the3rsss Posted October 23, 2011 Share Posted October 23, 2011 Ok. I've read a million threads about piston slap (mostly on gm forums), what causes it and what can be done about it. I have a few questions about it. Now, a lot of this is from my memory so bear with me. Lower end noise, big and small end bearings, crank bearings, etc. Get noisier and are more pronounced under load and on a warm engine. Valve train noise is the opposite, it is noisier at startup but never really good away when warm. Piston slap , for the most part, vanishes in ten or twenty min of driving. Do I have this right? Are there any other knocking noises that disappear once the engine warms? Quote Link to comment Share on other sites More sharing options...
johnceggleston Posted October 23, 2011 Share Posted October 23, 2011 the only correction i would make is, ''piston slap LESSENS as the engine warms up.'' it does disappear on some engines, but on my 97 obw it never really went away. what year, engine, trans, miles, car? Quote Link to comment Share on other sites More sharing options...
the3rsss Posted October 23, 2011 Author Share Posted October 23, 2011 99obw 140k Quote Link to comment Share on other sites More sharing options...
johnceggleston Posted October 23, 2011 Share Posted October 23, 2011 the one possibility you didn't mention is the timing belt tensioner. they can make noise when they get old and start flopping around. iirc, you can eliminate / identify piston slap by shorting out the spark on the suspect cylinder. if the noise goes away, it is piston slap. if the noise continues it is something else. but it has been a long time since i did this so you should double check the procedure. a mechanics stethoscope will help narrow down the area the noise is coming from. Quote Link to comment Share on other sites More sharing options...
the3rsss Posted October 23, 2011 Author Share Posted October 23, 2011 I have used a scope. The rap is much more pronounced on both rear piston. Does this by itself, eliminate the chance it could be lower end noise? Or , say, cam bearings? Quote Link to comment Share on other sites More sharing options...
the3rsss Posted November 3, 2011 Author Share Posted November 3, 2011 Just wanted to wrap this thread up. I tried a few different motor oils to see if it lessened the piston slap and here is what I found. 1. Mobil one 0 w40. This was by far the loudest and took the longest to go away. Even knocked a little when fully warmed. 2. Mobile one 10w 30. Still knocked though not as bad. Mobil 5000 5w 30. Quieted down the motor a bit. Fan best with this. Didn't seem to tolerate synthetics well at all. Just my 2 cents. Also, if I warm up the car with the block heater I get no slap. Quote Link to comment Share on other sites More sharing options...
johnceggleston Posted November 3, 2011 Share Posted November 3, 2011 Also, if I warm up the car with the block heater I get no slap. that is a very interesting piece of information. thanks. i have heard that a 10w 40, havoline i think, was good for keeping it quiet. Quote Link to comment Share on other sites More sharing options...
john40iowa Posted November 4, 2011 Share Posted November 4, 2011 Ok. I've read a million threads about piston slap (mostly on gm forums), what causes it and what can be done about it. I have a few questions about it. Now, a lot of this is from my memory so bear with me. Lower end noise, big and small end bearings, crank bearings, etc. Get noisier and are more pronounced under load and on a warm engine. Valve train noise is the opposite, it is noisier at startup but never really good away when warm. Piston slap , for the most part, vanishes in ten or twenty min of driving. Do I have this right? Are there any other knocking noises that disappear once the engine warms? Mine never completely went away on the' 99. After it started for about maybe a couple thousand miles it would diminish after warming up; from then on it was almost like listening to a ball peen hammer on steel and drove me crazy. I didn't try the different oils mentioned here, the solution was to have my engine rebuilt with New Pistons! Now about 50K city miles later I am happy to report no major problems which is pretty good I think for a twelve year old car. Doesn't use a drop of anything. Quote Link to comment Share on other sites More sharing options...
Lukas Posted November 4, 2011 Share Posted November 4, 2011 My 99 Legacy with the EJ20 engine had piston-slap when I bought it with 135.000 miles a year ago and it never got worse. It now has 160.000 miles on the clock and everything is fine after a short warming up period. My mechanic said it´s normal for an older Subaru-engine to have a bit of piston-slap, if you don´t race your cold engine, it will last a long time with it. Quote Link to comment Share on other sites More sharing options...
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