How to Replace Mini Coolant Pipe and Thermostat on 2nd Gen Models


Coolant pipes are one of those critical, yet relatively vulnerable parts of any car. Given enough time and exposure, any coolant hose or pipe will lose some of its integrity. Today we’ll talk about how to replace MINI coolant pipe and thermostat on the N12, N14, and N18 engines. Although relatively simple, this process will take some time so you better arm yourself with tools, patience, and most importantly, the right parts! 

Leaking coolant pipe N12 N14 N18 MINIArticle updated on 09/29/21. Original publishing date 12/11/19

What Causes MINI Coolant Pipe Failure?

Second-gen Minis are fairly solid cars, especially the non-turbo ones. Yet, every vehicle has one or more known issues that become obvious after the vehicle has been used for some time. For these Minis, it’s the coolant pipes, the water pump, and the thermostat.

Overall, the main cause of these failures is a series of built-in flaws that often cause the water pump to fail long before it should, or the thermostat housing to start leaking. Either way, if you own a second-generation Mini, there’s a solid chance you’ll have to deal with your coolant system at least once. The good news is that replacing faulty or compromized parts ensures that you won’t have these issues in the future.

Diagnosing Coolant Pipe Failure

Coolant leaks can be obvious, such as a pool of coolant on your garage floor, but they can also be pretty subtle. If you’re noticing that your coolant levels are dropping over time, that should be cause enough to start looking for leaks. Before you get down to testing the entire cooling system using a testing tool, we recommend that you check the area where the coolant pipe meets the thermostat housing. This is where you’re most likely to spot a leak.

If that didn’t work, your best bet is to do a thorough visual check and then do a coolant system pressure test.

How To Replace Mini Coolant Pipe

Replacing the Mini Coolant pipe (and the associated o-ring) requires the removal of the thermostat.  Therefore, we recommend that the coolant pipe and o-ring as well as the thermostat, always be replaced in tandem unless one or the other has recently been replaced.

The following DIY steps are specifically for the N14 engine (turbocharged) which is used in the 2007 through 2010 “S” models and 2011 through 2013 JCW models.  However, the majority of the steps are the same for all N12 (non-turbo), N14 and N118 engines used in the R55, R56, R57, R58, R59, R60, and R61 MINI models.

Follow along as we learn how to replace Mini Coolant pipe and the thermostat (due to a leaking coolant pipe) on a 2009 R55 Clubman S JCW.  Click HERE to order the replacement parts for your MINI, from eEuroparts.com.

Note that if you have an “S” model, it is also very advantageous to perform a walnut blast (de-carboning) on the intake ports/valves while the engine is disassembled for the coolant tube replacement.  Conversely, if a walnut blast is being performed, preemptively replacing the coolant tube (and thermostat) while the intake manifold is removed, is a smart move.  If the tube has not been replaced …. it is going to fail at some point.

Parts Needed:

How to replace MINI coolant pipe – PROCEDURE:

Before we get started, there are a few things you need to do. We recommend that the engine be cold or cooled off as we will be working closely around the engine and coolant. Have fresh coolant and distilled water at hand, for reassembly. Have a drain pan (for coolant) handy. Larger is better as the bulk of the coolant will drain on top of the transmission and down around the front and rear. A floor jack may be required to lift the front of the vehicle in order to slide the drain pan under the car. With that said, let’s get down to business!

Step 1 – Remove the Engine Air Filter Housing Cover and MAF

Unplug the MAF harness plug.

MINI coolant tube replace how to

Loosen the intake pipe hose clamp.

 how to replace MINI coolant tube

Loosen the filter cover securing screws (the screws stay captive in the cover).

MINI coolant tube replace how to

Pull up the cover and pull the MAF from the MAF to turbo pipe.

Step 2 – Remove the Filter and Lower Filter Housing

MINI coolant tube replace how to

Remove the two housing securing screws.
MINI coolant tube replace how to

Gently pry the housing upward from the rubber securing grommets, pull the intake elbow from the intake pipe and remove the housing.

Step 3 – Remove the Positive Crankcase Ventilation (PCV) hose

MINI coolant tube replace how to

MINI coolant tube replace how to

Pry up and remove the hose securing clip at the valve cover.

MINI coolant tube replace how to

Pull the end of the hose from the valve cover nipple.
MINI coolant tube replace how to

MINI coolant tube replace how to

Unclip the PCV heater harness plug and remove from the heater plug housing.

Step 4 – Remove the Intake Pipe

MINI coolant tube replace how to

Loosen the intake pipe to turbo hose clamp.

MINI coolant tube replace how to

MINI coolant tube replace how to
Pull the intake pipe from the turbo inlet nipple and remove the pipe.

Step 5 – Disconnect the Vacuum Pipe

At this point, go ahead and disconnect the vacuum pipe.

Step 6 – Pull the Pipe Connector Off

MINI coolant tube replace how to
MINI coolant tube replace how to

Pinch the unlock tabs and pull the pipe connector from the nipple on the vacuum pump.

