The N55 single-turbocharged inline-six replaced the N54 starting in 2011 and brought with it many of the same engineering philosophies - including the electric water pump. If you are driving an F30 335i, F22 235i, F10 535i, or any other N55-powered chassis made between 2011 and 2018, this guide is written for you. I have done this job dozens of times on F-chassis cars and while the engine itself is a refinement of the N54, the engine bay packaging is tighter and access to some components is slightly more awkward than on the older E-chassis. This guide walks through exactly what is different and what is the same.
Here is the thing most people do not realize until they dig into it - the N55 water pump is essentially the same Bosch unit used in the N54. Same pump body, same electrical interface, same failure modes. What changes is how you get to it. The F30 engine bay is more compact, the engine sits differently, and there is more ancillary hardware in the way. But the fundamentals of the repair are identical, and if you have done this on an E90, you will feel at home once you get past the additional disassembly steps.
Like the N54 job, I will not let you skip the thermostat. Replace both simultaneously. The labor overlap is significant - you are already draining the coolant, you already have your tools out, and the thermostat housing is right there. Doing them as a pair also gives you a clean bill of health on the most critical components in the entire cooling system, and you can drive the car hard knowing the basics are sorted.
Bosch electric (same as N54)
N55 Pump Model
60,000 - 80,000 miles
Pump Lifespan
~7.5 liters
F30 Coolant Capacity
3 - 4 hours
Job Time (DIY)
What Changed Between N54 and N55 - and Why It Matters for This Job
BMW refined the N55 cooling architecture in a few important ways. The N55 uses a single turbocharger (a twin-scroll design) versus the N54's twin turbos, which means the cooling circuit is simpler and there is one fewer auxiliary coolant pump to worry about. The main electric pump still handles primary cooling duties and the DME still controls its speed electronically.
On the F-chassis cars (F30, F22, F32, F10, and so on), the engine bay layout changed meaningfully. The charge pipe runs right through the middle of the engine valley and must be moved or at least loosened to reach the pump. The airbox is larger and positioned differently than in the E-chassis cars. And the coolant hoses use BMW's quick-connect system on some joints rather than traditional clamps - which is faster to work with once you know the trick, but confusing the first time you encounter it.
One important note for F10 535i owners - your access to the pump is slightly better than F30 owners because the 5 Series engine bay is wider. If you are on an F30, expect to remove a few more brackets and possibly the charge pipe before you have comfortable access to the pump mounting bolts.
Tools and Parts for the N55 F30 Water Pump Job
Parts list - Hepu or VDO water pump for N55 (part cross-references the N54 pump, double-check with your VIN), MAHLE or Behr thermostat housing assembly, two gallons of BMW-spec coolant premixed 50/50, fresh O-rings if not included with pump, and some clean shop rags.
Tools list - 10mm socket and ratchet, T30 Torx bit, hose pliers (Knipex makes excellent ones that work perfectly on BMW spring clamps), a small pry tool for the quick-connect hose fittings, drain pan, and a vacuum fill tool or clear bleed hose. I also strongly recommend an OBD2 scanner for fault code clearing at the end of the job.
If the charge pipe is coming out (which it often needs to on F30s), consider upgrading while you have it out. Stock N55 charge pipes are plastic and known to split at the lower elbow joint under boost pressure. An aluminum upgrade eliminates that failure mode entirely and adds maybe 20 minutes to the overall job. We cover that upgrade in detail in the /engine/charge-pipes section.
Draining the F30 Coolant System
Cold engine only. The F30 radiator drain petcock is on the lower driver side of the radiator. Pop the front undertray - two screws and four plastic push clips on most F30s - to access it easily. Position your drain pan and open the petcock. Remove the reservoir cap to speed the drain.
While the coolant drains, disconnect the battery negative terminal. On the F30, the battery is in the trunk under the right-side floor panel. Remove the panel, locate the negative terminal, and use a 10mm wrench to loosen and remove it. Disconnecting the battery here is especially important because the N55's pump is fully electrically controlled and the DME can command it to run unexpectedly during diagnostics.
With the coolant drained and the battery disconnected, remove the engine cover (plastic, lifts straight up on the N55 with a firm pull on the rear edge first), and then remove the intake duct from the airbox to the turbo inlet. On the F30 this is a large-diameter rubber hose secured with one spring clamp. Set it aside.
F30-Specific Access - Charge Pipe and Airbox
Here is where the F30 job diverges from the E90. On the E90 N54, the pump is relatively accessible once the engine cover is off. On the F30 N55, the charge pipe running from the turbo outlet to the intercooler passes directly in front of the pump mounting area. You have two options.
Option one - loosen the charge pipe connections at both ends and rotate it out of the way without fully removing it. This works on some F30 builds but not all, depending on engine bay configuration.
Option two - fully remove the charge pipe. This takes an extra 15 minutes but gives you clear access and is the approach I always take on F30s. While it is out, inspect it for cracks at the joints and bends. If it shows any cracking or whitening of the plastic, now is the time to replace it with an aluminum unit.
With the charge pipe out of the way, the pump is fully accessible. You can see the electrical connector, the two coolant hose connections, and the three mounting bolts.
Pump Removal and Thermostat Swap on N55
The procedure from here mirrors the N54 job. Disconnect the electrical connector (press and pull), release the hose clamps, pull the coolant hoses, remove the three 10mm mounting bolts, and pull the pump forward and out. Clean the mounting surface on the block.
For the thermostat, it sits just above and slightly to the right of the pump location on the N55. It has an electrical connector (the map thermostat is electrically controlled, same as N54), two or three mounting bolts, and two coolant hose connections. Remove it in the same sequence - electrical connector, hoses, bolts, housing.
