Gas Mileage

Guenther

Member
Dec 7, 2011
65
I don't want to hijack this thread but maybe this applies to someone else as well. I just ran an errand and noticed that my temp was at almost 207* when at speed (around 60mph). However when I accelerated hard the temp went down to 185* and then climbs back up. I'm wondering if my thermostat is weak even though it was replaced about 10,000 miles ago. :undecided:
 

MichEnvoyGuy

Original poster
Member
Dec 3, 2011
522
Guenther said:
I don't want to hijack this thread but maybe this applies to someone else as well. I just ran an errand and noticed that my temp was at almost 207* when at speed (around 60mph). However when I accelerated hard the temp went down to 185* and then climbs back up. I'm wondering if my thermostat is weak even though it was replaced about 10,000 miles ago. :undecided:

Weak? Sounds like the t-stat's spring is too strong. If its too tight, it wont open all the way when it should and that would result in hotter temps.
 

Jkust

Member
Dec 4, 2011
946
Guenther said:
On a new to me '04 Envoy SLT with 101,000 that I bought for my son a month ago I've done the following:

changed oil over to 5W-30 Castrol full synthetic
changed oil filter to K&N
changed transmission fluid
changed front differential fluid using Mobil 1
changed rear differential fluid using Mobil 1
changed transfer case fluid using GM fluid
changed both O2 sensors
changed brake fluid
changed power steering fluid
changed coolant using Prestone Dexcool
changed air filter using Purolator
changed front brakes to ceramic
changed front brake rotors
cleaned throttle body (was bad because PO did it about 10,000 miles ago and wasn't bad)
t-stat was changed by PO 10,000 mile ago (temp goes up and down between 201*-207* at speed using Torque program)
Seafoamed engine twice
ran bottle of Techron through tank of gas
tires are at 36psi and tracks straight as an arrow

First off, thank the Lord for the specials that have been going on at Advance Auto. Between the 40% and 50% off codes I've been doing tons of maintenance to the Voy, '08 Sable with 110,000 miles and '09 Tahoe with 42,000 miles. Secondly, with all that I've done to the Voy the mileage is around 17mpg highway and 14mpg city. I thought it should be higher, especially with the numbers that some people are throwing out here and on the "other" site. Were are into the winter gas here in Iowa so I'm hoping that is what is keeping the mileage down. From what I've read there isn't really anything else I can do maintenance wise to help. If there is, I'm all ears.

Relatively decent mileage is possible. For me it is 100% about my right foot and keeping at 61mph on the highway in the 60 zones. Even a little agressiveness or going over 65 and my mileage tanks. Both my 360's are v8's and maintained well also, but my deal with the devil for owning two v8's is keep the speed down. Both of mine have half the miles of yours as a newness reference point. As much as I want to put the v8's to their paces, you pay for it in the wallet. I also have full time on demand awd as well so I pay a one mpg penalty right out of the gate. I'll still give it a little juice once in a while or take a quick jaunt up to 100mph particularly in the 9-7 since it is so much more sporty handling-wise. The 9-7 is a real drivers car and the Rainier is a luxury ride. It is hard to believe they are one the same platform they are that different. Having owned three 360's over several years, I came to the conclusion the physics win the mpg battle with these vehicles.
 

Guenther

Member
Dec 7, 2011
65
MichEnvoyGuy said:
Weak? Sounds like the t-stat's spring is too strong. If its too tight, it wont open all the way when it should and that would result in hotter temps.


From everything I've read the temp should be right around 210* so that wouldn't make me too hot at 206.6*. Maybe I'm misunderstanding your post so please enlighten me if I am missing something. I didn't know if I should be concerned about the drop in temperature when accelerating hard or if that was normal for the TV. While parked at idle it sits right around 205*. I had a brand spanking new 2002 TB LTZ when they first came out but I honestly don't remember how the temp acted back then. However, I do remember the mileage being a little bit better. :thumbsup:
 

gmcman

Member
Dec 12, 2011
4,656
Just curious.....those of you reporting dismal fuel mileage, what tires are you running? Tires with low rolling resistance play a huge part in the mileage game.

I had a pair of Kumho Ecsta's after my cross terrains wore out, I lost 40 miles the first tank. Thinking it was a fluke, I babied the next tank....again 230 and some change down from 270. I pumped them up to 38 from 36 and the same deal, after 17K miles I sold them and went with the Lattude tour. What happened the first tank.....back up to 270-280.

When gas was $4.25/gal that was a big hit every tank. I cut my losses and went with a better tire, had I done so in the first place I would have payed less in the end.
 

Guenther

Member
Dec 7, 2011
65
gmcman said:
Just curious.....those of you reporting dismal fuel mileage, what tires are you running? Tires with low rolling resistance play a huge part in the mileage game.

I had a pair of Kumho Ecsta's after my cross terrains wore out, I lost 40 miles the first tank. Thinking it was a fluke, I babied the next tank....again 230 and some change down from 270. I pumped them up to 38 from 36 and the same deal, after 17K miles I sold them and went with the Lattude tour. What happened the first tank.....back up to 270-280.

When gas was $4.25/gal that was a big hit every tank. I cut my losses and went with a better tire, had I done so in the first place I would have payed less in the end.


Michelin Latitude Tours on mine as well.
 

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