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Car Forum / BMW Cars / August 2005Fuel Mileage Sucks on '94 325 Convertable
My old 325i (4-door) gave a consistant 25 combined mpg for the trips that I make. I managed to slam the car into the side of somebody making an illegal left turn, and replaced it with a convertable of the same year, 1994. The convertable only gives about 22.5 mpg for the same trips that the other car produced 25. Can there be something that isn't set up right on the "new" car that can be fixed, or does driving around with the top down cost 2.5 mpg? I wouldn't have thought the top down would be so expensive, but if it is, then I'll learn to adjust. I just wanted to know if something like plugs can use so much gas. Also, is my convertable a 325iC or 325Ci. I'm thinking it's an iC because the coupe is an iS, and the sedan is just an i. > My old 325i (4-door) gave a consistant 25 combined mpg for the trips that > I make. I managed to slam the car into the side of somebody making an [quoted text clipped - 7 lines] > then I'll learn to adjust. I just wanted to know if something like plugs > can use so much gas. First, are you basing mileage on the OBC (which is usually inaccurate) or on measured consumption? If the latter, then 22.5 mpg does seem pretty low in comparison. I don't notice any difference between top up and top down mileage in my Z4 3.0, so maybe you need to drive a bit with the top up and compare. If it is still 10% lower than your 4 dr., I'd have it checked out by a good mechanic. > Also, is my convertable a 325iC or 325Ci. I'm thinking it's an iC because > the coupe is an iS, and the sedan is just an i. I believe the "S" referred to the sport package - available on both 2 & 4 dr models. Currently, BMW uses 325Ci for both coupe and convertible - although I think I once saw a reference to a 325CiC! At any rate, enjoy your "new" ragtop. Tom >> My old 325i (4-door) gave a consistant 25 combined mpg for the trips that >> I make. I managed to slam the car into the side of somebody making an [quoted text clipped - 14 lines] > up and compare. If it is still 10% lower than your 4 dr., I'd have it > checked out by a good mechanic. Actual consumption. the OBC also reads much lower than the other car. Drive with the top up? Can you do that? ;-) > Drive with the top up? Can you do that? ;-) Yup, unless your 325 thinks it's a 50's British roadster! Tom > First, are you basing mileage on the OBC (which is usually inaccurate) > or on measured consumption? It's not on my E39. I've checked it against full tank to full tank x 3, and it was absolutely spot on. Of course if the mileage recorder is wrong, then so would be the real results. But although the speedometer is poor, the odometer seems pretty accurate - according to tests I've read.  Signature*If one synchronized swimmer drowns, do the rest have to drown too? Dave Plowman dave@davenoise.co.uk London SW To e-mail, change noise into sound. > I believe the "S" referred to the sport package - available on both 2 & 4 dr > models. No, at least not here in the US. The S in 325iS was used in the past to denote a 2 door (coupe), with or without the Sport package, but this has now been replaced with the leading C as in 325Ci. 4 doors are always called 325i whether they have the sport package or not. -Fred W > or does driving around with the top down cost 2.5 mpg? It's quite possible, IMO, as the coefficient of drag must increase by a good deal. The easiest way to check would be to drive the same route with the top up to compare. Also, the convertible is heavier I believe, which, too, may account for some of the mpg loss. Are the tires the same size and inflated properly? I'm assuming you've taken care of basic stuff like new air filter, sparkplugs, clearing error codes, and the likes? Cheers, Pete >> or does driving around with the top down cost 2.5 mpg? > [quoted text clipped - 6 lines] > > Are the tires the same size and inflated properly? Inflated properly is open to debate, but they are in fact the same tires. I took the tires from the wrecked car, 17" from an M3, and put them on the new convertable. Before anybody has to ask, both cars have the same transmission. That is, both cars have the 5 spd. The 4-door was built in Sep. 93 at the beginning of the production run, the rag top was built in July 94, I assume one of the last off the line for the '94 model year. > I'm assuming you've taken care of basic stuff like new air filter, > sparkplugs, clearing error codes, and the likes? The error codes are cleared, and the filter was inspected. The oil was changed the day before I bought the car - I know this happened because the dolt put both of the flat washers on the long bolt that holds the filter can closed. This resulted in an oil leak because the two washers are different sizes. > Inflated properly is open to debate, but they are in fact the same > tires. I took the tires from the wrecked car, 17" from an M3, and put > them on the new convertable. Have these the same overall diameter as the