WGBAB Coolant Thermostat Housing Assembly with Sensors — N20 2.0L
$31.59
Install the new thermostat housing first (it is easier to access before the new pump goes in). Use fresh O-rings or the gaskets supplied with the kit. Torque the mounting bolts to approximately 10 Nm - check the housing kit instructions for the exact spec as it can vary slightly by brand. Reconnect the electrical connector and hose connections.
Install the new pump. Seat the O-ring with a light coat of fresh coolant. Thread in the bolts finger-tight, check alignment, then torque to spec. Reconnect the hoses and the electrical connector.
Coolant Bleeding Procedure on the F30 - Critical Steps
The F30 cooling system has a reputation for stubborn air pockets. BMW added a dedicated bleed nipple on the upper radiator hose specifically to address this, and I always use it. Here is my procedure.
Reinstall the charge pipe and airbox intake hose. Reconnect the battery (wait two minutes after reconnecting before starting, per the IBS note above). Set the cabin heater to maximum heat, fan on high.
Open the bleed nipple on the upper radiator hose by half a turn. Begin filling the reservoir with premixed coolant. Keep filling until coolant - not air, but a steady stream of coolant - flows from the bleed nipple. Then close the nipple and continue filling to the MAX mark on the reservoir.
Start the engine and let it idle. You will hear gurgling for the first two to three minutes as residual air works its way out. Keep the reservoir topped off during this phase. After five minutes of idling, increase engine speed to 2,000 RPM for one minute to help purge any remaining air pockets.
| F30 Bleed Points | Location |
|---|---|
| Primary bleed nipple | Upper radiator hose, passenger side |
| Secondary bleed | Heater core inlet at firewall |
| Reservoir cap | Open during fill to prevent vacuum |
| Pump self-bleed | Occurs automatically at startup |
Let the engine reach full operating temperature (thermostat opens, upper hose gets hot), run for five more minutes, then shut it off. Let it cool, check the reservoir level, and top off to MAX. Repeat this top-off check after 50 miles.
Post-Install Scan and Road Test
Connect your scanner and clear any stored cooling system fault codes. On the N55, common pump fault codes include 4A81, 4A82, and 3010/3011 related to coolant temperature. Clear them and then take the car for a 20-minute drive covering both city and light highway conditions.
Watch the temperature gauge throughout. On the N55 under normal driving, the gauge should settle at roughly 12 o'clock. During spirited driving or pulling a long hill, it may creep slightly above but should return to normal quickly once you ease off. If the gauge climbs and stays high, pull over safely and diagnose before continuing.
Park and do a final visual inspection of all hose connections and the pump itself. A damp patch on the pump body or around a hose connection is normal for the first few minutes after a cold start on a newly installed system - old coolant residue burning off. But a sustained drip or puddle forming under the car means something needs attention.
Useful Links for N55 Cooling System Owners
For thermostat-specific guidance, head to /cooling/thermostats. For the full water pump comparison and buying guide, see /cooling/water-pumps. If you are dealing with charge pipe issues discovered during this job, our /engine/charge-pipes section covers every N55 option in detail.
N55 owners dealing with multiple issues at once should read the full breakdown at /articles/bmw-n55-common-problems. And to understand how the N55 compares to and relates to its B58 successor, see /articles/what-bmws-have-the-b58. All cooling system resources are indexed at /cooling.
Inspecting the N55 Auxiliary Coolant Pump
The N55 has a secondary auxiliary coolant pump that circulates coolant through the turbocharger after engine shutdown - this prevents heat soak from boiling residual coolant in the turbo passages, causing oil coking and bearing damage. This auxiliary pump is a small electric unit mounted near the firewall on the F30. It does not fail as commonly as the main pump but it is worth checking whenever the main pump is already out and the system is drained.
To verify it is working, start the engine from cold and then shut it off immediately. Listen near the firewall - you should hear the auxiliary pump running for 30 to 60 seconds as the DME-commanded post-drive cooling cycle activates. If you hear nothing, connect your scanner and check for auxiliary pump fault codes. A failed auxiliary pump on a hard-driven N55 leads to accelerated turbo bearing wear over time - an inexpensive repair now versus a turbocharger replacement later.
The auxiliary pump is accessed from below with the front undercover removed. It is held by two bolts and has one electrical connector and two small coolant hoses. Replacement Pierburg units are the OEM-spec choice and cost approximately $80 to $120. If the pump body shows cracking of its plastic housing or coolant weeping around the outlet, replace it while the system is already drained - there is no better time.
Inspecting Radiator Hoses and the Expansion Tank on F30
With the coolant system already drained for the pump replacement, spend a few minutes inspecting the upper and lower radiator hoses. On any F30 that has not had prior cooling system service, these are original rubber hoses that have seen years of thermal cycling. At 80,000 to 100,000 miles they can show swelling at the crimped ends or surface cracking along the hose body. A hose failure at operating temperature dumps coolant rapidly and causes overheating within minutes of the failure point.
Replacement hoses for the F30 335i cost $20 to $40 each for FEBI Bilstein or equivalent quality units. Replacing them while the system is already drained adds only 20 to 30 minutes to the overall job. Squeeze each hose along its full length - a healthy hose should feel firm and spring back immediately. Any hose that feels mushy or stays deformed after squeezing has internal layer separation and needs replacement. Also inspect the plastic coolant expansion reservoir for hairline cracks at the seams - the F30 reservoir is a common slow-seep source that is easy to miss until the coolant level drops noticeably over a period of weeks.
Resources: /cooling/water-pumps, /cooling/thermostats, /cooling. For N55 common failures see /articles/bmw-n55-common-problems.
