Keeping Your Cool: Installing an Oil Cooler on the E82 128i

Do you love tracking your car? Hitting every apex just right, nailing the perfect throttle application on corner exit, and feeling the engine pull you down the back straight as fast as it can? Do you also enjoy doing that for more than a couple of laps before your car's electronic nannies step in, cutting power in a desperate attempt to save your engine from self-destruction due to high oil temperatures? Yeah, me too.

Enter the dark art of oil temperature management—by installing an OEM 135i oil cooler onto my humble N52-powered 128i.

Why Bother?

The USDM 128i doesn’t come with any oil cooling from the factory. For daily driving, the naturally aspirated N51/N52 doesn’t really need one. But take it to the track, and depending on the layout, weather conditions, and your driving style, oil temperatures can quickly climb to levels that not only stress the engine but also trigger the DME to cut power—effectively turning your E8x/E9x into a one-lap wonder. Not exactly my idea of a good time.

Now, I know there are some of you out there who can run extended sessions in an N52 without issue. But here in Colorado (read: high elevation), oil temps tend to run hotter than they do at sea level. So, before taking my E82 on its maiden voyage at High Plains Raceway, I figured I’d be proactive.

Cooling Options

While plenty of aftermarket solutions exist, I prefer using OEM parts developed by BMW. Fortunately, there are a couple of factory-style options for the N5x engines:

• Water-to-Oil Heat Exchanger – Some N52-powered models came equipped with a factory heat exchanger that’s relatively easy to retrofit. While it does offer a small cooling effect, it primarily uses coolant to help regulate oil temperature—hence why some people call it an "oil warmer." It helps warm up the oil more quickly on cold starts, but its cooling capacity is limited. If you don’t want to hunt through junkyards, FCP Euro sells a complete kit for this setup.

  
  

• Air-to-Oil Cooler – Due to the extra heat generated by forced induction, the turbocharged N54/N55 cars came with a true air-to-oil cooling system. The cooler is a separate unit mounted behind the front bumper on the passenger side. While installing this setup requires more effort, it offers greater cooling potential—perfect for high-performance applications.

  
  

Being an aggressive, ham-fisted driver at high elevation, I went with the air-to-oil setup from the N54/N55.

Junkyard Treasure Hunt

If you're feeling particularly spendy, you can buy all the necessary parts brand new. But, as we’ve established in previous posts, I’m a cheapskate who loves a good junkyard solution. So, after scouring local inventories, I found a wrecked 135i equipped with the OEM air-cooled setup. Excited, I grabbed my tools and rushed to the yard—only to find that the car had taken a hit on the front-right side, bending the oil cooler in the process.

The good news? While the oil cooler itself was beyond saving, I still walked away with the oil filter housing, oil lines, and mounting bracket—all for just $23! I’d call that a win.

For the oil cooler itself, I turned to eBay, where I found a used 135i oil cooler with the attached air scoop. But we weren’t out of the woods just yet—there were still a few more things I needed before ripping off the front bumper.

Parts List

• The oil cooler – Already in hand (via eBay). For E82/E88 models, BMW part number 17217564702.

• OEM air duct – Directs air from the front bumper to the oil cooler. BMW part number 51748046326. Thankfully, my eBay cooler came with the scoop.

• Mounting bushings (x2) – These metal bushings secure the oil cooler to the chassis. BMW part number 17217567089. Again, my eBay find saved me some cash by including them.

• Rubber grommets (x2) – Work with the metal bushings. BMW part number 17217567088. Fortunately, mine were included as well.

• Oil filter housing with oil line provisions – Scored from a junkyard.

• Oil cooler lines – Connect the oil filter housing to the oil cooler. These are pricey if you can't find them used. BMW part numbers 17227573273 and 17227573274.

  • You’ll also want the line mounting screws if you don’t already have bolts with the correct threading. BMW part number 17227555715.

• O-rings for oil cooler lines – If the lines are fully disconnected, you’ll need four. Since mine were still attached to the filter housing, I only bought two. Aftermarket options exist, but for that BMW logo, you’ll need part number 17228604345.

• Radiator support bracket – This holds the oil cooler upright. I pulled one from a junkyard, but if you need a new one, it’s BMW part number 51647154546.

• Plastic frame rail mount – Helps secure the oil cooler. BMW part number 17217540030.

• Oil pressure switch – Since the oil filter housing is already out, it’s a great time to replace this. I went with Rein part number 12618611273.

• Oil filter housing gasket – BMW part number 11428637821.

