[Enkeiavalanche]

So anyway as I go to work in the morning there is a mile long hill I go down on Rt80. So most of the time I am going between 65-70 mph and I can coast the whole way down..I see about 99mpg on the DIC and it's in 4 Cyl mode. The other morning I had the AC on and it would only go to 77MPG as soon as I turned off the AC it went back to 99MPG....

What do you think?

 

[MrShorty]

I think that maybe the best way to dramatically improve gas mileage is to always drive downhill.

I expect the difference is either related to the additional drag created by the AC system, or something in how the DIC calculates MPG.

 

[phoebeisis]

On my 1998 2wd Suburban 1/2 ton- my Scangauge shows .7gph idling with the AC on, but .6gph with the AC off-so
your 99mpg vs 77mpg seems about right.

 

[stephan]

Wow that's about a 23% loss from the AC. Seems like something else is also comeing into play here. Was the weather different on those two days Enkei?

 

[Enkeiavalanche]

Nope.. Same hill same time as I go down it changes when I turn on or off the Ac. I can be going down the hill and turn on the AC and it goes from 99-77 right away..I know it runs on the same belt and all but that much in 2 feet?

 

[phoebeisis]

Stephan-I can buy the 23%-my 5.7 uses about 17% more- his more efficient "4CYL" will use a higher percent to run an extra load-the AC
Pretend the 5.3 uses 1 gph to idle-no ac(it doesn't- it probably uses .4gph in 4 cyl mode)
Pretend My 5.7 uses 2 gph to idle- no ac(it actually uses .6gph)
BUT THEY PROBABLY USE THE SAME EXTRA .1GPH to run the ac.(my gadget says mine uses .6gph no ac- but .7gph with ac- idling-stopped)-
Your more efficient vehicle uses-1.1 gph and extra 10% to run the AC
My less efficient uses 2.1gph-extra 5% to run ac.
The above numbers are just pretend numbers
My actual numbers are .6gph no ac and .7gph ac-17% or so
The better a motor is the "worse" it looks" when extra loads are added.

Hey how would you like to make a STRAIGHT UP trade for a genuine 1998 LS Suburban-5.7 2wd- with JUST 216,400 MILES??I could manage to "LIVE" with your Avalanche-HA,HA!!
Didn't think so!!
Charlie
PS Up on my roof for me now-our drought lifted-south Louisiana- about 4 weeks ago-
Our 24 yo roof leaking like a sieve- broke for another 19 months(62yo SS) so having to do cheap out "repairs". Maybe I'll luck out and get full time work!! Sub teach now $62/d.Roof materials maybe $3000-guess in 25 months I'll be learning how to DIY a roof!!




My point- finally- is the less a motor uses at idle(more efficient it is-like your cyl shutdown 5.3) the bigger the drop in mpg will be if you turn on the AC.
I can buy the AC making that big- 25% a difference idling/coasting.
FYI coasting downhill at 60 mpg my 5.7 will show no higher than 50 mpg I think

 

[stephan]

I can buy the 23%-my 5.7 uses about 17% more- his more efficient "4CYL" will use a higher percent to run an extra load-the AC

the less a motor uses at idle(more efficient it is-like your cyl shutdown 5.3) the bigger the drop in mpg will be if you turn on the AC.
I can buy the AC making that big- 25% a difference idling/coasting.
FYI coasting downhill at 60 mpg my 5.7 will show no higher than 50 mpg I think

Makes sense now Charlie.