Poor Fuel Economy

[PRM502STREET]

hello guys, I have owned my 99 gls 5 speed now for over 10 years. She has 150k on the odo now and still runs like a champ, but the idle surges sometimes when i stop @ a light in town. And my mpg has gone from 30 down to 24 in the last 2 months/1600 miles. There is no check engine light on, or any codes present. This car has not thrown any codes since I have owned it, or given me any problems. I am trying to figure out how to get my mpg back. Please help!

[geniushanbiao]

Engine surge is always caused by a vacuum leak or stucked throttle. Considering your mileage first check all vacuum hoses connected to intake manifold and clean the throttle. Vacuum leak is probably the #1 common problem on VWs.

Originally Posted by PRM502STREET

hello guys, I have owned my 99 gls 5 speed now for over 10 years. She has 150k on the odo now and still runs like a champ, but the idle surges sometimes when i stop @ a light in town. And my mpg has gone from 30 down to 24 in the last 2 months/1600 miles. There is no check engine light on, or any codes present. This car has not thrown any codes since I have owned it, or given me any problems. I am trying to figure out how to get my mpg back. Please help!

[PRM502STREET]

Thanks Bud, That sounds like a good place to start. Cant do anything till this weekend,but I sure appreciate your help!

[PRM502STREET]

O.K. Guys, check this out. I got gas @ a new station in town that is matching the price of wallymarts cheap,junk,probably made in china gas. At least the quality seems that way. So when I fill up at the new gas station selling quality gas,now Im geting my same 30 mpg I was geting 2 months ago without touching my car. It still surges every so often, usually after I run it pretty hard,but my mileage went up just from swithing gas stations??? I live in a small town,5000 where most people get gas from wallyworld. Could they be cheating???

[geniushanbiao]

Possibly. VWs are sensitive to gas quality due to their high compression ratio. I still think the surge is caused by vacuum leak so I suggest you check it out.

I have to say, gas made in China is not as bad as that can cause this problem...I'm from China I know about this. We have a lot of Audis and VWs in China and they all can run more than 100k miles(the relatively short life is due to poor engine oil quality and bad roads). Gas is a little bit worse than here but not bad enough to cause this kind of problems.

Originally Posted by PRM502STREET

O.K. Guys, check this out. I got gas @ a new station in town that is matching the price of wallymarts cheap,junk,probably made in china gas. At least the quality seems that way. So when I fill up at the new gas station selling quality gas,now Im geting my same 30 mpg I was geting 2 months ago without touching my car. It still surges every so often, usually after I run it pretty hard,but my mileage went up just from swithing gas stations??? I live in a small town,5000 where most people get gas from wallyworld. Could they be cheating???

[Smileybug]

I never had any problems switching between stations. Ran "cheap" gas in my car many a time and didn't change anything.

I love to laugh when people say "high compression ratio" for these cars. Yes, I know that its "high" in comparison to other gasoline cars, but my old diesel is 23.5:1 compression

[geniushanbiao]

Diesel engines have much higher compression than gasoline engines because they use compression to ignite fuel/air mixture instead of spark plugs used in gasoline engines. And diesel engines are built more tough, more durable, and more complex. They are not comparable.

So here I wanna explain what's the difference between good gas and bad gas. Gasoline is mainly made up of Heptane and Octane. During compression, Heptane is very unstable and can be ignited during compression while Octane is very stable. In gasoline engines we want to control the ignition timing electronically to avoid combustion knock so that we need to prevent Heptane from being ignited during compression. This can be done by reducing the ratio of Heptane in gasoline therefore the knock performance of gasoline is rated by the Octane percentage. However the reality is that it's very very difficult to separate Heptane and Octane. Adding Octane to increase Octane rating is not cheap either. Therefore people have another access that we can add some additives to help prevent Heptane from being ignited during compression. The early additive was tetraethyl lead which is the famous lead-gas. However lead can destroy oxygen sensor and catalytic converter so we require lead-free gas. Nowadays we have some chemicals that can help reduce knock like: Methylcyclopentadienyl manganese tricarbonyl (MMT), Ferrocene, Iron pentacarbonyl, Toluene, Isooctane, Triptane, etc. Also we have some other additives for some other purposes like antioxidants. So, the main difference is that in order to save money, some factory produce bad gas by adding a smaller amount of additives. Then the equal octane rating will drop significantly and cause your engine to knock. Engine knock will cause gas mileage issue and increase engine friction. Engines with higher compression ratio require higher octane rating and thus suffer more from bad gas.

