94vertluvr Posted September 23, 2010 Report Share Posted September 23, 2010 I haven't been on for awhile...but I had my mechanic find a 'good' 3.4 engine to replace mine with...supposedly it had around 82,000 miles. I did a compression test on all the cylinders just to see what I had, here's what I found out: All the cylinders had compression within 3 or 4 of 170 EXCEPT the rear far right cylinder had compression reading of 150. Another mechanic told me that from one cylinder to another it should not differ more than 10% and this is apparently VERY close to that. He also said this could be from a sticking ring since it had not been run for a bit or it could be a dirty valve or it could be starting to have a problem. I've sunk a good chunk in this engine exchange question: Should I be concerned with these readings? Did I buy a problem engine??? The engine does not smoke and there are no knocks or pings internally that can be heard. All gaskets have been replaced and the original mechanic said the parts all looked good before he put it all together. Please respond those of you who know these engines and let me know your thoughts. Thanks! Quote Link to comment Share on other sites More sharing options...
RobertISaar Posted September 23, 2010 Report Share Posted September 23, 2010 170-150 isn't bad at all for a motor that supposedly hasn't run for a while... you're supposed to do the test with the motor warm, at WOT with all of the plugs removed. oddly enough, it is cylinder 6 that sounds like it is the weakest, and IIRC, that is the cylinder that runs the hottest due to recieving coolant last. Quote Link to comment Share on other sites More sharing options...
spiderw31 Posted September 23, 2010 Report Share Posted September 23, 2010 All in all, those number sound pretty good to me. Quote Link to comment Share on other sites More sharing options...
AL Posted September 25, 2010 Report Share Posted September 25, 2010 Sound good to me too Quote Link to comment Share on other sites More sharing options...
Schurkey Posted September 25, 2010 Report Share Posted September 25, 2010 Two words: Leakdown test Compression test is flawed due to several factors. I'm not saying it's worthless--quite the opposite. But a compression test provides less info than a leakdown test; and ideally you'd have BOTH tests done. The leakdown test will tell you HOW MUCH compression is bleeding off; and WHERE it's going to. If you hear pressure escaping out the throttle body, you know the intake valve isn't sealing. You hear pressure escaping from the tailpipe, the exhaust valve isn't sealing. You hear pressure escaping out the oil fill cap, you know it's going past the rings. If the radiator explodes, the pressure is going through a defective head gasket or a cracked casting. (well, OK, you might want to remove the rad cap and look for bubbles instead.) You hear a LITTLE air coming out the oil fill cap; and the overall leakage indicated on the gauge isn't too high--no problem. As with all things, the leakdown test isn't perfect, either. The guy doing it MUST have direct experience with the leakdown tester in use; because there's no "industry standard" for the orifice size in leakdown testers; and some are just plain MORE SENSITIVE than others. So don't be fooled by some bozo telling you that "X" amount of leakage means the engine is shot. IT ALL DEPENDS ON THE TESTER IN USE. The tester I use--an ancient Snap-On MT240 (???)--is very sensitive; I don't get too worried about any cylinder showing less than 40% leakage unless it's very small-displacement. Quote Link to comment Share on other sites More sharing options...
94vertluvr Posted September 30, 2010 Author Report Share Posted September 30, 2010 Well this is the first time I've heard of this test. How do you ask a mechanic if he's a bozo or not? What kind of questions should I ask him so i know he knows what he's doing when it comes to this test? It sounds like it would be a helpful test to do! Thanks for the suggestion and info! Two words: Leakdown test Compression test is flawed due to several factors. I'm not saying it's worthless--quite the opposite. But a compression test provides less info than a leakdown test; and ideally you'd have BOTH tests done. The leakdown test will tell you HOW MUCH compression is bleeding off; and WHERE it's going to. If you hear pressure escaping out the throttle body, you know the intake valve isn't sealing. You hear pressure escaping from the tailpipe, the exhaust valve isn't sealing. You hear pressure escaping out the oil fill cap, you know it's going past the rings. If the radiator explodes, the pressure is going through a defective head gasket or a cracked casting. (well, OK, you might want to remove the rad cap and look for bubbles instead.) You hear a LITTLE air coming out the oil fill cap; and the overall leakage indicated on the gauge isn't too high--no problem. As with all things, the leakdown test isn't perfect, either. The guy doing it MUST have direct experience with the leakdown tester in use; because there's no "industry standard" for the orifice size in leakdown testers; and some are just plain MORE SENSITIVE than others. So don't be fooled by some bozo telling you that "X" amount of leakage means the engine is shot. IT ALL DEPENDS ON THE TESTER IN USE. The tester I use--an ancient Snap-On MT240 (???)--is very sensitive; I don't get too worried about any cylinder showing less than 40% leakage unless it's very small-displacement. Quote Link to comment Share on other sites More sharing options...
AL Posted September 30, 2010 Report Share Posted September 30, 2010 He should know what that test is... If he doesn't then find someone who does lol Quote Link to comment Share on other sites More sharing options...
Schurkey Posted September 30, 2010 Report Share Posted September 30, 2010 (edited) How do you ask a mechanic if he's a bozo or not? Well, if you're Patrick Jane (The Mentalist) you'd ask directly. "So...Are you a bozo?" Good luck with that; you'll get a fist in the face or be escorted back to the parking lot. What kind of questions should I ask him so i know he knows what he's doing when it comes to this test? It sounds like it would be a helpful test to do! Thanks for the suggestion and info! He should know what that test is... If he doesn't then find someone who does lol I'd ask to SEE his leakdown tester; and I'd ask what a "typical" good "reading" is. He looks at you blankly...you need another shop. If he says they just pump air into the cylinder and listen for problems; you need another shop. If he shows you a well-kept, non-greasy gauge that looks like it's been used, but not abused; and if he talks about various experiences he's had with it so it sounds like he's completely familiar with "typical" results from THAT leakdown tester...go for it. He shows you a brand-new gauge that looks unused...you need another shop. Edited September 30, 2010 by Schurkey Quote Link to comment Share on other sites More sharing options...
94vertluvr Posted October 7, 2010 Author Report Share Posted October 7, 2010 LOL LMAO that's funny! I just seen this comment for some reason I missed it!!! I watch that show and I can see/hear exactly what ur saying!!! Thanks for the good advice! Well, if you're Patrick Jane (The Mentalist) you'd ask directly. "So...Are you a bozo?" Good luck with that; you'll get a fist in the face or be escorted back to the parking lot. I'd ask to SEE his leakdown tester; and I'd ask what a "typical" good "reading" is. He looks at you blankly...you need another shop. If he says they just pump air into the cylinder and listen for problems; you need another shop. If he shows you a well-kept, non-greasy gauge that looks like it's been used, but not abused; and if he talks about various experiences he's had with it so it sounds like he's completely familiar with "typical" results from THAT leakdown tester...go for it. He shows you a brand-new gauge that looks unused...you need another shop. Quote Link to comment Share on other sites More sharing options...
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