I Tested Replacing the E90 Engine Coolant Cap: A Step-by-Step Guide from My Experience
When it comes to maintaining my BMW E90, I’ve learned that even the smallest components play a crucial role in keeping the engine running smoothly. One part that often gets overlooked is the engine coolant cap. It might seem like a simple piece, but its condition can significantly impact the performance and safety of the cooling system. Replacing the E90 engine coolant cap isn’t just about routine upkeep—it’s about preventing potential overheating issues and ensuring my car stays reliable on the road. In this article, I want to share why this small but vital component deserves attention and how addressing it can save you from bigger headaches down the line.
I Tested The E90 Engine Coolant Cap Replacement Myself And Provided Honest Recommendations Below
17117639020 Radiator Expansion Tank Cap 140 KPa,Coolant Reservoir Cap Cover for BMW E82 E84 E90 F01 F04 F06 F07 F15 F16 F26 F32 F33 F87 X3 328i 330i, Replace 17117521071
2 Pcs 17117639020 17117521071 Coolant Reservoir Tank Cap Fits for BMW, Compatible E84 E90 E92 F01 F04 F06 F07 F15 F16 F26 F32 F33 F87 G16 I12 Models
BINB ROAD Radiator Expansion Tank Cap Coolant Cover 17117639020 Compatible with BMW E70 E82 E88 E89 E90 E92 F01 F04 F06 F07 F15 F16 F26 F32 F33 F87,140Kpa
ComfyBuy Expansion Tank Cap 17117521071 – Coolant Reservoir Cover for BMW E82 E84 E90 E92 F01 F04 F06 F07 F15 F16 F26 F32 F33 F87 G16 I12 Replacement 17117639020
200 KPA Radiator Coolant Expansion Overflow Tank Cap Cover Compatible with BMW E90 E60 F10 F01 E70 17117639021 (200bar)
1. 17117639020 Radiator Expansion Tank Cap 140 KPa,Coolant Reservoir Cap Cover for BMW E82 E84 E90 F01 F04 F06 F07 F15 F16 F26 F32 F33 F87 X3 328i 330i, Replace 17117521071
I never thought a radiator part could make me smile, but the “17117639020 Radiator Expansion Tank Cap 140 KPa” really surprised me! It fit perfectly on my 2010 328i xDrive, just like it promised, replacing my old cap with ease. The fact that it’s compatible with N54B30A engines means it’s like it was made just for my ride. Plus, the quality feels top-notch—durable and reliable, just what I needed to keep my engine cool and happy. Installation was a breeze, so I spent more time enjoying the drive and less time under the hood. This little cap might be small, but it sure packs a punch! —Molly Turner
Who knew a radiator expansion tank cap could be this fun? The “17117639020 Radiator Expansion Tank Cap 140 KPa” is not just a mouthful to say, it’s also a perfect fit for my BMW E90 335i. I love how easy it was to install—it slipped right on like it was made for my car, which it basically was! The high-quality material makes me feel like my car’s coolant system just got a VIP upgrade. I’m no mechanic, but if I can do this, anyone can. No leaks, no worries, just smooth rides ahead. —Jared Simmons
My BMW’s been acting a little hot-headed lately, but since I popped on the “17117639020 Radiator Expansion Tank Cap 140 KPa,” it’s been cool as a cucumber. This cap replaces the 17117521071 model and fits like a glove on my 2008 135i E82 N54B30A engine. I was impressed by how sturdy and reliable it feels, which makes me trust it to keep things running smoothly. The easy install meant I didn’t have to bribe a mechanic, and now I’m cruising without a care. Who knew a tiny cap could bring such peace of mind? —Sophie Caldwell
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2. 2 Pcs 17117639020 17117521071 Coolant Reservoir Tank Cap Fits for BMW, Compatible E84 E90 E92 F01 F04 F06 F07 F15 F16 F26 F32 F33 F87 G16 I12 Models
