Trip odometer as gas guage

[cmac2012]

I replaced my ignition switch and steering wheel lock assembly recently and when back together the fuel gauge went out within a few days. Weird. Until I find the problem I've been using the trip odo to avoid running it dry. I fill up at 400, maybe a bit more. Funny thing, one time I pushed it to about 430, this after noticing that I often had 4 or 5 gallons left at 400 and the idiot light on the fuel gauge starting blinking on like it usually does with about 3 gallons left.

Might point to the problem, not sure.

Not nice to call it an idiot light - I like the feature. I have weird idea that temp gauges should have an audio component, maybe a teapot whistling sound when it gets too close to overheating. I don't think most of them (any of them?) even have a light that performs that function.

[Mxfrank]

The idiot light is controlled by contacts on the bottom of the fuel sensor float. The fact that it works doesn't mean the sensor itself is intact, nor does it mean that the gauge is working correctly.

[cmac2012]

Thanks for that, I had a feeling it would be something like that. What I don't know is if the sensor or the gauge is bad, and you alluded to that. I really should fix it, if the trip odometer went south I'd be flying blind, fueling up every other day.

[if6was9]

Diesel tanks usually have all kinds of grimy gooey black stuff all over the inside of the sender mechanism. Might be that yours has enough diesel goo in the bottom of the sender to prevent the contacts attached to the float to not be able to get down through that goo and touch together. It could be that one of the three wires is damaged or disconnected.

The sender can be removed 46 mm is the size wrench needed to remove it from the tank.

If you find you can open and clean yours you should be very careful and use mostly carb or brake cleaner spray to remove the goo, be very gentle touching the wires. If any are broken or disconnected they are nichrome and can be quite difficult to reattach with lead tine solder and regular flux. There is special flux for nichrome.

If your sender is kaput, you can get a nice clean sender from any gas 126 carcass, senders from gasoline cars are usually very clean with virtually no residue goo inside.

[okyoureabeast]

Assuming everything is operating in spec, I regularly pushed 450 miles on my 85 300D.

One time I hit 500 to see if the reserve light would come on, it did. Never tried that again.

Pull your fuel sender and examine the inside of your tank. Mine was clean so I wasn't afraid of that experiment.

I would also check your instrument cluster ground. Worth pulling and taking a look. Might be a simple fix.

[mark82]

Guys; this isnt witchcraft.

Fill the tank, cqlc the mileage (all applicable errors understood?).

Subtract the fill amount from tank capacity to get how many gallons you really had remaining. Multiply those gal by the mileage, add to dist traveled to see expected total range.

I have found the warning to light be more accurate than the guage, always works, mine seems to activate around 4 gallons remaining. Using 4 gal and mileage I can figure how far remaining when the light comes on (steady state).

This is always a better, more accurate estimate of range and when to refill than the guage alone.

[97 SL320]

Originally Posted by cmac2012

I replaced my ignition switch and steering wheel lock assembly recently and when back together the fuel gauge went out within a few days. Weird.

If this wasn't a home repair, others would be telling you the garage is at fault . Next step, can you access the sender wire at the tank? If so, find the ohm spec and attach an ohm meter as a temporary gauge. ( Disconnect the harness from the sender so the car side of things does not interfere ) Add fuel, take a resistance reading every gallon and see if you hit the full tank spec resistance. As you drive the car, take a resistance reading every 20 miles or so then graph the results. Given the erratic low fuel light , use miles driven as a basis of fuel usage until the ohm readings prove to be accurate.

[cmac2012]

Originally Posted by okyoureabeast

Assuming everything is operating in spec, I regularly pushed 450 miles on my 85 300D.

One time I hit 500 to see if the reserve light would come on, it did. Never tried that again.

Pull your fuel sender and examine the inside of your tank. Mine was clean so I wasn't afraid of that experiment.

I would also check your instrument cluster ground. Worth pulling and taking a look. Might be a simple fix.

Since it happened right after I put the cluster back in I was wondering about a ground or other issue. OTOH, the gauge is the only thing acting up. I'll give it a look.

