Fuel Lesson Learned

[MakinDoForNow]

From the looks of the top of the tank above where the filler line goes in - there are no penetrations for controlled air release. (unless the fuel pump doesn't really sit level, and filler line is higher than it appears, or I'm not seeing holes in those ebay pics)

So the fuel level goes up into upper area as much as the weight of fuel in the filler line can apply pressure. Which can't be much in comparison. Appears to be a big space for air only.
Seems like good method to contain fumes, as long as the fuel is high enough, nothing is coming out but fumes from surface area in filler line, only when it finally goes down to the filler line, or a steep down hill, would extra fumes escape.
So the splash back by constantly going past the auto-shutoff clicks is really only adding filler line quantity of gas.
Also why pressure needs to be released for hybrid when you push button for opening door.

Now I'm wondering if the 12V battery current is higher during sleep on low tanks due to fumes able to come out and canister gets them and checks are run, compared to high tank and it's blocked by the fuel.

I take back my comment about Ford attempting to lighten the load - 15 lbs can't be enough to make a difference, but from the design, it would always be in there anway.
The EB is just allowed to go lower than the hybrid.

There is a valve which is normally closed, trapping fumes in top of tank. The pressure release button opens the valve to allow them to pass through the charcoal filter and be trapped. Don't know the path the air escapes after passing through the filter. While ice is running air passes through the filter to dry out the charcoal and it is directed into the ice then. The filtered air must just pass into the intake?

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[MaverickDragon]

My post above with fillup amounts was never much past E.
Actually, E is a thick line, the right-side of E line.

And mostly got over 13.8.

This one was exactly 7 miles past 0 DTE, and city driving so easily half EV mode, little extra gas used.

Well, that's evidence for an even greater fuel capacity understatement.

If you get fuel when the warning light comes on, and you can put nearly a gallon over stated capacity, the stated 13.8 is clearly wrong unless the gas station pump is off by more than 5%.
That's doubtful.

Since there is likely additional fuel when the low level indicator comes on (maybe two gallons?) the stated figure is even more inaccurate.
I cannot imagine why Ford would intentionally misstate this, but it appears that they either did or just made a mistake that no one ever corrected after several model years of production.

In any case, this is really weird.

Once I use up fuel to the warning light I'll do a first click fill up from that point and see what gallons were delivered. Having another gallon to use would be a good thing.

 

[Roadrunner11]

2025 XLT AWD Hybrid. Pulled into refuel with 40 miles on DTE indicator. Low fuel warning came on at exactly 50. Truck took 13.4 gallons (13.8 capacity). Much too fine for me. I will refuel in the future before the 50 mile low fuel warning in the future.

Well A long time ago I was informed that it behooves you never to let your tank get below half because of accelerated evaporation.

 

[BLUEOVALRACER]

Did the weather change? Did you change brands? Both can make a difference. I believe this is when companies change to winter grade fuel . That reduces fuel economy some. Cold weather reduces it further. And stop and go driving kills fuel economy on regular non-hybrid engines. But 6 stop signs in 8 miles doesn't seem like that many, but the combination of colder weather and the stop signs may have a significant effect. Also, the engine sometimes takes a while to recalibrate to the different fuel formulation. At any rate, it'll be interesting to see if this was just a one time anomaly or an actual pattern

The 32 mpg was in the summer time on the highway not back and forth to work like the 21 mpg i'm getting now.

 

[Chops]

It seems the Hybrid & EB share the same external gas tank shell.

But how & why is the Hybrid’s tank pressurized? Are there internal pieces inside the hybrid tank taking up space? Also, is it negative or positive pressure?

 

[Darryl]

The 32 mpg was in the summer time on the highway not back and forth to work like the 21 mpg i'm getting now.

That's about how my old focus responded highway vs City driving

 

[Mavster Mechanic]

Well A long time ago I was informed that it behooves you never to let your tank get below half because of accelerated evaporation.

In a closed container you have no evaporation.

Most vehicles today are "zero evaporative emissions".

 

[Chops]

It seems the Hybrid & EB share the same external gas tank shell.

But how & why is the Hybrid’s tank pressurized? Are there internal pieces inside the hybrid tank taking up space? Also, is it negative or positive pressure?

