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      12-03-2010, 11:40 AM   #1
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Drives: 4 Wheels
Join Date: Aug 2007
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STETT Performance Stage 2 Oil Cooler Kit w/ 180F Thermostat **EXTENSIVE REVIEW/DIY**

As I have continued to modify and improve my BMW, I have constantly tried to address weaknesses inherent to our platform. One of the very well known weaknesses on the N54 is the high oil temperatures. Sadly, the N54 and high oil temperatures go hand in hand. Upgrading the oil cooler has been a must on my list for a long time, but obviously I haven’t completed the mod until now. To be completely honest, I have really struggled to find the right solution for my needs. I wanted a stock core upgrade, oil line upgrade, and a kit that upgraded the stock thermostat. One of the biggest hurdles in my opinion has been the 230-235F thermostat that regulates when the N54 will use is oil cooler. Basically, the stock thermostat means your oil cooler is worthless until the temperature goes over 230-235F with no exception. Whether you have 1 or 50 oil coolers on the N54 they are worthless until you go over 230-235F and that really stinks. I think this has been one of the biggest reasons I have shelved upgrading my oil cooler... until now.

Recently I heard STETT Performance had an oil cooler they were bringing to the 135i/335i market and this caught my attention. I have had great success with STETT Performance in the past, so I contacted them for more info. What I found is that STETT has 2 stages of oil cooler kits that are designed around replacing the weak spots in the stock oil cooler. Both stages included a larger Setrab Oil Cooler, Setrab Oil cooler fittings, an optional thermostat, new braided high quality oil lines, diffuser plate, STETT adapter plate / thermostat delete, gasket, etc. After seeing pictures of the kit, I really decided this kit would help me address the high oil temps inherent on the N54 so I ordered the stage 2 kit.

In this review of the STETT Performance Stage 2 Oil Cooler Kit I will cover my experiences with STETT, quality of the parts, extensive details DIY'ing the install, and share the results / analysis of my testing.

Experience With STETT Performance & Detailed Pictures of the Kit

I seem to be saying this often, but my experiences with STETT Performance have been superb and I expected nothing less. From day 1, STETT was very responsive to my emails and questions. Chad Stett responded normally within a few hours of every email I sent. Chad's expertise was apparent every time we spoke and I feel lucky to have had the opportunity to tap into his wisdom. After ordering the kit, STETT emailed me the day that my package would be shipping and FedEx tracking info was active that same night. I was able to track the package to my house, so I could re-organize my schedule for the install. I should note a few parts changed along the way, so I waited until I got the finalized kit before completing the install and writing the review.

The STETT Oil Cooler Kit includes:
  • Setrab Oil Cooler Core (2 stage options)
  • Setrab Oil Fittings/Adapters
  • Lightweight Braided Oil Lines
  • STETT Performance CNC Cut Billet Aluminum Adapter Plate and Thermostat Delete
  • STETT Performance Diffuser Plate
  • STETT Performance Wrinkle Coated Oil Cooler Mounting Plate
  • STETT Performance Wrinkle Coated Spacer Plate
  • Mounting Hardware
  • BMW Gasket
  • -- Optional -- 180F Thermostat
  • -- Optional -- Oil Line Heat Shielding
When the STETT Performance Stage 2 Oil Cooler Kit arrived, it was very well packaged.

All items were protected by styrofoam peanuts and individually wrapped where necessary.

I removed all of the items from the box and got my first glimpse of each product. The Setrab core is just huge and the quality of each part is off the charts!

The STETT CNC laser cut billet aluminum adapter plate is an absolutely beautiful item.

BMW gaskets for the adapter plate.

The braided oil lines, Setrab fittings, and optional 180F thermostat.

You can get the oil lines in two different version. Since I added the thermostat after the initial order, STETT sent me a second set of oil lines with the agreement that I would return the original lines. It should be noted STETT Performance will cut oil lines if you order the optional thermostat or let you cut them to the length you want. I chose to have STETT cut them to the correct length and mount the fittings in-house. In the picture below, you can see the uncut oil lines on the right and the cut-to-length oil lines on the left.

The braided oil lines, Setrab fittings, and optional 180F thermostat.

The Setrab fittings and adapters are very nice!

The braided lightweight oil line is high quality.

Optional heat shielding for the oil lines. I chose not to use them since the braided lines look so good. Haha!

