JerryU

This is a pic from the C7 Service Manual. Note the resistor portion of the fuel sender is near the top of the tank. It is the same type system that has been used for 75 years! Installed a similar fuel sender in my street rod. Easy to do and if it failed I would just drop the tank with a few bolts and replace. The float at the bottom just moves a wiper on the resistor on top! Adding to other than a near full tank is not much help for the sender!

In the C7 that is a many step process to replace the sender starting with removing mufflers, the transmission etc etc! Expensive and even if in warranty would not what to hope the dealer reassembled correctly! I use a bottle of Techron every few months, just as a precaution.

joemessman

I use Chevron gas. I wonder if there is enough techron in that to maintain the sending unit?

KenHorse

I've run my C4, C5, C6, C7 (and my soon to have GS) pretty much exclusively on Shell V-Power with the occasional Chevron Supreme tankful

In over 200K miles of accumulated miles between them all, only the C6 had the problem

bjones7131

Curious if Seafoam will do the same as Techron? I use it on all my vehicles and lawn mowers.

jphillpott

Since my original post last year about the fuel gage, I have added several more bottles of Techron, and it seems
to be ok now.

I suspect even with the so-called top tier gas, we occasionally get "Bad Gas". I'm putting in a bottle of Techron
about every other tank, and the "Problem" seems to have gone away.

JP

Red86Cfour

I'm glad to see that techron seems to have cleaned up the level sensors so well. I wasn't so lucky in my GMC Sierra that had this problem for the last 17 years I've owned it. Maybe it was too far gone. Fortunately, replacing it and the fuel pump at the same time is a bit easier than in our 'vettes! I would have left it alone, but regardless of how much was in the tank, it usually read either full or empty. That was a problem because in order to get the evap monitor to run, the tank needs to be approximately half full at cold start up to run, and it never provided a consistent reading to do so.

jimmbbo

Good news on Techron clearing the problem...
Top Tier gasolines meet the TT standard. Top Tier fuels may differ from one another as the companies add proprietary or branded additives for performance or marketing purposes (e.g; Chevron's Techron)

JerryU

FWIW, this was from a Technical Service Bulletin by the National Highway Traffic Safety Administration re sulfur in the fuel.. BUT it's quoting a Chevron Manager as to why Techron works:
"What is happening? The silver in the sending units is tarnishing just like your good knives, forks and spoons. That is why silverware comes on those lovely boxes lined with sulfur-free cloth.
Silver reacts readily with sulfur compounds to create that tarnish--silver sulfides. Though it is fairly easy to clean off (remember cleaning your mother's silverware?), it is difficult to keep it from returning.
Fuel sending units suffer the same fate, and the problem gets worse in the heat.
Chevron Techron additives. Chevron Techron Concentrate Plus is the product GM dealers use.
We spoke with Scott Cushing, fuel system additives manager at Chevron.
And even the "top tier" gasolines, those with high doses of additives, don't adequately protect, according to Cushing. They don't have the filming agent. This coating, which is left behind, protects the sending for around 3,000 miles. "We suggest that motorists treat their fuel every time they get their oil changed," said Cushing.
Cushing says two tanks treated with the Chevron product usually can clean sulfur deposits from the sending unit and should be blended at a ratio of about one ounce per gallon of gasoline." (My Note: Folks who have tried say it may take more than 2!)

Mad*Max

why would they use parts that dont like sulphurb when gas contains the same?

owc6

Most likely money.

Sure, they could use gold to plate the contacts, but multiply that by however many thousands of units, and the extra cost ads up quickly.

JerryU

^^^
Lisa, but as you reported you had to have done out of warranty (with your ~100,000 miles) although gold contacts cost more would appear for those where it's done on warranty, it would not take many to pay for gold versus silver!

As I recall you always used Top Tier! I decided it's less expensive to save ~$5 fill-up and get Sam's Club High Test (which only has the Federally mandated "cleaners" but not Top Tier) and add a bottle of Techron about every ~4th fill-up!

Red86Cfour

Considering it costs close to, if not more, than 3K to have a shop drop the drivetrain and rear suspension to get to the tanks to R&R a sender, gold plated sending units seem to be a bargain!

volvos80

I own a 2014 C7 which after filling up the gas tank had the fuel gauge drop to 0 as well as the digital gage showing - - - instead of miles left to empty. There are no failure codes associated with the gage showing 0. Apparently this is a common problem as I read on forums many other C7 owners have had the same issue. I also read that the repair by a dealer will be expensive, but as I love the vehicle I took it to my dealer (Village Chevrolet in Minneapolis, MN) and was told they wanted $175.00 to diagnose the problem first. As I asked for a ballpark price to repair, I was told they have done several fuel sensor replacements and the cost will be just a bit above $4,000.000 – yes that is a bit above four thousand Dollars! So how can the C7 design be so bad that most of the drive train and rear axle has to come off before they can start taking down the fuel tanks? My vehicle has 17,000 miles and has always been driven on COSCO premium fuel. I am ready to dump the car and purchase something else non-GM related.

JerryU

^^^
Yep, it's a bit crazy design. but as my post 31 above showed that was Lisa's car who always used Top Tier gas. CASCO is Top Tier. Believe she said she had ~100,000 miles when she had the sender replaced. BUT she has said she used Techron before and it solved the issue. Worth a try.

Read through this Thread. I had a number of posts. The basic issue is apparently the silver electrical contacts on the fuel level sender that sits in gasoline can tarnish as does silverware. Then the contact to the wiper is lost or the resistance changes.

I don't always use Top Tier gas! Didn't on my C7s all the time. Don't on my C8, where it's said GM uses a different measuring method. I use Sam's high test because it's typically $0.40 to $0.50 / gallon cheaper than even other low cost places like Raceway. BUT as I did in my C7s I added a bottle of Techron every few months. It is what is in some of the Top Tier fuels as an additive. If I were you I would do what I believe Lisa said she did. Add about 3 bottles of Techron and run though that tank. May solve the issue. If not repeat. Cheaper than $4000 labor to replace a `$50 item!

If you store the car, say in the winter only keep it 25% or less full of gas. That has been the new recognition versus full. That keeps the fuel sender electrical part out of the gas with it's sulfur! GOOD LUCK.

jlbruggeman

GM has been recommending Techron (which, as someone else pointed out, is the same as the GM product) for the gas gauge problem for 24 years, since the first C5s started getting the problem. It works best when the tank is almost empty, right before a fill up. I buy it by the case when it goes on sale at an auto parts or farm supply store.

jphillpott

Thanks for sharing your info. Since the problem happened on my '17 when it was new, I have added a bottle of Techron about every three months.

After the first two bottles, the fuel gauge settled down, and I've had no more problems with it. The gauge is accurate and working well.

Thanks for the info.

JPhillpott