Proper oil quiets motor
 

I recently bought this cx7. When I went to go see it and test drive it, it was great, nice quiet engine, etc. Make a deal, the car lot replaced a leaky motor mount on the upper right and changed the oil for me. The day I go to pick it up. Its tapping and clacking, noisier then days prior. I ask them about it, they say they never noiticed it and maybe it was just me. So i take the car, expecting to be replacing the timing chain soon, but hoping it happens under the time I have there warrenty.

Fast foward 3 months, time for oil change. I get some Castrol HM 10w-40 and filter. Drain the oil and its darker then tar and thin as water. Add new, replace filter, start it up and boom, no more noise, its gone. Back to normal engine sounds. So I guess the dealer put in regular oil.

Amazing how important proper oil is to an engine.

Well, considering this engine is only supposed to have 5w-30 or 5w-40 in it, your use of thicker oil *could* also be detrimental to performance, longevity, etc.

Castrol HM 10w40 has two problems:

1. It’s the wrong viscosity. To properly lubricate some of the very tiny oil passages in cold weather you need a 5w-30 or 5w40 oil. A 10w40 may sound quieter, but it may fail to reach every rotating or moving surface in cold weather.

2. Castrol HM is not full synthetic. It is a semi-synthetic blend. It will have a lower coking and ash formation point than full synthetic oil. The center shaft of the K04 is lubricated by engine oil. It spins at about 150,000 rpm! Temperatures can reach over 1,500 degrees F. Your turbo will last longer with full synthetic which can handle the higher heat without decomposing, forming hard carbon deposits and ash.

Best to run a full synthetic 5w40.

10w40 is fine - not optimal but fine. If you're in a cooler climate I would change to 5w30 now but if you are in a warmer climate I would just wait for the next oil service to change.

My bet is the dealer put in 0w20 - oil that the CX-5 uses. Dealers are't the smartest (oddly enough) when it comes to our MZR-DISI engines.