One of many leak sources.

One of many leak sources.
"In this entry, I document the Genuine BMW oil cooler failure I experienced - and that you more than likely will during your V10 ownership.

I discuss the performance replacement options and I unbox & install the uprated permanent fix: the S85 Performance Oil Cooler.

- Matt

Rings and cracks. 

Prior to purchasing the M5, I had a PPI complete by a shop I was referred to in Alberta. They had identified a slight oil leak, noticeable by oil found across the undertray starting from the absolute front of it. They could not locate the source upon inspection. 

2 months into ownership, oil consumption was further accelerated. I would quickly learn the signs of a common E6x M5/6 failure: the oil cooler cracks and its o-rings decay. 

The oil cooler on the V10 is relatively large, sitting at angle in the lowest part of the front bumper to optimize surface area, still leaving cold air for the radiator, and AC condenser. 

The leak will be prevalent on the passenger, that's where the fittings are. 

The 2 fittings have o-rings inserted here, and they tend to decay. If you're lucky, that's the culprit - but it's only a matter of time before this section cracks. 
The old o-rings are on the right. I picked slightly larger replacement o-rings. One of them is on the left. 
I assume the steel material of the oil cooler eventually gives out from vibrations and temperature changes over time. Ultimately, all original and OE replacement oil coolers will all fail at varying mileage and age. 

The Performance argument.

It's important to understand the technical purpose of these performance replacements: to sustain adequate engine oil temperatures and performance for a longer period of time than than OEM.

If your oil temperatures get too high, the MSS65 will put you into limp mode, after reducing ignition timing. 

As such, performance oil coolers will not make your engine operate at lower engine oil temperatures per say. It will however give the capacity to manage the heat better: by slowing down the oil temperature increases under loads and accelerating the return to median engine oil temperatures during cool downs. 

With the upcoming S85-EVO high duration camshaft packages allowing more power, at higher RPM, I did want to preventively upgrade the cooler. 

I personally have had no issues with the OEM oil cooler's capacity to sustain 250km high speed drives with standard bolt-on upgrades. I run out of fuel before I run out of cooling capacity! 

The candidates. 

Whenever I come across a potentially reccuring failure point on my M cars, I try to develop or source an uprated performance variant, and a permanent solution to the underlying failure as part of my Maintenance Programs

In the case of this oil cooler, the market was limited to 3x options: RPI, Mishimoto and Radtec.


Mishimoto's oil cooler is the sucker's choice. Most V10 owners often aren't aware of any other alternative, and Mishimoto is sold by every other shop in the world.

Their cooler does offer a permanent solution to the fix. For me, it starts and ends at there: it's made in China. At 625$, I'd recommend the OE oil cooler kit instead if you are budget focused. 


They make the highest performance option when reviewing their core: it's massive! Being 30% more efficient than stock, it's also the most expensive at 1,300 USD + shipping. It's a quality piece made in the USA. and is finished in raw aluminum. 

While I do not curate it on EuroConnex, I wouldn't hesitate to recommend it to anyone looking for the best oil cooling performance if their application requires it. 


RadTec is a UK based manufacturer of cooling solutions for OEM automotive manufacturers such as Koenigsegg and has created various aftermarket solutions for BMW M cars. 

They created an S85 solution that combines quality, performance, aesthetics and pricing that hits the mark for my use. 

I do not track the M5, however Quebec's weather varies from -40 to +40C. An uprated variant was going to be useful to sustain engine performance over a longer period of time. 

There are 2 key signature aesthetic features of the RadTec unit: the added cowl and the matte black powdercoated finish like the original BMW unit. 

The cowl maximizes the air directed towards the oil cooler without increasing its height over the radiator. 

Its design remains compatible with the front bumper and lower grill. No cutting is required.  

The complete cooler is manufactured from commercial grade 1050 aluminum and TIG welded in England. 

The core is uprated to 60mm, allowing an extra +/- 0.5 liters oil volume inside the cooler. 

Most importantly, the Radtec design promises to fix the cracking issues of the OE units, and is warrantied for 1 year. 

It slides into the OEM mounting points using the same fitment pins on the sides of the cooler. 

It's a bumper off affair, and will require an oil top off. 

Will I feel this performance upgrade?
Probably not. 

Will I sleep better knowing another failure point got solved?

Will it help me sustain the S85-EVO's performance?
Most likely. 

I source and most often keep the Radtec cooler in stock here

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