Piston Slap: The Heat Is On!

Sajeev Mehta
by Sajeev Mehta
We’re committed to finding, researching, and recommending the best products. We earn commissions from purchases you make using links in our articles. Learn more here
piston slap the heat is on

Ramin writes:


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.

Sajeev Mehta
Sajeev Mehta

More by Sajeev Mehta

Join the conversation
3 of 5 comments
  • Sajeev Mehta Sajeev Mehta on Jul 16, 2012

    Good point. Perhaps the fluid boiled over and air got in as it cooled?

    • Poltergeist Poltergeist on Jul 16, 2012

      More likely high underhood temps take their toll on the o-ring(s) in the suction side of the p/s hydraulic circuit (or possibly a return hose). Biggest clue is the OP's statement that situation is worse with cold engine/outside temps. Cooked O-ring (or hose connection) shrinks in the cold, allowing air to be sucked in, aerating the fluid and causing noise and poor p/s performance.

  • Rum Rum on Jul 16, 2012

    Hi everyone, I am Ramin. I just registered to post my thanks and to give an update on the situation. Since I posed the question to Sajeev a couple months back, I tried to seal up that top o-ring referenced by DIYer. I failed miserably. When I restarted the car, there was much more noise and shuddering in the system. I must have made it worse and now air was definitely getting sucked in through that spot. At one point, two days later, there was so much foaming in the system that it overflowed the reservoir and spilled all over one of the headers - smoke and all. It freaked me out, and I broke down and bought a new pump. The Subie pumps come as an assembly with the referenced plastic fitting and new o-ring. I installed it a couple days later, flushed new fluid through, and the problem went away. Now my attention is focused toward keeping the second pump from failing. Sajeev, thanks for your tip re: racing fluid. I will look into it as well as the heat wrap. I have seen forum threads where folks are actually putting fluid coolers in. I don't know if I want to go that extreme, but anyway there you have it.

  • 28-Cars-Later "But Assemblyman Phil Ting, the San Franciscan Democrat who wrote the electric school bus legislation, says this is all about the health and wellbeing of Golden State residents. In addition to the normal air pollution stemming from exhaust gasses, he believes children are being exposed to additional carcinogens by just being on a diesel bus."Phil is into real estate, he doesn't know jack sh!t about science or medicine and if media were real it would politely remind him his opinions are not qualified... if it were real. Another question if media were real is why is a very experienced real estate advisor and former tax assessor writing legislation on school busses? If you read the rest of his bio after 2014, his expertise seems to be applied but he gets into more and more things he's not qualified to speak to or legislate on - this isn't to say he isn't capable of doing more but just two years ago Communism™ kept reminding me Dr. Fauxi knew more about medicine than I did and I should die or something. So Uncle Phil just gets a pass with his unqualified opinions?Ting began his career as a real estate  financial adviser at  Arthur Andersen and  CBRE. He also previously served as the executive director of the  Asian Law Caucus, as the president of the Bay Area Assessors Association, and on the board of  Equality California. [url=https://en.wikipedia.org/wiki/Phil_Ting#cite_note-auto-1][1][/url][h3][/h3]In 2005, Ting was appointed San Francisco Assessor-Recorder in 2005 by Mayor  Gavin Newsom, becoming San Francisco’s highest-ranking  Chinese-American official at the time. He was then elected to the post in November 2005, garnering 58 percent of the vote.Ting was re-elected Assessor-Recorder in 2006 and 2010During his first term in the Assembly, Ting authored a law that helped set into motion the transformation of Piers 30-32 into what would become  Chase Center the home of the  Golden State Warriorshttps://en.wikipedia.org/wiki/Phil_Ting
  • RHD This looks like a lead balloon. You could buy a fantastic classic car for a hundred grand, or a Mercedes depreciationmobile. There isn't much reason to consider this over many other excellent vehicles that cost less. It's probably fast, but nothing else about it is in the least bit outstanding, except for the balance owed on the financing.
  • Jeff A bread van worthy of praise by Tassos.
  • Jeff The car itself is in really good shape and it is worth the money. It has lots of life left in it and can easily go over 200k.
  • IBx1 Awww my first comment got deletedTake your “millennial anti theft device” trope and wake up to the fact that we’re the only ones keeping manuals around.