SOLVED! Gas tank check valve replacement/repair, help needed

[02FailBlazer]

2002 TrailBlazer LTZ, ~198K miles.

As in my previous thread relating to this, the seal around the check valve on my gas tank failed, causing it to vent gas vapor into open air. I attempted to replace it with the Dorman valve and completely butchered my tank, making it unusable.

I was lucky enough to find and acquire a tank that was not punctured from an Envoy at a scrap yard, but I still have a problem - do I epoxy the seal on the "new" tank and use it as-is, or try again to perform the Dorman replacement?

The check valve on the new tank does not appear to be stuck at all, the "plunger" is loose to the touch. There are several epoxies I could try, assuming they hold up to fuel. These include Pegatanke black (which claims to be good for fuel tanks and which has so far successfully stuck to my old tank in a small test) or their putty version, G/flex 650, and Loctite AA 3035.

Alternatively, I could try the Dorman 577-106 replacement again, but I NEED info from someone who has done it before. I have NO IDEA how to get the factory check valve out without mauling the tank. Attached is a labeled photo of the check valve - where exactly am I supposed to try cutting this thing off, and with what? The instructions Dorman provides are useless and the web has sparse info on doing this repair.

 

[Mooseman]

Given your luck with the Dorman part, I'd go with the epoxy. The Pegatanke black looks good but I wouldn't use the putty version as that wouldn't penetrate into the cracks. I'd give the whole area a good cleaning with brake cleaner and a light sanding to give the epoxy a good bite into the plastic and use it all the way around to support the whole inlet.

Curious, how did you get the Pegatanke black? Seems to be available only in Ecuador.

 

[02FailBlazer]

Given your luck with the Dorman part, I'd go with the epoxy. The Pegatanke black looks good but I wouldn't use the putty version as that wouldn't penetrate into the cracks. I'd give the whole area a good cleaning with brake cleaner and a light sanding to give the epoxy a good bite into the plastic and use it all the way around to support the whole inlet.

Curious, how did you get the Pegatanke black? Seems to be available only in Ecuador.

It's available on Amazon and eBay. I still need to cut off a piece of my old tank and try a submersion test next. I'll stick it to the plastic and dunk it in gas, let it sit for as long as I can stand not having this vehicle back together, and see what happens.

 

[02FailBlazer]

Hey all, this is the grand conclusion to my gas tank repair saga, as seen in this thread and this one. [Mod edit: Merged the two threads to keep things together]

Before anyone asks yes I bought an OEM Bosch pump and used that instead, so there.

Anyway, this is in regards to repairing a leaky inlet check valve seal on Trailblazer and Envoy gas tanks. If you don't know, the seal where the inlet check valve meets the tank can fail over time, causing an EVAP code and venting fuel vapor into the air. My tank's seal had failed due to age and thus needed fixing.

After butchering my original tank trying to do the Dorman 577-106 check valve replacement, I bought another tank off an Envoy. I anticipated that the seal on that tank might also be bad (or was soon to be bad) since it was just as old, so I wanted to seal it up before installing the tank. These tanks are, as far as I know, made of HDPE, which means practically nothing sticks to it, especially not anything that can also resist fuel vapors. This means your long-term options for repairing this issue are extremely limited. Enter one possibility I haven't seen mentioned anywhere else - plastic welding.

I bought the Chicago 1600 watt plastic welding kit from Harbor Freight, SKU 59646, and used the included speed feed tip that allows you to feed and heat a plastic rod while also heating the substrate. Heat setting was around 1.5 to 2, DO NOT EXCEED HEAT SETTING 3. I bought 1/8" thick HDPE rods on eBay. I practiced my technique on my old tank before trying anything on the new tank.

Some tips - you have a VERY THIN margin for error. The temp has to be just right - hot enough to put enough energy into the HDPE that it will soften and bond, but not so hot that it bubbles or otherwise irreversibly damages the plastic. This is harder than you might think, and you get practically no warning before things go wrong, so get something to practice on first. These tank's are somewhere around 3/8" thick by my estimation, so get a substrate of similar thickness as this will affect how much heat the plastic can soak up. Use WHITE welding rods - I tried other colors, but the white rods are helpful in that they turn clear when they reach (as it seemed to me) the appropriate temperature for bonding, so you get a visual indicator of how hot the rod is.

Other than that, I just did my best to make sure the rods were bonding to the seal by manipulating the hot plastic with the V-shaped end of the speed tip, which you can use to kind of mash the rod and the substrate together. Again - PRACTICE THIS FIRST.

Here's some pics of the weld I did. It's messy and I'm sure very much imperfect, but my EVAP code is gone and the tank has been holding pressure without returning an EVAP code for several weeks now. I can't necessarily attribute that to the weld rather than the original seal as I couldn't test this tank before installing, but at the very least it doesn't appear to have done any harm. You can see a bit of surface wrinkling on the check valve body, that was my doing. Think the plastic just got too hot but again, it's holding up fine.





It should also be said that heating the seal might be an easier way of removing the old check valve if you want to try the Dorman fix instead - I think if you get the seal hot enough, you might be able to yank the whole valve out with some effort. Would probably be easier with two people - one heating the seal in a circular motion, the other pulling on the valve.

 

[Mooseman]

Would you have a link to the plastic welder?

I did something similar to a tank I got from the U-Pull yard but was punctured to drain it. I used pieces from the old tank with my soldering gun with plastic smoothing tip, which was either too hot or not hot enough with its two temp settings. It did work eventually but took many tries to stop it from leaking gas.

 

[02FailBlazer]

Would you have a link to the plastic welder?

I did something similar to a tank I got from the U-Pull yard but was punctured to drain it. I used pieces from the old tank with my soldering gun with plastic smoothing tip, which was either too hot or not hot enough with its two temp settings. It did work eventually but took many tries to stop it from leaking gas.

This is it.

The speed tip isn't pictured and you can tell it was made separately then added to this bundle at some point so it feels like an afterthought, but it works. You have to put one of the other tips on to use as an adapter since it doesn't have the threads needed to screw directly to the welder. I used the basic angled tip, worked fine.