Why You Shouldn’t Top Off Your Fuel Tank
Why You Shouldn’t Top Off Your Fuel Tank
We’ve all done it — standing at the gas pump, trying to squeeze in that last bit of fuel or round the price up to an even dollar. It seems harmless, right? Unfortunately, topping off your fuel tank can cause real damage to your vehicle’s emissions system and lead to costly repairs down the road.
At Automotive Blessings, we recently had a vehicle come in with a damaged charcoal canister. What we found is a great reminder of why stopping when the fuel handle clicks is so important.
What the Charcoal Canister Does
Modern vehicles are equipped with a charcoal canister — a part of the evaporative emissions system (EVAP). Its job is to capture and store fuel vapors from the gas tank so they don’t escape into the atmosphere. When the engine runs, the Engine Control Module (ECM) triggers a “purge event,” pulling those vapors into the engine to be burned like regular fuel.
What Happens When You Overfill
When you’re filling up and the fuel handle clicks, your tank is full. Anything added after that point risks pushing liquid fuel into the charcoal canister. The canister is only designed to hold vapors, not liquid. Once liquid fuel enters the canister, it saturates the charcoal and ruins its ability to absorb vapors. During a purge event, instead of pulling in fuel vapors, the system pulls in liquid fuel. The result? Your Check Engine Light comes on, and your vehicle may start running either too rich (too much fuel) or too lean (too little fuel). This back-and-forth cycle can cause poor performance, and eventually damage to other emission components.
A Real-World Example
In the photo above, that black material on the ground isn’t dirt — it’s charcoal from inside a damaged canister. When we removed it from the vehicle, liquid fuel poured out, followed by pieces of broken charcoal. The driver had a habit of “topping off” the tank every time they filled up, which led to this failure.
Replacing a charcoal canister is entirely avoidable.
The Takeaway: Stop After the Click
Next time you’re filling up, remember: When the pump clicks, your tank is full. Don’t try to round up to the next dollar. Protect your vehicle’s emission system — and your wallet.
Automotive Blessings
📍 840 Shallowford Rd, Kennesaw, GA 30144
📞 770-575-0400