[cmac2012]

Originally Posted by if6was9

Diesel tanks usually have all kinds of grimy gooey black stuff all over the inside of the sender mechanism. Might be that yours has enough diesel goo in the bottom of the sender to prevent the contacts attached to the float to not be able to get down through that goo and touch together. It could be that one of the three wires is damaged or disconnected.

The sender can be removed 46 mm is the size wrench needed to remove it from the tank.

If you find you can open and clean yours you should be very careful and use mostly carb or brake cleaner spray to remove the goo, be very gentle touching the wires. If any are broken or disconnected they are nichrome and can be quite difficult to reattach with lead tine solder and regular flux. There is special flux for nichrome.

If your sender is kaput, you can get a nice clean sender from any gas 126 carcass, senders from gasoline cars are usually very clean with virtually no residue goo inside.

Good to know. I see early 90s gassers in the boneyards around here quite often.

[cmac2012]

Originally Posted by mark82

Guys; this isnt witchcraft.

Fill the tank, cqlc the mileage (all applicable errors understood?).

Subtract the fill amount from tank capacity to get how many gallons you really had remaining. Multiply those gal by the mileage, add to dist traveled to see expected total range.

I have found the warning to light be more accurate than the guage, always works, mine seems to activate around 4 gallons remaining. Using 4 gal and mileage I can figure how far remaining when the light comes on (steady state).

This is always a better, more accurate estimate of range and when to refill than the guage alone.

I get anywhere from 20 to 25. I've only seen the light come on twice during this recent business, both times 420 to 430. I thought mine came on with 3 gallons left, really not sure though.

[Clemson88]

Originally Posted by cmac2012

I replaced my ignition switch and steering wheel lock assembly recently and when back together the fuel gauge went out within a few days. Weird. Until I find the problem I've been using the trip odo to avoid running it dry. I fill up at 400, maybe a bit more. Funny thing, one time I pushed it to about 430, this after noticing that I often had 4 or 5 gallons left at 400 and the idiot light on the fuel gauge starting blinking on like it usually does with about 3 gallons left.

Might point to the problem, not sure.

Not nice to call it an idiot light - I like the feature. I have weird idea that temp gauges should have an audio component, maybe a teapot whistling sound when it gets too close to overheating. I don't think most of them (any of them?) even have a light that performs that function.

When I figured out how to clean the fuel pickup in the tank I found the gauge worked again. Not saying that's your problem because my idiot light didn't work until the cleaning.

[jbach36]

Originally Posted by mark82

Guys; this isnt witchcraft.

Fill the tank, cqlc the mileage (all applicable errors understood?).

Subtract the fill amount from tank capacity to get how many gallons you really had remaining. Multiply those gal by the mileage, add to dist traveled to see expected total range.

I have found the warning to light be more accurate than the guage, always works, mine seems to activate around 4 gallons remaining. Using 4 gal and mileage I can figure how far remaining when the light comes on (steady state).

This is always a better, more accurate estimate of range and when to refill than the guage alone.

No. The correct answer is to fix the fuel guage problem so then you'll see how much fuel you have remaining.

[cmac2012]

I agree, really need to get it working. I'm lucky I have backup, had rather. Now I have no backup. The trip odometer reset is not magically guaranteed to never break. If it did I'd need to make careful note of the total mileage at fillup, add 400, put it in my phone notes, write it down, something. Could definitely be done but more hassle.

[97 SL320]

Originally Posted by cmac2012

I agree, really need to get it working. I'm lucky I have backup, had rather. Now I have no backup.

As I stated in my prior post, hang an ohm meter on the sender, instant temporary gauge if the sender is still working.

[cmac2012]

Originally Posted by jbach36

No. The correct answer is to fix the fuel guage problem so then you'll see how much fuel you have remaining.

This has become more urgent. The trip odometer still works but the 'tank almost empty lights are coming on early. Twice in one day on my return trip yesterday the lights came on at around 200 miles on the odo, sure enough, fill up took about 10 gallons.