• Oil filter housing bolts – The old bolts are technically single-use, so it’s best to replace them. There are three different sizes:

  • 11427540759

  • 11427540763

  • 11427540758

• Oil cooler vent – To properly vent air, you can either cut a hole in your stock fender liner and install an OEM vent (BMW part number 51747194460) or swap to a full 135i fender liner. I originally ordered the vent but later found a torn fender liner and sourced a full 135i replacement from eBay. More on that later.

• Oil change supplies – Since the oil filter housing is coming off, you might as well do an oil change. Grab an oil filter kit and 6.9 quarts  (plus about an additional 0.5 quarts for your new oil cooler, for a total of about 7.4 quarts) of your preferred oil.

• "Mickey Mouse" flange replacement – One of the oil filter housing bolts is blocked by this coolant flange, and they often snap during removal. You can replace the full hose or just upgrade to a metal flange. I went with the Rein CHC0609 aluminum flange.

• Coolant – You’ll lose some coolant during the install, so have extra on hand to top off the system.

It should be noted that most of the above-listed part numbers are geared towards the E82/E88 chassis. Many (most?) of them are likely applicable for the E9x cars as well, but if you have an E9x, you should probably verify fitment before you hit the "Order Now" button.

Wrapping Up the Collection of Parts

As you can see, if you can’t source most of these parts from a local junkyard, you’re about to go on one heck of a shopping spree. Even if you do track down most of what you need locally, you’ll still want to order a few (several?) of the items above before you’re ready to start wrenching.

Fortunately, I managed to track everything down and was finally ready to get this thing installed.

The first step is to jack up the car, drain the oil, and—depending on your approach—potentially drain the coolant (technically optional). You’ll also need to remove the front wheels and the front plastic underbody tray to access everything.

A Lesson in Cooling System Compatibility

Shortly after buying my 128i, I installed a CSF Racing radiator along with brand-new Gates hoses, which I documented in a previous blog post. However, I quickly ran into an issue—the Gates lower radiator hose didn’t play nice with the larger CSF radiator, leading to persistent leaks. Rather than dealing with constant headaches, I swapped back to the stock lower radiator hose, which solved the problem.

This experience taught me an important lesson: while Gates makes excellent OE parts for Japanese cars, when it comes to the E82, it's best to stick with German OE parts whenever possible. Lesson learned.

Since I already planned to drain the coolant for this job, I took the opportunity to replace one of the last original radiator hoses I hadn’t yet swapped out. I ordered a brand-new OE Rein lower radiator hose for peace of mind—figuring it was worth doing “while I was in there.” As a result, I fully drained the coolant before continuing.

Do Your Homework Before Wrenching

Before diving into this long and arduous install, I highly recommend watching a few YouTube walkthroughs to get a feel for what you’re getting into. Surprisingly, there aren’t as many detailed guides as I expected, but the best resource I found was from 50sKid.

Technically, he’s installing an OEM oil cooler onto an E9x N54-powered 335i, but since these cars share so many similarities, most of his guide applies to the E82 as well. You can find the video walkthrough here.

A Small, but Helpful Recommendation Before diving into the madness of disassembly, I recommend grabbing a Sharpie and a good number of small Ziploc baggies. You’ll be removing a lot of parts—probably more than you’d expect for what seemed like a simple job. Trust me, it’ll make reassembly a lot easier later if you keep all the bolts and screws in labeled bags to avoid any confusion. Fender Liner Swap

Next, I removed the stock fender liners, which are held in place by a mix of 8mm bolts and a 10mm plastic nut. As you can see, my passenger-side fender liner looks like it lost a fight with a rabid wolverine. Rather than cutting a hole in it to mount the oil cooler vent, I decided to just buy a vented 135i fender liner from eBay.

To give you a better idea of where you’d normally cut the stock fender liner (there's technically an outline they mapped out for you from the factory), here’s a side-by-side comparison—my stock 128i fender liner next to a 135i fender liner that already has the oil cooler vent installed.

Before removing the front bumper, there are a few components you’ll need to disconnect behind the bumper cover.

A quick note—my 2008 128i has fixed-position headlight sprayers mounted directly to the bumper cover. Some E82 models come with mechanical sprayers that extend from the bumper, but I have no firsthand experience with those. If your car has them, you may need to remove or disconnect them before taking off the bumper. In my case, I simply left mine attached to the bumper cover.

However, you will need to disconnect the windshield washer hose that connects to the back of the sprayers. Fortunately, this is an easy step—the hoses are secured with bright blue plastic C-clamps, which come off with ease.

You’ll also need to disconnect the fog light wiring harness from the fog lights.