The ignition timing of diesel engines are actually not controlled by computer so the only thing we can do is to make the engine more tough in order to tolerate more knock. This is why gasoline engines tend to run more quiet, higher rpm and diesels more noisy, low rpm.

One of my friends has a '03 passat V6 and he can significantly feel the difference between using 87 gas and 93 gas. That car requires using gas higher than 91, said by the sticker on fuel door. Although new beetle 2.0L engine requires only 87, my wife and I both can feel the difference between 87 and 91 so I ask my wife to fill with premium. All the other cars I ever had, including a '02 Honda Accord, '01 Toyota Echo, '94 Mercury Sable, '99 Ford Taurus, I can never feel the difference between 87 and 93. Maybe you are lucky since you live in an area with good gas quality. I notice that in some areas gas is really bad though.

Originally Posted by Smileybug

I never had any problems switching between stations. Ran "cheap" gas in my car many a time and didn't change anything.

I love to laugh when people say "high compression ratio" for these cars. Yes, I know that its "high" in comparison to other gasoline cars, but my old diesel is 23.5:1 compression

[miffmole]

Originally Posted by PRM502STREET

O.K. Guys, check this out. I got gas @ a new station in town that is matching the price of wallymarts cheap,junk,probably made in china gas. At least the quality seems that way. So when I fill up at the new gas station selling quality gas,now Im geting my same 30 mpg I was geting 2 months ago without touching my car. It still surges every so often, usually after I run it pretty hard,but my mileage went up just from swithing gas stations??? I live in a small town,5000 where most people get gas from wallyworld. Could they be cheating???

The culprit could be ethanol...Gas with ethanol typically reduces your gas mileage by as much as 10%. I know that it does with my car. Maybe the new station is selling 100% gasoline.
Here's how I feel about ethanol:

[Smileybug]

I know why diesel has a higher compression ratio...I can still laugh at thinking a gasser has a "high" compression ratio.

And you may "feel" better performance in the 2.0 with higher octane fuel, but it really isn't doing much for you. Its been a debate on here and many other places for a long time. And with premium costing 30-40 cents more a gallon here, yeah if the car calls for 87, I run 87. My GTI calls for 91...93 is all we got here. Ran 92 in VA once, no difference at all.

[IndyTom]

Originally Posted by PRM502STREET

hello guys, I have owned my 99 gls 5 speed now for over 10 years. She has 150k on the odo now and still runs like a champ, but the idle surges sometimes when i stop @ a light in town. And my mpg has gone from 30 down to 24 in the last 2 months/1600 miles. There is no check engine light on, or any codes present. This car has not thrown any codes since I have owned it, or given me any problems. I am trying to figure out how to get my mpg back. Please help!

WOW, you are used to getting 30mpg? That's great! When NEW the 2.0l was only rated as 19 City and 26 Highway for the Automatic and 21City and 28Highway for the Manual tranmission with an average about 22 -24mpg. So the 24mpg you are getting is pretty normal to slightly above normal for when it was new.

Try taking off your Throttlebody and cleaning it. Or on your next fill up put a bottle of "Seafoam" in the tank prior to putting in the gas. That stuff works great in freeing up clogged injectors. Worn out/old O2 sensors and failing catylitic converters also can contribute to lower gas mileage. As suggested do check your vacuum lines. Those old fabric coated rubber lines wear out very quickly and if you never replaced them I bet there are several on their way out.

Good Luck and keep us posted!

[geniushanbiao]

While let's see the fact. The '99 new beetle with 2.0L engine has a compression ratio of 10.0:1. For the other cars I had, '02 Honda Accord 2.3L F23A4 is 9.3:1, '99 Ford Taurus 3.0L Vulcan is 9.1:1, '94 Mercury Sable 3.8L essex is 8.6:1. Now the newest VWs and Audis increase compression to 12-14:1(excluding some old engine model used on new cars like Jetta..) while Japanese and American models are still at 10-12:1.

