Good old vapor lock - hot weather tip (reminder)

[D Seattle]

Been running the car every day in Seattle.  Outside temps getting kind of hot.  For around here anyway.

 

Came out from the grocery store today around 4 after running it hard.  Car turned over quick and fired up, and instantly died.  Did it again.  And again.  And again.  Pushed it back into the spot...  Clearly had spark, and the battery was good.  Seemed gas starved.... but why?

 

Was wondering when this now useless piece of knowledge would come back in handy.

 

Took gas cap off.  Turned it over. Took a couple of times.  But eventually fired up and ran like nothing happened.  Good old, old school no vent gas gap with fuel system in full vapor lock mode.

 

last time that happened it was over 15 years ago in an 80'ish full size suburban stuffed to the gills hauling 3 kids, wife, mother in law, and boat through the Syskous in California (for you non west coaters, big, steep mountain pass) in dead of summer.  Truck just lost all power, died, and on restart had about 25 percent horsepower.  Nothing othewise seemed amiss.  Cranked fine.  And it woudl start.  Just no go.   Eventually had to have suburban *and* boat towed to a shop.  Three hotel rooms and  Wife pissed and yelling later... still not sure why... next morning shop calls me up and says, hey, this thing is perfect, how much do you want for it? 

 

Vapor lock strikes again.  Forgot about that from when I was a kid.   Could have avoided a lot of agony by a taking the gas cap off.  

 

Anyway, ever since then, oddly, I"ve been wondering (hoping) it would happen again so "this time" I would know what to do.  Of course, with modern cars and vented caps, this never happens...

 

Just passing this along in case, as the weather heats up, anyone else has this flash-back problem. 

Edited June 22, 2021 by D Seattle
Typos

[NickVyse]

Petrol tank is vented on the 02 - I know some US cars had a charcoal filter, but was that not vented too? Could also be blocked.

[Lorin]

All fuel tanks are vented, some at the cap others via a hose like our cars. 
 

Vapor lock went away with fuel injection. 

[D Seattle]

 

 

3 hours ago, Lorin said:

All fuel tanks are vented, some at the cap others via a hose like our cars. 
 

Vapor lock went away with fuel injection. 

Yup.  Wish I had fuel injection. Would love to have a tiii.   

 

All fuel tanks have some time of return line.  Even old cars have that.  But old gas caps are not vented and cars used to often get vapor lock.  Hence the name.  Granted, did not happen everytime it go hot.  If it did, some eningeer would have figured out a more reliable way to fix it.  

 

 

[John76]

Vented gas caps went away with the crankcase vent tubes...loooong time ago.

Our cars have (should be) vent tubes from the rubber tank fitting in the trunk. The later ones also had a fuel return valve that worked by manifold vacuum. Not sure if this helped with the tank venting...but makes sense.

Yes, the charcoal filter is vented to atmosphere. See sketch for '76 system.

 

[Lorin]

44 minutes ago, D Seattle said:

 

 

Yup.  Wish I had fuel injection. Would love to have a tiii.   

 

All fuel tanks have some time of return line.  Even old cars have that.  But old gas caps are not vented and cars used to often get vapor lock.  Hence the name.  Granted, did not happen everytime it go hot.  If it did, some eningeer would have figured out a more reliable way to fix it.  

 

 

Not true. Lots of old cars don’t have return lines to the tank, I daily drive one. It does not have a vented cap just like a 2002 and it has an external fuel tank vent to atmosphere. 
 

Vapor lock is fuel boiling (vaporizing) and until your fuel returns to liquid in your carb and or fuel pump the car is going to run like crap. No matter what you do to the fuel cap. 
 

If your system is faulty and you are building pressure or vacuum in your fuel tank, opening the cap can improve that situation. 
 

A vented cap doesn’t magically raise fuel’s boiling point. 

 

[2002FjordBaur]

Had the very same thing happen to me a couple of weeks ago after a long sunny drive then parked up for 30 mins... came back to a still hot car. It started fine but then died and cranking did nothing, left the car to cool down for an hour and the next turn of the key it burst into life.
My Baur has simple single barrel Weber and mechanical pump. I took the petrol cap off, squeezed the fuel pipes, tapped the pump and kicked the tires, but nothing worked until the car had cooled down.

But my UK 02 forum did mention a fix for carb engines... apparently, remove the airfilter and put a hand over the carb intake and crank the engine (or unless you have really long arms, get another to help!)
Apparently, thats a guaranteed fix... i havent had to try that yet but may give that a go if ever stranded again?
Also, i've been advised to move fuel lines away from hot areas and also insulate lines with aluminium foil.

 

Not a major issue with UK summers, but if i can make my car more reliable...
 

Edited June 22, 2021 by 2002FjordBaur

[John76]

Not sure what the best solution might be.

The float bowl is vented to atmosphere, and modern fuel has a very low vapor pressure index compared with the fuel of 50 years ago.

Heat from the engine causes rapid evaporation from the bowl, fuel lines, and probably the pump and filter, leaving nothing but air.

Modern FI systems are totally sealed, so no evaporation...no problem!

[D Seattle]

Ah... this was more intended as a lark, an offside quip about the gremlins of old cars and a half funny story.  

 

I don't know what I don't know.  All I know is when I was kid, and my dad wrenched and so did my uncle, 'vapor lock' was a thing and taking the fuel cap *always* did the trick.  Maybe the cap is a loch ness monster thing.  People see something for sure, but its not a sea monster.

 

Maybe taking the cap off is just something that takes some time to do, and in the meantime who knows what is happening... the car is no more cooler than it was 10 second earlier when it would not start.  But, like fonzie hitting the juke box, it perceptually did the trick.

 

Just a for a laugh guys.  Take care.  D

Edited June 22, 2021 by D Seattle

[Son of Marty]

The only sure fix I've been able to come up with is use a electric pump, back by the tank, as a booster pump or main pump to replace the boiled off fuel before starting. Todays fuel boils at a ridiculously low temp and the mechanical pump has to reprime before it fills the float bowl. The first step anyway you go is the fuel system is in good shape with no air leaks at the hoses and connections.

[John76]

12 minutes ago, Son of Marty said:

The only sure fix I've been able to come up with is use a electric pump,

If you don't want to go electric all the time, just use it as a temporary primer with a push button.