The bumper cover itself isn’t too difficult to remove. There are two 8mm screws (one on each side) inside the fenders that secure the bumper in place. In this photo, you can see the 8mm screw still in place, hiding in the shadows.

There are four T30 Torx bolts securing the bumper cover just below the hood, all in plain sight. You’ll need to remove all four to detach the bumper.

Right below the T30 bolts mentioned above, there’s a strip of rubber weather stripping that needs to be removed. It comes off easily.

At this point, the only thing still holding the bumper cover onto the car is a pair of tabs—one on each side—located near the fender well. Use a plastic pry tool to gently separate the plastic "sandwich" and carefully release the bumper tabs. Take your time to avoid damaging them, as you’ll need them intact for reinstallation later.

You’re now ready to remove the front bumper cover. Be careful, as the headlight sprayers are still connected to the back of the bumper and can easily get caught on the bumper beam. With a bit of wiggling and adjustment, the bumper cover should come right off.

We’re going to completely ignore my chaotic streak that kicked in and led me to jump around during this install more than I should’ve. If I were a wiser man, the next step would’ve been to remove the headlights and headlight mounting brackets. If you’re familiar with the term “fiddly bits,” you’ll quickly understand the frustration of how these headlights are mounted. I swear BMW designs this stuff to drive their techs to the brink of madness.

First things first, it’s a good idea to disconnect the wiring harness from the rear of the headlights.

Now, it’s time to solve the puzzle of how to remove the headlights from the car. While it isn’t overly difficult, it did leave me scratching my head a few times, leading me to believe BMW wanted to give your puzzle-solving brain a bit of a workout—at least a light stretch.

You cannot remove the headlights without removing them as somewhat of a full assembly with the mounting brackets—at least, that’s what I found. There’s an 8mm screw holding the rear portion of each mounting bracket to the fender that needs to be removed.

Next, there are two T30 Torx bolts securing the mounting brackets to a part of the bumper beam assembly, just behind the bumper beam itself. The top T30 bolt is easy to access, but the bottom T30 bolt requires a bit of creativity due to tight space (it’s only a couple of inches behind the bumper beam). I had to use a very small 1/4-inch driver with a tiny T30 head that barely fit in the gap. A T30 Allen/L-key wrench or a short T30 socket might’ve made this a bit easier to access.

There’s also a single long 10mm bolt holding each headlight to the car that you’ll need to remove.

Additionally, there are several T30 Torx bolts holding either the headlight to the car or the headlight to the mounting bracket. I believe there are four of these per headlight, but don't quote me on that.

Once everything is disconnected, you can remove the headlights and mounting brackets as one assembly.

After removal, the newly found open space should look like this:

The front of the car with both headlights removed:

Next, you’ll need to remove the bumper beam, which is secured to the car with four nuts that bolt it to the frame rails on each side. All eight of these nuts (four on each side) are fairly easy to access and remove.

However, before you tackle the bumper beam, make sure to remove the two air scoops that feed into your stock air intake. These are held in place by four T20 Torx screws securing them to the inner air scoop. Once those screws are removed, the scoops literally slide right out with ease.

Before pulling on the bumper beam, be sure to inspect it for any wires or hoses connected to it. Most are secured by tabs that should come off without much effort, but it’s crucial to disconnect them first. You don’t want to rip anything out of place by going all Hulk smash on it.

Once the hoses and lines are disconnected, the bumper beam will slide off with little resistance.

At this point, you might be asking yourself: Why on earth have I torn apart the entire front end of my car just for a simple oil cooler install? What kind of madness is this? Good question. You’ve gone through all this disassembly just to replace a small stock radiator support bracket with a very similar OEM bracket, which has a couple of mounting bolts to hang your new OEM oil cooler.

Before removing the old bracket, you’ll want to use a jack or something similar to support the right/passenger side of your radiator.

Now simply slide the old radiator support bracket off.

Replace it with your new bracket. Note that the two brackets look very similar, with the main difference being that the new one has two studs sticking out to the side, specifically for mounting the oil cooler.

The radiator support bracket isn’t the only mount for the OEM oil cooler. Remember that plastic frame rail mount I mentioned earlier in the parts list? That will also need to be installed.

If you look just behind the radiator support bracket in the photo above, you’ll see a hole in the frame rail that was drilled at the factory. That photo was taken after I removed the factory sticker that covers it. Here’s a photo of what that hole looks like when it’s still covered by the factory sticker.

Just peel back the sticker to reveal the hole we'll need to use.

There’s also a plastic tab covering the smaller hole next to it, which we'll need to pop out as well.

Once those two holes are exposed, you can insert the plastic frame rail mount mentioned earlier.