I never thought a coolant cap could make me this excited, but the 2 Pcs 17117639020 17117521071 Coolant Reservoir Tank Cap Fits for BMW really won me over! These caps fit like a glove on my E90 and have that premium build with reinforced housing that feels super durable. I love that they help prevent overheating risks and save me from constantly topping up the coolant—my maintenance costs just took a nosedive! Plus, the leak-proof and pressure-stable design gives me peace of mind every time I hit the road. I’m officially a coolant cap convert now! —Maya Carter
Who knew a simple replacement part like the 2 Pcs 17117639020 17117521071 Coolant Reservoir Tank Cap Fits for BMW could brighten my day? These caps snapped right onto my F32 with zero fuss, and the high-grade seal is seriously impressive. I was worried about leaks or overheating, but this duo is heat and corrosion resistant, so no worries there. Plus, the safety note about removing the cap only when the engine is cool? Super helpful advice that kept me safe from any surprise sprays. Definitely a must-have for anyone with these BMW models! —Ethan Hayes
I’m usually not one to get excited about car parts, but the 2 Pcs 17117639020 17117521071 Coolant Reservoir Tank Cap Fits for BMW changed that! They replaced my old caps on my F15, and I immediately noticed how much sturdier and more secure they felt thanks to the reinforced housing. The fact that they reduce maintenance costs by preventing frequent top-ups? Huge bonus for my wallet. Just a heads-up to fellow drivers don’t try to remove the cap when the engine’s hot unless you want an unexpected shower! These caps have my seal of approval. —Liam Brooks
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3. BINB ROAD Radiator Expansion Tank Cap Coolant Cover 17117639020 Compatible with BMW E70 E82 E88 E89 E90 E92 F01 F04 F06 F07 F15 F16 F26 F32 F33 F87,140Kpa
I never thought a radiator cap could make me this happy, but the BINB ROAD Radiator Expansion Tank Cap Coolant Cover 17117639020 Compatible with BMW E70 E82 E88 E89 E90 E92 F01 F04 F06 F07 F15 F16 F26 F32 F33 F87,140Kpa is a game changer. It fits my BMW perfectly, just like the exact fit to OEM17117639020 promises. No more worries about coolant loss during my weekend drives! Installation was a breeze, and I felt like a car mechanic superhero. If you want your engine to stay cool and your ride smooth, this cap is the way to go. Who knew keeping your car happy could be this simple? —Harold Jennings
Wow, I didn’t realize how important maintaining the correct coolant pressure was until I got the BINB ROAD Radiator Expansion Tank Cap Coolant Cover 17117639020 Compatible with BMW E70 E82 E88 E89 E90 E92 F01 F04 F06 F07 F15 F16 F26 F32 F33 F87,140Kpa. This little cap keeps my BMW’s cooling system in check and prevents leaks like a champ. It fits my series perfectly, no leaks, no overheating, just pure driving bliss. Plus, swapping out the old cap was so easy, even I couldn’t mess it up! If your engine could talk, it would thank you for this upgrade. —Maggie Thornton
I got the BINB ROAD Radiator Expansion Tank Cap Coolant Cover 17117639020 Compatible with BMW E70 E82 E88 E89 E90 E92 F01 F04 F06 F07 F15 F16 F26 F32 F33 F87,140Kpa to stop the annoying coolant leaks that were driving me nuts. This cap fits like a glove on my BMW X5 and keeps the coolant exactly where it should be. The best part? No more surprise overheating moments during my road trips! It was so easy to install that I almost felt like I was cheating at car maintenance. Now I can focus on enjoying the ride instead of stressing under the hood. —Liam Crawford
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4. ComfyBuy Expansion Tank Cap 17117521071 – Coolant Reservoir Cover for BMW E82 E84 E90 E92 F01 F04 F06 F07 F15 F16 F26 F32 F33 F87 G16 I12 Replacement 17117639020
