Car Talk Community member “Johnznot” recently wrote in asking for advice from the CarTalk Community, saying “I just purchased a 2017 Outback. I noticed a rattling noise (like marbles) coming from the engine upon startup in the morning only. The noise goes away after a few seconds. To me, it sounds like bearings rattling due to low oil pressure, but the dealer says that every Outback and Legacy does this. It has a timing chain, and the engines use 0-20 synthetic oil. Is this normal.”
(Subaru)
A healthy and spirited debate followed. As a four-time Subaru owner, I wondered if what Johnznot heard was anything more than the usual rattle of a 2.5-liter, four-cylinder Subaru engine. First things first, though. I did a bit of digging to confirm that indeed there is a timing chain system in the Outback’s 2.5-liter engine (as opposed to a timing belt). Next, I wondered if the new Outback had switched to direct fuel injection. Direct injection is noisy and can sound like anything from a loud static hiss to a close approximation of the sound a diesel engine makes. Nope. No direct injection yet in the Subie 2.5i.
(John Goreham)
Johnznot got some got advice from member Tester who said simply, “Go back to the dealer and ask them to start another 2017 Outback to listen if it makes the same noise. If it does, then it's normal. If it doesn't, then it's not normal.”
Johnznot called first and asked his dealer if the sound was a problem. The dealer said, in essence, “They all do that.” Not being the kind to trust that sort of easy answer Johnznot returned to the dealership where an associate started not one but three new Outbacks. They all did that.
Before we debate if there is a problem with the 2017 Outback, let’s step back and consider what we Subaru lovers know; Subies sound different. Whether it has to do with the horizontally-opposed “boxer” engine design, or not, the four-cylinder Subarus are, shall we say, “automotively verbose.”
(John Goreham)
A look at the engine bay of a modern Subaru will reveal quite a bit of sound insulation. The best (least expensive) way to silence an engine isn’t with fancy mechanical wizardry. Rather, stuff some mouse fur in the cracks so the sound can't escape!
The fact is that Subarus have always had a distinctive engine sound. A can of marbles seems like a bit of an exaggeration, but when they are cold, those 2.5i engines do have quite a clatter, particularly compared to counter-balanced in-line fours like one might find purring under the hood of an Accord, or an in-line six, or V6 in pretty much any car.
Johnznot reports that his Subaru dealer told him that the “…rattle upon startup was normal (due to the boxer engine design), and that no harm is being done. It is low oil pressure caused by the car sitting for an extended period ( 8 hours or so). The noise is caused by the timing chain and tensioner.” We reached out to Subaru of America to see if they could (would) explain the unique sound quality of the engines, so many of us know and love. Subaru’s Jessica Tullman was very helpful and she did some digging. Subaru offered the following explanation for the distinct sound that may give some folks cause for concern. Subaru says:
The new engines, especially the four-cylinders, are extremely efficient so they have very low friction. Because of that, this process assists the engine behavior at start up to help them warm up. When the engine coolant temperature is approximately 158 degrees Fahrenheit or below, the ignition timing map in the ECU is changed to retard the engine timing. This timing change is done in order to quickly heat up the exhaust catalyst to reduce emission gases. This change causes part of the combustion process to occur as the exhaust valves are opening in the cylinder head. The release of the high-pressure combustion gasses entering the exhaust system causes this noise. Depending on several different inputs into the ECU, such as engine coolant temperature and throttle opening angle, this noise could occur until the engine coolant temperature reaches the desired temperature. The timing change logic is slightly different from model to model. This slight difference means that some vehicles have different noises. The noise is not harmful to the engine or exhaust system. It's important to note that during normal driving this mapping is ignored.
We think given Subaru’s explanation, Johnznot having had a dealer start three random new Outbacks on the lot, and our experience with this type of sound, it is fair to say "They all do that."
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