My mom just got a 2004 avalanche and i was just trying to figure out which engine is in it. It has a lot of get up, and go. going up hills it hardly ever downshifts, and even driving nice it gets horrible mpg (15-16 hwy) so I'm thinking it has the 8.1L in it. did they put the 8.1L in the avalanche 1500?

no the 8.1 was only in 2500's. It would be a 5.3 liter

I kinda thought that to but i was looking in the manual and according the vin it says it has the 8.1L. seems kinda weird to me. Ill get the vin tomorrow and post it in the vin check area.

look for the emissions sticker in the engine compartment, should be up front by the airbox IIRC--it'll tell you

i thought those had the 6.0L i guess i was wrong.

Your Mom's Avalanche can't be an 8.1 because 15 - 16 mpg isn't bad enough to be an 8.1. If it was 11 - 12 mpg, you might have something there. :D:eek:

15-16 is fine. 2500 CC's with the 6.0 are lucky to get 12-13.

My mom just got a 2004 avalanche and i was just trying to figure out which engine is in it. It has a lot of get up, and go. going up hills it hardly ever downshifts, and even driving nice it gets horrible mpg (15-16 hwy) so I'm thinking it has the 8.1L in it. did they put the 8.1L in the avalanche 1500?

IMO,a 5.3 will beat most 8.1's empty(depends on configurations. My brothers 01 5.3 is the heaviest 1500 6 lug pickup there is being a 4x4 long bed excab loaded 5.3. My 83K mile 2001 8.1,even with the PCM tune,gapped plugs and t stat barely can beat his bone stock 5.3 with 240,000 miles on it.He has an old hypertech download tuner on it,thats it. If we both hook to a trailer ita different story. He gets 15mpg in mixed driving, i get 10-12.

pop the hood. if its the 8.1 the plastic cover will have 8100 on it. it will also have 8 lug nuts.

ya its a 5 lug, and the top cover doesn't say anything on it at all. so its a 5.3? sweet. Thanks for the help guys.