BMW 645CI Convertible Fuel Tank Sending Unit 637.BM1F04

( Manufacturer Part Number: 645CI ), ( Part Type: Fuel Tank Sending Unit ), ( Conditions Options: Convertible, E63 ), ( Genuine Oem: Yes ), ( Ipn: 637.bm1f04 ), ( Manufacturer Warranty: 60 Day )

Review BMW Convertible Fuel Tank Sending Unit fits 650I E63 E64 2004–2010

The **BMW 637.bm1f04 Fuel Tank Sending Unit** is a precision-engineered component designed exclusively for the **E63 (645Ci) and E64 (650i) convertible models** produced between **2004 and 2010**. This high-performance unit is a critical part of the vehicle s fuel management system, responsible for accurately measuring the remaining fuel level in the tank and transmitting this data to the engine control module (ECM). Crafted from durable materials, including a robust metal float arm and a reliable potentiometer mechanism, this sending unit ensures consistent and precise readings, even under the demanding conditions of high-performance driving. Its compact yet sturdy design allows for seamless integration into the vehicle s fuel tank, maintaining optimal functionality while minimizing the risk of leaks or malfunctions. Whether installed in a classic BMW convertible or restored to its original specifications, this sending unit guarantees reliable performance, helping to prevent fuel gauge inaccuracies and potential fuel system issues. Built to meet BMW s stringent quality standards, it is an essential replacement part for owners seeking to restore or maintain the integrity of their E63 and E64 models, ensuring smooth operation and long-term reliability.

### **Pros and Cons of Buying a BMW 6 Series (E63/E64) Convertible (2004-2010) with a Faulty Fuel Tank Sending Unit**

#### **Pros**

1. **Performance and Driving Experience**

The BMW 6 Series (E63/E64) is renowned for its refined luxury, sporty handling, and powerful engines. The **645Ci** and **650i** variants feature high-performance V8 engines (4.4L or 4.8L) that deliver strong acceleration, smooth power delivery, and engaging driving dynamics. The convertible top mechanism is generally reliable, though some models may have minor wear over time.

2. **Luxury and Comfort**

The interior is upscale, with high-quality materials, premium sound systems (especially in later models), and excellent ergonomics. The seating position offers a commanding view of the road, and the ride is well-balanced between comfort and sportiness.

3. **Resale Value (Compared to Peers)**

While not as high as newer BMWs, the 6 Series retains decent resale value relative to its class, especially the **650i** variant. The convertible body style is less common, which can make it more desirable to enthusiasts.

4. **Aftermarket Support**

The E63/E64 platform has a strong aftermarket presence, with readily available parts, tuning options, and performance upgrades. This makes maintenance and modifications more accessible than on older BMWs.

5. **Convertible Appeal**

The ability to lower the roof for open-air driving adds significant enjoyment, especially in pleasant weather. For those who value the convertible lifestyle, this is a major selling point.

---

#### **Cons**

1. **Fuel Tank Sending Unit Failure**

The most critical issue with these models is the **fuel tank sending unit (FTSU)**, which often fails due to corrosion or electrical failure. Symptoms include:

- The fuel gauge showing erratic readings (e.g., "full" when empty or fluctuating wildly).

- The "check fuel" warning light illuminating.

- Difficulty starting the car due to incorrect fuel level feedback.

- **Repair Cost:** Replacing the sending unit typically costs **$200 $400** (parts labor), though some owners opt for a full fuel tank replacement ( $800 $1,500) to avoid future issues. This is a significant upfront cost that deters some buyers.

2. **Convertible Top Reliability**

While generally sturdy, the **soft-top mechanism** can develop leaks, sagging, or electrical issues over time. Regular maintenance (lubrication, inspections) is required to prevent water leaks into the cabin or electrical shorts.

3. **Electrical Gremlins**

- Faulty sensors (e.g., oil pressure, coolant, or speed sensors).

- Intermittent issues with windows, locks, or infotainment.

- Infotainment glitches (especially in earlier models with the iDrive system).

- **Solution:** A thorough electrical diagnostic is recommended before purchase.

4. **Maintenance Costs**

- Timing belt replacement (critical on the N62/N63 engines; failure can cause catastrophic engine damage).

- Cooling system flushes (to prevent overheating, a common issue in V8 models).

- Suspension wear (struts, bushings, and control arms may need replacement).

- **Budget:** Expect **$1,500 $3,000/year** in maintenance if the car is well-kept.

5. **Fuel Economy and Running Costs**

The **645Ci (4.4L)** gets around **14 16 MPG combined**, while the **650i (4.8L)** averages **12 14 MPG**. High fuel consumption, along with premium fuel requirements, adds to operating costs.

6. **Common Engine Issues**

- **N62 (4.4L) Engine:** Generally reliable but prone to **oil consumption** and **carbon buildup** (requires periodic decarbonization).

- **N63 (4.8L) Engine:** More powerful but can suffer from **valve spring failures** (especially on high-mileage examples) and **turbocharger issues** (if equipped with the **650i xDrive**).

- **Solution:** A pre-purchase inspection (PPI) with a **compression test, leak-down test, and oil analysis** is essential.