originals? If not, the odometer will be inaccurate. Signature*Just remember...if the world didn't suck, we'd all fall off. Dave Plowman dave@davenoise.co.uk London SW To e-mail, change noise into sound. >> Inflated properly is open to debate, but they are in fact the same >> tires. I took the tires from the wrecked car, 17" from an M3, and put >> them on the new convertable. > > Have these the same overall diameter as the originals? If not, the > odometer will be inaccurate. I am comparing the mileage of two cars with the same tires. Not the same KIND of tires but the actual same tires. The original fitment isn't part of the equation. I had a 4-door, now I have a rag top. The mileage in the rag top is lower and I am wondering if the rag top itself is the problem, or if there is something in the Engine Management Systems that I should be looking for. > > Have these the same overall diameter as the originals? If not, the > > odometer will be inaccurate. > I am comparing the mileage of two cars with the same tires. Not the same > KIND of tires but the actual same tires. The original fitment isn't > part of the equation. It is if the diameter is different to the original spec. Signature*I couldn't repair your brakes, so I made your horn louder * Dave Plowman dave@davenoise.co.uk London SW To e-mail, change noise into sound. >> > Have these the same overall diameter as the originals? If not, the >> > odometer will be inaccurate. [quoted text clipped - 4 lines] > > It is if the diameter is different to the original spec. Dave, The original spec. doesn't matter. The comparison is being made on two cars with the same set of tires. The significant difference is one car is a 4-door and the other is a rag top. Having said that, the tires that both cars used came off of an M3, and are within a quarter inch of the same diameter as the tires that are included in the Sports Package in 1994. Here is the problem, again. I owned a car that was wrecked. I bought another car and took the tires from the wrecked car and put them on the replacement car. Then, I noticed that the replacement car doesn't give as good fuel mileage as the wrecked car. The wrecked car was a 4 door, the new one is a rag top. Other than the doors and top, all other parts of the car should be the same, therefore the question is, what makes the mileage worse on the rag top car? >>> > Have these the same overall diameter as the originals? If not, the >>> > odometer will be inaccurate. [quoted text clipped - 21 lines] > car should be the same, therefore the question is, what makes the mileage > worse on the rag top car? Is it possible that the convertible has shorter gearing to compensate for the additional weight? Mike P >>>> > Have these the same overall diameter as the originals? If not, the >>>> > odometer will be inaccurate. [quoted text clipped - 25 lines] > Is it possible that the convertible has shorter gearing to compensate for > the additional weight? I don't think so. I have a Bentley manual, and I'll check. But when I looked at the gearing tables in the past, I don't recall that the convertables have different ratios. >> Is it possible that the convertible has shorter gearing to compensate for >> the additional weight? > > I don't think so. I have a Bentley manual, and I'll check. But when I > looked at the gearing tables in the past, I don't recall that the > convertables have different ratios. FWIW, a perusal of the BMW NA website indicates shorter gearing and on the current E46 convertible (compared to the coupe) - but only with the manual gearboxes. Weight is 10% higher for the ragtop. I still think that 22.5 mpg is low, unless it includes a high concentration of stop & go traffic. Tom >>>>> > Have these the same overall diameter as the originals? If not, the >>>>> > odometer will be inaccurate. [quoted text clipped - 29 lines] > looked at the gearing tables in the past, I don't recall that the > convertables have different ratios. Well, It's not directly comparable, but I went from a 1997 M3 4dr to a 1999 M3 convertible - and they had different final drive ratios. Both were E36 automatics. Driving on I5 for long distances sorta burns the speedo and tach readings into your brain. Mike P > >> I am comparing the mileage of two cars with the same tires. Not the > >> same KIND of tires but the actual same tires. The original fitment > >> isn't part of the equation. > > > > It is if the diameter is different to the original spec. > Dave, The original spec. doesn't matter. The comparison is being made on > two cars with the same set of tires. The significant difference is one > car is a 4-door and the other is a rag top. And do they have identical gearing.? But I'd also be interested in what the original wheel/tyre size was on each. > Having said that, the tires that both cars used came off of an M3, and > are within a quarter inch of the same diameter as the tires that are > included in the Sports Package in 1994. So both cars originally had the same wheel/tyre size? In which case, disregard everything I've