Ok, I’ll answer my own questions…
Well - google etc helped:

“ The Ford Maverick Hybrid (equipped with the 2.5L Atkinson-cycle engine) manages gasoline evaporation—primarily fuel vapors from the tank—to comply with strict EPA emissions standards. This is handled by the vehicle's **Evaporative Emission Control System (EVAP)**, a standard feature on all modern gasoline-powered vehicles, including hybrids. The system captures, stores, and recycles these vapors to prevent them from escaping into the atmosphere, reducing pollution and improving fuel efficiency.

Maverick Hybrid's gasoline engine requires this setup since it uses a traditional fuel tank (13.8 gallons usable capacity, though the physical tank is larger at around 16.5 gallons to accommodate EVAP components).

#### How the EVAP System Works in the Maverick Hybrid
The EVAP system in Ford hybrids like the Maverick uses a **vacuum-based design** with adaptations for hybrid operation (e.g., the engine may not run constantly for purging vapors). Here's a step-by-step breakdown:

1. **Vapor Capture (Storage Phase)**:
- As gasoline evaporates in the heat (due to temperature changes or refueling), vapors build pressure in the sealed fuel tank.
- These vapors flow through vapor lines into the **EVAP canister** (a charcoal-filled container, often located under the vehicle near the rear axle or spare tire area). The charcoal adsorbs (absorbs) the hydrocarbons, temporarily storing them.
- The tank is designed to handle slight pressurization (up to a few PSI) without venting to the air, which helps minimize evaporation losses. The Maverick's hybrid-specific tank includes internal baffles and equipment to maintain this seal while avoiding submersion of components.

2. **Leak Detection and Integrity Check**:
- The **Powertrain Control Module (PCM)** monitors the system using sensors like the **Fuel Tank Pressure Sensor (FTPS)**.
- During a drive cycle (after an engine-off soak period of several hours), the PCM performs a **natural vacuum leak detection (NVLD)** test or enhanced EVAP integrity check:
- It closes the **Canister Vent Solenoid (CVS)** to seal the system from outside air.
- Engine vacuum (or a small pump in some Ford hybrids) pulls a slight negative pressure on the system.
- The PCM measures pressure changes over time. If it holds vacuum (with less than 0.02–0.04 inches of water loss), the system is leak-free. A failure triggers a check engine light (e.g., codes P0451 for small leaks, P0496 for EVAP flow issues, or P04EE for larger leaks).
- Hybrids like the Maverick may use an **Evaporative Leak Check Monitor (ELCM)**—a small electric pump—for more reliable testing when the engine isn't running often.

3. **Vapor Purging (Recycling Phase)**:
- When the engine is running (typically above 40–50 mph or under load), the PCM opens the **Canister Purge Solenoid (CPS)**.
- Engine vacuum draws fresh air through the vent line, flushing stored vapors from the canister into the intake manifold.
- The vapors mix with incoming air and are burned in the engine during combustion, effectively recycling them as fuel. This process is metered by the PCM to avoid rich/lean conditions.
- In hybrids, purging is optimized for the Atkinson-cycle engine's efficiency, contributing to the Maverick's EPA-rated 42 mpg city/33 mpg highway.

#### Hybrid-Specific Considerations
- **Engine Runtime**: The gasoline engine in the Maverick Hybrid only activates as needed (e.g., for highway speeds or heavy loads), so EVAP tests and purging are scheduled opportunistically. Ford's system includes safeguards like the ELCM to ensure compliance even during extended EV-only driving.
- **Tank Design Impact**: The hybrid's tank has extra space for EVAP gear (e.g., fuel pump sump and vapor management modules), reducing usable capacity to 13.8 gallons. Running the tank completely dry (below ~2–3 gallons) can expose the pump or disrupt EVAP function—Ford recommends refueling before the low-fuel warning.
- **Refueling**: The system includes a refueling vent valve to prevent spills and over-pressurization. "Topping off" after the pump clicks can flood the canister, causing leaks or codes.

#### Common Issues and Maintenance
While reliable overall, the EVAP system can trigger warnings due to wear:
- **Purge Valve Failures**: The CPS is a frequent culprit (codes like P0496), often failing around 40,000–50,000 miles. Replacement costs $100–200 (parts/labor) but is covered under the 8-year/80,000-mile emissions warranty.
- **Leaks**: Small cracks in hoses or a faulty canister (P0451/P04EE) may set codes; smoking or gas smells indicate issues.
- **Maintenance Tips**:
- Use top-tier gasoline to reduce deposits.
- Avoid overfilling; let the pump auto-shutoff.
- If a check engine light appears, scan for codes (e.g., via OBD-II tool) and visit a dealer—many fixes are warranty-covered.
- The charcoal canister doesn't need routine replacement but can saturate over time”

 

[Roadrunner11]

Recharging an EV takes about 1 hour.
Sometimes 45 minutes.

