hyeflight

Hello all,

I have a 2016 E350 and I have a rattling noise that we cannot fix. It typically makes the noise while accelerating, going uphill at lower speeds. It sounds like it is coming from under the engine area, just under the center dash. My mechanic heard it but was unable to find the source. We are unable to duplicate while on a hoist. He thought it could be the heat shields, catalytic converter or the tensioner, but so far no luck.

Does anyone here know anything about this type of issue? I am hoping someone had this same problem and can give some guidance.

thanks.

KanataSteve

Are you using fuel with the correct octane rating?

hyeflight

I use 91 and 89 octane, but how would that make the rattling noise at low speeds driving uphill? Seems more like something is lose, but my mechanic couldn’t find anything

KanataSteve

Check the sticker on the door to your gas cap, it will show the minimum octane requirement - pretty sure yours will indicate 91 - all of mine have. I have found that using low octane fuel e.g. 87 & 89 octane (on multiple Benz models) can cause rattling (knocking) at low acceleration or uphill driving. If you have access to 94 octane (Petro-Can in Canada) you'll see a marked increase in pep, and actually see some fuel savings. Did the math on a C300 during normal highway driving. Higher octane seems to give better fuel economy, each step you make in octane.

Does the rattling go away if you press on the gas pedal a little harder?

hyeflight

Yes, if I press harder on the accelerator or take my foot off, the rattling goes away. Seems to happen more frequently when the engine is warmer.

if you think it’s the gas octane, how long after my next 91 fill-up should the rattling go away by?

thanks!

KanataSteve

In my experience, it went away fairly quickly - unless you have a lot of lower grade gas in the tank. Lower grade gas in the tank will dilute the higher grade you're putting in.

Maybe try letting your tank get fairly low, then put some 91 octane in. Unless you've got some other problem, it should go away fairly quickly. Make sure to go to a reputable gas station, you always hear stories of cheaper stations selling just that - cheap gas.

Another thing to consider is the spark plugs. Are they clean and the correct ones (I hope?). Let's see how the gas works, it may need to do a little cleaning inside, it might take a bit of time. Another option is injector cleaner too, they might be gucked up and not spraying well.

chassis

Run a full tank of premium fuel and report back.

hyeflight

Will do, thanks!!

btw, I don’t drive that often, so it could take a while