Mechanics

POOR FUEL ECONOMY

Chevrolet Other

I have a 2000 s10 4 cyl 2 wheel drive ext. Cab, with 76000 miles. I am having a problem with poor fuel economy, this occured almost over night. The most recient work done to the truck was an oil change, penszoil 10w30, 4.5 qt. I usually get about 27 mph but now it's more like 12mpg. Could the oil change have caused this? And if not what would be my best course of action to trouble shoot this problem? Thanks
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Morrow79
December 23, 2006.



The troubleshooting information I 'm going to present here are general information that can be usesd to assist in determing problems with most makes and models of vehicles, However, , for the proper spesifications and more detailed troubleshooting information for a particular vehicle, refer to vehicle service manual; However, I doubt the oil change has caused this problem.

Start checking for a binding chocke valve or linkage, Too rich idle mixture, power valve stuck open, restricted exhaust system, Dragging brakes or underinflated tires, Defective transmissin or drive train, Misaligned wheels
this is just to name few.

Tiny
Mathiaso
Dec 23, 2006.
Thats a hefty loss in a short period. Something that bad should leave clues, such as smell of raw fuel, excessive drag or a performance change.

I would recheck my math first. Then run another half a tank and recheck the mileage.

I reched my math and ran one full take through, the first half tank fuel economy was at about 21 mpg, the last half was about 17 mpg. Truck is alittle sluggish, but not very noticable, seems to get better after it warms up. No gas smells, confirmned e brake is not on. Still suckin' down gas. Driving condition were 10% city, and 90% highway, conservative on the pedal at 70mph. Thank you for your continued help : )

Tiny
Morrow79
Dec 25, 2006.
If your thermostat is stuck open, You will take a hit on the economy. The more short trips the worse it will be overall. How long does it take before you get hot air from the heater? The motor wants to hog all the hot coolant until it gets warmed up, then it can back off on the fuel consumption. When it's warm it will share the heat with you. If the stat is stuck open, there is more volume of coolant to heat up, causing more fuel to be expended.

Another thing that may affect it is if the computer " thinks" the engine isn't getting hot because of an input, such as an coolant temperature sensor.

Thre truck warms up remarkably well, I usually let it warm up for about 3-5 minutes in the morning, long enough to get pulled out of the garage, spark up a cig, and close the door. I'll drive for about a mile gradually making it up to 45mph, I don't rhomp on it since the engine is still cool, after the first mile the defrost is warm enough to defrost the entire windshield, 5 minutes later there's enough heat belting out of the vents to where you can't hold you're hand infound of the vent for more then a few seconds before it starts to hurt. Usually when i'm driving the truck puts out enough heat to actually not have heater on at all, just adjust the temp to make it cumfortable. However the temperature gague reads with in normal operation temp.
When a sensor, such as the coolant temperature sensor, is possibly falty, is there any way to test or is it pretty much replace and see if there are any changes?

Tiny
Morrow79
Dec 26, 2006.
I am on the verge of saying more than I know. In our shop we can monitor both the wave pattern of the sensor and the actual temperature with our scanner. I don't want to send you on an expensive wild goose chase.

Other inputs that I would be more apt to consider (since the truck heats up promptly) would be the O2 sensors. If they both weaken over time, the CEL(check engine light) won't necessarily lite up. They are compared to each other and if the comparison falls within an acceptable range, they are assumed okay. When one finally falls under it's specific parameter it will trigger the CEL. You replace it, now the CEL comes on becasue the new good one is compared to the weak one because the range is so far apart.

Mathiaso has mentioned tire inflation, I assume that was checked. Air restriction such as a plugged air filter may be part of it. Since it happened so sudden, I'm inclined to think those are fine.

You mentioned it runs a little sluggish. For the heck of it if you can find a scanner (autozone?) See if any codes are present. Codes can be set withour the CEL illuminating. Without checking the O2s, I don't know they are bad, but may be : How old are the spark plugs?

I had the computer tested, no codes have been thrown, however, it was tested at an Advanced Auto parts store. I'm going to get it tested at a mechanic repair shop because they have better testers. I tried replacing the fuel filter today, but it was the wrong one, news to me! My truck is a equipped with a flex fuel system, which makes the filter 5 times more expensive and out of stock at most places, I've always ran regular gas through it though, not too fimular with flex fuel systems.
I believe the spark plugs to be o.E. But I've been told those are platnium plugs and shouldn't need to be changed for 100k.

Tiny
Morrow79
Dec 27, 2006.
They are the double platinum plugs, but they don't always get 100,000 miles, some go more some go 60,000. Post what you find out from the garage.