Originally Posted by Smileybug

I know why diesel has a higher compression ratio...I can still laugh at thinking a gasser has a "high" compression ratio.

And you may "feel" better performance in the 2.0 with higher octane fuel, but it really isn't doing much for you. Its been a debate on here and many other places for a long time. And with premium costing 30-40 cents more a gallon here, yeah if the car calls for 87, I run 87. My GTI calls for 91...93 is all we got here. Ran 92 in VA once, no difference at all.

[IndyTom]

Originally Posted by geniushanbiao

Possibly. VWs are sensitive to gas quality due to their high compression ratio. I still think the surge is caused by vacuum leak so I suggest you check it out.

I have to say, gas made in China is not as bad as that can cause this problem...I'm from China I know about this. We have a lot of Audis and VWs in China and they all can run more than 100k miles(the relatively short life is due to poor engine oil quality and bad roads). Gas is a little bit worse than here but not bad enough to cause this kind of problems.

LOL, YOu guys are funny Unfortunately we don't get any gas from "China" otherwise it would be a lot cheaper and it would still have lead in it Walmart gets their gasoline from the "Murphy USA Marketing Co." which was recently aquired by the Valero Energy Corporation (based in San Antonio Texas). Oh and the refinery is Meraux Refinery in Louisana. So, sorry to say the gas is made in the USA. Gasoline come all from a handful of refineries here in the US and then is mixed with the different additive packages of the different brands like Shell and BP etc... So the gasoline is pretty much the same except for the additive package. More than likely it could be a problem with old outdated tanks. Water/moisture can enter these underground tanks and dilute the gas you put in your car.
Most of these station are inspected on a regular basis but it still happens even here in Indianapolis a fairly large city where there have been incidents (mostly at older or smaller stations) where vehicles got stranded after filling up from these stations. I personally go to Sam's Club to fill up since it is about 20 cents cheaper for gas there then most stations. Never had any issues with their gas and they use the same gas then Walmart does.

[IndyTom]

Originally Posted by geniushanbiao

Diesel engines have much higher compression than gasoline engines because they use compression to ignite fuel/air mixture instead of spark plugs used in gasoline engines. And diesel engines are built more tough, more durable, and more complex. They are not comparable.

So here I wanna explain what's the difference between good gas and bad gas. Gasoline is mainly made up of Heptane and Octane. During compression, Heptane is very unstable and can be ignited during compression while Octane is very stable. In gasoline engines we want to control the ignition timing electronically to avoid combustion knock so that we need to prevent Heptane from being ignited during compression. This can be done by reducing the ratio of Heptane in gasoline therefore the knock performance of gasoline is rated by the Octane percentage. However the reality is that it's very very difficult to separate Heptane and Octane. Adding Octane to increase Octane rating is not cheap either. Therefore people have another access that we can add some additives to help prevent Heptane from being ignited during compression. The early additive was tetraethyl lead which is the famous lead-gas. However lead can destroy oxygen sensor and catalytic converter so we require lead-free gas. Nowadays we have some chemicals that can help reduce knock like: Methylcyclopentadienyl manganese tricarbonyl (MMT), Ferrocene, Iron pentacarbonyl, Toluene, Isooctane, Triptane, etc. Also we have some other additives for some other purposes like antioxidants. So, the main difference is that in order to save money, some factory produce bad gas by adding a smaller amount of additives. Then the equal octane rating will drop significantly and cause your engine to knock. Engine knock will cause gas mileage issue and increase engine friction. Engines with higher compression ratio require higher octane rating and thus suffer more from bad gas.

The ignition timing of diesel engines are actually not controlled by computer so the only thing we can do is to make the engine more tough in order to tolerate more knock. This is why gasoline engines tend to run more quiet, higher rpm and diesels more noisy, low rpm.

One of my friends has a '03 passat V6 and he can significantly feel the difference between using 87 gas and 93 gas. That car requires using gas higher than 91, said by the sticker on fuel door. Although new beetle 2.0L engine requires only 87, my wife and I both can feel the difference between 87 and 91 so I ask my wife to fill with premium. All the other cars I ever had, including a '02 Honda Accord, '01 Toyota Echo, '94 Mercury Sable, '99 Ford Taurus, I can never feel the difference between 87 and 93. Maybe you are lucky since you live in an area with good gas quality. I notice that in some areas gas is really bad though.