STETT Performance Diffuser to channel air to the oil cooler core. This item has the distinctive STETT powder coating I love!

STETT Performance oil cooler mounting plate and spacer. Notice the beautiful laser cut logos, CNC cut plates, and wrinkle coating.

Now onto the big boy... the stage 2 Setrab oil cooler. It is a BIG.

It is 11" wide and 10" tall.

The STETT stage 2 oil cooler kit is absolutely top shelf in every way. Honestly, I don't think they cut a single corner on the kit. I am absolutely very happy with it!


DISCLAIMER: You work on your car at your own risk and take full responsibility for any damage caused to your vehicle. Please understand you can injure yourself or kill yourself if you do not take proper precautions when working on your vehicle. Please use extreme caution when working underneath your car. Allow your oil to cool before working on your car. This DIY is simply an example of the way I installed the STETT Performance Stage 2 Oil Cooler Kit on my own vehicle.

STETT Performance does include instructions with the kit that you download as a PDF. The instructions were decent, but I think could have been better, so I will supplement them and go through the entire install. Basically if you could install an intercooler, then you can install an oil cooler. I will say it is not for everyone to DIY, but since I consider this only a moderate level install, I will cover the entire install. This will be a long DIY with 63 pictures to aid your efforts. I will attempt to be very thorough.

Standard tools are required for this install. If you are metric, some larger box wrenches up to 27 mm will help. AN tools are also handy to tighten the Setrab fittings, but not necessary. Before you start the install, I would go to your local Lowe's or Home Depot to pick up some painter's drop cloths and have a supply of rags on hand.

You should also have an oil catch container.

The installation begins with some small prep work. You will need to remove the splash shield under the car and the passenger side fender well. There are a number of DIYs covering this, so I will defer to them. Here they are removed from the car.

This will expose the stock oil cooler. In case you didn't know, the stock oil cooler sits inside the bumper on the passenger side of the car near the fender well.

Next you will need to remove the front bumper. Again, with plenty of DIYs on the front bumper removal, I will defer to them. This will expose everything you need to jump into this install.

I started the project by removing the brake duct and oil cool plumbing on the passenger side of the car.

There are a couple of obvious bolts to remove so you can remove the ducting.

After removing the bolts, take the duct work out and set it aside. You will not re-use this.

This is really the only prep work that needs to be done prior to removing the crash bar on the front of the car. This is the big black metal bumper that you exposed when you removed the bumper skin. To start the process of removing the crash bar, you will remove the wire from the snaps on the top of the crash bar. This is for the ambient temperature sensor.

Next, you will remove the torx screw that holds the re-inforcing vertical bar.

From here, you need to unscrew, unplug, and remove the horns on either side of your crash bumper. They are held on by a single nut. Set them aside as you will re-install them later.

Now we are ready to remove the front bumper. Each model year BMW appears to be different. Some have a rivet in additional to nuts/bolts holding on the front bumper. My car had the rivets, so I drilled them off first. Use a 3/16" drill bit and just drill the rivet head off on both driver's side and passenger side of crash bar.

Two nuts hold the top and two nuts hold the bottom of the crash bar. This is the same on the driver's and passenger side of the car.

I would keep one nut loosely attached to the crash bar so you can brace it as you get ready to remove it. When you are ready, simply pull the bar out of the car and set it aside.

If you did have the rivots, just pop the rest of the rivot out of the crash bar mounting area now with a small phillips screw driver.

This basically covers the work necessary to get to the install and fully exposes the stock oil cooler.

From here we will move onto the process of removing the stock oil cooler and lines. The stock oil cooler is sealed, so it will not leak. Let's unbolt the stock oil cooler which is held in place with 2 bolts on the driver's side and 2 bolts on the passenger side.

Leave the oil cooler hanging and now we need to prep the engine bay so we don't get oil everywhere. Grab your rags and drop cloth you bought earlier. This will make things a LOT cleaner and easy to clean up after.

You just want to cover everything other than the oil filter adapter and oil lines, so the oil will not get all over your engine bay when you remove the stock oil cooler.

Place the oil catch container under the part you are working on to catch the oil as it leaks out. First we are going to remove the stock oil cooler itself, so place the oil catch can under the lines shown below. Remove the single bolt and slide the hoses apart then remove the oil cooler. It is normal for to leak oil out of the lines.

