Adding an Easy to Install Heavy Duty Power Steering Cooler to the E39 BMW M5

When changing the radiator on Project E39 M5 to a CSF Racing performance part, we noticed that our power steering system was suffering from age-deteriorated lines and was leaking fluid.  We decided to change these parts out “while we were in there” and with a little research determined it was super easy to significantly upgrade the system to include a big factory-engineered cooler.  When we drove the car hard on the track, we noticed that we had a little fluid boilover seeping out of the reservoir, and with extreme use like autocross or drifting the steering would sometimes pump up.  These were symptoms of the fluid getting too hot and a common issue with other BMW models of the same era.

We replaced our old leaking lines with new genuine BMW parts.  Genuine parts are usually always higher quality than aftermarket stuff.

We also replaced the system’s fluid reservoir. The power steering system’s filter is integrated into the reservoir and it is not a serviceable part. Since all of the plumbing was getting replaced we did not want to skimp on this.

When researching the proper replacement parts we noticed the cooler for an automatic transmission E39 had a superior and large tube and fin heat exchanger.  The M5’s stock power steering cooler was simply a row of bare pipes that sit on the front of the radiator.  We ordered the automatic transmission cooler and proceeded to see if it was a direct bolt-in replacement for the poor minimalistic stock cooling pipes.

To get to the cooler, you have to remove the stock radiator.  First, you have to remove the coolant overflow bottle and loosen the fan shroud.  Then you have to remove the bolt that holds the fan in place.

The shroud and fan are removed together.


  1. Hold the phone, is that a mechanical/clutch fan for the engine? Have you considered an electric one which also would free up some space in that tight area? And the added benefits of freeing up a little HP.

    1. Nope. This upgrade was prompted by the leaks we found during our radiator install. So we did not go through the process of gathering before data.

  2. Great article but you really need to include the part number for the new cooler or at least what specific year and model E39 it’s from. The photo is not clear enough to read the full part number.

    1. Agreed. Part numbers would have been great to add to the article. FWIW, the part number shown in the pic is 0159-1042.

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