xt2005bonbon Posted April 23, 2015 Share Posted April 23, 2015 I've been having the privilege of performing leakdown tests on my two OBXTs for various reasons. I keep reading that you should do these tests with a warm engine. I did these tests with cold engines. On car 1, cylinder #2 has 2.5% leakdown. On car 2, cylinder #2 and #4 have 6% and 5.5%, respectively. My question is: would those results be better or worse if the engine was warm? My guess is better due to pistons rings providing a better seal. But how about the valves? Do valves provide better or worse seals when the engine is warm vs. cold? I guess that was two questions... Link to comment Share on other sites More sharing options...
xt2005bonbon Posted April 24, 2015 Author Share Posted April 24, 2015 Anyone? Link to comment Share on other sites More sharing options...
heiche Posted April 24, 2015 Share Posted April 24, 2015 The main difference that i can think of is if you have a situation where your valve clearances are too tight. You can have a case where COLD the clearance might be below spec, but the valve is still seated firmly. But then when the engine gets HOT and everything expands a bit, that small clearance disappears, and there might be enough pressure to ever-so-slightly lift the valve off the seat, and it's at that point where the compression and/or leakdown indicates a problem. BtSsm - Android app/Bluetooth adapter. LV, logging, gauges and more. For 05-14 Legacy (GT, 2.5, 3.0, 3.6), 02-14 WRX, 04-14 STi, 04-14 FXT, 05-09 OBXT Link to comment Share on other sites More sharing options...
xt2005bonbon Posted April 24, 2015 Author Share Posted April 24, 2015 OK. I think I understand. So the interesting thing is car 1 which has 2.5% leakdown on #2 on a cold engine, was giving me some roughness counts at idle only when the engine was warm. car 2 which has 6% leakdown on #2 on a cold engine, is giving me some roughness counts at idle only when cold. For car 1, I have checked spark plugs, coil pack, and injector. It may be that for that car, the injector was not sitting properly (see my unburned fuel thread). But it is important to note that valve clearance was adjusted 10k miles ago. So maybe they did not really do a good job and it gets tight when the engine is warm.. For car 2, I have checked spark plug, coil pack, but have not swapped injectors yet. When warm, roughness is completely gone. So from my result, and what you're saying, it should be an injector issue (or intake gasket--haven't changed those yet). Thoughts? Link to comment Share on other sites More sharing options...
heiche Posted April 25, 2015 Share Posted April 25, 2015 On car 1, my guess would be those valve clearances are too tight, since you checked just about everything else. and the condition does seem to get worse when the engine is hot. i assume 10k miles ago they just adjusted the existing valves? that's typically good enough, but maybe on this cylinder the valves (assuming exhaust valves) need to be replaced? of course that wouldn't be good news since i'm sure you don't feel like pulling another engine! if you can, perhaps a compression/leakdown test on engine when hot will help determine this? or maybe others can think of something else that would cause this, that hasn't been tested yet? On car 2, it's a little scary that the leakdown test is a bit higher on #2 - wonder how it compares to the other cylinders in the same car? i'd try out your ideas. maybe replace the tgv o-rings since those are notorious for causing vac leaks when the engine is cold in the morning, even though it seems to be cyl #2. Sure, moving the injector is a great test to see if the misfire moves with it. BtSsm - Android app/Bluetooth adapter. LV, logging, gauges and more. For 05-14 Legacy (GT, 2.5, 3.0, 3.6), 02-14 WRX, 04-14 STi, 04-14 FXT, 05-09 OBXT Link to comment Share on other sites More sharing options...
xt2005bonbon Posted April 25, 2015 Author Share Posted April 25, 2015 On car 1, once I put everything together I will see hiw the car performs. If roughness is still there, I will do a leakdown test when hot. On car 2, I did do a leakdown test on the adjacent cylinder and essentially gave me the same result (close to 6%). That cylinder does not have roughness count at all. Since the roughness count is gone when warm and it does not burn oil, and the adjacent cylinder is giving almost the same leakdown result, I would think internals are ok. But we shall see when I inspect the injector. In any case, this car runs great though. Very rarely fkc and free of flkc. Link to comment Share on other sites More sharing options...
heiche Posted April 25, 2015 Share Posted April 25, 2015 sounds good! BtSsm - Android app/Bluetooth adapter. LV, logging, gauges and more. For 05-14 Legacy (GT, 2.5, 3.0, 3.6), 02-14 WRX, 04-14 STi, 04-14 FXT, 05-09 OBXT Link to comment Share on other sites More sharing options...
GTTuner Posted April 25, 2015 Share Posted April 25, 2015 6% isn't a lot of leakage. Link to comment Share on other sites More sharing options...
xt2005bonbon Posted April 25, 2015 Author Share Posted April 25, 2015 6% isn't a lot of leakage. That's what I thought, especially knowing the engine has 133k. But then, I did it cold. So my guess is if I do it hot, the rings would provide an even better seal, which could potentially decrease leakage, but valves may not seal as well, which would increase leakage. But I don't get roughness when warm, so I would think valves are not leaking. Who knows... Anyway looks like the answer to my original question is leakdown test should be performed warm to rule out valve clearance issues. Link to comment Share on other sites More sharing options...
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