tank problems and vapor lock

On hot days (110 or hotter), the fuel in the tank starts to bubble by the time it flows thru the fuel filter (clear, ziptied in engine bay at the AC metal line). I have an inline electric fuel pump mounted in front of the rear pass. side tire. So not a mech pump issue. Also the gas seems to evaporate when i let the truck sit for a few days. i lost about 2 gallons after not driving it it was 112 outside. I have had many other older vehicles, a carbed converted 97 burb gmt400, and they never had this issue, Prior to buying this burb in 2015 i had never even heard of this being a possibility.

Is my tank itself gettin too warm from the outside temp? hot pavement alone? the dual exhaust pipes that come str8 back emitting too much heat?? What can be done, as im considering pulling a 42 gallon tank (from a 95 burb) and swapping it as i only have the 31 gal tank.

80goldenburb said:

On hot days (110 or hotter), the fuel in the tank starts to bubble by the time it flows thru the fuel filter (clear, ziptied in engine bay at the AC metal line). I have an inline electric fuel pump mounted in front of the rear pass. side tire. So not a mech pump issue. Also the gas seems to evaporate when i let the truck sit for a few days. i lost about 2 gallons after not driving it it was 112 outside. I have had many other older vehicles, a carbed converted 97 burb gmt400, and they never had this issue, Prior to buying this burb in 2015 i had never even heard of this being a possibility.

Is my tank itself gettin too warm from the outside temp? hot pavement alone? the dual exhaust pipes that come str8 back emitting too much heat?? What can be done, as im considering pulling a 42 gallon tank (from a 95 burb) and swapping it as i only have the 31 gal tank.

Click to expand...

I have a few thoughts and suggestions here. Glass filters and plastic filters of any opacity are a no-no. You need a metal canister filter because if that weaker one ruptures, that could be devastating. I can appreciate the novelty of wanting to see what the fuel is doing as much as the next guy, but it's not worth it in the long run. Also, is your fuel line tied to the high side line? If so, you're exposing your fuel line to a lot of extra heat conduction coming from that when the A/C is on. I'd make sure that the fuel line is as far away as possible from the red hot stuff under the hood, and I'd also check your rubber lines near the tank to make sure they're not cracked. If you have any doubts when you perform this inspection, I'd replace. If you do end up removing the tank, I'd also clean the tank and replace the strainer sock for good measure. Finally, if you have concerns about fuel evaporation (which is possible), I'd replace the fuel cap. When the seal starts to fail, vapors can surpass it.

1987 GMC Jimmy said:

I have a few thoughts and suggestions here. Glass filters and plastic filters of any opacity are a no-no. You need a metal canister filter because if that weaker one ruptures, that could be devastating.

Click to expand...

true. it could be if the gas were to leak on the headers, but thats why I have it mounted away from there. im actually considering mounting it further than where its at.

1987 GMC Jimmy said:

Also, is your fuel line tied to the high side line? If so, you're exposing your fuel line to a lot of extra heat conduction coming from that when the A/C is on.

Click to expand...

No A/C working as of now

1987 GMC Jimmy said:

Finally, if you have concerns about fuel evaporation (which is possible), I'd replace the fuel cap. When the seal starts to fail, vapors can surpass it.

Click to expand...

Cap is brand new, possibly the tank sending unit venting where it should be capped off? (mech fuel pump return line is non existant)

I hear you on the cap. The only places I can think of that evaporation could even potentially happen are at the sending unit o-ring or maybe in the vapor lines like you said. Is the evap canister there and hooked up?

1987 GMC Jimmy said:

I hear you on the cap. The only places I can think of that evaporation could even potentially happen are at the sending unit o-ring or maybe in the vapor lines like you said.

Click to expand...

i did drop the tank before to replace cracked lines. i never thought of that o-ring being bad but i know that I have four hose ports on the sender and two of them are open/unplugged. i noticed the other day, it smelled of gas fumes when i got under the tank near the filler neck.

1987 GMC Jimmy said:

Is the evap canister there and hooked up?

Click to expand...

Nope, non existant also. when i bought the truck. One of the previous owners sometime after '96 yanked the evap canister, mech fuel pump return line and any other factory smog equipment when they swapped in this over the counter Gen V 502. So more work for me once i do the swap. i think the sending unit might be bad also.

Following as I kind of have the same problem. I have 0 emission on my truck. I dont know what hacky jobs the Prev. Owner did, but when the temp is high, 85 and above, I cannot fill up the gas tank.

Now I havent been under it yet to see if anything is capped off, but by the amount of fuel smell, I am assuming that nothing is plugged.

Hmm... You have a four line sender and two of them are unplugged. I'm guessing a fat one is unplugged. That goes to a hard line that runs parallel to the filler line. I don't know if the return or the vapor line is the one unplugged on the sender. Is there still a vapor line running to the engine bay? If so, it needs some kind of inline filter because it's just sucking dirt and trash into the sender. If the return line is the one that doesn't have a line, I'd just cap it for good measure and go to a three-line sender whenever you replace. If it were me, I'd just clean it all up now with a three-line sender, a two-line mechanical pump, and that inline filter on the vapor line. Not to mention re-cleaning if it's been sucking in dirt and whatever else for an indeterminate amount of time. I'd say that would 100% fix your evaporation/fuel odor issue. It would likely fix the vapor lock symptoms, too. It's up to you, but you could get away with those repairs for around $80 dollars on RockAuto (less if you kept the electric pump), and it'd be good preventative maintenance.