Place the stock oil cooler and lines in the oil catch container for a while to drain them. Now let’s move over to the oil adapter/thermostat area. We will first remove the remainder of the oil lines. Again, slide the oil catch can under the area you are working on. These lines are held on by a single bolt under the thermostat housing.

Finally, we will remove the thermostat housing. It is held on by three torx screws as shown below. Remove the torx screws and take off the thermostat housing.

Remove the gasket from the housing and replace it with the new one from the STETT kit.

Clean things out as necessary and prep the housing for the install of the STETT adapter plate / thermostat delete. The STETT part re-uses the stock bolts. Just line it up and tighten it down.

If you bought the 180F thermostat then now is a good time to install it. I mounted mine by the vacuum canisters because it was inline with the hoses and looked OEM. If you choose this route, simple remove the frame that holds the vacuum canisters. It is held on by one bolt and two nuts.

Now lift out the frame and canisters so you can trace and drill the mounting holes.

Drill two 5/8" holes in the canister framing to mount the thermostat bracket on. Once you verify the holes are large enough for the bolts, mount the bracket. A step drill bit can be really helpful as you slowly increase the diameter of the drilled holes.

We will now prep the oil cooler for mounting and test fit it. Attach the oil cooler to the STETT mounting plate using the supplied hardware.

In case you were curious about the size difference between the STETT Performance stage 2 oil cooler and stock, well here you go. The STETT is huge! To be honest, it is almost funny how much larger it is than the stock oil cooler.

With the oil cooler mounted to the bracket, test fit it by placing it on the 4 studs on the passenger side where the crash bumper was mounted. I found interference with a small bracket and removed it to clear the oil cooler. The small bracket can be seen below as indicated by the red arrow. It is held on by a torx bolt shown by the blue arrow.

I just removed the small bracket and replaced the bolt. Again, test fit the mounting bracket and you should have no clearance issues now. If you have eliminated all clearance issues, then move forward.

I would run your oil lines at this point, but don't tighten the fittings yet. A few things to note. Make sure you follow the orientation suggested in the oil thermostat paperwork... the supply side of the thermostat (spring) on top and the return side of the thermostat (bar) on bottom. The supply side of the STETT adapter plate is the passenger side and the return side is the driver's side of the STETT adapter plate. Attach the lines from the thermostat and route them through the fender well to where you will mount the oil cooler. Leave the lines hanging and protected from debris.

With everything ready to go, it is time to fill the oil cooler with oil. As easy as this sounds, you should be precise here. If air bubbles get trapped in the oil cooler it can cause some oil pressure issues. The standard way to fill an oil cooler is with openings facing up or vertical. This means air bubbles can easily escape. I filled the cooler to the top then connected the oil lines to the cooler. Setrab recommends using oil on the rubber gaskets on the fittings and grease on the threads.

Now it is really time to start to button things up. Mount the oil cooler on the 4 studs where the crash bumper mounts up to on the passenger side. Mount the STETT spacer plate on the 4 studs on the driver's side where the crash bumper mounts. Reinstall the crash bumper, horns, and wire for your ambient temperature sensor. Leave the nuts loose for now on the crash bumper.

Before final fitment, we need to mount the diffuser to route the air to the oil cooler. When lining up the diffuser, I had a clearance issue with a small bracket near the oil cooler as shown below.

I used my dremmel and simply sanded the interfering part off.

Next, I lined up the holes in the diffuser and drilled small holes to mount it in the plastic frame on the side of the intercooler. Once drilled, I installed the diffuser plate using the sheet metal screws included.

Now it is time to really button things up. I would lift up on the outside of the oil cooler to ensure it is as vertical as possible and tighten down the crash bumper nuts. That should lock the oil cooler in place. Route your oil line and tuck excess above the oil cooler itself.

This is a good time to torque all the fittings down. You will need a 23mm and 27 mm box wrench to tighten things down. I used painter's tape to protect the fittings during the torquing process.

After the fittings are tight, remove the painters tape and mount thermostat in the bracket. Everything should look very clean and tidy at this point.

Now we are in the final stages of the installation. Test fit your bumper to assure clearance as it will be tight on the stage 2 kit.

If your bumper fits with no clearance issues, then bolt it back up. Don't forget to reconnect the fogs and TPMS on the driver side. You will need to relocate the TPMS on the passenger side.

