What effect will replacing manifolds with headers have on oil temperature?

Question

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?

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