86 Cabby - Fuel Gauge (as related to fuel mileage)

[NCCabby]

I've searched and can't seem to come up with the angle I'm looking for on this issue.

First, is the stock fuel gauge/sending unit, etc., inclined to show more mileage on the last "half of the gas tank", according to the gauge?

Odometer is broken (going to try to check to see if the plastic gear is cracked on the speedo), and trying to get an idea on fuel efficiency. I'm guesstimating around 120 miles and it says I'm close to the half tank mark.

Second, it seems like it may be natural for the float to be sensitive and show the guage move rather significantly (quarter tank or so) over inclines/declines/turns. Is this normal?

I have read that the regulator could cause misreadings and sways in the gauge, but i also know older cars weren't very accurate to begin with. B/w this and no odometer, it makes it more of a challenge to use the whole tank of gas (if needed) and feel confident about not running out of gas.

My apologies if there is a thread I couldn't find on this; I tried.

Thanks in advance!

[cedge88]

I can't really give you a definitive answer. However I own a 84 Rabbit GTI and I run into the same exact problem. Actually yesterday I filled up the tank and after driving only 50 miles today it reads that I am already at a half tank.

I've just averaged it out and kept a mental note.

[WaterWheels]

First, is the stock fuel gauge/sending unit, etc., inclined to show more mileage on the last "half of the gas tank", according to the gauge?

Second, it seems like it may be natural for the float to be sensitive and show the guage move rather significantly (quarter tank or so) over inclines/declines/turns. Is this normal?

I have read that the regulator could cause misreadings and sways in the gauge, but i also know older cars weren't very accurate to begin with.

First - No. That short answer said, you will understand or see more information below.

Second - The part which moves the contact over the resistor board is just what you called it, a "float". So it is normal, natural if you like, for it to be effected by vehicle motion or angle. Diferent makes and different models will react in different ways. The same goes for like make and models that have had repairs done and things not installed in the exact correct position. i.e. If someone replaced the transferpump and installed the unit say 5° off, it will react different from one set from the factory.

The regulator, if you mean voltage regulator, should have no effect. The voltage the gauge uses is maintained at a constant 10v for the reason you stated. But fuel gauges can and do read odd for the most part due to many things. Wear in the resistor board, old and failing gauge, bad contacts in the wiring, floats which have become bad or wear of the assembly itself are some reasons. I have always found the gauges to read slower for the firts quarter, then about normal in the middle and faster in the last quarter. Even with the odometer not working, you should be able to get a good fuel consumption figure using the speedometer. If your tire sizes are not standard this will throw the reading off also.

[NCCabby]

Thanks, guys!
I appreciate the responses. Glad to hear it is common.
For done reason i thought there might be a resister that would slow swings in the guage reading due to sudden movements, but I'm probably making that up.

I suppose the next course of action, until I pull the cluster and see if I can fix the plastic gear, is to guesstimate mileage and then see how much fuel i used when i add more the next time. Until i can figure that out, I'll just have to be safe and stop for gas when i get towards the bottom of the gauge...

[NCCabby]

First - No. That short answer said, you will understand or see more information below.

Second - The part which moves the contact over the resistor board is just what you called it, a "float". So it is normal, natural if you like, for it to be effected by vehicle motion or angle. Diferent makes and different models will react in different ways. The same goes for like make and models that have had repairs done and things not installed in the exact correct position. i.e. If someone replaced the transferpump and installed the unit say 5° off, it will react different from one set from the factory.

The regulator, if you mean voltage regulator, should have no effect. The voltage the gauge uses is maintained at a constant 10v for the reason you stated. But fuel gauges can and do read odd for the most part due to many things. Wear in the resistor board, old and failing gauge, bad contacts in the wiring, floats which have become bad or wear of the assembly itself are some reasons. I have always found the gauges to read slower for the firts quarter, then about normal in the middle and faster in the last quarter. Even with the odometer not working, you should be able to get a good fuel consumption figure using the speedometer. If your tire sizes are not standard this will throw the reading off also.