Relocating the TPMS on the passenger side is a piece of cake. Just pull the tabs out, drill new holes above the stock oil cooler vent on the fender liner, and re-secure the tabs.

The last step in this process is cutting a large exit for the air to leave your fender after passing through the oil cooler. A dremel with cutting wheel works beautifully here. Just put the fender up to the oil cooler, trace the opening and trim away. Since the stock oil cooler vent lines up well, I just extended opening itself.

I shaved the back of the stock oil cooler vent as well to assure no clearance issues.

Finally, I used some weather strip from Pep Boys to keep it clean looking.

Now re-install the fender liner and connect the TMPS. Again, here is what the final product looks like from above and when looking at the front bumper.

This is not a novice install, but I do not think this is an expert install by any means or I would not DIY the process. If you are comfortable installing a methanol kit or intercooler, then this is well within your skill level. The STETT kit is built very, very well and installs very easily.

Results & Analysis

Quality and well fitting parts are great, but the bottom line is they must perform or they have no place on my car. When I decided to get this oil cooler, I knew I wanted to log performance gains on my car. I set out to get a baseline standard data set from the stock oil cooler that I could compare with the new STETT Performance stage 2 oil cooler kit. All of the data was taken under the following conditions:
  • A/C and heat were turned off during all runs.
  • Max boost was set to 16 psi for all runs.
  • JB3/4 tune was used during all testing.
  • Water/Methanol kit was not used at all during any of the testing to normalize the data.
I do want to give a huge thanks to Terry at BMS. The new JB4 now uses CAN data which means the BT cannot log while the JB4 is intercepting CAN data. Terry was able to quickly allow me to log the oil temperatures using the JB4 so I could complete the testing. Terry has been so helpful in every review I have written and this was no exception.

The initial testing on the stock oil cooler was with 78F ambient temperatures over a specific course. What I did not expect was the temperatures would not get close to that number in my area after the STETT oil cooler install. That leaves quite a dilemma for me unfortunately. I could repeat the exact course again without a problem, but to do a true comparison I need to have the same ambient temperature or I will be the first to admit that it has bias and is not a completely fair comparison. Again, the bad news is that I will not be near the initial 78F ambient for the short term foreseeable future so I had to complete the testing on at 40F ambient. I decided it was still worth completing the testing with the known bias and promise as soon as that ambient is 78F to repeat the testing.

My hope is this data sheds light on how the stock oil cooler performs and how the STETT stage 2 oil cooler compares.

The testing procedure was as followed on both the stock oil cooler and STETT stage 2 oil cooler kit:
  • 19 minute warm-up
  • First 6 minute hard spirited run
  • Second 6 minute hard spirited run
  • 10 minute highway roll
  • 12 minute normal driving
Stock Oil Cooler Testing
The stock oil cooler testing was done on a day where the ambient temperature was 78F.

19 minute warm-up with stock oil cooler

This simply gives a comparison for us to estimate how fast the car will warm up with the STETT stage 2 oil cooler with 180F thermostat. You can see how the car rapidly approaches the 230-235F thermostat temperature at about 19 minutes then levels off. It will be interesting to see if the new oil cooler show a similar characteristic.

First 6 minute hard spirited run with stock oil cooler

As stated above, this run was a 6 minute hard, spirited, high rpm drive. You can see the oil temps on this run start around 234F… around where the stock thermostat allows oil to your stock oil cooler. Notice the long and high rpm pulls over and over. After 6 minutes of continued hard, spirited driving I was able to easily get an oil temperature of 262F. That is really disturbing that you can drive the oil temps so high so quickly even with an oil cooler on my car.

Second 6 minute hard spirited run with stock oil cooler

Again, this run was a 6 minute hard, high rpm drive conducted immediately following the first spirited run. I simply stopped, exported the log, and went in the opposite direction over the same course. During this run you can see the oil temps consistently hold around 248F to 255F. I think it is important to note that 255F+ oil temps are not difficult to get on a modded 335i. I am not sure about other guys, but I am not comfortable at all with how easy it is to get my oil temperatures so high. 260F is too hot in my opinion.

10 minute highway roll with stock oil cooler

This run was completed directly following the second 6 minute spirited run. I simply stopped, exported the log, and continued driving. You can see the 260F oil temperatures I started with sank quickly to near 245F after the spirited run then settle to about 240F. Nothing ground breaking here.

