Bought a 2010 JCW in March and just did the first oil change since I've owned it. Previous owner ran Castrol 5W30. I switched to Mobil 1 0W40 since I had good results with it on my MCS... Runs smoother and quieter. Anyway the JCW use to pop like crazy - good loud ones whenever you let off the gas. Now, after switching oil, no more pops. It just gurgles now. Could the change of oil weight really have affected that?

 

I would say that just an oil change would be impossible....
Was the file of the car stock or it was tuned? Maybe they did an update on ecu and car was tuned with pops and bangs and now its not/?

 

Did you take it to a dealer or do the change yourself? Did you disconnect the battery while changing the oil? I would guess more that something along the lines of resetting adaptations happened than the oil change affecting your pops. Pops is all ignition timing and fuel trim, I highly doubt the oil has anything to do with it.

 

No tune (yet), still factory JCW mapping. Did the oil change myself. No, didn't disconnect the battery. I just did a standard oil and filter change, no other changes to the car other than the oil weight, which is why I'm left scratching my head. We've driven the car at least 100+ miles and a few drive cycles since then so the ECU should have made adjustments by this point, but the change in the exhaust pops was apparent on the first drive.

 

The only way to test the hypothesis would be to drain the 10W40 and put in 5W30 and see if the "pops" return. You could recover the new 10W40 oil in a clean container for another time so you don't waste money and oil.

I, too, don't see how oil weight would affect a byproduct sound originating from ignition timing.

 

He used Mobil 1 - 0w40 which should be fine.

 

Should be fine, yes. But, the OP's running hypothesis is that the oil weight change coincided with reduced engine "pops." That can easily be tested and eliminated as a possibility with an oil exchange back to the original weight.

Also, make sure the correct amount of oil was added. Overfilling might have some affects on sound resonances.

 

In the 2013 you need to press the "Sport" button for pops, is that true for a 2010?