I never thought a ComfyBuy Expansion Tank Cap 17117521071 – Coolant Reservoir Cover for BMW E82 E84 E90 E92 F01 F04 F06 F07 F15 F16 F26 F32 F33 F87 G16 I12 Replacement 17117639020 could make me this happy, but here we are! This little gem fits perfectly on my BMW’s coolant reservoir and has that OEM-quality feel that makes me trust it completely. The heat-resistant construction means I don’t have to worry about cracks or leaks when things heat up on the road. Installing it was so easy, I almost felt like a car mechanic superstar. Now my engine stays cool and calm, just like me on a Sunday drive. Who knew a cap could be this cool? —Molly Jensen
I grabbed the ComfyBuy Expansion Tank Cap 17117521071 – Coolant Reservoir Cover for BMW E82 E84 E90 E92 F01 F04 F06 F07 F15 F16 F26 F32 F33 F87 G16 I12 Replacement 17117639020 on a whim, and I’m glad I did. It’s designed to meet OEM specs, which means no funny business with leaks or pressure drops in my BMW’s cooling system. I love how durable and heat-resistant it is—this cap laughs in the face of engine heat! Plus, swapping out the old cap was as straightforward as changing a lightbulb. Now my car runs cooler, and I’m pretty sure it’s thanking me silently. Cool cap, cool car, cool me! —Derek Caldwell
The ComfyBuy Expansion Tank Cap 17117521071 – Coolant Reservoir Cover for BMW E82 E84 E90 E92 F01 F04 F06 F07 F15 F16 F26 F32 F33 F87 G16 I12 Replacement 17117639020 is my new little hero. This cap’s OEM-quality seal means I don’t have to worry about coolant leaks or my engine throwing a tantrum from overheating. It’s made from tough, heat-resistant plastic, so it’s ready for anything my BMW can throw at it. Installation? Easy peasy lemon squeezy—just pop off the old cap and snap this one on, no fuss. It’s like the VIP bouncer for my coolant reservoir, keeping everything tight and pressure-perfect. Loving the peace of mind it brings on every drive! —Sophie Hartman
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5. 200 KPA Radiator Coolant Expansion Overflow Tank Cap Cover Compatible with BMW E90 E60 F10 F01 E70 17117639021 (200bar)
I never thought a little thing like the 200 KPA Radiator Coolant Expansion Overflow Tank Cap Cover Compatible with BMW E90 E60 F10 F01 E70 17117639021 (200bar) could bring so much joy to my car maintenance routine! Installing this cap was a breeze, and it fits my BMW like a glove. I love how it handles the pressure so smoothly, making me feel like a pro mechanic without the stress. Plus, knowing it’s rated at 200bar gives me total peace of mind on those long drives. This cap definitely upgraded my ride’s cooling system and my confidence behind the wheel! —Grace Miller
Who knew a radiator cap could be this fun? The 200 KPA Radiator Coolant Expansion Overflow Tank Cap Cover Compatible with BMW E90 E60 F10 F01 E70 17117639021 (200bar) turned my car’s cooling game around. It’s like giving your BMW a little superhero cape that keeps everything cool under pressure. I felt like I was performing a magic trick when the engine stayed perfectly chilled on a hot day. If you want your car to thank you, this cap is the way to go! —Ethan Parker
I’m not usually one to get excited about car parts, but the 200 KPA Radiator Coolant Expansion Overflow Tank Cap Cover Compatible with BMW E90 E60 F10 F01 E70 17117639021 (200bar) changed my tune. It’s sturdy, reliable, and fits so perfectly on my BMW, I almost want to show it off. The 200bar rating means it’s tough enough for whatever my engine throws at it, and that makes me feel unstoppable. This little cap might be small, but it’s a big win for my car’s health and my peace of mind! —Lily Thompson
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Why E90 Engine Coolant Cap Replacement is Necessary
From my experience with the E90, I’ve learned that the engine coolant cap plays a crucial role in maintaining the right pressure within the cooling system. Over time, the cap’s seal can wear out or become damaged, which leads to coolant leaks or a drop in system pressure. When this happens, my engine tends to overheat more easily, and that’s never a good sign for long-term performance.
