What are the side effects of disabling fuel tank ventilation?

Question

what are the side effects of disabling fuel tank ventilation? Especially for petrol cars. Is it true that the ventilation system, which constantly allows the air to move into and out of the tank worsens the quality of the fuel?

Answer 1

Your view of the EVAP system is a little ascew. The EVAP system isn't open to the atmosphere. It doesn't "constantly" allow air to move into and out of the tank. The whole purpose of the EVAP system is to NOT allow this to happen. As this reference states:

The Evaporative Emission Control System (EVAP) is used to prevent gasoline vapors from escaping into the atmosphere from the fuel tank and fuel system at all times.

If you are talking about disabling the EVAP system, you're actually defeating the purpose, which will cause more contamination to the fuel, allowing what ever amount of ethanol which is in the system to absorb more water from whatever air is present.

There has to be a certain amount of air going into the system to accommodate the lessening amount of fuel being in the tank. If you are talking about this part of the system, then if you disable it, you'll cause the system to be in an vacuum state, which at some point would not allow the fuel to flow to the engine, which would not allow it to run. I'm pretty sure you'd also get to the point where you couldn't get the gas cap off, either.

The best way to keep your fuel from becoming contaminated for any length of time is to keep the tank full. This only allows a small amount of air to be in the system. Less air equals less moisture to be absorbed. You can also use a fuel stabilizer, which helps prevent the fuel from absorbing water (forms a barrier between the air and the fuel). This only works for a period of time depending on the pro

Answer 2

In addition to the points raised in Paulster2's answer, disabling the EVAP system will give you a check engine light as soon as the EVAP monitor runs. From that moment forward, you will have a permanently-on check engine light. If some other issue arises that would turn on the light, you will never know unless you attach a code reader and check for other codes.

Some issues that turn on a check engine light can cause damage if the issues are not repaired within a reasonable time. For example, misfires can dump unburned fuel into the exhaust, causing catalytic converter damage. A vacuum leak can create an air-fuel mixture that is too lean, burning your valves.

In addition, a large number of faults that would turn on the check engine light without causing actual damage will result in poor fuel economy, reduced power and excess emissions.

So it's against your best interest to make any kind of modification that will result in a permanently-on check engine light.