Not hours.

There are rare cases you'd need to wait in line. But EV drivers are chill by nature. So it's not a problem.

Had to giggle; mine does take hours. But then I don’t have a level 2 charger at home.

 

[MakinDoForNow]

Ok, I’ll answer my own questions…
Well - google etc helped:

“ The Ford Maverick Hybrid (equipped with the 2.5L Atkinson-cycle engine) manages gasoline evaporation—primarily fuel vapors from the tank—to comply with strict EPA emissions standards. This is handled by the vehicle's **Evaporative Emission Control System (EVAP)**, a standard feature on all modern gasoline-powered vehicles, including hybrids. The system captures, stores, and recycles these vapors to prevent them from escaping into the atmosphere, reducing pollution and improving fuel efficiency.

Maverick Hybrid's gasoline engine requires this setup since it uses a traditional fuel tank (13.8 gallons usable capacity, though the physical tank is larger at around 16.5 gallons to accommodate EVAP components).

#### How the EVAP System Works in the Maverick Hybrid
The EVAP system in Ford hybrids like the Maverick uses a **vacuum-based design** with adaptations for hybrid operation (e.g., the engine may not run constantly for purging vapors). Here's a step-by-step breakdown:

1. **Vapor Capture (Storage Phase)**:
- As gasoline evaporates in the heat (due to temperature changes or refueling), vapors build pressure in the sealed fuel tank.
- These vapors flow through vapor lines into the **EVAP canister** (a charcoal-filled container, often located under the vehicle near the rear axle or spare tire area). The charcoal adsorbs (absorbs) the hydrocarbons, temporarily storing them.
- The tank is designed to handle slight pressurization (up to a few PSI) without venting to the air, which helps minimize evaporation losses. The Maverick's hybrid-specific tank includes internal baffles and equipment to maintain this seal while avoiding submersion of components.

2. **Leak Detection and Integrity Check**:
- The **Powertrain Control Module (PCM)** monitors the system using sensors like the **Fuel Tank Pressure Sensor (FTPS)**.
- During a drive cycle (after an engine-off soak period of several hours), the PCM performs a **natural vacuum leak detection (NVLD)** test or enhanced EVAP integrity check:
- It closes the **Canister Vent Solenoid (CVS)** to seal the system from outside air.
- Engine vacuum (or a small pump in some Ford hybrids) pulls a slight negative pressure on the system.
- The PCM measures pressure changes over time. If it holds vacuum (with less than 0.02–0.04 inches of water loss), the system is leak-free. A failure triggers a check engine light (e.g., codes P0451 for small leaks, P0496 for EVAP flow issues, or P04EE for larger leaks).
- Hybrids like the Maverick may use an **Evaporative Leak Check Monitor (ELCM)**—a small electric pump—for more reliable testing when the engine isn't running often.

3. **Vapor Purging (Recycling Phase)**:
- When the engine is running (typically above 40–50 mph or under load), the PCM opens the **Canister Purge Solenoid (CPS)**.
- Engine vacuum draws fresh air through the vent line, flushing stored vapors from the canister into the intake manifold.
- The vapors mix with incoming air and are burned in the engine during combustion, effectively recycling them as fuel. This process is metered by the PCM to avoid rich/lean conditions.
- In hybrids, purging is optimized for the Atkinson-cycle engine's efficiency, contributing to the Maverick's EPA-rated 42 mpg city/33 mpg highway.

#### Hybrid-Specific Considerations
- **Engine Runtime**: The gasoline engine in the Maverick Hybrid only activates as needed (e.g., for highway speeds or heavy loads), so EVAP tests and purging are scheduled opportunistically. Ford's system includes safeguards like the ELCM to ensure compliance even during extended EV-only driving.
- **Tank Design Impact**: The hybrid's tank has extra space for EVAP gear (e.g., fuel pump sump and vapor management modules), reducing usable capacity to 13.8 gallons. Running the tank completely dry (below ~2–3 gallons) can expose the pump or disrupt EVAP function—Ford recommends refueling before the low-fuel warning.
- **Refueling**: The system includes a refueling vent valve to prevent spills and over-pressurization. "Topping off" after the pump clicks can flood the canister, causing leaks or codes.