7. **Rust and Bodywork Concerns**

- **Floor pans and wheel wells** are common rust hotspots, especially in snowy or salted regions.

- **Convertible frames** may develop rust if not properly maintained.

- **Solution:** Inspect for rust during test drives and consider a **rustproofing treatment** if buying in a high-corrosion area.

8. **Depreciation and Reliability Concerns**

- The E63/E64 is **notoriously unreliable** compared to BMW s later models (e.g., F12/F13 6 Series).

- **Electrical failures, transmission issues (especially in automatic models), and suspension wear** are common in high-mileage examples.

- **Transmission:** The **ZF 6HP21 automatic** is generally robust but can develop **slippage or delayed shifts** over time.

---

### **Key Considerations Before Buying**

1. **Verify the Fuel Tank Sending Unit Condition**

- Ask the seller for **proof of recent replacement** or a **test drive where the gauge behaves normally**.

- If the unit has failed, **budget for replacement** it s a dealbreaker if ignored.

2. **Check Engine and Transmission Health**

- **Compression test** (should be above 150 PSI per cylinder).

- **Leak-down test** (should be

- **Transmission fluid condition** (should be clean, not burnt or foamy).

- **Listen for unusual noises** (knocking, whining, or grinding).

3. **Inspect the Convertible Top**

- **Test the motorized operation** (no jerks, delays, or unusual noises).

- **Check for leaks** (water stains on the ceiling or electrical shorts).

- **Lubricate the tracks** if the top is raised and lowered multiple times.

4. **Review Maintenance Records**

- **Timing belt replacement** (must be done every **60,000 100,000 miles**).

- **Cooling system flushes** (every **60,000 miles**).

- **Suspension and bushings** (should be replaced as needed).

5. **Test Drive Thoroughly**

- **Acceleration and braking** (should be smooth, no hesitation).

- **Steering and handling** (no excessive play or vibration).

- **Electrical systems** (windows, locks, lights, infotainment).

---

### **Conclusion and Recommendation**

#### **Who Should Buy?**

- **Enthusiasts who prioritize driving pleasure and luxury** over absolute reliability.

- **Owners who are prepared for maintenance costs** and can budget for potential repairs (especially the fuel tank sending unit).

- **Those who value the convertible experience** and are willing to maintain the top.

- **Buyers who find a well-documented example** with a **clean service history** and **no major electrical or mechanical issues**.

#### **Who Should Avoid?**

- **First-time BMW owners** unfamiliar with the brand s quirks.

- **Those on a tight budget** who cannot afford unexpected repairs.

- **Buyers in high-corrosion areas** without rustproofing.

- **People who dislike mechanical work** (these cars require regular upkeep).

#### **Final Recommendation**

**A recently replaced fuel tank sending unit** (or proof it s functional).

**A clean engine and transmission** (verified via tests).

**No major rust or electrical issues**.

**A well-maintained convertible top**.

then it can be a **fantastic purchase** one of the last great BMW convertibles before reliability declined in later models.

**However**, if the **fuel tank sending unit is failing or unknown**, the **car has high miles with no service records**, or **major components (engine, transmission, suspension) are worn**, **walk away**. The potential for hidden problems outweighs the enjoyment.

- **Get a pre-purchase inspection (PPI) from a BMW specialist.**

- **Negotiate a lower price** if issues are found.

- **Budget for immediate repairs** (fuel tank, timing belt, cooling system).

- **Be prepared for ongoing maintenance** to keep the car running smoothly.

If the fuel tank sending unit is a dealbreaker, look for a **non-convertible 6 Series (E63/E64) with a known good fuel system** they are often cheaper and more reliable in the long run.

Details:

These extra attached parts are not covered by any warranty. Donor Vehicle: model: 645CI. Many electronic modules and components require programming. BMW 645CI 650I E63 E64 Convertible Fuel Tank Sending Unit Fits 04-10: Review photos this is your actual part.

Miles: 140000 - N/A or Unknown. Parts are not covered for external fluid leaks. Major components are stamped and may have heat sensitive tabs attached to indicated overheating that would void warranty. Stock #: 240325.

Warranty covers the base component and none of other attached parts.

specifications fueltanksysteme:

• for models: 650i, E63, E64
• for makes: Bmw
• for years: 2004-2010
• mpn: 645ci
• part type: Fuel Tank Sending Unit
• conditions options: Convertible, E63
• genuine oem: Yes
• ipn: 637.bm1f04
• manufacturer warranty: 60 Day

offer fueltanksysteme:

• sold: 0
• availability: In Stock
• quantity: 1
• best offers: True
• options: Ship-to-home
• started: March 3, 2026

returns fueltanksysteme:

• time: 30 Days
• paid by: Buyer
• policy: Returns Accepted

payments fueltanksysteme:

• wallet: Google-pay
• other
• credit card: Mastercard

general fueltanksysteme:

• Car Truck Parts Accessories > Air Fuel Delivery > Fuel Tanks Filler Necks
• condition: Used

seller fueltanksysteme:

• # reviews: 10780
• city: Port Washington, Wisconsin
• rating: 99.4%

shipping fueltanksysteme:

• class: Standard
• type: Fixed
• transit: 2-6 Days
• cost: $15.99
• service: Standard

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