Misfiring, then rod noise?

[Nut124]

Sorry about a boring daily driver question but this is what I'm dealing with currently.

Is there any chance this is anything but rod brg noise?

My 2010 4-cyl Subaru has been having occasional misfiring lately. Today, upon entering a highway, the misfiring was severe, followed by loud mechanical noise, rattling, like a rod brg I presumed. Oil pressure light never lit up until I pulled over and was coasting to a stop.

I know it was low on oil but not empty. Burns oil.

After adding oil, it starts and oil pressure light turns off. No pressure gauge.

If I rev it in neutral, it will start rattling above 3000rpm. If I put it in gear, it will sound OK at 2000rpm under load and I can drive it at slow speed w/o noises.

Can load make rod noise disappear?

Could this be something else, like the variable cam timing thing?

[4vpc]

Inspect the oil filter, that'll tell you straight away.

[Tuner]

Spun rod bearing, bearing shells overlap and take up the clearance so very little audible knock at low RPM, high RPM centrifugal force moves bearing halves to outside of crank throw so with no bearing in the rod cap the piston bounces off the head.

[mag2555]

That loud bang could have been all of that unburned fuel from all the missing lighting off in the exh system all at once!
That could have blown out a part of the exh system or its many gaskets it has and your hearing a exh leak now and not a rod knock.

The two exh manifold gaskets are famous for this, and yes it can sound like a there, not there rod knock,

I own a Subaru, so ask me how I know this!

If worse comes to worse at least that oil pan is cake to get off the motor to stuff in new Bearings.

[Nut124]

I have the oil filter out.

How do I assess what is in it and whether it came from the bearings?

[dannobee]

Cut it open and look for metal in the paper media.

When we say "cut it open," don't use a hack saw. There are filter cutters made for that, or use a muffler pipe cutter or even a chisel. You want to open it like a tuna can, not add more debris into the mix.

[Nut124]

A lot of sparkling metal debris in the filter.

The 4-cyl Subaru rog brg replacement may be easy. Mains not so. What are the odds of this just being the rods?

[KnightEngines]

Almost certainly rod bearing, they do it if you look at them the wrong way.
Likely killed the crank too.

[BCjohnny]

The 4-cyl Subaru rog brg replacement may be easy. Mains not so. What are the odds of this just being the rods?

If you're thinking of maybe trying to do it in the chassis, I doubt it's going to happen

As KnightEngines says, they usually eat the crank, and normally rod also, when they rattle ...... so a grind, shells, 'new' rod etc ...... full stripdown regardless usually

Across the range they're known for losing BEs, although the mains usually escape relatively lightly IMLE

[dannobee]

At dealership level, we would never rebuild a subie short block. It was always a new short block and rebuild the heads if needed.

[n2omike]

At dealership level, we would never rebuild a subie short block. It was always a new short block and rebuild the heads if needed.

At one time you could buy new short blocks from Subaru at a reasonable price. Not sure if that is still the case for the timing belt engines. I don't believe they are still available. If memory serves, they were around $1,600. Getting them 'right' once you split the cases is supposed to be an issue for someone who is not familiar with these engines.

As for pulling the engine, it's not that hard on these cars. It comes out fairly easily... as far as new cars go. Once you've done it a time or two, it's actually pretty quick.

Subaru use a timing belt all the way up to around 2012. I think the timing chain engines started in 2013. The belts last 10 years of 100k miles. They are fairly easy to change.

Yea, a little rambling... Unless the car is super nice with barely any miles, I'd just find a used engine for it. You'll also want to make sure someone has installed MLS head gaskets on it, or you'll need to do it yourself, as the graphite head gaskets installed on the standard (non-turbo) engines go bad. The graphite degrades away, and they leak oil. Initially they leak oil to the outside. They then leak coolant... sometimes to the inside. Just be sure it is the same exact powerplant, as some things were changing. There are Subaru forums that can help you with that. You'll also want to install new valve cover gaskets and spark plug tubes before installation... as the spark plug tubes leak after a few years/miles... and can be a PITA to change with the engine in the car. A new timing belt/tensioners/pulleys is also a good idea. A LOT of the timing components out there are junk. You'll want factory level parts. The ASAIN kit is a good one. The Gates setup contains Chinese bearings. The ASAIN kit is all Japanese.

Good Luck

[dannobee]

2010 should still be the old EJ25 (255 or 257), right? Those short blocks are still available brand new for about $2k.