BMW E90 320d: M47 and N47 Diesel Engines—Problems, Longevity, and Maintenance
Quick Summary
The BMW E90 320d (2005–2012) is one of the best diesels in its class: rear-wheel drive, solid performance, and about 39 mpg on the highway from a 61-liter tank add up to a range of more than 620 miles. Under the hood sit two generations of engines: the M47N2 (163 hp) and the N47D20 (177/184 hp). The key is knowing their weak spots—the timing chain on the N47 and the swirl flaps on the M47. Properly maintained, these engines last 155,000–249,000 miles without a rebuild.
The Problem
You get into an E90 320d, fire up the cold engine—and hear a metallic rattle coming from the transmission. That’s the timing chain, and the repair won’t be cheap. Or the opposite: an M47N2 suddenly loses power, and teardown reveals that shattered intake swirl flaps have made it into the cylinders. Both scenarios trace back to design quirks you need to know about before you buy.
Symptoms
- Rattle from the rear of the engine on a cold start
- Vibration when pulling away and a knock at idle
- Power loss and rising fuel consumption
- Fault code P0299 — insufficient boost pressure
- Burning smell in the cabin
- Fault codes for EGR, DPF, MAF, and NOx sensors
Causes
The M47N2 (2005–2007) is the final evolution of the cast-iron M47. Cast iron makes the engine exceptionally durable, but its Achilles’ heel is the swirl flaps in the intake manifold. Their plastic shafts break down over time, a flap drops into a cylinder, and that means an engine rebuild.
The first-generation N47D20 (2007–2010) switched to an aluminum block and put the timing chain at the flywheel end—the rear of the engine. Replacing the chain means removing the transmission. A weak tensioner and a chain that isn’t strong enough lead to a skipped tooth or a snapped chain, and the valves meet the pistons.
The second-generation N47D20 LCI (2010–2012) is the most reliable version: the chain is stronger and the tensioners are improved. The Efficient Dynamics variant (163 hp) is mechanically identical to the standard N47 but returns lower fuel consumption thanks to engine mapping and aerodynamics.
The Fix
Timing chain on the N47. Any rattle from the rear of the engine on a cold start calls for immediate diagnosis. Replacing the chain, tensioners, and chain guides is a labor-intensive, expensive job.
Swirl flaps on the M47. The most reliable fix is to physically remove the flaps and blank off the ports with the intake manifold out. As prevention, this is typically done around 62,000 miles.
P0299. In 70% of cases it’s caused by the VNT mechanism (the turbo’s variable geometry) sticking from carbon buildup—not a dead turbo. Cleaning the actuator and the VNT mechanism often sorts it out. If the turbo has actually failed, fitting a quality remanufactured unit is a major expense.
EGR cooler leak. BMW officially acknowledged the defect and ran a recall. The replacement is free even years after the warranty expires—check your VIN with a dealer.
Clogged DPF. Once a month, take the car on the highway and hold 30 minutes at 2500–3000 rpm—that’s enough to burn off the soot. If it’s critically clogged, a shop can run a forced regeneration.
Flywheel and clutch wear. Replacement at 93,000–124,000 miles is typical. Symptoms: vibration when pulling away, a knock at idle, a metallic clatter when shifting. Don’t put it off—a disintegrating flywheel will damage the transmission.
Prevention / Checklist
- Oil—LL-04 5W-30 only, changed every 6,200 miles
- Fuel filter—every 19,000–25,000 miles
- Air filter—every 12,400–18,600 miles
- Coolant (antifreeze)—every 3–4 years
- Differential oil—every 50,000–62,000 miles
- ZF 6HP automatic transmission oil—every 37,000–50,000 miles (common practice, despite the “non-serviceable” label)
- Intake manifold cleaning—every 62,000–93,000 miles
The Bottom Line
The BMW E90 320d is a genuinely good car that rewards attentive owners with years of pace and frugality. The one to buy is the 2010–2012 LCI with the second-generation N47D20 (184 hp): the strengthened chain and improved tensioners minimize the main risk. Before you buy, listen to the chain on a cold start, check the service history, and run the VIN for open recalls. Follow one rule—don’t skimp on maintenance—and the engine will cover 155,000–249,000 miles without a rebuild.