NOTE: Steps 7 through 14 detail removal of the intake manifold.  Note that, while this job can technically be done without removal of the intake manifold, the coolant pipe is fully hidden and rather difficult to access, remove and accurately replace, without removing the manifold.

Step 7 – Disconnect the Intake Manifold PCV Hose

MINI coolant tube replace how to
MINI coolant tube replace how to
MINI coolant tube replace how to

Pinch the locking ring and pull the hose connector from the valve cover nipple.

Step 8 – Disconnect the Manifold Absolute Pressure (MAP) Sensor Harness Plug

MINI coolant tube replace how to
MINI coolant tube replace how to
Pry the locking tab up and pull the harness plug from the MAP sensor.

Step 9 – Remove the Charge Pipe Intake Elbow Hose

MINI coolant tube replace how to

Loosen the hose clamp on the upper end of the hose.
MINI coolant tube replace how to

Pry the securing clip on the lower end of the hose.  The clip does not need to be fully removed.
MINI coolant tube replace how to

MINI coolant tube replace how to

Pull the lower end of the hose up from the connector  and pull the upper end of the hose off of the plastic intake charge pipe.

Step 10 – Remove the “Sound Generator” Assembly

MINI coolant tube replace how to

Remove the securing screw.

MINI coolant tube replace how to

Pull the connector end from the firewall connector.

MINI coolant tube replace how to

Loosen the hose clamp securing the sound generator tube to the intake tube.

MINI coolant tube replace how to

Pull the hose from the nipple on the intake tube and lift the assembly out.

Step 11 – Remove the Lower Intake Charge Tube From the Throttle Body

MINI coolant tube replace how to

Loosen the hose clamp that secures the tube to the throttle body.

MINI coolant tube replace how to

Gently twist and pull the tube from the throttle body and pull the tube up and out.

Step 12 – Remove the Intake Manifold

MINI coolant tube replace how to

MINI coolant tube replace how to
MINI coolant tube replace how to
Remove the intake manifold support screw.  This screw is under the manifold and is difficult to access.  You can see the screw using a mirror and a light.  It is above and to the inside of the throttle body.  You can just feel the screw if you reach over the intake manifold and around the rear and under.  Use a 1/4″ drive ratchet, extensions, and 10mm socket.
MINI coolant tube replace how to

MINI coolant tube replace how to
Disconnect the vacuum tube elbow from the fuel tank breather valve (driver side) by pinching the locking tabs on the elbow housing and pull the elbow from the valve nipple.

MINI coolant tube replace how to

Remove the 5 intake manifold securing nuts. Pull the manifold slightly away from the cylinder head, but do not attempt to fully remove it yet.

MINI coolant tube replace how to

Pry the harness securing clip from the tab on the intake manifold (passenger side).

MINI coolant tube replace how to

Pry the harness securing rivet from the intake manifold.

MINI coolant tube replace how to

Pull the manifold off of the studs and away from the cylinder head (do not attempt to fully remove yet).

MINI coolant tube replace how to

MINI coolant tube replace how to
Pry the harness securing rivet from the throttle body hosing, just above the throttle body harness plug.

MINI coolant tube replace how to

MINI coolant tube replace how to
Unclip and remove the throttle body harness plug.

MINI coolant tube replace how to

Pull the pressure converter valve rubber hanger from the flat metal mounting tab.

MINI coolant tube replace how to

Pry up the locking tab and remove the fuel tank breather valve harness plug. You should now be able to lift and remove the intake manifold.  Carefully watch for any stray harness clips that may need to be disconnected.

Step 13 – Disconnect the Intake Camshaft Position Sensor Harness Plug

MINI coolant tube replace how to

Pry up the locking tab and disconnect the intake camshaft position sensor harness plug.

MINI coolant tube replace how to
Pry the harness securing clip from the tab on the valve cover.

Step 14 – Disconnect the Vacuum Hose From the Vacuum Pump and the Turbo Wastegate Vacuum Valve

MINI coolant tube replace how to
MINI coolant tube replace how to
MINI coolant tube replace how to

Step 15 – Pry the Locking Tab and Disconnect the Thermostat Temp Sensor Harness Plug

MINI coolant tube replace how to

Step 16 – Disconnect the oil pressure sensor harness plug

MINI coolant tube replace how to

Step 17 – Remove the DME (Digital Motor Electronics …. the engine management control unit) Harness Cover

MINI coolant tube replace how to
Remove the securing screw.
MINI coolant tube replace how to

Unclip the securing tabs and remove the plastic cover.

Step 18 – Disconnect the Two Rearward DME Harness Plugs

MINI coolant tube replace how to
Lift the locking levers and pull the harness plugs up and out of the DME connector housings.

