Hi there. Stock 04 wrx with 78,000 mi on it. I've been running Mobil 1 on it since ~30,000, changes every 4000 mi or so.

I have grown used to what I believe (based on many threads) is piston slap on cold startups. Quiet ticking noise (almost like a diesel engine?), audible at idle and under load. It has become more noticeable as the engine ages, but always goes away after a few minutes of warm-up.

But two times now after the car has been sitting for many days without running, there is a much louder noise that occurs for about a second on startup. The noise is similar to the piston slap but way louder, almost sounds like there is no oil in the engine. Both times it has been ~50 degrees F at startup, but when it was sitting was lower. Oil level shows just above low mark when cold and not run for 24 hours, just below full when warm and engine shut off for ~15 minutes to allow oil to drain to pan.

Any input as to whether this is something I should worry about? It's kinda hard to replicate, so I'm not sure taking it in somewhere and having them cold start it would help.

Thanks for any info.

 

In all honesty, I've been in many of Subaru's, especially WRX & STi. I have never heard a OEM engine have a noise of piston slap. Never.

Built blocks, sure. Piston slap is somewhat normal for built engines.

How much oil are filling it with? 5w30?

 

It is not piston slap, it is the sound of the lifters. If it was piston slap, your engine would have failed some time ago. Boxer configurations are not tolerant of piston slap, unlike pushrod motors.

 

Yeah it's not Piston Slap- but I do now what your talking about. I also have the same noise under the same conditions- I have 55k on my clock and all I did, is change oil weights to 10-40 and that seemed to help some (stayed w/ synthetic). Always check oil levels, I can tell that my oil is low when the noise gets a bit louder. hope this helps!

 

I've noticed this noise on mine as well. Sounds like lifter noise (pretty sure it isn't exhaust). I'm still somewhat of a n00b to the boxer motors. Any adjustments that could be made or anything that could be done to help with the noise? (Drives me nuts when I'm driving next to concrete barriers on the freeway cuz thats when I can actually hear it).

 

Looking back at searched threads, there are many terms thrown around for a noise like this including piston slap and lifters. But with my limited engine knowledge, they're all just terms to me. I'll look more into it, thanks for the replies.

As it's getting warm-ish again up here, I will try going to 10W30 next oil change and see if that makes a difference.

 

I too have never heard of piston slap on a Boxer engine either.
Because of the engine configuration I don't think it's possible.
I know alot of pushrod engine are notorious for piston slap
like the LS1 pushrod engine in GM vehicles.The 2001-2002
LS1 cars were very prone to this engine problem.