Again, i appreciate you expounding on it a little bit, if not for me, it may help someone else who wasn't thinking the same thing!

[NCCabby]

Where's the best place to make a vehicle thread, following issues and fixes as I work on this car?
Couldn't seem to find a good place that was more than just posting pictures, but technical and semi-restoration oriented...

[WaterWheels]

Seems I read your original post wrong. You stated the odometer was not working and I understood it as the tripometer (the one you can reset). So what I said about using the speedometer to get your consumption is just plain old dumb as the odometer does not work. But to be honest on repairing it, just getting a good used one is often much more simple. If you want to tinker with the workings of it that's fine, but I would just get a good one from say Ebay or a stripyard. Then you can rip appart and play with the bad one while driving the car. Your call though.

As for a "log" kind of post for working on your car I would say the Golf II/Jetta II forum. This one really was intended for "8v engine" posts. As many cars have an 8v engine in them people seem to think that this is the forum for all their problems because they have an 8v engine. Most times it really doesn't matter but it does seem odd often when people post about their transmission, fuel injection system, brakes or radio issues as there are forums created just for those things. But so long as there is no real control from the site itself or it's appointed goonies, I say post where you like and feel comfortable.

[kamzcab86]

Where's the best place to make a vehicle thread, following issues and fixes as I work on this car?

http://forums.vwvortex.com/forumdisp...?152-Cabriolet

That's also the place to be if you have questions regarding your convertible.

As for a "log" kind of post for working on your car I would say the Golf II/Jetta II forum.

1980-1993 Cabriolets are not Golf/Jetta IIs.

[WaterWheels]

1980-1993 Cabriolets are not Golf/Jetta IIs.

Correct, I looked at the date and didn't even notice the model.

[ziddey]

Since you're saying you believe the plastic gear is cracked, I'm assuming the speedometer itself is working, just the odo/tripmeters are done for.

Makes you feel any better, it's extremely common. You may be able to pop off the gear, apply some glue and clamp it together until it sets. I recently drove cross country in a VW with a broken speedometer cable. Lots of fun. Probably ended up driving slower than I would have otherwise

[NCCabby]

Thanks for the responses, guys!
I'll definitely probably start a little thread with my name in the title over there, so feel free to watch for it if you think you can help me out with what answers i can't find searching.
I don't like asking for help with things that are easily searched for...but i often find done things to be situational, and some if these posts just don't answer all my questions or the angle I'm looking for on it. Ha

And yes, i should have explained that the odometer and tripometer ate the only things not working. Speedometer is good (although i will probably lube it up with graphite soon to help avoid any iterates).
I thought of getting a new (used) gauge cluster, but i think the mileage on the vehicle its pretty close to what the odometer says when it suck (within reason; I'm guessing maybe 10k or so). So...if probably like to see if i can fix this one...but we'll see!

[ziddey]

I'm not familiar with the A1 odometers, but if it's anything like the A2's, you can tamper with the odometer pretty easily. Just holding the individual gears to the side a little lets you turn the digits.

[NCCabby]

I'm not familiar with the A1 odometers, but if it's anything like the A2's, you can tamper with the odometer pretty easily. Just holding the individual gears to the side a little lets you turn the digits.

I sure hope so! I don't want to buy another cluster...

[ziddey]

Not sure about the salvage yards in your area, but if I remember right, picknpull charges almost $50 for a whole cluster, but "just" $15 if you pull the speedometer out. Of course, dismantler type yards would charge more. Maybe check the classifieds / post a wanted if you can't get the gear working again. There used to be someone who just sold the gears. Maybe he still exists.

[NCCabby]

Not sure about the salvage yards in your area, but if I remember right, picknpull charges almost $50 for a whole cluster, but "just" $15 if you pull the speedometer out. Of course, dismantler type yards would charge more. Maybe check the classifieds / post a wanted if you can't get the gear working again. There used to be someone who just sold the gears. Maybe he still exists.

Just got the Bentley in the mail, so I may try to fix it first, if possible.
We'll see how that goes. If not, your advice may be deployed! Thanks!