#### Common Issues and Maintenance
While reliable overall, the EVAP system can trigger warnings due to wear:
- **Purge Valve Failures**: The CPS is a frequent culprit (codes like P0496), often failing around 40,000–50,000 miles. Replacement costs $100–200 (parts/labor) but is covered under the 8-year/80,000-mile emissions warranty.
- **Leaks**: Small cracks in hoses or a faulty canister (P0451/P04EE) may set codes; smoking or gas smells indicate issues.
- **Maintenance Tips**:
- Use top-tier gasoline to reduce deposits.
- Avoid overfilling; let the pump auto-shutoff.
- If a check engine light appears, scan for codes (e.g., via OBD-II tool) and visit a dealer—many fixes are warranty-covered.
- The charcoal canister doesn't need routine replacement but can saturate over time”

So the clicking and other noises 6-8 hours after parking is the (item #2) EVAP system checking. (at least some of the middle of night noise). Maybe periodically runs longer to maybe help EVAP fumes captured by charcoal canister. Maybe the people whose battery died frequently need to have their EVAP canister replaced????? If not clogged enough to trip a code but has to run quite-a-bit?

 

[MaverickDragon]

Ok, I’ll answer my own questions…

Thanks for post #113.
No point in further experimentation or conjecture from my perspective.
It seems obvious that the Ford Maverick Hybrid is a different beast, and the stated capacity by Ford was stated for a reason.
The recommendation to fill up at ~ 1/4 tank and no top up after the first click isn't different than I've been doing since cars began using evaporative capture systems.

 

[Chops]

So the clicking and other noises 6-8 hours after parking is the (item #2) EVAP system checking. (at least some of the middle of night noise). Maybe periodically runs longer to maybe help EVAP fumes captured by charcoal canister. Maybe the people whose battery died frequently need to have their EVAP canister replaced????? If not clogged enough to trip a code but has to run quite-a-bit?

Not sure why the EB does not have the same complicated & power using EVAP system as the Hybrid - but I’m not complaining. My battery isn’t complaining either!

The “parasitic” drain from the EVAP electronics is good for the EPA - but not so good for the battery?

 

[MaverickDragon]

Not sure why the EB does not have the same complicated & power using EVAP system as the Hybrid - but I’m not complaining. My battery isn’t complaining either!

I think the answer to that was in your previously posted reply.
The engine in the ecoboost runs continusousy like most ice powered vehicles, where the hybrid's fuel powered engine powers up and turns off repeatedly while the truck is being driven.
The extra equipment in the hybrid is to maintain the integrity of the vapor recovery which isn't needed in the ecoboost version of the vehicle.

As far as that equipment being the "dreaded battery drain", it may be a part of it, but I imagine that the cycle in normal circumstances isn't a long or ongoing process that would kill the battery.
From what I've read on this forum, a culprit in many circumstances seemed to be related to software in the ACCS (Air Conditioning Control System)...

 

[Chops]

I think the answer to that was in your previously posted reply.
The engine in the ecoboost runs continusousy like most ice powered vehicles, where the hybrid's fuel powered engine powers up and turns off repeatedly while the truck is being driven.
The extra equipment in the hybrid is to maintain the integrity of the vapor recovery which isn't needed in the ecoboost version of the vehicle.

As far as that equipment being the "dreaded battery drain", it may be a part of it, but I imagine that the cycle in normal circumstances isn't a long or ongoing process that would kill the battery.
From what I've read on this forum, a culprit in many circumstances seemed to be related to software in the ACCS (Air Conditioning Control System)...

Good point about the ACCS. Although there could be multiple culprits - some “guiltier” than others.

 

[HeyBales]

So the clicking and other noises 6-8 hours after parking is the (item #2) EVAP system checking. (at least some of the middle of night noise). Maybe periodically runs longer to maybe help EVAP fumes captured by charcoal canister. Maybe the people whose battery died frequently need to have their EVAP canister replaced????? If not clogged enough to trip a code but has to run quite-a-bit?

Well - the extraction of fumes happens when running. So part of the DCDC powering then.

The pressure checks just need to be done every so often, nothing to do with collecting fumes, as it states has to close the valve to the canister to test pressure.
Obviously an opportunity for a process to glitch and stay on too long, extra micro-drain on battery then.

I posted somewhere recently the ECU stats for engine run time, idle time, coast time - and included in there was the EVAP tests and time since last test.

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