Hey everyone. I have had 3 separate fuel tank issues that are likely unrelated, but I wanted to know if it is related to the below zero temperatures or could I have a different issue.

1. I was on I-88 in upstate NY and after driving about 20 miles (I had a third of a tank of gas. Normally I don't run it below that.) I noticed my gas gauge went down to around 1/4. Over 2 miles my gas gauge went from 1/4 creeping all the way to E until the low fuel light went on. I pulled off the roadway at an exit and checked the fuel used counter and it was around 12 (I reset it every fillup and it is accurate). I checked under the truck and there were no leaks in the tank, the lines or the filler neck. The check engine light is not on. When I saw the price of gas, I continued to my destination (only 5 miles) with the gauge hovering a notch above E and put cheaper gas in and it confirmed that the fuel used counter was correct since the pump stopped a full gallon before the level used on the counter (the counter said 12.5, the pump stopped at 11.5 and then I pumped it up to 12.6). It returned to F when I started the truck, so it seemed okay at the time. The fuel pump was replaced 20k miles ago with a Walbro TU429 unit and the gauge seemed pretty accurate before tonight and I use Techron every few thousand miles, so that can't be it.

2. My gas mileage sucks big time. 80% highway driving, but I am only getting about 14-16 this tank, but the truck seems to have better pickup and I seem to be using less throttle to maintain 65 on the highway. I used the instant economy gauge and the only time I was getting above 18 was on a 1-2% downhill grade with the cruise control on. This was during the same trip when it was below zero outside.

3. This is likely the unrelated one since the cause is obvious, but my gas cap lock seemed to have gotten some water in it because I was unable to insert the key to the last set of pins and I couldn't turn it. I sprayed PB Blaster into the lock and after waiting a minute, I got it to turn and I was able to put gas in the truck. I put Lucas and gas in the tank and that was it, but was PB Blaster the right thing to use? How do I remove it from the key? They had no lock deicer and I was out of WD-40.

So was all of this a fluke because of the temperature or could I have some issue with the tank?

 

So, did I read that correctly? It runs ok and your gauge works fine? (F vs E, and everywhere in between?). Sounds like a typical chevy-- freakin' reliable. Below half tank can be detrimental to our fuel pumps, anyway.

I'd ditch the locking gas cap if I were you; they're totally pointless/annoying unless you have people dump stuff in your tank frequently. You can't get a siphon hose in through the fill tube, anyway. There's a giant check ball in the way designed to prevent fuel from flooding out during a roll over. If I wanted your gas, I'd drill a hole in the tank and insert a petcock valve... Or splice into the supply line and apply 12v to the pump.

 

All seems normal and on par with these vehicles. As usual, you are over analyzing things on your truck.

 

Runs okay, but the gauge went down fast as if there was a leak somewhere. Never has done that before. Not being over analytical, but when problems like this occur, I find that asking the questions is alot better than not and finding out later that it is a warning sign of a bigger, more expensive and disabling problem. I had probably over a third of a tank (I don't normally run it down like that. I was driving back to my apartment and gas is normally cheaper there than some gas station near the highway), but the way the gauge went from 1/4 all the way to E with the low fuel light over only 2 miles of driving suggested a major leak somewhere at the time. There has been some discrepancy between the fuel used counter/gas gauge and what I am actually putting in the tank, so I am hoping there isn't some internal leak somewhere.

I have had threats before and someone did try to dump something in the tank. That was foiled by the locking cap. The flap at the top of the fill hole was damaged by a siphon hose years ago. There is a check ball? Good to know, but I am more concerned about someone dumping something destructive or dangerous in the tank. Yea I have been in situations where people have wanted to do damage to this truck and they think it is a joke. Personally I would have liked to have them arrested to make a point that I have a zero tolerance policy for things like that, but without cameras, fingerprints and evidence it is hard to prove.

And you would really go through that much trouble for gas? Wow. LOL JK. Yea the cap is annoying but at least it is one less point of easy vandalism.

 

- It was below zero outside. When that happens, the engine will run a little richer.. and the air is really freaking dense so you will not open the throttle as far for the same air volume. Not to mention parasitics from cold stiff lube in your axles. Wind drag is higher... yadda yadda.

Put your mind at ease: do a FP and leakdown test. If leakdown is good, and your codes read good / no SES light and you dont smell gas around the truck, you're fine

Added:
Walbro makes an assy for the blazer!! Go figure. Couldnt find one when I needed it
Except, of course they dont make the assy itself, just -we hope- the pump.

That assy may be the same one Airtex uses in which case wouldnt surprise me the sensor is flaky.

 

So the cold explains it all then. Obviously the frozen gas cap but also the bad gas mileage and the gas gauge. The cold gear oil in the drivetrain really makes a difference? Wouldn't it heat up because I was going highway speeds?

Leakdown test? Is that the one where I have the fuel pressure tested and see if it holds pressure? Unless the truck was sitting for a couple days or overnight in cold temperatures (which it would take an extra second), it starts right up. What would it mean if it failed a leakdown test? I don't recall smelling gas around the truck and I haven't had an SES light since I got the truck 4 years ago.

Walbro does make an assembly for the Blazer. I got it cheap at $138 + ~40 for "overnight" shipping once they got it from the manufactuer, which in this case I had it sent to the shop and it arrived via FedEx while my truck was on the lift getting brake lines replaced also. Ironically, the pump failed in the parking lot just after I drove it there because I ran it down to 1/8 of a tank since I was having the pump replaced anyway since they had to drop the tank to get to the rear brake line that I was having replaced due to rust Walbro TU429 OE Replacement Fuel Pump Kit from Fuel-Pumps.net . Only drawback is that they have to special order it from the manufacturer, so it takes an extra couple days. They actually called me since the shipping and billing addresses were different and explained the whole situation with the special order. They seemed pretty honest. It is pretty quiet most of the time unless the fuel filter wasn't changed recently (I have it done every other oil change) or the tank is below half, then I can hear it if I get close to the wheelwell. I had it installed September 2010 at 93,000 miles and now I have 113,5** on it.