1973 Bus Fuel Gauge Trouble

Moderators: Sluggo, Amskeptic

Post Reply
User avatar
satchmo
Old School!
Location: Crosby, MN
Status: Offline

1973 Bus Fuel Gauge Trouble

Post by satchmo » Mon Jul 21, 2008 3:44 pm

My fuel gauge is acting up. I guess it is entitled to since it has been measuring fuel levels in the tank since 1973 and for 178K miles. I bet the fact that gas has gone from $0.25 per gallon in 1973 to $4.25 per gallon now must have something to do with it.

Anyway, a week ago, the gauge just dropped off to below reserve from a half a tank, then came back up a bit, then down again. I filled the bus with gas, expecting no real response, but it went right to full. With driving, it goes down faster than normal to one half tank, then takes a free fall from there to empty. It moves around a lot with the inclines and whether or not I am turning, which I interpret as pretty normal, but the swings in the needle are a bit more than usual, and take longer to get back to the real fuel level than they used to.

I have read the Bentley. It mostly discusses testing for a bad fuel gauge sender. I think my problem may be in the gauge itself? Got any suggestions? Thanks.

Tim
By three methods we may learn wisdom:
First, by reflection, which is noblest;
second, by immitation, which is easiest;
and third, by experience, which is bitterest. -Confucius

User avatar
dtrumbo
IAC Addict!
Location: Mill Creek, WA
Status: Offline

Post by dtrumbo » Mon Jul 21, 2008 4:42 pm

EDIT: Hold the phone!! You say you have a '73. First you need to determine what type of gauge you have. The posting below is for the new style gauge which started at chassis #2132138901. If your bus is older, you have the old style gauge which does not use a vibrator and your problem is most likely the tank sender, but could be either a loose connection somewhere or the gauge is intermittent. Testing the gauge is the same procedure that I mentioned below. We now return you to my original post.


The first thing to check is the vibrator which is this doo-dad.

Image

It's held on to the back of the instrument cluster by the hex-headed screw you see in the overexposed portion of the picture. That screw does more than just hold it there, it also provides the ground connection for the vibrator to work properly. If that screw isn't good and snug, your vibrator and subsequently, your fuel gauge will be erratic at best.

If that all seems proper then you can test your gauge by grounding the terminal that the brown wire is connected to in the picture. When that terminal is grounded, your gauge should read full. When it isn't grounded, your gauge should read empty. If that all checks out, your likely culprit is your tank sender (warning, pain in the ass to change). Good luck and report back your results.
- Dick

1970 Transporter. 2015cc, dual Weber IDF 40's
1978 Riviera Camper. Bone stock GE 2.0L F.I.
1979 Super Beetle convertible.

... as it turns out, it was the coil!

vdubyah73
IAC Addict!
Status: Offline

Post by vdubyah73 » Mon Jul 21, 2008 5:01 pm

Question...Why is it called a vibrator when all that is inside of it is what appears to be an interior light light bulb? That is what is inside of the one in my 77.
1/20/2013 end of an error
never owned a gun. have fired a few.

User avatar
dtrumbo
IAC Addict!
Location: Mill Creek, WA
Status: Offline

Post by dtrumbo » Mon Jul 21, 2008 5:03 pm

Here's a great article that explains it all.

http://www.nls.net/mp/volks/htm/fuel_ga.htm
- Dick

1970 Transporter. 2015cc, dual Weber IDF 40's
1978 Riviera Camper. Bone stock GE 2.0L F.I.
1979 Super Beetle convertible.

... as it turns out, it was the coil!

User avatar
satchmo
Old School!
Location: Crosby, MN
Status: Offline

Post by satchmo » Mon Jul 21, 2008 5:51 pm

Well, this isn't something I really want to announce on a public forum, but yes, I do have a vibrator.

All the connections are good and the attachment is solid. I need to get a meter with alligator clips since laying upside down in the footwell and holding a flashlight doesn't leave me enough hands to test the leads with the meter I have. I suppose I could take the instrument cluster out again (just did that a month ago - those clips always get lost somewhere).

If the sender is a problem, then it is not a big deal. It seems like I take an engine out of one vehicle or another every winter. This one would be no different.

Nice article, dtrumbo. The picture was good too. Did you take it in-situ? Amazing.

