6mpg drop!?

zibzer · December 9, 2006

So i filled up today and my 4300 vortec welcomed me with 15.5mpg. ive only had the truck 1 month. when i first got it i calculated 20mpg... i tuned it up with new oil,plugs,wires and got 22mpg afterwords...... now that the cold weather has come i changed my tires from 235/75/16 to 245/75/16 winter snows. and at the same time my truck started making a gurgling sound in the dashboard. and at the same time my MPG dropped from 20-22 to 15.5mpg...... anybody want to shed some light onto how i lost at least 5mpg

cmoore74 · December 10, 2006

Was the 20+ MPG a long mostly highway road trip? I ask because the initial MPG sounds almost too good to be true, even with the V-6.

My last truck was a 2000 S-10 with the same motor (4.3L V-6) and the only time I saw 20+ MPG was on long road trips which was highway only and not towing or heavily loaded and driving at a reasonable speed.

Normally I would see about 17-18 MPG with the regular fuel, but every year when the Winter fuel came out my MPG always dropped to around 15.

The snow tires may have had something to do with the loss in MPG, but doubtful it would explain all of it.

A gurlging sound under the dash would probably be from the heater core. Make sure your anti-freeze isn't low. Also, make sure your anti-freeze doesn't look chunky. I had a problem with a clogged heater-core on the old truck. One day the heat was blowing only cold air. A chemical flush cured it.

Schmids5.3l · December 10, 2006

Probobly the winter fuel, my mileage has been blowing lately too. Gotta also consider the cold air. Cold air is more dense, so more fuel basically. Loseing 5mpg is pretty bad tho. When my trucks cold on the highway it reads around 14mpg, then when its warm it gets 18-19mpg. In the summer it was 20-23. But thats the info thingy on the odometer, the mpg changes every second on that bad boy.

Mark_in_Tulsa · December 10, 2006

You also have taller tires now. That will throw off your odometer, which also will throw off you mpg calculations.

zibzer · December 10, 2006

the 20 mpg was 50/50 highway city

the 22 was right after a tuneup and was mostly city... some highway

the 15.5mpg was almost all city

ken1mod · December 10, 2006

Cold weather driving and rain on roads really affect gas mileage. I have had several cars with mpg readouts and these things make an amazing difference. Make sure when you see a light turn red ahead of you that you get off the gas and coast as much as traffic allows. Burning energy into the brakes makes a huge difference too. My 5.3 is getting over 18 mpg and I squeak the tires at least once a day.

ken

04silverado1500 · December 10, 2006

i had an 01 blazer that had that gurgeling noise turns out it was a bad timing chain it also in my words sounds like a shovel being dragged across the groung under acceleration. could be different then whathappened to me but the 4.3 has a problems with this all the time and gm announced it. im not trying to bash you in anyway but i hated that motor i get better mileage with my 5.3 now then with the 4.3 and that motor was throttle body and made from chopping off two cylanders on a 350. doesnt sound like they took to much time on that one. this is the reason why i dumped my blazer turns out 1,500 miles later the tranny went out keep in mind this all happened at 70K mi. now this was my problem some people love them.

Rolandd · December 10, 2006

Someone suggested that the gurgling could be a bad head gasket in another thread. Also, winter gas will cut your milage, aggressive winter tread on the tires will lower milage, Christmas crazed traffic sucks and more dense air will all have an impact. I am suspicious of your original high milage unless you were able to verify it over many tanks of gas. Also, have you changed brands of gas and have you changed driving habits--more short hop driving where the engine never has a chance to really warm up?

zibzer · December 10, 2006

Someone suggested that the gurgling could be a bad head gasket in another thread. Also, winter gas will cut your milage, aggressive winter tread on the tires will lower milage, Christmas crazed traffic sucks and more dense air will all have an impact. I am suspicious of your original high milage unless you were able to verify it over many tanks of gas. Also, have you changed brands of gas and have you changed driving habits--more short hop driving where the engine never has a chance to really warm up?

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well ive only had the truck for a few weeks so i calculated every tank ive had since i bought it. 20, 22, then 15.5

the 15.5 could have been because of all the snow we have had the past couple of days. and i let the truck warm up for 5 minutes for a 10 minute commute to work.. so maybe its just this one tank.... ill check my next tank and see if it has changed at all/.

i should also note it is a standar cab, 2wd, shortbox, stepside...... so it is the lightest silverado you can possibly buy

frdfandc · December 11, 2006

I'm guessing you missed the one reply above. Your current tires are taller, giving you a false odometer reading, therefore giving you a false fuel mileage estimation.

Also with you having snow and such, I'd be willing to bet your actual mileage is around 17 mpg.

svensk · December 11, 2006

These trucks eat gas standing still. So yeah, letting it warm up for 10 minutes at a time will screw your milage.

asilverblazer · December 11, 2006

Taller tires, uses more gas to turn.

+

Incorrect odometer reading.

+

Winter blend fuel

+ (big plus )

Ideling in the morning, 0 mpg.

+

Winter driving.

=

5 mpg loss.

Sounds reasonable to me.

cmoore74 · December 11, 2006

The change in tire size was not all that much to be the culprit alone:

"235/75/16 to 245/75/16"

diameter only increased by 15 mm which on that size tire is a 2.0% increase in overall diameter and hence tire circumference. The size would probably only explain about 0.5 MPG due to the speedometer calibration being off.

The difference in rolling resistance between the two tires on the other hand could have hurt quite a bit.

Long idle times, Winter fuel, and more stop and go will dramatically hurt the MPG.

zibzer · December 11, 2006

ok, sounds like there is nothing to worry about. The snow is melting now so next time i fill up if it is in the 17+ range i'll be happy. ill keep us posted.

oh and btw, the gurgling sound is slowly disappearing... each time i start it up in the morning it gets quieter and quieter. if i drive it for over 5 minutes. it almost completely goes away.

Mark_in_Tulsa · December 12, 2006

The change in tire size was not all that much to be the culprit alone:

"235/75/16 to 245/75/16"

diameter only increased by 15 mm which on that size tire is a 2.0% increase in overall diameter and hence tire circumference. The size would probably only explain about 0.5 MPG due to the speedometer calibration being off.

The difference in rolling resistance between the two tires on the other hand could have hurt quite a bit.

Long idle times, Winter fuel, and more stop and go will dramatically hurt the MPG.

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