Twilightblue28A

I have been told that under no circumstances am I to continue filling my cars fuel tank after the nozzle shuts off. I have been told that overfilling the fuel tank may or will cause significant engine damage. The source of the information I am providing is from another owner whose mechanic was told, supposedly from the factory. I pressed the other owner and the owner was unable to support the type of damage that may or does occur.
Has anyone heard of damages caused by overfilling your fuel tank, and if so, what specific damage? This question relates to naturally aspirated engines as well as fuel injected engines.
Thank you!!

Twilightblue28A

I may be dumb, but not that dumb!!

​​​​​The concern raised is as a result I had with another owner, sober, who claimed his mechanic told him never to overfill the fuel tank.
I asked for the source of his information and was told his mechanic. I then asked the source of his mechanics information and his response was the manufacturer.
I have been trained to challenge everything. I felt maybe one of our members may know of this potential .
Thanks again!!

jimbo3

Have you considered googling this subject? Plenty of information on line on this as well as pretty much anything/everything you'd like to challenge. A vehicle's owner's manual may say something about it as well. The very first thing under refueling in the manual for my Escape warns not to overfill due to the potential for the added pressure forcing a leak. Others warn that it could force liquid gasoline into the charcoal evap canister and ruin it, causing the engine to not run properly. There may be other risks as well.

rcg412

LimeyBoy

Generally: I'm not sure how fuel level could impact the engine unless that level is affecting fuel pressure or flow. Tank and filler pipes are factory leak checked (your tank will have a label on it with a leak rate test result i.e. "4.6e-6") all the way up to where you put the nozzle when filling, so if you 'overfill' and have issues it is likely to be old age affecting a part and you have a leak from a point not usually submerged. However, youd probably smell that issue pretty easily. Check valves and solenoid valves are designed to seal against vapour and pressure which means they easily seal against liquid and the return pressure into the tank should always be higher than the tank presssure. These valves can fail (to carbon canister etc) but again, that would be age not overfilling.
I'd be interested in knowing if I'm wrong and there is a specific potential issue with our fuel tank system.

pp000830

Topped off fuel could conceivably back up into a tank venting emission filter canister. I am not sure our cars have one of these. Even in this case, I can't see how it would impact the engine. I believe emissions control, related to overflow spilling, is the reason not topping off the gas tank is suggested. Think about it probably from a parts per million basis one drop of gas hitting the pavement and evaporating is equivalent to driving your car a a good distance.

LexVan

The biggest risk is to your freshly wax front left fender and 303 dressed black vinyl fuel flap.

pp000830

+1

LexVan

And if you're not dressing your black vinyl fuel flap with Aerospace 303 you have bigger issues and are unworthy.

*works best if you remove the two screws, soak, and saturate overnight.

Gbos1

Primary Risk: make sure your not smoking a cigarette when overfilling your gas tank.

Railmaster.

Long shot but serious! If You fill the tank with cold petrol all the way up the filler neck and park the car in hot sun the petrol will expand it's volume and flood the tank!

serval

"This question relates to naturally aspirated engines as well as fuel injected engines."

You are mixing up NA vs Turbo and Fuel injection vs carburetors.

The counterpart to a naturally aspirated engine is forced induction (whether Turbo or compressor/supercharger) and refers to an engine air feeding mechanism.
Fuel injection (in all its guises) vs carburation refers to engine fuel delivery system.

Having said that, I see no mechanical reason why overflowing the tank may damage the engine. There is no mechanical connection between the tank and the engine other than the fuel pump and fuel flow is computer metered not gravity fed, and even then I can't see the impact of a liter or two above and beyond capacity.

centerpunch

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nile13

I'm fairly well amazed that this is not in all bold letters as per usual. The content, however, is fitting. Good, important stuff.

However, I've learned here that the flap shouldn't go undressed. I'll run out with my bottle of 303 and address it immediately. I would also like to apologize profusely to this great community for not doing so earlier. Bad, bad me.