help.

 

Wash and wax!























Front O2 sensors maybe? They do ware out and your at 100k mile.

 

Its cold outside so it takes longer to warm up...

 

You think that would make that much of a difference with like 20 minute trips at least on average?

 

i wouldnt think so

 

Do they use a different winter blend oxygenated gasoline where you live? They do here in Jersey, and it's good for about a 2-3 mpg loss...

 

Really? I have no idea. I'm in lafayette, IN.

One thing I was thinking is that I think my thermostat is stuck open too, so that would only amplify the effect of it getting colder and taking longer to warm up.... what do you think? Would that do it?

 

Normal driving I get 12-13, but when its really cold and im not making long trips and a bunch of shorter ones instead, ive gotten 9ish before.

 

Another thing I thought of to multiply the effect of the cold, along with the stuck thermostat, is the torque converter doesn't lock forever because it's cold. It took well over 5 miles on the highway for it to lock up the other day. I drove about 10 minutes, with most going 65 before it locked up in 16 degree weather.

 

yes.some things change when it gets cold out,like warming it up,and it being cold.
once spring rolls in it should get better.

purdue sucks