Thanks, Tim
By three methods we may learn wisdom:
First, by reflection, which is noblest;
second, by immitation, which is easiest;
and third, by experience, which is bitterest. -Confucius

vdubyah73
IAC Addict!
Status: Offline

Post by vdubyah73 » Mon Jul 21, 2008 6:04 pm

Sorry but that link didn't explain the light bulb in a box. I swear that is what I have. The metal box has separated from the base and I have a friggen light bulb in mine. It looks just like an interior light light bulb. and it does indeed light up when I turn the key on. I haven't looked to see if the brightness changes with the level of the fuel. Weird.
1/20/2013 end of an error
never owned a gun. have fired a few.

User avatar
Amskeptic
IAC "Help Desk"
IAC "Help Desk"
Status: Offline

Post by Amskeptic » Mon Jul 21, 2008 6:08 pm

satchmo wrote:Well, this isn't something I really want to announce on a public forum, but yes, I do have a vibrator.
Yeah, but does your fuel gauge have the instantaneous reading, or does it slowly glide to the indicated level?

My December 1972 bus has the balance coil gauge with no red reserve warning area.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

User avatar
dtrumbo
IAC Addict!
Location: Mill Creek, WA
Status: Offline

Post by dtrumbo » Mon Jul 21, 2008 7:51 pm

satchmo wrote:Nice article, dtrumbo. The picture was good too. Did you take it in-situ? Amazing.

Thanks, Tim
Not my article, not my pic. Found the article in a Google search, stole the pic from TS Gallery. I just replaced the sender in my wife's '70 because it would read almost full when the tank was full and as soon as you got to about half a tank, it would drop to pretty much empty. Sounds similar to yours in some ways. I haven't tested my new one because Daryl is still rebuilding the transmission. :blackeye:
vdubyah73 wrote:Sorry but that link didn't explain the light bulb in a box. I swear that is what I have. The metal box has separated from the base and I have a friggen light bulb in mine. It looks just like an interior light light bulb. and it does indeed light up when I turn the key on. I haven't looked to see if the brightness changes with the level of the fuel. Weird.
Very weird! Perhaps someone used a light bulb to act as the heater for the bi-metal? Complete guess there. You could check to see if the light flickers with the key on.
- Dick

1970 Transporter. 2015cc, dual Weber IDF 40's
1978 Riviera Camper. Bone stock GE 2.0L F.I.
1979 Super Beetle convertible.

... as it turns out, it was the coil!

User avatar
satchmo
Old School!
Location: Crosby, MN
Status: Offline

Post by satchmo » Fri Jul 25, 2008 1:30 pm

Update on the Fuel Gauge:

My testing pointed to a problem in the sender. So today I cut a hole in the rear package tray to access the sender. I had the forethought last time I pulled the engine to mark the area I would need to cut to access the sender in case this repair was ever necessary (which doesn't happen very often, the forethought, I mean).

The sender is of the newer type with the float on a lever/arm that moves a little wiper across a resistor. It was the original sender as far as I could tell. Testing the wiper with an ohm meter shows infinite resistance until about the 3/4 full mark, and then it goes to zero at that point. I tried cleaning the unit and varying the pressure of the wiper on the resistor, but got the same result. Looks like I need a new sender.

Thanks for everybody's help.

Tim
By three methods we may learn wisdom:
First, by reflection, which is noblest;
second, by immitation, which is easiest;
and third, by experience, which is bitterest. -Confucius

User avatar
IFBwax
IAC Addict!
Location: PDX
Status: Offline

Post by IFBwax » Fri Jul 25, 2008 2:43 pm

That's the ticket.. sounds right. After you get it in there, you may want to make a few adjustments. Sometimes out of the box they show really full and then when you're empty, the gauge only shows just the beginning of reserve. I'd rather start BARELY full and have more room on the bottom end to save me from running out. Either way, you can bend that little arm a bit to fool the sender into thinking it's less full than it is or vice versa.
The best navigators aren't sure where they're going until they get there. And then they're still not sure.

Frank Bama

http://www.partypickle.blogspot.com

User avatar
bretski
Ellipsis-Meister
Ellipsis-Meister
Location: out of hibernation...for now
Status: Offline

Post by bretski » Mon Jul 28, 2008 3:43 pm

Yup. The senders being sold today are not very accurate out of the box. Count on having to bend the arm to get an accurate reading. Like IFBwax stated, have your gauge err to the conservative side.

I've been through 2 senders in the last 15 years, and both of them read about 1/8 tank too low as shipped from the factory...better than the other way around, I guess. :blackeye:
1978 Deluxe Westfalia - "Klaus"

"transcripts are overrated. hardware store receipts: those are useful." --skin daddio

Post Reply