Fuel Tank getting hot/Sucking fumes.

[Patrick Tollett]

I have a mechanical non retun fuel pump on my 81 k5, evry time my fuel tank gets hot i stall out, start sucking pure fumes, and little liquid fuel. What causes this and how may i fix it. New fuel sender new pump. Everything is good until it gets hot. I live in Texas, its always hot during the day. No vacum lines connected to tank either.

 

[mechted]

Are you sure its the fuel tank itself that is getting hot? Like have you measured it with a temp gun?
The situation you are describing is called vapor lock. Usually it happens to the line from tank to the carb. Typically it happens because the fuel line is too close to the exhaust line. The fuel line runs down the inside of the passenger side frame rail, so it tends to get close to A) the passenger side exhaust manifold/header or B) dual exhaust running over the transfer case. Usually occurs when the truck is allowed to sit at low fuel demand for a few minutes, or after shutdown. No fuel moving through the line = heat soaks in and vaporizes it in the line. The mechanical pump cant pump vapor, thus no fuel delivery to the carb. Typically doesnt affect the fuel tank itself.

To fix this: you can add heat shield to the fuel line, https://www.summitracing.com/parts/dei-010457/overview/
OR/AND you can change the pump out for a return style http://www.rockauto.com/en/moreinfo.php?pk=296000&cc=1050455&jsn=440
and then add in a return line back to the tank (there may be a "vapor return line" on the passenger frame rail as well that can be used for this... typically its hooked up to the charcoal canister) A return style pump will always flow some amount of fuel from the tank up to the pump, then back to the tank to prevent this heat soak from occurring.

 

[Carcinogen]

One other possible solution, other than the excellent advice above, is a fuel filter with a return fitting on it instead of the whole pump.

 

[diesel4me]

A WIX 33040 filter might work ,that one has a "third nipple" for vapor return, it takes 5/16" fuel lines and the vapor return is smaller, 1/4"...my '66 Buick Electra with A/C and 401 V8 used that filter..

Some older Mopars used a similar filter,that may be 3/8" fuel line size,if 5/16" isn't large enough..

 

[handloader90]

Wix 33041 is the same deal but it has a 3/8" inlet and outlet and a 1/4" barb for the vapor hose.

 

[Patrick Tollett]

Thanks all. This has been a helpfull learning experience for me. Vacume vapor score one.

 

[Patrick Tollett]

Now I got a new issue. 350 stoped shifting into third. At first it would drop back down to second then jump back up. Now it wont shift up out of second. I tried replaceing the vacum lines to my module. After doing that it slips goung in reverce. Still dont shift to third. If i disconect the vacum, reverse is fine after reverseing once or twice.

 

[PWagon]

I had a very similar issue last summer. Today's ethanol blend boils at a very low temp (compared to non ethanol blends). The result is called vapor lock (mentioned above by another CK5 member). I fixed my issue by using a heat shield type resistant product that can be easily found on Amazon, Summit Racing, or many other places. My vapor lock issue came about after I did my LS swap and routed new rubber fuel lines up to the engine. The heat from the exhaust along with any outside temp above 80 degrees would boil my fuel if I let it sit after driving it. As long as the truck was running and fuel was moving then there were no issues. I highly recommend the heat shield stuff. One side opens and closes by velcro, so it's easy to install. Hope this helps.