Our 2004 C5 last had a fill up this past March. Gauge shows 7/8 full. I had my right knee replaced 5April and the left replaced 24May. Being a six speed, no driving it. I replaced the 2/2012 Optima with a 34/78 Odyssey and started it this past Sunday. Started right up with no apparent problems and idled for thirty minutes before taking for a short drive. The exhaust smells terrible. I do run, do not laugh, Marvel Mystery Oil in the gas in every vehicle we own. Is there any possible negatives for putting a 20oz bottle of Techron concentrated system cleaner in the fuel being the driver's side tank will receive the Techron and already full of fuel? No even distribution between the two tanks.
Thanks for any info.
Chas
Sad to say only driven 400 miles since last oil change, 15Jan2021

 

Absolutely no negatives...just dump it in.

 

The Chevron Techron product might help with the fuel gage indication problem; it will homogenize throughout the system once your run the car for some time, how much, I do not know. I used it successfully to correct fuel level indication problem on a 2001 Z06 I used to own. Run the car for at least 20 miles to get the cats hot, they may clear up. Short runs that do not allow the cats to warm up is not good for their operation and life cycle. For a car that sits you are better off using STABIL rather than Marvel Mystery Oil.

 

Wait till your fuel gauge is less than 1/2 tank or so to add the Techron. If your exhaust smells you should get your hands on a scan tool to look at your O2 sensors and fuel trims…if your O2’s are “stuck” below 450mv the car will run rich.

 

I will say that I expect that your cats do not really like the Marvel Mystery Oil. (The smell cold be them voicing their displeasure at what they're being fed.)

The 20 oz bottle of Techron is rated to handle a 20 gallon tank. I'd throw one of those in (the jet pump in the tank should distribute it fairly quickly). Run it down to half a tank, and see how things are doing. You could always add in another 12 oz can of Techron.

 

chasb you mention the exhaust smells terrible, care to elaborate? Do you mean pig rich, rotten eggs (sulfur), or like it's burning oil or something else not intended for combustion? Any smoke puffing out the exhaust?

Also, any idea how much ethanol was in the fuel from the March fillup? If memory serves that was around the time gas prices were spiking and there were talks of increasing the amount of corn liquor being blended in to increase profits, err I mean reduce costs. Having owned a boat that's sat for years at a time without use I can attest to the fact that ethanol blends if left to sit for prolonged periods will "striate" or fall out of suspension. The times I drained the tank I found the fuel at the bottom of the tank was clear and higher in concentration of ethanol as it's bonded to any water molecules, and the gasoline and oil additives (I use Sta-Bil) with the red dyes were at the top of the tank.

What I would suggest is to make sure you have the number of a towing company in your phone and then go ahead and dump a bottle of techron in and go for a 50-75 mile drive at highway speeds. Don't sit in the driveway letting the car idle, just get out and go so the cats light off as quickly as possible.

If it's running ok at the end of the drive and there's no smoke emanating from the exhaust and no MIL (aka check engine light) I would proceed to drive the rest of the tank out as much of a challenge as it may be (you didn't mention how your new left knee is tolerating the clutch) before filling with fresh 93 octane. Also, please don't tell us you're using anything less than 93 octane. Sure the computer will adapt and pull timing, but trust me - you don't want that.

I can sympathize by the way - mine are both giving me trouble, and I've decided to run miles up on my '95 M6 instead of the 2001 until my left knee either gives out or stops complaining so much. As my wife reminds me all to frequently, sucks getting old, huh?

 

I feel your pain with the knee as well. I had my left done in '16 and my right done about 4 months ago. I have an auto however the fresh right knee still does not like getting into the car.

 

I'd been using a lot of Speedway gas all Summer. On the trip from Michigan to Florida I used mostly Sam's Club premium. By the time I got here, gauge was funky again. 1 bottle of Techron, and a Shell fill up did nothing. Just dumped another bottle of Techron in, and 17 gallons of Shell helped quite a bit. Just filled up with another tank of Shell premium, and all is well in gas gauge land. I live 30 miles round trip from nearest Shell in Michigan, so I don't get to use it much. Here in Florida, there's a Shell only 1/4 mile away. So I use it all the time. BTW, I passed a Texaco today that had a sign out front stating 'Contains Techron.' IDK about other states, but it appears Florida Texaco stations use Techron, FWIW......

 

I have also used BG44K which works as good or better than Techron in some circumstances.

2 Bottles of New BG 44K Platinum + Free Shipping (amazon.com)

 

I have used Techron a couple times to successfully clear up the issue with the gas gauge going from 1/4 tank to empty in the blink of an eye.

 

Mine had a slight stumble right off idle, a bottle of Techron seems to have cleared it up.

 

I've used Techron routinely for the 98's entire 25 years, never had a fuel gauge or engine miss problem.