Hello all,

I have a 2015 RDX which so far has been perfect. Recently I noticed a low frequency humming sound. It only happens when the engine is under a load. It will happen then I am doing 30mpg and the RPM is right at 1,300. If I take my foot off the gas or switch to a lower gear the sound goes away immediately. It will also happen when I am going 75pmg and the engine is at 2,000 RPM.

Anyone else have this problem?

 

Does that Rumble happen only when you drive in the Bronx??

 

I think he was listening to this guy on satellite radio:

 

Its the engine in VCM mode. (cylinder deactivation)

Its perfectly normal and is simple science really. Three cylinders providing power and three robbing (a little) bit of power is just mechanically not in balance. Its actually quite a feat that Honda/Acura is able to make it as smooth as they do. Most people don't notice it.

We had a 14 Odyssey and at 25mph it was noticeable. I felt it was annoying but my wife hardly noticed. I think each year they are getting better and better w/engine damping and ANC (active noise cancellation) tuning.

At the heart of it all is the govs mandate of mpg.
https://www.whitehouse.gov/the-press...iency-standard

 

This is my second Honda 3.5 V-6. They both have had the sound/vibration you speak of.

This is a very different engine from those in other automobiles. That is because of the V-Tec ( or, iV-tec in its current incarnation). When power is demanded of normal engines at low RPM, they respond by lugging down, knocking, and basically losing power rather than gaining it. That's because a "normal" engine cannot adjust intake, exhaust, and timing to move/burn fuel at low RPM. My first impression of the RDX, when I got it, was how well it pulls at very low RPM. That low end torque makes driving much more pleasant and economical.

Whenever that grunt comes through the other sounds of driving, I enjoy the heck out of it. It is the car's way of telling me how much money I'm saving on fuel!

I think it's wonderful that Honda could achieve this amount of torque without a V-8, a diesel, or a gutless long stroke four.

John Deere tractors, Harley-Davidson motorcycles, and diesel trckuck pull at low RPMs. But, they all have lots of vibration and noise.

Honda really set the shift points low on this car. And, they made it very responsive in the process. I can drive the car all day, at any speed up to 70 MPH, and never top 2000 RPM. I get outstanding milage as a result.

Honda really did a fabulous engineering job on this drivetrain if you ask me. I find the "mumble" reassuring, as I've said.

 

Doesn't every brand have some version of variable valve timing, a.k.a vtec? Ford calls it tivt or something like that, toyota is vvi or vvt, bmw was valvetronic stepless variable valve lift.

I think the reason this engine feels as powerful as you think is because they made the first 2-3 gears quite low and it weighs pretty light too. It doesn't exactly make enough power to right home about.

Not knocking the engine, your post, or the vehicle. Just that I don't see what you see. But you know what they say about opinions.....

 

Actually it's a dated design because of it's single cam configuration. Most modern engines are twin cam designs that can adjust the intake and exhaust timing events independently for maximum efficiency and power throughout the operating range. They don't need VCM to achieve good fuel economy.

It's a typical Honda design and there is not much to find fault about it but it is getting long in the tooth.

I'm pretty sure Honda will follow suit and replace the V6 with a Turbo 4 in the next iteration.

 

Thanks for responses. That rumbling is sounds exactly like an engine imbalance. As long as it is normal, and I am getting great MPG, I am good!

 

I don't see a Turbo again. The V6 is such a superior motor which is much smoother and quieter. My 11 RDX(my Wife's) to my 14 is a prime example.

 

With the NX sold with a Turbo, and the new Accord/TLX going turbo as well, I am sure you will see a turbo again...

 

Small displacement forced induction engines coupled with electric motors are going to be the norm in the very near future.

 

This is actually sort of a brilliant idea. Start of acceleration on pure electricity until the motor has spooled the turbo enough, and then either let off the electric assist or keep it going with the gas motor. This both provides instant power and no lag, and also a smoother overall driving experience and better fuel economy.

Something else that would be cool would be a electric-turbo diesel combo. Diesels get amazing highway economy and hybrids get amazing city economy. Best of both world and that wonderful TORQUE!!

 

I see the potential for a lot of torque! Good as it is, the old school RDX V6 has got to be pretty much tapped out with what they can do to improve mileage.

 

2.0L 4 with twin induction, supercharger and turbo coupled with an electric motor, no reason you can't have 400+ HP and 500+ Tq. when both are utilized. Electric only for those short gas guzzling trips around town, cruising a fuel efficient 2.0L 4 and a power mode when both are utilized.

 

VCM