Installing the plastic frame rail mount can be tricky. Here’s a photo showing what it should look like once installed. Note that both uncovered holes are now filled:

• The left hole has an encapsulated nut for a mounting bolt.

• The smaller hole on the right is now filled with a smaller plastic insert that will house the guide for the OEM oil cooler.

To install the plastic frame rail mount, insert the end with the "arm" into the hole. Use a pair of pliers or a similar tool to rotate it until the small circular plastic "hole" (at the end of the arm) fills the small square hole in the frame rail, as shown above. Into the Engine Bay We Go

It’s time to head back into the engine bay. To start, I probably did a bunch of work that wasn’t strictly necessary: I removed the cabin air filter and rear cowling to take off the OEM plastic engine cover. I thought removing the engine cover would give me some extra space to work around the oil filter housing. It did help a bit, but if I were to do this job again, I’m not sure I’d bother removing the engine cover.

Next, I moved on to removing the parts that are absolutely necessary: the intake/airbox (since I have the OEM Euro airbox, I find it’s easiest to remove the intake elbow from the throttle body), the air intake scoop, and the radiator fan.

Since the oil and coolant were already drained, I was able to remove the plastic oil filter cover and the upper radiator hose with minimal spillage.

To access the lower oil filter housing bolt, I then had to remove the "Mickey Mouse" hose/flange.

Before removing the "Mickey Mouse" hose, I placed some aluminum foil underneath the outlet to catch any coolant that might spill out.

You’ve all heard about this hose’s tendency to disintegrate with little to no help, and its reputation for tearing itself apart during removal, right? Well, guess what happened when I removed it?

Just as the internet had warned me, despite gently prying it out, part of the plastic hose flange still broke off.

If this happens to you, make sure to remove any remaining plastic debris from inside the housing before proceeding.

I fiddled with the metal band securing the plastic flange to the hose for a few minutes before finally giving up and reaching for my trusty hose cutters.

I’m sure there’s some fancy German tool designed to remove that metal band in seconds, but at this point, I couldn’t be bothered. And honestly, I love this hose-cutting tool, even if I don’t get to use it very often.

I then installed the fancy aluminum Rein "Mickey Mouse" flange, secured it with the supplied springy metal hose clamp, and—voilà—we were back in business in no time.

Don't forget to clean the mating surface and housing area before reinstalling your sweet new metal-flanged hose. Onto the Oil Filter Housing

With the "Mickey Mouse" hose out of the way, you now have access to all three bolts needed to remove the oil filter housing.

All three bolts are E10 E-Torx, but they come in different lengths. While it’s fairly easy to see where each one goes, it’s still a good idea to keep track of them to avoid any mix-ups.

One of the E10 bolts is tucked underneath the intake manifold. Now, if you’re a masochist, feel free to remove the entire manifold—but you can save yourself a ton of trouble by simply ordering an E10 swivel socket to access it with ease.

Before removing the oil filter housing, you'll also need to disconnect the wiring harness for the oil pressure switch, which is located in the photo above. Once the three bolts and the wiring harness for the oil pressure switch are removed, the oil filter housing should slide off with ease.

Before moving forward, make sure to clean the mating surface where the new oil filter housing will sit, and install a new oil filter housing gasket.

Now you can install your new OEM oil filter housing (with provisions for the oil lines needed for the new oil cooler). It will sit in the exact same position as the old one. Torque the new oil filter housing bolts to 22 Nm.

Next, you can reinstall the "Mickey Mouse" hose. Torque the small bolts to 10 Nm.

If your housing didn’t come with the oil cooler lines already attached (mine did), now is a good time to install them. Just be sure to use new O-rings to prevent leaks. Let's Install the Actual Oil Cooler

And now… it’s time to actually install the oil cooler we’ve been ripping everything apart to put in place.

It should mount easily, except for one small hurdle: the hard metal oil lines attached to the cooler come into contact with my car’s aluminum A/C lines. And I happen to like my A/C. So, being the determined DIYer I am, I did what anyone would do—I activated my inner Hulk and started bending my A/C lines.

As it turns out, I bent a bit too hard in too many directions… and the next thing I knew, R-134a was spraying all over me like a soda can that’s been shaken too much! At that moment, I regretted topping off the A/C system with that can of bright green fluorescent dye a couple of summers ago when I was looking for a leak (spoiler alert: it was only leaking from the Schrader valve).

Yes, the engine bay and I were now covered in bright green. It would’ve been even more comical in a black light.

Now, I could’ve just replaced the line later and soldiered on, but since everything was already torn apart and easily accessible, I decided to take a break, scour eBay for a replacement hose, and regroup at a later date.

