Coolant DYI

So I finally got around to changing the coolant in my 325i. I didn’t take any pictures (sorry) because I didn’t want to dirty up my nice camera, and anyway I left it in the trunk and realized it after I had the car in the air and the coolant was draining. I’ll be descriptive enough for you guys that you won’t need pics.

This DYI assumes you have a decent skill set at turning wrenches and have a pretty good set of tools, and you are familiar with the E9x engine compartment. You should also know that coolant hoses stick to their attachment points and need to be “finessed” off.

The tools needed are:
• 10mm socket
• 10mm wrench
• 8mm socket
• 8mm wrench
• 6mm socket
• 6mm wrench
• Big flat blade screwdriver
• Small flat blade screwdriver
• 1/4drive ratchet
• 1/4 drive nut driver
• Coolant catchpan
• Shit load of red shop towels and paper towels
• I suggest getting some floor-dry compound to soak up any spilled coolant. Cat litter will do.
• Large Zip tie or small-diameter rope

For nomenclature purposes, the right side of the engine is the passenger side and the left the driver’s side. Note: you will be wrenching on mostly plastic screws and small hose clamps, so don’t over torque them when tightening!

Our cars have an electric water pump and electric thermostat. Both the thermostat and water pump housings are on the front right side of the engine next to each other just above the steering rack.

The basic procedure is:
1) Remove the engine underpan
2) Move the steering fluid cooling hoses out of the way
3) Drain the coolant
4) Open a hose to drain the engine block (the N52 doesn’t have a block drain)
5) Refill the coolant
6) Vent the coolant – bleeds the air out of the system using the water pump
7) Top off the coolant

Steps:

1) Open the hood and open and remove the coolant reservoir cap.
2) Just for good measure, open the coolant reservoir bleed screw (it is the cross-headed button next to the cap where the overflow hose comes in to the reservoir).
3) Lift the car off the ground so you can get underneath it. Lift the front and rear so the car is level in the air.
4) Remove the engine underpan (the big plastic cover under the engine compartment). It is held in place by 10 or so 8mm-head bolts.
5) Remove the plastic shield covering the radiator. It has two 8mm head bolts. Then it has two clips that attach to the cross member, then it just slides rearward. There are two aluminum brackets that come off with it. Make a note how they are installed.
6) Un-attach the power steering cooling hose and move it out of the way. The hose is two parallel hoses that loop around (with a horseshoe metal pipe in a rubber isolator) that runs next to and is attached to the steering rack. It’s mounted in two places – you need only to remove the right-side mount. Remove the mount by removing the 10mm bolt on the steering rack flange. Tie off the hoses out of the way.
7) Place a catchpan under the left side of the radiator and open and remove the blue plastic radiator coolant drain screw on the left side of the radiator. You need only to remove the blue screw (it threads into a white nut – don’t remove the nut!)
8) Let coolant drain. It takes about 10 minutes or longer (it pees like a chick at a frat party). You can get more coolant out by squeezing the lower radiator hose on the right side of the radiator.

Here’s the hard part…

To drain the coolant from the engine block you need to remove a few hoses from the water pump and thermostat housing. The BMW TIS procedure calls for removing the lower radiator hose that goes into the front of the thermostat housing. That hose has the funky BMW plastic coolant hose fitting and is a PIA to get loose. I chose to remove the u-shaped hose running from the back of the thermostat housing to the water pump and the hose from the block to the water pump (nothing really came out so you don’t need remove that hose). The hoses I removed use regular BMW hose clamps w/ 6 mm bolt heads
9) Place the coolant catchpan underneath the thermostat/water pump housings.
10) Remove the u-shaped hose running from the thermostat housing to the water pump. About 16 ounces or more of coolant will come out.
11) Once the coolant has drained, reinstall the u-shaped hose, re-attach the powersteering hose, and reinstall the blue radiator bleed screw.

Coolant Refill procedure

12) If you didn’t open the bleed screw on the coolant reservoir, open it now (about 4 turns)
13) Slowly fill the system with a premixed 50/50% mix of BMW coolant and distilled water.
14) Fill the reservoir all the way up to the bottom of the filler neck. The bleed screw will bleed air as it gets trapped in the reservoir. Keep filling until the bleed screw is passing coolant with no bubbles in it. (Keep a papertowel handy to soak up the coolant coming out of the bleed screw).
15) Close the bleed screw.
16) Once the reservoir (system) is full (it will take almost two gallons of antifreeze) fully close the reservoir cap.

Venting Procedure (to get the trapped air out of the system)

17) Insert the key into the dash slot and hit the starter button (but don’t start the engine – e.g. keep your foot off the bake/clutch).
18) When the ignition is on, set the heater to the highest temp (84 deg.) and set the fan on low.
19) Hold down the accelerator pedal for 10 seconds then release. This activates the water pump and it will cycle for about 12 minutes to vent all the trapped air into the coolant reservoir (it sounds like a min washing machine). Don’t open the reservoir cap or bleed screw during the venting process! (you’ll have start the process over) You may want to hook up a extra battery to the under-hood jumper points to keep the car’s battery from running down.
20) Once the water pump stops after 12 minutes, open the reservoir cap (it will hiss a little) and add coolant until the measuring stick (ball indicator) is 6 mm above the top of the filler neck. (review the manual procedure for checking the coolant level so you know what I’m saying)
21) Close the cap and check for leaks in the system (the hose connections you took off)
22) Reinstall the plastic radiator shield and engine underpan. The job is complete.