said. ;-) > Here is the problem, again. I owned a car that was wrecked. I bought > another car and took the tires from the wrecked car and put them on the [quoted text clipped - 3 lines] > of the car should be the same, therefore the question is, what makes > the mileage worse on the rag top car? Assuming the mechanical spec is identical, I'm not sure. Rag tops are often heavier due to the extra 'chassis' stiffening needed and the motor and pump for the power hood. etc. They also have worse CD. But I'd not expect this to make a vast difference under the conditions where you're getting low 20s. Might be so at the speeds where you'd be getting in the 30s with a 4 door. Have you the handbooks for both cars? Is the mpg quoted the same? Is the gearing (mph/1000) the same? Signature*It's a thankless job, but I've got a lot of Karma to burn off Dave Plowman dave@davenoise.co.uk London SW To e-mail, change noise into sound. >> >> I am comparing the mileage of two cars with the same tires. Not the >> >> same KIND of tires but the actual same tires. The original fitment [quoted text clipped - 8 lines] > And do they have identical gearing.? But I'd also be interested in what > the original wheel/tyre size was on each. Well, the 4-door had the Sports Package that came with 225/55x15s and the rag top had 205/60x15s. The M3 rims that I have carry 225/45x17s. The overall diameter of these is 24.74, 24.69, and 24.97, respectively. Regardless of what the tires sizes were at one time, both cars ran with the M3 wheels, and this is the mileage benchmark that I am using. >> Having said that, the tires that both cars used came off of an M3, and >> are within a quarter inch of the same diameter as the tires that are >> included in the Sports Package in 1994. > > So both cars originally had the same wheel/tyre size? In which case, > disregard everything I've said. ;-) No, they both have the same size now, but different mileage numbers. >> Here is the problem, again. I owned a car that was wrecked. I bought >> another car and took the tires from the wrecked car and put them on the [quoted text clipped - 10 lines] > getting low 20s. Might be so at the speeds where you'd be getting in the > 30s with a 4 door. I was thinking the same thing, the CD difference ought not be the explanation for a 10% variance in fuel mileage on two otherwise similar cars. > Have you the handbooks for both cars? Is the mpg quoted the same? Is the > gearing (mph/1000) the same? > I am comparing the mileage of two cars with the same tires. Not the same > KIND of tires but the actual same tires. The original fitment isn't part > of the equation. I think he is talking about the original tires on your new car. If the tires which were installed previously were larger or smaller, the odometer will be inaccurate if not recalibrated. >> I am comparing the mileage of two cars with the same tires. Not the same >> KIND of tires but the actual same tires. The original fitment isn't part [quoted text clipped - 3 lines] > tires which were installed previously were larger or smaller, the odometer > will be inaccurate if not recalibrated. They are within a quarter inch of being the same diameter, so that isn't the trouble. Both cars had the same tires and presumably the same gearing, therefore they should have the same speedo error, and the mileage should then be the same. >>>or does driving around with the top down cost 2.5 mpg? >> [quoted text clipped - 15 lines] > of the production run, the rag top was built in July 94, I assume one of the > last off the line for the '94 model year. What about final drive ratios? Are they the same? Just a thought... -- -Fred W >>>>or does driving around with the top down cost 2.5 mpg? >>> [quoted text clipped - 17 lines] > > What about final drive ratios? Are they the same? Just a thought... According to Bentley, the trans and final drive are the same. I think the consensus is that the rag top weighs more, and thus sucks up more gas. Basing this on the E46, across the range the convertible gives 1 - 2mpg less than the equivalent coupe, 1-3 mpg less than the saloon, and as much as 4mpg less if you're comparing diesels! Convertibles have to be heavier, I guess weight really does make a big difference, but it sounds like your car is working as it should. According to BMW. you have a Ci. It turns out that I might be mashing the pedals with more gusto than when I had the sedan. I'll be watching this and let you know. > My old 325i (4-door) gave a consistant 25 combined mpg for the trips that > I make. I managed to slam the car into the side of somebody making an [quoted text clipped - 10 lines] > Also, is my convertable a 325iC or 325Ci. I'm thinking it's an iC because > the coupe is an iS, and the sedan is just an i. > My old 325i (4-door) gave a consistant 25 combined mpg for the trips that > I make. I managed to slam the car into the side of somebody making an > illegal left turn, and replaced it with a convertable of the same year, > 1994. The convertable only gives about 22.5 mpg for the same trips