Is it normal on hot days for fuel to boil in tank? Mine did this in '92 and always has. I always chalked it up to Texas heat. It seems these threads always end up on a dead end, never give a definitive answer as if this is normal or not.

 

Certain components of gasoline (which is a mixture of several types of hydrocarbons with different vapor pressures, etc) will boil around 100 degrees F. So in Texas heat and with engine heating of the fuel rail and then returning it to tank..... yes you're going to have some boiling most likely - though the boil point will rise with pressure in the tank. So the answer is - it depends. How hot the fuel is, and how much pressure your system is/can hold in the tank.

GD

 

I believe that is why GM switched to return-less fuel systems where they could, to stop picking up latent heat from the engine compartment. Ethanol in the gasoline probably doesn't help with the boiling point either.

 

It is "normal" in the sense that it happens ALOT. It is NOT "normal" in the sense that it's "acceptable".

A properly functioning vent system, that maintains pressure in the tank, helps minimize it. Routing fuel lines away from heat sources (exhaust parts), along with making sure that the return is exposed to NON-HEATED air passing over it for as much of its length as possible, is a BIG help.

 

maybe i should have said is this built into the design of these cars? it seems what is occurring (source of fuel being heated aside) is that fuel gets hot, boils, and then enough pressure builds up to cause the vent valve to open to release the pressure, then boiling subsides.

my hypothesis, not proven......

source of heat is hot day, and damn return line being snuggled right next to driver side head with about a 3mm gap and sandwiched under alternator. in TPI design anyway


practically touching head

 

Releasing pressure would lower boiling point, thus causing it to boil more, not less, when pressure goes down.....

 

good point.

how about this:

hot fuel is returned to tank, boils and turns gaseous, then enough pressure builds up to cause the vent valve to open to release the gaseous fuel, then boiling subsides because hot fuel is now vented to atmosphere???

some of the hot fuel heat is absorbed by cool fuel in tank, the rest turns gaseous and vents

 

No, not quite. Boiling fuel (vapor) would be cooled by the cooler fuel and would condense.

If the fuel boils in the tank, it's because it's ALL hot.

These cars didn't have this problem when they were new. I don't think it's so much a question of the cars being new though, more that the fuel in those days was less volatile than it is today. Quicker-evaporating fuel is good for gas mileage, power, and emissions; but it had to be made less volatile back when carbs, at atmospheric pressure, were still common. Now that everything is FI, and operates at very high pressure, keeping the fuel liquid at low pressure isn't as important.

Best things to do are, keep the fuel from heating up in the lines, so that the temp in the tank doesn't gradually rise; and make sure the fuel system seals, so that whatever pressure DOES build up, is retained.

 

was just looking at boiling points. looks like gasoline avg is about 100, which is easily hit in these parts.

https://www.firehouse.com/operations...r-is-it-part-2

 

That's only PART of the truth.

Read the fine print. Note that that is AT ATMOSPHERIC PRESSURE. Raising the pressure increases it SUSTANTIALLY.

 

My car is my daily driver , so except for days with snow&salt it gets driven year round . In Summer , we have anywhere between a week to maybe 20 days of temperatures in the 90 to 95 degree range . Sometimes (rarely , maybe a day or two) even close to 100 . All parts of the fuel , exhaust , and cooling systems are completely stock and functional as designed . Not once has my fuel boiled in the tank , ever .

So my answer is , Is it normal ? No . Does it happen ? Well I read plenty here about it happening and I've always wondered , on the cars that it does happen to , ARE all the systems perfectly functional as designed ? Does the tank hold the required pressure , has anything been done to the engine that would cause it to run warmer (power upgrades,that sort of thing) ?

All these threads about fuel boiling never seem to get down to the real question , since some report fuel boiling and some never experience it ;

What IS the difference between the cars that causes some to boil and some not ? Or if the difference isn't the cars themselves , could the fuel being sold in the different regions be that much different as to cause the boiling ? I live quite a bit north from Texas and I would hope that if there were a fuel blend least likely to boil that it would be sold in Texas before it's sold here up north ..

 

orange that is why i started this thread. what causes this? my car has done it since new. from the factory. all stock, no modifications

Sofa - good point on higher pressure/higher boiling point. what pressure does our valve open so we can calculate temp of fuel we are hearing boil?

 

Boiling gasoline? Don't have a BLEVE!!!

 

IIRC, on a '92 the vapor control valve for the CCP system opens at just under a psi of pressure. I have posted it someplace on TGO. That is from the factory service manual.

RBob.