BMW 4 Series (F32/F33/F36): Buyer’s Guide and Weak Spots
Quick Summary
The BMW 4 Series (F32/F33/F36) is a sports coupe, convertible, and Gran Coupe built on a single platform and produced from 2013 through 2020. Under the hood sit three turbocharged gasoline engines: the N20 (2.0 L, 4 cylinders), the N55 (3.0 L, 6 cylinders), and the B58 (3.0 L, 6 cylinders). The N20 is the troublemaker; the B58 is the most reliable. The main weak points: the timing chain on the N20, the water pump and VANOS on the N55, and the intercooler charge pipe on every engine. The key takeaway: prevention costs less than repair.
The Problem
You’re shopping for a used BMW 4 Series, or you already own one, and you don’t know what to expect from the engine. Pre-2015 N20, N55, or B58—the engine choice determines not just performance but the budget for future maintenance. Pick wrong, and you could face an engine rebuild within your first months of ownership.
Symptoms
- Timing chain stretch: rattle at cold start, timing correlation fault codes
- PCV valve failure: high oil consumption, whistling from under the cover
- Valve cover gasket leak: oil seepage on the block
- Charge pipe failure: power loss, boost whistle
- N55 water pump failure: engine overheating with no warning
- VANOS solenoids: fault codes, power loss, rough running
- Carbon buildup on the intake valves: loss of power, rising fuel consumption
- F33 convertible top: jerking, stalling mid-cycle
Causes
N20 is the Achilles’ heel: the timing chain and its plastic guides. The plastic cracks under load and temperature swings, and the chain stretches. Skip the preventive replacement and the chain can jump—valves meet pistons, and you’re looking at an engine rebuild. The PCV valve is integrated into the valve cover, so a failed valve means replacing the cover as an assembly.
N55 is more reliable than the N20, but it has its own issues. The electric water pump fails after 62,000 miles, often without warning. The VANOS solenoids go bad—fault codes appear and power drops. Valve cover gasket leaks and PCV failures show up here too, just as on the N20.
B58 is the evolution of the N55 and the most reliable engine in the 4 Series lineup. Its one serious problem is the plastic intercooler charge pipe blowing off: the plastic can’t handle boost pressure and heat.
All the turbo engines suffer from cracking charge pipes and carbon buildup on the intake valves—with direct injection, fuel never washes over the valves.
Solutions
N20 Engine: Timing Chain Is a Must
Preventive timing chain replacement at 59,000–81,000 miles is mandatory. Use an upgraded aftermarket chain kit—the OEM kits don’t always solve the problem. Check whether the chain was already replaced under the recall.
Charge Pipe: Aluminum Instead of Plastic
Swapping the plastic charge pipe for an aluminum one is the only reliable fix for the N20, N55, and B58. It’s a one-time spend that ends the problem for good—one of the first upgrades owners recommend.
N55: Water Pump and VANOS
Replace the water pump preventively after 62,000 miles. If VANOS fault codes appear, run diagnostics and replace the solenoids.
Valve Cleaning: Walnut Blasting
Walnut blasting the intake valves (walnut blast) every 37,000–50,000 miles restores power and improves fuel economy.
Fuel: Top Tier Only
For direct-injection engines, use Top Tier fuel with detergent additives—it reduces carbon deposits on the valves and fuel injectors.
F33 Convertible: The Roof
Once a month, cycle the top up and down—that keeps the hydraulics from seizing and the seals from drying out. At purchase, run the roof through a full cycle: check the speed, the smoothness, and listen for any odd noises.
Maintenance Schedule
| Parameter | Value |
|---|---|
| Oil change interval | 7,500 miles, BMW LL-01 approval |
| Timing chain (N20) | preventive at 59,000–81,000 miles |
| Walnut blast valve cleaning | every 37,000–50,000 miles |
| Charge pipe | replace with aluminum (N20, N55, B58) |
Pre-Purchase Checklist
- Confirm the timing chain was replaced under the recall (N20)
- Inspect the charge pipe for cracks and chips
- Check the valve cover for traces of oil
- Cycle the convertible roof (F33) through a full operation
- Plug in a scan tool: check for VANOS and boost pressure fault codes
The Bottom Line
The BMW 4 Series is a strong car on design and dynamics, but its reliability depends on the engine. The N20 needs a preventive chain replacement, the N55 demands attention to the water pump and VANOS, and the B58 needs its charge pipe swapped. Stick to the schedule: oil every 7,500 miles with BMW LL-01 approval, walnut blasting every 37,000–50,000 miles, and an aluminum charge pipe. Prevention is always cheaper than an engine rebuild.