If you ask most car enthusiasts, who drive modern BMW’s, their opinion on the factory cooling system in their cars, responses will often range from “My Honda never had it’s water pump explode,” or “I hate it,” to “what’s a cooling system, and who are you?” These are all valid points. BMW models of yore were never renowned for their cooling systems, but the switch the all electric water pump has further increased the volatility, with the car offering no warning sign before the water pump seizes and the motor overheats.

When you pack a long Straight-6 engine into a small engine bay, cooling that 3-liter-heater will be tricky. I am working on a new project to help the car run better at the track, but in the mean time, I want to cover any angle I can find, that might give me an edge in lowering operating temperatures. So, it’s time to HEAD TO THE INTERNET GARAGE!

Jokes on you, I had already went to the Internet, and armed myself with knowledge (Read: hearsay). After five years, it was time to flush the engine coolant with distilled water.

From the factory, 135i are filled with a 50/50 mixture of BMW coolant and distilled water. Contrary to the sound of the name, coolant isn’t particularly great at cooling the engine, the water does that job. Vehicles are filled with coolant to prevent the water from freezing in cold climates. The glycol-based coolant actually reduces the capability of the water to cool the system. 100% distilled water will more efficiently “grab” heat and disperse it than a glycol-water mixture. Conversely, as the coolant:water ratio is increased, the cooling system is able to protect from freezing at progressively colder temperatures.

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That’s well and dandy, but I live in SoCal, where if it gets below 50*, the locals think the world is ending. Antifreeze only offers one perk then for me, which is offering additives to lubricate the water pump and other bits in the cooling system. Fortunately for me, the aftermarket has stepped in and developed solutions for this.

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Redline Oils, and several other manufacturers have developed water “wetters” or additives to add to your cooling system to help the efficiency and lubrication of large mixtures of distilled water. They all make some pretty bold claims on that efficiency bit:

Not sure how much I believe that, but it’s worth a shot, and I will take any little bit that I can get.

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Did you know that draining the radiator on a turbo BMW is way more of a pain in the ass than other cars? I guess this is what I get for mocking those whose cars have difficult to reach oil filters. Oh well.

Step 1: Break a Bunch of Clips While Removing the Front Bumper.

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Watch out for the headlight sprayers, you have to slip their caps off the remove the bumper. They will fight you the whole time, and you will wonder if they’re even worth having when it rains three times a year in Southern California.

Step 1 complete:

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Step 2: Ogle at Things Previously Hidden.

Passenger-side oil cooler, and ducting. They really packed a lot of stuff in a small space. We will be revisiting this to get more cooler in there…somehow.

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Vented access cover for the cooler in the wheel-well. Not much to optimize here in terms of heat extraction without compromising the shielding benefits of the shroud. Booo.

Step 3: Remove ze Intercoola.

Ha, and you thought removing the bumper to reach the radiator was silly, the intercooler also has to be removed to even see the bottom of the radiator. Oh joy.

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Fortunately, besides the additional plastic clips that I broke, removing the OEM intercooler is a breeze, the piping is plastic and they snap together with C-Clips. Simply wave your flat head screwdriver at them like a wizard’s wand, and poof (or, pop?), they’re off!

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Let’s check the intercooler plumbing for oil blow-by. I installed my catch can around the 32,000 mile mark, but before that, it was as it left the factory. Let’s see how much oil we can find!

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The tubing has a light sheen of oil on it, and the ribbed edge of the collectors have accumulated a teeny-tiny bit, but not enough to drip down the piping, or pick up with my gloved fingers. Doesn’t look too bad to me for a car that he seen a lot of hard miles, and has been tuned to 14PSI of boost since ~15k miles.

Step 4: Wonder Why This Required the Three Prior Steps.

Turbo problems, I tell ya. Okay, whining over, we now have access to the radia…what the hell is this?

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There is a small cooler in front of the A/C condenser and radiator. My car is a manual-trans N54 car, do these things have transmission fluid coolers? I can’t think of what else this narrow little thing would be for. Any idea, Internet?

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Looking beyond that, I spy with my little eye, something green and blue.

Jackpot.

Now Internet, I’m glad I sought council with you before trying this, otherwise, I would have broken it. You don’t remove the whole drain plug, like you do on most cars. Instead, you unscrew the inside blue piece only, and not with a screwdriver, that would be too easy. No, you need to use a quarter, due to the weird shape of it. If I didn’t read someone’s story about how they broke this thing the first time they tried to drain the radiator, I would have done the same damn thing. Another fine example of German engineering, Ladies and Gentlemen.

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I drained the radiator, topped off the expansion tank, cycled the electric water pump, and drained again, until most of the water coming out had run clear. I’m guessing that there is some residual coolant in the system since there isn’t a coolant drain plug on the engine block (?). That’s fine, again lubricate the cooling system, blah blah blah, lest we upset the fiddly electric water pump and blow this whole operation sky high.

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Perhaps we should still plan on offering a monthly sacrificial feast to the BMW Gods to ensure that the water pump doesn’t grenade itself, just in case.

Can we go back to that whole electric water pump thing? It does do one pretty cool trick. With modern BMW’s you don’t need to manually “burp” the cooling system after draining and refilling the radiator, there’s an easy trick to make the water pump burp the cooling system for you.

Fill the expansion tank to a bit below the normal level mark, leave the cap off and do the following:

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Put the key in ignition, tap the power button once, so the car is in the “on” position, floor the accelerator for ten seconds. You will hear a loud whirring sound, and presto, your electric water pump is cycling the system for you. Check it out:

This takes about 10 minutes in total, but once it’s started, you don’t need to stay on the throttle or do anything else, the car takes it from there.

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After that, the level in the expansion tank was a bit low, as anticipated, so I poured that bottle of water wetter in there, bled the cooling system again for good measure, checked the level, and then reassembled the car.

Track day at Buttonwillow was the following week, so that would be a perfect arena to test the efficiency of the stock cooling system “optimized” with a mixture of mostly distilled water and water wetter. Stay tuned.