Ac mpg drain?

I have a 03 alh jetta engine is stock for now besides stock exhaust being fully gutted and i actually feel the differnece when i turn the ac on been driving back and forth to my shop every day about 20 miles each way with the ac on full cause have my puppy in the car and dont want to risk him getting brave and try jumping out at a light or something and filled up and got a whomping 34mpg still wayy bettee then my cummins but does anyone else get this terrible mpg im seeing people get like 45-50mpg out of these thing everything is brand new on the car tires are 225/40/18 on the 16 spoke volkswagen wheels tires are bald too pumped up to 50psi just would like to get up to 40-45mpg thanks for all the help in advance

When I purchased my MK4 golf the previous owner mentioned that having the ac on would impact MPG and power. That’s been a fair assessment thus far. Whether or not this is normal, I can’t say.


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Go on a long (200 mileish) trip at cruising speed with the rpms right around 2k, then check your mileage. In-town mpg can vary greatly based on several factors.
Also, have you read through this?
http://forums.tdiclub.com/showthread.php?t=342274

I just came home from a 280 mile round trip today had the cruise control mostly set on 75mph at 2600rpms then i went passed one of those speed radar sign things on the pa turnpike and saw i was only doing 71 so bumpe it up to 2800rpms-80mph and im about 1/4 tank now and around 450ish miles on my trip which is going to be around 34-38mpg when i fill up

AC knocks the FE back a solid 10% in my tdi converted truck and this summer, so far, i've been running it nearly every day

I average 49-52 with the ac on 2003 Jetta wagon 5 speed.

Hard to believe, what speed 50-55 mph??? What’s your IQ set at? And timing? I only get 48 at 80-85 at 5500 ft altitude...

Back and forth to work stop and go for 54 miles each way. Went to the mountains last month mostly interstate at 75 mph and the rest in mountains 49.75 mpg with ac on.

Timing is sit around 5.5 degrees advance i know its right on the green line on the chart with vcds i have my iq all the way up on stock injectors stock tune i was doing 75-80 speedo indicated i passed one of those signs that says ur speed and at 75 said 71 mph

Try bumping your timing up a little.make sure your tires are aired up good and that your brakes ain’t dragging. Also check your air filter.

Man the grammar patrol is gonna getchu.
Just commenting on the thread title. If the drop is excessive, check the pulleys, tensioner, idlers.

At least on highway, I've noticed no more than a 2 mpg drop.

Mine is touching the blue line(advanced) IQ set at 4.5 should I change it? Running 38lbs on tires, I know our speedos are off by 3-4 mph at that speed

4.5 is nice, but it's not as critical as it seems (range is 2.2 to 9). The RC-2 tune I used to have parked right at 5.
Seems like almost all speedometers are 3-4 mph high.

I'd wager if you backed the speed off a little you'd get better mpg too.

It's always seemed to me that there's a little bit of a drop-off point with the Jetta sedans right around 70 indicated (about65-66 actual). I tend to keep my speedo needle around 70, and only go a little higher if needed.

I do 50-52 miles one way to work (I-78 and GSP typically), and see some slow traffic nearly every day. Even with AC on and the 01M automatic I'm still in the 41-43mpg range without really working at it.

Couple questions:

1. How hard are you accelerating? the harder/faster you do this, the more fuel you're using
2. Are you throwing black smoke when accelerating? If so, do you know what injectors you have in there?
3. You mentioned tire size, 18-inch rims are heavier than the 15-inch ones that most likely came on it stock. more weight=less mpg, but I don't know if the rims would account for all of it. What brand/model are the tires? If they're high-performance and sticky, they might be sapping a little MPG too.

i can tell a big difference when i use the ac on my 03 alh 5 speed . It really drags the motor down . But i dont use it , I get around 45 mph around town driving .

Rob mayercik i am also in new jersey rigt now im traveling some back roads and traveling 1-195 passed 6 flags in jackson but just traveled out to dover PA about 120 miles down the pa turnpike im right around 450 on my trip and im about 1/4 tank i am not blowing black smoke or anything i have stock injector size but planning on doing dlc 1019’s tuning and couple air mods the tires are 225/40/18 and idk the model but believe there falkens and there beyond bald like should have been replaced 10k miles ago when i get back to work next month i will be traveling about 50 miles each way to work instead of 20 to my shop and back i have the tires aired up to 50psi and brakes are all new all the way around and nothing is dragging if the cars in N just leaning on the car will let it roll away

What is your IQ set at??? And timing????

I cant remember what my IQ is set at right now I would have to double check and timing is right around 5.5 btdc advanced

Is it almost touching on green line??

So what was it when you filled up yesterday? Has the mileage ever been better or are we helping interweb troubleshoot an unknown? Did you get some ideas from Post #4?
Low fuel economy is a common complaint, you can find many threads here, a few even have solutions.

I just filled up and got 465 miles on the tank as i rolled into the fuel the light popped on the car it has the vent mod and filled to the brim with 14.1 gallons and got like 33 mpg car is lowered roof racks egr delete no tune with 18in wheel and see cars getting 40-50mpg what could make it barley getting 30 mpg

Do you know for sure that the odometer is correct? The larger diameter tires/wheels will roll up less miles on the odometer than actual, maybe by as much as 5%. Also, the taller tires require more leverage (power) to do the same as stock tires/wheels, thus cutting into the MPGs. (For clarification: Say the OE tire rotates 850 times in a mile. A taller tire may only rotate 800 revolutions in a mile resulting in the odometer registering less!) You can find a tire size calculator on-line and do some comparisons.

Until I retired 10 years ago, I was rolling up 36k miles per year. I had very few tanks below 50 MPG. The worst was 43 MPG but that was because I was stuck in a back up for 6 hours due to a wreck (snow and cold). (Manual 5-speed)

Good catch Andy - being the owner of a modified Jeep with oversized tires, I should have caught that (but then, I'm not fluent in P-metric size to diameter conversion).


A "back of the envelope" way to get a correction factor is to compare one mile on your odo to one mile using the mile marker signs on any highway (or, on many interstates, the exit numbers). Once you know how (approx) many miles your car registers for one mile based on the markers, you can rescale the trip-odo number you posted above and get "true miles" to recalculate that tank's MPG more accurately, which will give both you and us a clearer picture of how well the car seems to be running.