Not sure what you are smoking but Heptane and Octane are just used for the Ron and MOn rating scale they by themselves are not added or reduced in order to make gasoline.

Gasoline is produced in oil refineries. Material that is separated from crude oil via distillation, called virgin or straight-run gasoline, does not meet the required specifications for modern engines (in particular octane rating; see below), but will form part of the blend.

Some of the main components of gasoline: isooctane, butane, an aromatic compound, and the octane enhancer MTBE.
The bulk of a typical gasoline consists of hydrocarbons with between four and 12 carbon atoms per molecule (commonly referred to as C4-C12).[3]

The various refinery streams blended to make gasoline have different characteristics. Some important streams are:
straight-run gasoline is distilled directly from crude oil. Once the leading source of fuel, its low octane rating required lead additives. It is low in aromatics (depending on the grade of crude oil), containing some naphthenes (cycloalkanes) and no olefins. About 0-20% of gasoline is derived from this material, in part because the supply of this fraction is insufficient and its RON is too low.
reformate, produced in a catalytic reformer with a high octane rating and high aromatic content, and very low olefins (alkenes). Most of the benzene, toluene, and xylene (the so-called BTX) are more valuable as chemical feedstocks and are thus removed to some extent.
cat cracked gasoline or cat cracked naphtha, produced from a catalytic cracker, with a moderate octane rating, high olefins (alkene) content, and moderate aromatics level.
hydrocrackate (heavy, mid, and light) produced from a hydrocracker, with medium to low octane rating and moderate aromatic levels.
alkylate is produced in an alkylation unit, involving the addition of isobutane to alkenes giving branched chains but low aromatics.
isomerate is obtained by isomerizing low octane straight run gasoline to iso-parafins (like isooctane).

The terms above are the jargon used in the oil industry but terminology varies.

Overall, a typical gasoline is predominantly a mixture of paraffins (alkanes), naphthenes (cycloalkanes), and olefins (alkenes). The actual ratio depends on:
the oil refinery that makes the gasoline, as not all refineries have the same set of processing units;
crude oil feed used by the refinery;
the grade of gasoline, in particular, the octane rating.

Currently, many countries set limits on gasoline aromatics in general, benzene in particular, and olefin (alkene) content. Such regulations led to increasing preference for high octane pure paraffin (alkane) components, such as alkylate, and is forcing refineries to add processing units to reduce benzene content.

Gasoline can also contain other organic compounds, such as organic ethers (deliberately added), plus small levels of contaminants, in particular organosulfur compounds, but these are usually removed at the refinery.

Running Higher Octane gas in a car that doesn't require or need it is a waste and may actually make the car run worse in some cases. Sure there may even be a placebo effect that tells your brain it costs more has higher octane and therefore it must be better for my car. As long as you believe it then it must be true and as long as it makes you feel better then go right ahead and use it. Besides the Oil Sheiks will love you for it

[IndyTom]

Originally Posted by miffmole

The culprit could be ethanol...Gas with ethanol typically reduces your gas mileage by as much as 10%. I know that it does with my car. Maybe the new station is selling 100% gasoline.
Here's how I feel about ethanol:

You are absolutely correct! However the mileage difference is only about 3% for gasoline that has the standard 10% Ethanol added. Now for the E85 gasoline the difference is 25%.
Almost all gas stations in the US sell gasoline with some percentage of Ethanol added. It makes Gas a lot cheaper and people like cheap. Besides it is suppose to be better for the environment and we do love the environment
Some states still require them to list the Ethanol content on their pumps but a lot of states no longer require this since 2010. So the chances are that most of the gasoline you put in your car has some percentage of Ethanol added to it. There is a list of Stations which only sell "Pure" gasoline. You can go to this site and download it.
Ethanol-free gas stations in the U.S. and Canada

I was surprised to only find "ONE" gas station in Indianapolis that sells Pure GASoline and it's not even a brand name station. Here in Indiana they no longer have to mark the pumps if they contain 10% or
less Ethanol. I am sure it's the same way with a lot of other states as well.

