It’s been a while since I talked about the planning and research that goes into a BMW DIY project. Right now I’m in the midst of deciding how to tackle replacing the radiator on my 2002 BMW E39 M5.
To the best of my knowledge the current radiator is original to the car. It now has over 117,500 miles. There is nothing visually wrong with the radiator, and the cooling system of the E39 M5 is stronger and more durable than other E39 5 Series cars. However, the car does seem to run hot on warm days and will be 24 years old in January. Preventative replacement seems prudent.
Research into the right parts to buy can save a lot of frustration later in the middle of your BMW DIY project. RealOEM.com is a fantastic resource for finding any BMW part. You simply enter the serial number of your vehicle (the last seven digits of your VIN), and then scroll to the specific diagram you need like the ones in this post. The searching and categorization isn’t always intuitive, but you can’t beat this free tool for understanding what you’re getting into with your project.
Years ago I wrote about how much money you can save by buying original equipment (OE) parts for your car. And prices have gone up dramatically since then. Here’s a good discussion from FCP Euro on the topic.
For example, the genuine BMW radiator for my car is currently listed by FCP at $565 – on special clearance! But the same radiator built by the same manufacturer Mahle/Behr is listed by FCP at $315. But we’re not done yet – that same radiator at well-known parts supplier RockAuto is only $230. FCP does offer a lifetime replacement guarantee but for me RockAuto gets the business here.
The pricing for the expansion tank – basically a piece of plastic – is even more absurd. The price on FCP for genuine is $315 – as expensive as the radiator! And there is no OE option provided. On RockAuto a different brand is offered for $163, still crazy. These increases are relatively recent – thankfully I bought this expansion tank for $85 a couple of years ago. I knew this coolant refresh project would eventually be needed.
Often with BMW DIY projects there is the question of how much to replace “while you’re in there.” I replaced the thermostat on the M5 in 2023, which was not an easy job. There are four hoses that connect to the radiator, two large and two small. Should I replace them? Presumably they are all original, although the upper radiator hose (#1 in diagram below) is branded Continental and looks pretty fresh. Replacing them increases the time, expense and complexity of the job. From what I’ve read hoses are an example of when going genuine BMW makes sense.
While definitely not an easy job for someone with my moderate DIY skills, I want to tackle this project myself. It seems relatively straightforward. Here’s an excellent, thorough tutorial video from Ryan at E39Source, an E39 M5 expert. This shows just the radiator, not replacing any of the hoses. Except for draining the coolant the job can be done without raising the car. This could be important, because the BMWCCA DIY events frown on jobs that could take more than two hours.
Which means if they don’t OK me doing this at an upcoming event I could be doing it in my driveway. That would not be optimal, since I don’t have access to a lift otherwise. And I don’t want to return to being on my back underneath the car. Of course, I could purchase the parts and bring them to a shop to have the job done. That’s sometimes the right move after doing your research.
How will my M5 radiator project unfold? Stay tuned and I’ll update this post!