12 minute normal driving with stock oil cooler

This run was completed directly following the 10 minute highway roll. I simply stopped, exported the log, and continued driving. On this run, oil temperatures remain steady around 235 – 240F. Again, there is nothing ground breaking, but the data was worth collecting.
STETT Performance Stage 2 Oil Cooler with 180F Thermostat Testing
The testing with the STETT Performance stage 2 oil cooler kit was done on a day where the ambient temperature was 40F. The testing should be done on a day with identical ambient temperatures, but unfortunately that was not possible.

20 minute warm-up with STETT Performance Stage 2 Oil Cooler Kit

The same procedure of warming up my car was used here. No high rpm pulls and no boost. Notice the same exact shape of the curve as our stock oil cooler, except here it levels at the new thermostat temperature of 180F. In my opinion, this is a much better oil temperature to run.

First 6 minute hard spirited run with STETT Performance Stage 2 Oil Cooler Kit

This test again was done immediately following the warm-up procedure. Again this was sustained high rpm, spirited driving. The hottest I could get the oil temperature was 212F and that was really pushing the car as hard as I possibly could. That is nothing less than an enormous difference from the stock oil cooler. It is impossible to quantify exactly how much the colder ambient temperatures effected things, but I personally don’t think they can account for the 50F difference I saw. The thermostat opens faster on the STETT kit and you have a useful oil cooler now from 180F up.

Second 6 minute hard spirited run with STETT Performance Stage 2 Oil Cooler Kit

The testing again was done immediately following the first spirited run. I simply stopped, exported the log, and re-ran the exact same course. One thing I noticed is the car bled the heat off the oil much faster, but that is likely the much colder ambients biasing things a bit here. After 6 more minutes of very hard driving, I could not get the car over 210F. The STETT oil cooler here outperformed the stock oil cooler by nearly 45F.

12 minute highway roll with STETT Performance Stage 2 Oil Cooler Kit

This testing was done immediately following the second spirited run. Notice how the oil temperatures rapidly converge on the new 180F temperature on the STETT oil cooler. This is as expected, but nice to see how much cooler the car drives! The car is basically running with oil temperatures about 55F colder.

12 minute normal driving with STETT Performance Stage 2 Oil Cooler Kit

This testing was done immediately following the highway runs. The characteristics of the car remain the same as stock, but run about 50-55F colder. In my opinion, this is a very good thing.

A comparison between the STETT Performance Stage 2 Oil Cooler Kit and Stock Oil Cooler

This really has to be the money shot. It is known how easily the N54 can limp with hard pulls, especially when we are on the track due to high oil temperatures. The STETT kit is allowing you to start using your oil cooler at 180F instead of 230-235F. Under the hardest runs with the stock oil cooler, I hit around 262F but on the STETT oil cooler kit I hit 212F. Again, it is impossible to quantify the exact difference the ambient made, but I think it is safe to say the STETT kit is huge improvement over the stock oil cooler! There is a difference of 50F on my oil temperatures after installing the STETT kit.


STETT Performance really has been a rock of consistency for me in the entire time that I have owned my BMW. Their communication was superb. Chad Stett offered his expertise on numerous occasions and helped with any install questions I had. The package was well protected and shipped with prompt tracking info. The STETT Performance Stage 2 Oil Cooler Kit is simply a superb quality kit. From the CNC cut adapter plate, to the lines, to the mounting brackets, to the core… this kit is absolutely top shelf.

With the STETT stage 2 oil cooler kit and 180F thermostat, the car simply ran cooler. My car warmed up to operating temperature in nearly the same time as the stock oil cooler, my car ran cooler at highway speeds, and my car ran cooler in normal traffic. In the most important spirited runs, the car ran an incredible 50F colder. It is impossible to say how much the different ambient temperature affected things and more testing will be needed when the weather allows. In theory, 40F colder ambients will not create 40F colder oil temperatures, so we know a big portion of the improvement must be attributed to the kit.

I think STETT approached improving the oil cooler on the N54 the right way… a stock core upgrade, better oil lines, better hardware, and a lower temperature thermostat. I couldn’t be more pleased with what I got from STETT Performance. I have said this before and I will say it again, I would not hesitate for a second to purchase from STETT Performance again.