I drive a big heavy car (2011 Mercedes E63, somewhere around 4200lbs) that I take to the track. It has the NA 6.3L engine (M156) with no modifications.

I struggle with oil temperature issues on hot days when I'm at the track, but after adding a bigger oil cooler I'm at the point where a few degrees either way makes all the difference in whether or not I get thermal warnings. I can basically always stay cool enough if I short shift at around 6K instead of letting it spool out to the 7.2K RPM redline, even at full throttle. I've observed consistently that part throttle but higher RPM generates far more heat in the oil than full throttle lower RPM does.

As a data point, I've heard from many reliable sources that this engine is pretty choked up by its stock exhaust, to the point that adding longtube headers with high-flow cats can free up 50-60 HP (from the stock 525 to ~580, getting it much closer to the ratings of the SLS which has a free-flowing exhaust).

Now the question:

Since this isn't adding power by changing the cam profile or adding boost, simply by removing restrictions, would this be more likely to let the engine run a bit cooler or would the extra power generated make my heat issue worse?

As a corollary question, even if it didn't reduce the temperatures running flat out, might it allow more power when short-shifting it than it currently produces when driven the same way?

Thanks for any advice, and please let me know if there's any additional information I can provide!

Random ps - the coolant rarely heats up more than a few degrees even in a 25 minute session, where the oil temperature will rise rapidly. Is this normal or something to be concerned about?

  • While not an answer to the heat issue, I found this article to have merit with how to size a header for your needs (what differences in the header do what for the engine). Oct 4, 2016 at 16:13
  • Interesting - so for a 6K RPM sweet spot, 2" primaries make sense (which happens to match the Weistec headers). Thanks for sharing :)
    – RJStanford
    Oct 4, 2016 at 18:11
  • You will probably find you'll either be limited by what you can find for your car or you'll have to have custom headers built or build your own. I don't know the availability of headers for an AMG. Also, you'll probably want to wrap the headers. This will improve under hood temps and I believe it helps keep the exhaust velocities up. Ceramic coating the headers inside and out will help as well. I'm sure an AMG 63 would sound wicked with headers! Oct 4, 2016 at 18:18

1 Answer 1


I would seriously look at improving your oil cooler.

I doubt going "larger" is the immediate solution, I'm betting it's the airflow across the heat exchanger. Relocate the cooler, modify/improve the ducting, find cooler air to flow across it, etc.

On my FPROD '72 BMW 2002tii, I was able to drop oil temperatures from a frightening 280 F peak, to a more managable 240 F, even over a 4 hour enduro. This from a small 12" x 8" cooler... BUT mounted directly behind the missing left headlight opening, and "forcibly" ducted with thin aluminum sheet.

Corky Bell's book Maximum Boost: Designing, Testing and Installing Turbocharger Systems has an excellent section on intercooler design, as well as some information on ducting. While an oil cooler is not an air-air intercooler, the same ducting and efficiency principles apply.

If you only have 25 minute sessions, you might be able to rig an "ice-chest" arrangement with a separate oil cooler. Probably not a solution you'd want to consider for your (ostensibly) daily driver.

Also consider a flash that makes you a bit richer at WOT (Wide Open Throttle). Although this might cost you a few horsepower, you could easily dramatically lower oil temperature.

Or, improve your intercooling. Lower temperature charge means more power (higher boost and timing advance possible) and less heat into the oil. Here's an inexpensive solution [cough] from guys that know:

Weistec M157 E63 Cooling Upgrade

  • You have have a 2002? Respect to you @steveracer. Oct 5, 2016 at 3:10
  • Thanks for the input - I went with a FluidMotorUnion oil cooler that replaces the factory unit and dominates the lower grill after seeing reports of success from other people. Considering the placement ( you can see it in this pic from COTA ) and the fact that its a large three section piece I'd really hoped that it would be the "overkill solution". The 6.3 is NA, so no intercooler.
    – RJStanford
    Oct 5, 2016 at 11:12
  • @SteveRacer I'll reach out to a couple of the tuners to see if their tunes are already covering running richer. If that's a viable solution then its a simple one, so thanks!
    – RJStanford
    Oct 5, 2016 at 11:13
  • @RJStanford Oh, I thought that was a twin turbo V8. Ignore every single thing I said, past, present, and future. (But richer at WOT is cooler. THAT I will swear by.)
    – SteveRacer
    Oct 6, 2016 at 3:53
  • @SteveRacer no worries :) Going to check out the tune option this weekend. My main issue is that it sure feels as if I should be getting adequate cooling at these RPMs and power levels, especially with the new cooler. Hence my brainstorming about opening up the breathing - I know that instinctively "more power == more heat" but I'm wondering if something more nuanced couldn't also be true.
    – RJStanford
    Oct 7, 2016 at 16:28

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