2008 Loud Engine Noise

Hello all, its been a while since I posted here lately. In the last few months my '08 Prius' engine has gotten progressively louder. I have tried fuel injector cleaner, Techron to be specific and that doesn't seem to have helped much if at all. The car drives fine for the most part but on occasion when I ease up on the accelerator, such as when I'm approaching the top of a hill, I can feel what seems like a miss or stumble. I have no check engine light or error codes. The spark plugs were changed around 110K miles with the correct ones. Current mileage is nearing 130K.

Oil level is about a 1/4" below the top mark and I have regularly used Castrol Syntec 5W-30, but on the last change I got Mobile1 5W-30 Synthetic but no change in the noise level there.

I did have an issue several months ago where I had reduced power from the engine and the battery was compensating for, which seemed to have been caused by a fouled igniter and went away after I replaced it. I know the engine is typically loud in cold weather during cold starts but now it sounds loud almost all of the time unless the engine has been thoroughly warmed up. I don't notice any loss of power particularly.

I have uploaded a short clip on YouTube of the sound here:

The whooshing sound I am unable to hear in person, so it may be some distortion from an echo or just my phone's mic. The engine noise is somewhat amplified by my phone, but it is still very much noticeable when walking by if the engine is running compared to a co-worker's G2 which sounds nearly silent with the heat and engine on.

Any suggestions on things to check or do before I head to a shop will be greatly appreciated!

 

Hi Lucifer, was that causing a similar sound and behavior in your Prius? I'm really hoping it's something as simple as a DIY repair.

Edited for autocorrect.

 

Yeah, for some reason the recording is louder than it actually is, but I'll take a look this weekend. Oddly enough I haven't had any noticeable drop in fuel economy since this started happening. Granted I do expect it to be lower in the winter any way. I'll see if I can get the car on a lift this weekend and probe around.

 

Ok, checked the air input hose and all good there, same with the air cleaner box, it was tight and the clamp was securely fastened. I raised the ol' gal up on some rhino ramps and felt around. It was a little hard to tell but the doughnut gasket does look a little suspect, but I can't say for sure. Will probably replace that anyway. The exhaust manifold looks pretty rusty, but I need to get up on a proper lift before I start poking around there. I'll get some pics next time and report back.

 

Finally got some decent enough weather and no back issues to get under the car. I didn't let it cycle through it's warmup until I could get it on the ramps and get back underneath. Felt around with my hand and sure enough, where all the exhaust header pipes come together, I could feel hot exhaust blowing out. Seems like it rusted through enough in a joint where it eventually cracked. I'll look around for a replacement, possibly from a low mileage wreck, new gasket and bolts. This doesn't look like it will be a fun job to do but seems it won't be so expensive.

Thanks everyone for the help!

Attached is the photo I snapped from under the engine on the backside showing the rusted header.

 

Yeah, the only thing that I can think of is perhaps road salt playing a role in this although I'd have to say I'd expect to see more Prii with the issue, and I can't find any references to anyone having had to replace the exhaust manifold for a similar reason.