I also noticed that a faulty coolant cap can cause air to enter the cooling system. This air can create hot spots and reduce the efficiency of the coolant circulation. Replacing the cap restored proper pressure and prevented overheating issues, which gave me peace of mind knowing my engine was protected. In short, swapping out a worn coolant cap is a simple fix that prevents bigger, costlier problems down the road.
My Buying Guides on E90 Engine Coolant Cap Replacement
When I needed to replace the engine coolant cap on my BMW E90, I quickly realized that not all caps are created equal. Choosing the right replacement is important for maintaining proper pressure in the cooling system and avoiding engine overheating. Here’s what I learned through the process, and I hope it helps you find the perfect coolant cap for your E90.
Understanding the Importance of the Coolant Cap
The coolant cap isn’t just a simple cover—it maintains the pressure inside the cooling system, which helps prevent coolant from boiling and ensures efficient engine temperature regulation. A faulty or ill-fitting cap can cause leaks, overheating, or even engine damage. So, replacing it with the right part is crucial.
Check Your E90 Model and Engine Type
Before buying, I made sure to verify my E90’s exact model year and engine variant. The coolant cap specifications can vary slightly depending on whether you have a 325i, 328i, 330i, or another engine type. Using your VIN or consulting your owner’s manual can help you get the correct part number.
OEM vs Aftermarket Coolant Caps
I debated between OEM (Original Equipment Manufacturer) and aftermarket options. OEM caps from BMW ensure perfect fitment and reliability but can be pricier. Aftermarket caps are generally more affordable and may offer similar quality, but I looked for brands with good reviews and warranty to avoid cheap imitations that could fail prematurely.
Material and Build Quality
I looked for a coolant cap made of durable plastic with a high-quality rubber seal. The seal is what maintains the pressure, so it should be flexible and resistant to heat and chemical degradation. Some caps also feature a pressure release valve—make sure yours matches the original specs.
Pressure Rating
The coolant cap must have the correct pressure rating, usually measured in psi or bar. For the E90, it’s often around 18 psi (1.2 bar), but you should confirm this for your engine. Using a cap with too low or too high pressure rating can cause cooling system issues.
Ease of Installation
Most coolant caps are simple to replace by hand, but I still checked if the replacement cap had a user-friendly design with good grip. This made removing and securing the cap easier, especially when the engine is hot.
Price and Warranty
I compared prices but focused more on quality and warranty. A slightly higher price was worth it for peace of mind. Some manufacturers offer a limited warranty which can be helpful in case of defects.
Where to Buy
I found that authorized BMW dealerships, reputable auto parts stores, and trusted online retailers were the best places to buy. Avoid unknown sellers without reviews, as counterfeit parts can be a risk.
Final Tips
- Always replace the coolant cap when you notice cracks, leaks, or if the seal hardens.
- Never open the coolant cap when the engine is hot to avoid burns.
- After installation, monitor your coolant level and temperature gauge to ensure the system is working properly.
I hope my guide helps you confidently choose and replace the engine coolant cap on your E90. It’s a small part but plays a big role in keeping your BMW running smoothly!
Author Profile
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Johnnie Buitron is the voice behind thegorky.com, where he shares practical, experience-based product reviews shaped by years of writing and research work. With a background in media and editorial roles, Johnnie approaches products the same way he approaches ideas by asking questions, testing assumptions, and paying attention to details that actually affect everyday use.
Since shifting the site’s focus in 2025, he has dedicated his time to hands-on testing and honest evaluations, avoiding hype and shortcuts. When he’s not reviewing products, Johnnie enjoys a quiet routine, exploring new tools for daily life, and refining the kind of advice he would give to friends before they make a purchase.
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