[IndyTom]

Originally Posted by geniushanbiao

While let's see the fact. The '99 new beetle with 2.0L engine has a compression ratio of 10.0:1. For the other cars I had, '02 Honda Accord 2.3L F23A4 is 9.3:1, '99 Ford Taurus 3.0L Vulcan is 9.1:1, '94 Mercury Sable 3.8L essex is 8.6:1. Now the newest VWs and Audis increase compression to 12-14:1(excluding some old engine model used on new cars like Jetta..) while Japanese and American models are still at 10-12:1.

The New 2012 Beetle 2.0TSI has a compression ratio of 9.60 and actually runs on Regular Gas

[Smileybug]

If your car is designed to run on a certain grade of fuel and you run higher, its pretty much worthless unless your car is tuned for it...If I could be running 91 I would but they don't sell that anywhere here that I've seen...just 93.

I wish they still had to mark the pumps here...they haven't had to since I think '07 here. Hate it. I definitely dropped mpgs after the ethanol was added. I never saw much over, if at all, 30mpg highway after that happened. *le sigh*.

[geniushanbiao]

My main point is to talk about the knock performance, not the components. Yes gasoline is complex and contains from C4 to C12. Although they have different components in some manners result from (M+N)/2 method can be converted to RON method and they are comparable. Actually these references are talking about the knock performance which can be expressed by octane rating. Every organic compound in gasoline has its octane rating and if we integrate them together then we get the total octane rating. Among them heptane's octane rating is 0 and octane's octane rating is 100 so heptane contributes a lot(might be most) to the reduction of octane rating. Some bad gas stations use some wierd method to calculate octane rating so that the 87 gas they give is actually calculated like 83 or lower by our "normal" method.


Theoretically running higher octane gas shouldn't make difference. However the fact is like this: for current vehicles whose compression ratios are higher than 10.0, pre-ignition cannot be completely avoided as long as the octane rating is not 100. In order to increase compression ratio manufacturers use a lot of technologies to compensate for this problem. So this is the fact: for a new engine whose CR is 11.0, the technologies used on this engine makes it capable of running smooth even with 87 gas. If we use 91 gas, then it will be more smooth. If we use 93 gas, then it will be more more smooth. Therefore the manufacturer might tell us that the lowest is 87. This is not the same as old cars like some old cars have CR of 9.0, then 87 gas is more than enough to make it smooth and 89, 91 gas don't make any difference.

Originally Posted by IndyTom

Not sure what you are smoking but Heptane and Octane are just used for the Ron and MOn rating scale they by themselves are not added or reduced in order to make gasoline.

Gasoline is produced in oil refineries. Material that is separated from crude oil via distillation, called virgin or straight-run gasoline, does not meet the required specifications for modern engines (in particular octane rating; see below), but will form part of the blend.

Some of the main components of gasoline: isooctane, butane, an aromatic compound, and the octane enhancer MTBE.
The bulk of a typical gasoline consists of hydrocarbons with between four and 12 carbon atoms per molecule (commonly referred to as C4-C12).[3]

The various refinery streams blended to make gasoline have different characteristics. Some important streams are:
straight-run gasoline is distilled directly from crude oil. Once the leading source of fuel, its low octane rating required lead additives. It is low in aromatics (depending on the grade of crude oil), containing some naphthenes (cycloalkanes) and no olefins. About 0-20% of gasoline is derived from this material, in part because the supply of this fraction is insufficient and its RON is too low.
reformate, produced in a catalytic reformer with a high octane rating and high aromatic content, and very low olefins (alkenes). Most of the benzene, toluene, and xylene (the so-called BTX) are more valuable as chemical feedstocks and are thus removed to some extent.
cat cracked gasoline or cat cracked naphtha, produced from a catalytic cracker, with a moderate octane rating, high olefins (alkene) content, and moderate aromatics level.
hydrocrackate (heavy, mid, and light) produced from a hydrocracker, with medium to low octane rating and moderate aromatic levels.
alkylate is produced in an alkylation unit, involving the addition of isobutane to alkenes giving branched chains but low aromatics.
isomerate is obtained by isomerizing low octane straight run gasoline to iso-parafins (like isooctane).

The terms above are the jargon used in the oil industry but terminology varies.

