Piston Slap: The Heat Is On!

Ramin writes:

Sajeev,

I am not a TTAC member, but I read it almost daily. I suppose I should join soon. Anyway having read your “piston slap: we need your help” post, I have one that has been stumping me for about a year now:

The car is an 08 Impreza STI. For the past year or so, the power steering struggles and whines. It is much worse when the car is cold, doubly so when the weather and the car are cold. There is no belt squeal. I have tried flushing and bleeding, both with factory fluid and also with the Lucas stop-leak stuff. Modest initial improvement only lasts a little while. Subaru forum posts suggest the STI cooks its PS fluid because the fluid lines route near hot turbo components. However it seems now even with fresh fluid, the problem persists, leading me to suspect a component has gone bad. I don’t want to drop over $600 for a new pump. Are there any tricks you know of, like for example, replacing a particular gasket? Or, better yet, some advice on narrowing down exactly what the culprit is (short of replacing the whole freaking pump)?

Thanks a lot and keep up the good work – I love the site and what you all have done with it.

Sajeev answers:

Thanks for your kind words. I never thought that an unemployed (Lincoln) forum moderator could eventually be the ring leader of this crazy Piston Slap thing I created. Apparently my unemployment period was good for me, and perhaps it enriched/enriches your life. So there’s that.

I am a little concerned you put Lucas Stop Leak in a system that never leaked: stop leak products tend to gum up areas that don’t need gumming. But that might be unfounded, go ahead and verify on the forums. In general avoid stop leak products unless you 1) have a leak and 2) really don’t give a crap about the leaky vehicle in question.

I think the knowledge you gained on the forum is right. The fluid lines are in an unfortunate location, and Turbos make a TON of heat. There are two things I’d recommend:

1. Switch over to a racing grade Power Steering fluid, if it has a higher boiling point than the stock stuff. Several oil companies supposedly offer a fluid with a higher boiling point, as googled here. I will not speculate or endorse one over the other, and I am sure the forums have already covered this.

2. Protect those steering lines! You need to shield them from the turbo’s heat. I would use an insulating heat shield wrap for the lines, and possibly make a sheet metal sleeve in this general area, to further help isolate the lines from the Turbo.

Why am I saying this? Because I’ve raced a couple of late model Corvettes, and they do suffer from clutch fluid problems in a Texas summer with a hamfisted AutoJourno behind the wheel. So do them both. The same thing applies here, especially when we talk the heat of a Turbocharger in a tight Subie engine compartment.

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry.