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I did a compression test on my friend’s car and it had bad compression. The rings on the piston are leaking. They are not broken or any thing the rings just have carbon deposits on them. My question is that is the best thing that he can do. I don’t want to go to a shop and get it Carbon clean. Too much money. I know that you can add some stuff to your gas that will help clean the stuff off. But what is the best to use.

 
Rep Power: 329

If you did a compression test and it was low, then pretty much nothing you can do short of new rings, bore new pistons that will ensure good results. If anything by cleaning the carbon off ive seen more problems pop up like the engine will start to smoke.....

 
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it could be a couple things other than bad rings... like for instance valves not seating properly. it will most likely be the rings but in either case the engine will prolly need to be torn down for a rebuild.