Overall, a typical gasoline is predominantly a mixture of paraffins (alkanes), naphthenes (cycloalkanes), and olefins (alkenes). The actual ratio depends on:
the oil refinery that makes the gasoline, as not all refineries have the same set of processing units;
crude oil feed used by the refinery;
the grade of gasoline, in particular, the octane rating.

Currently, many countries set limits on gasoline aromatics in general, benzene in particular, and olefin (alkene) content. Such regulations led to increasing preference for high octane pure paraffin (alkane) components, such as alkylate, and is forcing refineries to add processing units to reduce benzene content.

Gasoline can also contain other organic compounds, such as organic ethers (deliberately added), plus small levels of contaminants, in particular organosulfur compounds, but these are usually removed at the refinery.

Running Higher Octane gas in a car that doesn't require or need it is a waste and may actually make the car run worse in some cases. Sure there may even be a placebo effect that tells your brain it costs more has higher octane and therefore it must be better for my car. As long as you believe it then it must be true and as long as it makes you feel better then go right ahead and use it. Besides the Oil Sheiks will love you for it

[geniushanbiao]

9.6 is not a high CR. This 2.0L engine is an old engine. Take a look at the Audi A6 3.2L or Passat 2.8L engines they have high CRs. As I said, every engine runs on regular gas but the problem is how they run on regular gas. I don't know whether you have this feeling but I have: VWs and Audis tend to have a shorter engine life compared with American and Japanese cars when running on regular gas. This is especially recognized in China where German technologies are believed to be the best. However I have some mechanics in China they all say that if they receive 10 cars need engine rebuild, then 9 of them would be VW or Audi. Over half of VW and Audi over 100k miles in China have the problem of burning engine oil.

Originally Posted by IndyTom

The New 2012 Beetle 2.0TSI has a compression ratio of 9.60 and actually runs on Regular Gas

[IndyTom]

Originally Posted by geniushanbiao

9.6 is not a high CR. This 2.0L engine is an old engine. Take a look at the Audi A6 3.2L or Passat 2.8L engines they have high CRs. As I said, every engine runs on regular gas but the problem is how they run on regular gas. I don't know whether you have this feeling but I have: VWs and Audis tend to have a shorter engine life compared with American and Japanese cars when running on regular gas. This is especially recognized in China where German technologies are believed to be the best. However I have some mechanics in China they all say that if they receive 10 cars need engine rebuild, then 9 of them would be VW or Audi. Over half of VW and Audi over 100k miles in China have the problem of burning engine oil.

Well, China is in a Economic BOOM and they are buying anything German right now. Mercedes, BMW, Audi, VW. If they do have VW's that have more than 100k miles with oil burning issues than it is probably from neglect and not using the proper oil or change intervals. However, I would put any German Made car against any American Made car and would say the German made car will last longer. Only in recent years have the American Car makers really caught onto the quality and technology of forgein car makers. I personally think Ford is doing an incredible job with all it's new inovations and even Chevy is back on top pushing Toyota down from it's throne.
Regardless, I think VW makes some good quality cars which also came a long way. And let's face it any 10 Year old car is expected to have some issues. Sure, cars do last longer than ever before but they don't last forever and some parts just wear out. BTW, the 2.0TSI isn't that old. Don't compare it with the 2.0L engine or the 2.0FSI engine they are nothing alike. This is actually the 2nd Generation TSI motor and it only has been around for a couple of years. Previously the 2.0FSI had a timing belt and 10.5 compression putting out 200HP and required Premium GAS. The New 2.0TSI has a Timing Chain that never needs replacing and with a compression ratio of 9.6 it only required regular gas and still puts out the same 200 HP. Wait until the new 2.0TDI hits the market. It will feature a 140HP/236lbs torque engine which is an increadible powerful motor (2.0TSI only has 208lbs of torque) and it will get over 43mpg. In Europe they give you discounts in insurance and tax credits if you drive a diesel. And Diesel is also about 2 dollars a gallon cheaper there than regular gas. Not sure why Diesel is more expensive in this country than anywhere else in the world.
Oh well, it is what it is.

[Smileybug]

The 2.0TDI is already out, just not in the Beetle Test drove a Golf TDI...that was one sweet ride.

And yes, the TSI is a 2.0T, not the 2.0L of the mk4 days (though there is a plane jane 2.0L in the mk6 Jettas...)