Tracking down cause of poor MPG.
Generally speaking, how much time would it take an experienced mechanic to try and track down the cause of poor MPG.
I have a 2002 chevy express 2500 with a 5.7L and get 9.5 mpg / city with the van empty. Mainly very short trips, which I would think 9.5 is still poor. This is beyond the scope of my ability and will have to hire someone to do it. Just wondering if it is worth the cost or just sell it and get another one since it's old and not really worth that much. |
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You are guzzling quite a bit. Since there are many causes for this, I can't say how long it would take without more information. It could be anywhere from a 5 min fix to a new engine. How much on the odometer? Do you have a check engine light? Have you checked the usual suspects? (air filter, tire pressure etc.) Do you do regular maintenance? |
Originally Posted by Roger1
(Post 388577)
I have a 2002 chevy express 2500 with a 5.7L and get 9.5 mpg / city with the van empty. Mainly very short trips, which I would think 9.5 is still poor.
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A friend of mine used to do those MPG tests, and they're done on a Dyno. No wind, no weight drag. Considering the age, you probably can't do much better. The newer ones do better. My '16 w/6.0 averages about 12 to 13. And I have a heavy foot.
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The sticker MPG numbers used to be based on wind tunnel tests in unrealistic conditions.
I think the EPA MPG numbers are based on statistics. |
Over inflate your tires 5-7 lbs. Get a clean air filter. Check your tranny fluid. If it's dirty and smells burnt it's on it's way to death. Jack it up and see if your brakes are dragging. Disconnect the AC compressor for a while. It runs when you use the defrost. It takes a tol of gas to move a 5000 lb box down the road.
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Originally Posted by Roger1
(Post 388577)
Generally speaking, how much time would it take an experienced mechanic to try and track down the cause of poor MPG.
I have a 2002 chevy express 2500 with a 5.7L and get 9.5 mpg / city with the van empty. Mainly very short trips, which I would think 9.5 is still poor. This is beyond the scope of my ability and will have to hire someone to do it. Just wondering if it is worth the cost or just sell it and get another one since it's old and not really worth that much. |
Hi Roger,
Couple questions, has the van always done this since you have owned it or has it changed over time? What is the temp outside there? How short are these trips? Before paid a mechanic, I would troubleshoot it by taking a little road trip on a relatively flat piece of highway. Find someplace to have lunch that takes a tank of gas to get there and back. Then if you are in the 12-14 range you may be ok. Like others have suggested, a tune up cant hurt. John |
I had the same van. Mine was a passenger model.
I got 12 to 13 mpg city, and 16 hwy. I had michelin ltx 245 75 16 load range e tires. The factory tire size is 225 75 16. factory inflation is 50 psi front 80 psi rear. I ran about 76 rear since 80 psi is the max for those tires. What tires are you running? what pressure? When were the front wheel bearings last packed and lubed? Are your brakes in top order? No dragging and all parts moving freely. How old is the exhaust? My muffler started to go, and the new one made a little improvement. When was the air filter last replaced? The manual says about 50 000 kms....However its worth it to do once a year. Are the points under the dizzy cap clean? Right spark plugs? (iridium) Have you checked for codes? Your o2 sensors may need changing. They help to control fuel mixture among other things..... Also, the picture Joe posted is from fuel economy.gov Its a great website and the numbers are posted by owners, not the manufacturer. It is usually pretty close. |
Answers to everyone's questions.
It has 157K on it. I've only owned it for about 7 months and have put less than 1K on it. I had been looking for some time for a van, but here in the Tamps Bay area vans are overpriced and I will only buy something that is a good deal. My plan was to buy something newer with less miles, but I snagged this one super cheap and figured it would be OK for the time being. Air filter is only a few months old. Tires 225 75 16 have less than 500 miles on them. Upon purchasing the tires I didn't check to see what air pressure was put into them. Brakes have less than 750 miles and bearing where repacked at the same time. Have not done a tune up. No idea how old exhaust is. If I rev the motor it does make a crackling noise. We don't have any emissions laws here in FL Have not checked for any codes / haven't had check engine light ever come on. The overwhelming majority of my trips are 2-6 miles round trip. At what speeds should the tranny shift at when driving normally up to 45 mph. I will be driving to GA next month and can see what it gets HWY. |
Originally Posted by Roger1
(Post 394627)
If I rev the motor it does make a crackling noise.
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Originally Posted by mountainmanjoe
(Post 394950)
Clogged cat?
We don't have emissions here, so it's not on the top of my list. |
OK... I was under the impression that you wanted to fix your mileage.
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Originally Posted by mountainmanjoe
(Post 395068)
OK... I was under the impression that you wanted to fix your mileage.
I'm not a mechanic and don't know a lot of this stuff. I'm not good at diagnosing things. If I know what the problem is, then I can figure out how to fix. |
An engine has pistons, right. It's a glorified pump. Air and fuel goes in one end, exhaust comes out the other, and you make power in the process. What do you think will happen to your power when you block a pump? Why do people upgrade their exhaust to make more power?
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Originally Posted by mountainmanjoe
(Post 395256)
An engine has pistons, right. It's a glorified pump. Air and fuel goes in one end, exhaust comes out the other, and you make power in the process. What do you think will happen to your power when you block a pump? Why do people upgrade their exhaust to make more power?
Can I just throw on the cheapest cat available for it? What if I straight piped it? |
Anything would be better than a blocked cat but the top of your list should be to diagnose your problem, not throwing money at parts until it goes away. At least give the cat a bump to see if that's where the rattle comes from.
If you're unwilling to investigate yourself, then have a mechanic look at your van. He might find the problem right away and be able to give you an estimate to repair it. He might say it will take longer, so just set yourself a limit on how much you're willing to sink into tracking the problem down. |
Originally Posted by Roger1
(Post 394627)
Answers to everyone's questions.
It has 157K on it. I've only owned it for about 7 months and have put less than 1K on it. I had been looking for some time for a van, but here in the Tamps Bay area vans are overpriced and I will only buy something that is a good deal. My plan was to buy something newer with less miles, but I snagged this one super cheap and figured it would be OK for the time being. Air filter is only a few months old. Tires 225 75 16 have less than 500 miles on them. Upon purchasing the tires I didn't check to see what air pressure was put into them. Brakes have less than 750 miles and bearing where repacked at the same time. Have not done a tune up. No idea how old exhaust is. If I rev the motor it does make a crackling noise. We don't have any emissions laws here in FL Have not checked for any codes / haven't had check engine light ever come on. The overwhelming majority of my trips are 2-6 miles round trip. At what speeds should the tranny shift at when driving normally up to 45 mph. I will be driving to GA next month and can see what it gets HWY. |
Ditto on Silents comment. The cat takes a while to heat up, and they only work when hot. Short trips are killer.
The cat and its performance affect fuel mixture etc. It could also be an internally messed up muffler. Try banging on the muffler with your hand or a rubber hammer. Does it sound loose inside? Def check for codes, and have your exhaust looked at. Not having emissions laws is beside the point. Your van needs to run smoothly to get the best mpg. |
Yes the engine is less efficient when cold, but I've never gotten 9mpg even on short trips.
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Originally Posted by Roger1
(Post 394627)
We don't have any emissions laws here in FL
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Originally Posted by Doug D
(Post 397469)
Florida may not have any state laws regarding emissions or emissions testing, but federal law supercedes any state law or lack thereof. It is illegal to remove or have a shop remove a catalytic converter if you were thinking of doing that.
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What is your axle ratio? I had the 3.73 on my 2002.
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Originally Posted by canucklehead
(Post 399619)
What is your axle ratio? I had the 3.73 on my 2002.
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Run your VIN through the decoder at the top of the pge, under "Tools". It will tell you lots of things, including gear ratio.
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it's irrelevant.
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