Step 19 – Disconnect the Harness Plug Just Forward of the DME

MINI coolant tube replace how to
MINI coolant tube replace how to

Step 20 – Pull the Harness Toward the Passenger Side

MINI coolant tube replace how to
MINI coolant tube replace how to
Slide the plastic engine harness housing upward from the cylinder head until it is free from the mounting bracket. Pull all of the harnessing over toward the passenger side.

Optional Step (This gives more working room) – Disconnect Ignition Coil Harness Assembly

Unclip and remove the coil harness cover. Disconnect the ignition coil harness plugs and ground connectors. This now gives more room to pull the engine harness over to the passenger side, for additional clearance.

Step 21 – Disconnect the Upper and Lower Radiator Coolant Hoses

MINI coolant tube replace how to
Pinch the hose clamp on the upper radiator hose and pull it back over the hose (off the thermostat nipple). Pull the hose off the thermostat nipple.

MINI coolant tube replace how to

Repeat for the lower radiator hose.

Step 22 – Disconnect and Remove the Thermostat to Coolant Reservoir and Turbocharger Coolant Hose

MINI coolant tube replace how to

Loosen and remove the coolant pipe banjo bolt at the turbocharger.

MINI coolant tube replace how to

Remove the hose assembly mounting bracket bolt. Pinch and pull back the hose clamp at the thermostat nipple.

MINI coolant tube replace how to

Pull the hose from the thermostat nipple and from around the turbocharger housing.

Remove the remaining two coolant hoses for the heater, at the rearward side of the thermostat, by pinching that clamps, sliding them back over the hoses and removing the hoses from the thermostat nipples.

MINI coolant tube replace how to

MINI coolant tube replace how to
Note the plastic coolant pipe in the area under where the intake manifold was mounted.  Pull the thermostat to coolant pipe securing clip away from the pipe, using a small screwdriver or pick tool.  You must reuse this clip with the new pipe …. don’t lose it.

Step 23 – Remove the Thermostat and Coolant Pipe

MINI coolant tube replace how to
Remove the three bolts securing the thermostat to the cylinder head.
MINI coolant tube replace how to

Carefully pull the thermostat away from the cylinder head while pulling the connection elbow from the coolant pipe. Remove the Coolant pipe securing bolt at the tab on the middle area of the pipe.

MINI coolant tube replace how to

Carefully pull the coolant pipe from the mounting hole in the passenger side of the engine block (water pump mounting boss).

MINI coolant tube replace how to

MINI coolant tube replace how to

If the coolant pipe has been leaking, you will likely find that the o-ring and some broken plastic bits are still lodged into the mounting hole.  Carefully remove these pieces and the o-ring.

Assembly

Reassembly is the opposite of removal.
Oh come on … it’s a joke……

Really, though, the assembly is pretty much just reversing the steps that got you to this point following our how to replace MINI coolant pipe DIY.  However, see the notes detailed below, as you reassemble. You may wish to take this opportunity to replace any (or all) of the Coolant hoses that may show deterioration or have known long life on them.  You will also need new Intake manifold gaskets.

MINI coolant tube replace how to
Lubricate the o-ring, on the end of the Mini Coolant pipe, with silicone grease before inserting into the water pump mounting boss hole.

MINI coolant tube replace how to
Clean up the thermostat gasket mounting area on the cylinder head.

Lubricate the o-ring on the thermostat nipple (a new thermostat is recommended) before inserting it into the coolant tube. Clean up the intake manifold gasket mounting areas on the intake side of the cylinder head.  Use new Intake manifold gaskets.

When all assembled, fill and bleed the cooling system.

Bleeding the Cooling System

  • Fill the expansion tank with a 50/50 mixture of new Fresh coolant and distilled water.  Use the same type of coolant that is already in the system (while you may have a favorite brand, the important part is the color, which tells what type of coolant it is).
  • Open the bleeder screw/plug of the top of the thermostat housing (right next to the temp sensor), by inserting a screwdriver straight down from above.  Do not remove the screw, just loosen it a couple turns.
  • Start the engine and let it idle.
  • Fill the expansion tank as the coolant level lowers.
  • Watch the area at the base of the bleed screw on the thermostat.  You will likely initially see nothing, then bubbles and then, eventually, coolant.
  • When coolant is coming from the bleed hole, close the bleed screw (not tightly).
  • Keep an eye on the coolant level in the expansion tank and assure that there is no overheat warning in the instrument cluster.  If you have an OBD-II scan tool that allows live engine data reading you can watch the actual temperature.
  • Alternate between bleeding, running the engine and adding coolant until the temp and the coolant level have stabilized and there are no more air bubbles coming from the breeder.

Where to Find Parts for Mini Coolant Pipe Replacement?

We’ve shown you how to replace Mini coolant pipe and thermostat. Now let us show you where to find all the parts you’ll need for this project! All you need to do is head over to our online store, select your vehicle from the drop down menu, and you’ll be presented with a complete list of parts that are guaranteed to match your car. Search for coolant components, and you’ll see our full offering of OEM, Genuine and aftermarket products that match your search.

Posted in DIY How-To, Mini

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