that > the other car produced 25. I don't know about the 4-doors, never had one, but I have a 1996 328 5-speed convertible, it gets better mileage. On road trips at 60-65mph, it averages close to 30mpg, round about town about 23 to 25. The car would be heavier than a non-convertible, there would be a little more wind drag from the soft top. I must say that I also have the removable hardtop for my car, and find little difference in gas mileage when it is on (although the car would weigh another hundred pounds or so). The above figures of mileage are for conservative driving (not as conservative as possible, but changing gears at about 2300 to 2600 rpm. Mileage drops below 20 with spirited driving. Having the air conditioner running makes maybe 1mpg difference. Jim > My old 325i (4-door) gave a consistant 25 combined mpg for the trips that I > make. I managed to slam the car into the side of somebody making an illegal [quoted text clipped - 7 lines] > learn to adjust. I just wanted to know if something like plugs can use so > much gas. Could be the O2 sensor? Could also be the increased weight of the convertible. Yep, that's right, the added frame below, designed to improve the chassis stiffness, is heavier than the missing roof above. > Also, is my convertable a 325iC or 325Ci. I'm thinking it's an iC because > the coupe is an iS, and the sedan is just an i. You are correct. 325Ci would be a coupe. 325iC is a convertible. 325CiC is sometimes used to denote a 2 door convertible, but it's redundant since there are no 4 door BMW convertibles. -- -Fred W Can't you people read! ;-) It's a Ci, irrespective of it being a coupe or convertible. If you still don't believe me go here : http://www.bmwusa.com/vehicles/3/330ciconvertible/default or here : http://www.bmw.co.uk/bmwuk/pricesandspecifications/0,4637,1156_1515__bs-Mw%253D% 253D%2540bb-Q0E%253D%2540sit-bmwuk,00.html And I've already posted the OFFICIAL BMW mpg stats for coupes v convertibles v saloons, and it show convertibles use more fuel! Your car is fine, there are no faults, it's just heavier. > Can't you people read! ;-) > > It's a Ci, irrespective of it being a coupe or convertible. If you still > don't believe me go here : > http://www.bmwusa.com/vehicles/3/330ciconvertible/default The Sticker Price hasn't changed much in 12 years, my car has the original window sticker, and the price in 1994 was pushing $42,000 (USD). or here : > http://www.bmw.co.uk/bmwuk/pricesandspecifications/0,4637,1156_1515__bs-Mw%253D% 253D%2540bb-Q0E%253D%2540sit-bmwuk,00.html > > And I've already posted the OFFICIAL BMW mpg stats for coupes v > convertibles v saloons, and it show convertibles use more fuel! Your car > is fine, there are no faults, it's just heavier. After getting over the thrill of having the wind whistling across my massive expanse of a forehead -- it extends most of the way to my shoulders these days -- I find that I am getting pretty close to 24mpg, whereas my old car was giving 25mpg. I haven't left the top up long enough to find out if aerodynamics is part of my fuel loss, but I'm pretty sure the weight is my most significant issue. I was hoping you guys would come up with a more temporary cause of my low mileage -- something along the lines of the O2 sensor causing it to run rich -- that I could fix, but it turns out the rag top is hauling around extra baggage that eats into the gas tank. > My old 325i (4-door) gave a consistant 25 combined mpg for the trips that > I make. I managed to slam the car into the side of somebody making an [quoted text clipped - 10 lines] > Also, is my convertable a 325iC or 325Ci. I'm thinking it's an iC because > the coupe is an iS, and the sedan is just an i. I once read that as rule of thumb every 100 kg in the boot add about 1 litre per 100 km fuel (whatever that is in gallons per mile). 0.26 US gal per 62 miles...you work it out from here... DAS For direct contact replace nospam with schmetterling --- [...] > I was hoping you guys would come up with a more temporary cause of my low > mileage -- something along the lines of the O2 sensor causing it to run > rich -- that I could fix, but it turns out the rag top is hauling around > extra baggage that eats into the gas tank. [...] >After getting over the thrill of having the wind whistling across my massive >expanse of a forehead -- it extends most of the way to my shoulders these [quoted text clipped - 7 lines] >rich -- that I could fix, but it turns out the rag top is hauling around >extra baggage that eats into the gas tank. The weight of the car won't help it, but having the top down gives you the aerodynamics of a sale boat side on! All that wind and buffeting you hear with the roof down is turbulence, turbulence is bad... It resists your smooth passage through the air. Over here in the UK they even try to encourage people to remove their roof racks when they don't need them because of the increased fuel consumption. Dodgy. SignatureMUSHROOMS ARE THE OPIATE OF THE MOOSES |
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