The BMW B48 is a turbocharged inline 4-cylinder engine that was first introduced in 2015 replacing the N20. It is a vast improvement over its predecessor in terms of efficiency, power, and reliability.
Is the B48 reliable? Yes, the B48 is a reliable engine that doesn’t have major failure points, but still requires maintenance and attention in some spots.
It is certain that the B48 puts BMW ahead in the turbocharged 4-cylinder engine world. Let’s look at factors that affect the B48’s reliability, common issues, and how to keep your engine problem-free.
Common BMW B48 Engine Problems
1. Coolant Loss
One of the most common reliability concerns with the B48 is coolant loss. This is usually associated with a difficult-to-spot coolant leak. Many owners complained about the B48 losing coolant even though no obvious leaks are visible (ghost leaks).
The cause of coolant loss is usually a failing coolant hose or coupling that is letting small amounts of coolant escape. If left unchecked, the engine could run low on coolant.
How to fix:
Pressure test the cooling system to attempt to find the leak. Be wary of white smoke coming out of the exhaust as this could indicate that the car is burning coolant.
2. Turbo return line leak
A fairly common issue on early-production BMW B48’s issue is a turbo return line leak. One of the lines that connect to the turbocharger may start leaking oil. This issue is caused by an incorrectly assembled “asbestos-free” gasket.
How to fix:
It’s a fairly simple fix and is covered under warranty. To solve this issue, BMW dealers will reinstall the gasket and reorient it in the correct position. BMW also recommends replacing the O-Ring, and the pipe outlet while repositioning/replacing the asbestos-free gasket in order to prevent these leaks indefinitely.
Note this is an issue that only affects early B48 engines.
3. Brittle coolant hoses
Old coolant hoses, connectors, and couplings can get notoriously brittle, especially if located near the hottest engine parts. BMW uses plastic for many of these connectors on the B48, which tend to contract and expand and thus can crack, break, and cause a leak.
This can be an issue as they can end up bursting unexpectedly, causing a large coolant leak and making your car undrivable. Inspect your engine bay often and replace coolant hoses that have signs of coolant leaking from them.
4. Water pump failure
The B48 has a split cooling system with two water pumps. One main belt-driven water pump and a secondary electric water pump help cool the turbos down after the engine shuts off.
Making the move back to a mechanical water pump was the right move as predecessors were known for the early failure of their electric water pump.
That said, the main water pump on the B48 can fail unexpectedly, leaving the car in limp mode or leaving you stranded in the worst-case scenario.
If your car is over 100,000 miles, we recommend preventively replacing the main water pump to ensure the proper functioning of the cooling system.
5. Carbon buildup
Carbon buildup is a common issue that can affect any engine with direct injection such as the B48. Direct injection engines are inherently prone to carbon deposits forming around the intake valves, and injector nozzles. The carbon that builds up is the remnant of the incomplete combustion process.
Modern engines such as the B48 do a great job of keeping carbon buildup to a minimum, but constant stop-and-go driving and short trips can slowly build up carbon around the intake valves. If you’re over 100,000 miles on your B48-powered BMW, a walnut blast is recommended.
Keeping engine problems in the B48 to a minimum
- Common BMW B48 maintenance items besides from oil and coolant changes are: water pump, spark plugs, ignition coils, and accessory belt. If you take proper care of each of these, your B48 should be able to stay trouble-free for the most part.
- Ensure you let the engine reach operating temperature when putting high loads on it. Cold oil does not lubricate as well, and high RPMs on a cold turbocharged engine can reduce the life of the engine.
- Try not to drive your car for short distances only. It’s a good idea to take your car out for a prolonged drive every few weeks in order for it to properly warm up all the fluids, and this can also help control carbon buildup.
B48 long-term reliability
It’s difficult to tell how well the B48 is going to fare long-term as the engine is still fairly new. However, you will need to replace/rebuild the turbocharger at some point if you plan on keeping the car for a very long time
The B48 uses higher-quality gaskets compared to older BMW engines which does play a part in the B48 not leaking oil as much as older BMW engines are known for. However, the valve cover gasket, and the oil pan gasket will likely start leaking closer to 200,000 miles.
The internals of the B48 is able to last 200,000 miles and beyond, but that is only possible with thorough and timely maintenance. Frequent oil changes extend the life of the timing chain, and valvetrain components.
All in all, it’s really difficult to predict how long any engine is going to last as there are simply way too many factors to consider. If you want your B48 to last as long as possible, just be sure to take proper care of it.
Is the B48 reliable?
Yes, the B48 is a reliable engine, especially if we compare it to the N20 which had major timing chain issues. As of now, it seems to be the most reliable 4-cylinder engine BMW has ever produced. Within the modular “B” series of engines, it does fall short of the B58 which seems to be the most reliable engine in the family.
Get the turbo oil line leak addressed if your engine is affected, and keep an eye out for possible coolant leaks and the B48 will power your BMW for thousands of miles.