2015 CX-5 2.0L — Light Knocking Sound at Idle After Cold Start?

[RAVIBAI]

Hey everyone,

My wife and I purchased our 2015 Mazda CX-5 with the 2.0L engine brand new, and honestly, it’s been one of the most trouble-free vehicles we’ve ever owned. We’ve always taken meticulous care of it; early oil changes (2500 - 5000 miles or every 6 months), using only top-tier oil brands like Amsoil and, more recently, Pennzoil 0W-20.

For about the past year (maybe a bit longer), I’ve noticed something a little puzzling. After a cold start, once the idle comes down, there’s a faint knocking sound coming from the lower end of the engine; or at least that’s what it sounds like. This only happens at idle.

The CX-5 still drives just as solid and smooth as it always has, and it’s been a fantastic, well-built vehicle overall. We’ve since passed it down to our daughter, and I continue to maintain it carefully.

Has anyone else here experienced this same sound, or is there already a thread about this that I might have missed? I’d really appreciate any feedback or insight you might have.

Thanks in advance!

 

[Mazdiod2]

So, it's about 10 years old, how many miles?
Have you used a stethoscope or something to listen to the knock? Does the knock go away, or is it worse if you stop and idle after a long drive?
Have you ever replaced items like the water pump, or idler pulley on the serpentine belt?

 

[RAVIBAI]

@Mazdiod2 — I appreciate your reply and the questions.

The CX-5 currently has 77,334 miles on it, and none of those suggested maintenance items have been completed yet. Here’s where things stand on the maintenance schedule:

Maintenance Item	Due Date	Due in Miles	Due in Time	Date Completed
Spark Plugs	—	143,000	—	—
Cabin Air Filter	—	100,000	—	—
Brakes	—	140,000	—	—
Brake Fluid	9/5/25	108,000	2 Years	—
Engine Coolant	11/1/27	118,000	5 Years	—
Clean Air Filter	—	90,000	—	—

I haven’t found a specific water pump replacement interval, likely because this engine uses a timing chain. That said, it doesn’t mean the water pump couldn’t be failing in some way. The idler pulley is considered a lifetime part and only needs replacement if it becomes defective, which could be the case here. As for the serpentine belt, it’s recommended to visually inspect it every 75,000 miles or every 5 years.

All solid advice; I’ll move forward with an inspection to see where things stand at this point. Thanks again for all of your input!