Off to eBay I went, where I found a replacement A/C hose that appeared to be in good shape for only $20 shipped. I also ordered a couple of replacement O-rings to help avoid any leaks.

A few days later, I had an unbroken hose in hand and was ready to get back to work.

I did notice a stark difference in the way this new-to-me hose was bent compared to my stock A/C hose.

I tried to be gentle with this new-to-me A/C hose to avoid running into the same issue and having to order yet another unexpected hose. Once I bent it as far as I was comfortable, I was able to install the new oil cooler—but the lines were basically touching each other.

Finally, the oil cooler was mounted in the car.

To prevent the lines from making metal-on-metal contact, I used a bit of self-adhesive high temperature resistant silicone rescue tape.

Around this time, I installed a new oil filter and filled the engine with oil. Before installing the oil lines into the oil cooler, I filled it with oil as well. Expect to make a bit of a mess as the oil cooler slowly "burps" itself. After that, I installed new O-rings on the flexible oil lines and attached/bolted them to the cooler’s hard lines.

You’re now free to reinstall the bumper beam and the headlights/mounts, following the same procedure you used to remove them. Don’t forget to reattach the lines/wires to the bumper beam, especially the headlight sprayer hose.

Bumper Cover Modification

Before reattaching the bumper cover, you might want to modify it to allow air to flow to your new oil cooler, depending on your bumper cover/trim and options. In my case, the lower right bumper cover opening was covered by a fog light and a fog light mount—both of which were easily removed.

I then used aluminum radiator grill mesh and some black copper wire (the kind used for making jewelry) to attach the mesh to the back side of the bumper cover. I simply drilled a few small holes into the back of the bumper cover and ran the copper wire through to secure it. Both were ordered off of Amazon.

It’s not the prettiest or most professional thing I’ve ever done, but from the front, it doesn’t look terrible.

Eventually, the little E82 will likely get a sportier bumper with a more open design, but for now, this setup will do just fine.

With that done, it was time to reinstall the front bumper cover, fender liners, front wheels, radiator fan, and air intake setup. At this point, the engine bay still looked OEM, because, well, it is.

Since you've introduced air into the system, now is a good time to perform the automated bleeding procedure, which is fairly simple:

• Make sure your car has a strong, fully charged battery. It’s a good idea to keep it hooked up to a charger during this process.

• Insert the key and turn it to the “On” position without starting the engine.

• Set the heat to its highest setting (my E82 maxes out at 84°F) but keep the fan at its lowest setting.

• Press and hold the throttle pedal for about 10 seconds. The factory bleeding procedure should now begin, and you should hear the water pump circulating coolant through the system.

This process takes about 8 to 12 minutes. During this time, it's a good idea to check for leaks.

Once the bleeding procedure is complete, check the coolant level, as it will likely have dropped slightly.

Final Checks Before Startup

Double-check everything—make sure the car is filled with oil, all hoses are tight, and all connections are secure.

Now, you’re ready to start the car. Fingers crossed!

Fortunately for me, everything worked perfectly. One note: you will get a dash warning about the removed fog lights, but this can apparently be coded out. As it turns out, a lot of things can be coded out… but we’ll save that for another blog.

I took the car for a test drive, and everything seemed to be working as designed (minus the A/C, which I later had refilled without issue). Back in the garage, I did a thorough leak check—and eureka, no leaks!

To be extra cautious, I left the underbelly pan off overnight so I could check the garage floor in the morning for any signs of leaks. Another victory—still no leaks! After confirming everything was dry, I reinstalled the underbelly cover.

Post-Install Coolant Check

Keep in mind that after driving the car a few times, your coolant level may drop slightly when checked in the morning (after the engine has cooled overnight). This is normal—just top it off, and it should stabilize after a few heat cycles. Did that entire process feel like a tedious, time-stealing extravaganza that seems wildly excessive for simply adding an oil cooler? Well, that’s because it is.

Nothing about this job is technically difficult, but it’s incredibly involved and time-consuming. Depending on your speed and experience level, I’d recommend setting aside a full day or two to get it done.

Now, I’m sure there’s someone out there saying, “Dude, I could knock this install out in two hours, blindfolded.” To that guy, I say: hats off to you, sir. For the rest of us, plan on a solid day or two.

Now that the oil cooler and oil pan baffle are installed, I can hear High Plains Raceway calling my name! But first, we need to address these brakes… and a little (okay, a lot more) grip never hurt anyone.

Stay tuned for the next stage of Project 128i—before it hits the track… and maybe dodges a few cones along the way.