Hi all Seem I have a strange affliction, must be a Z addiction. I'm looking a late model Z32 TT for sale, series 2 engine 177,000km. I asked the guy to get it compression tested which he happily did. Auto Masters did the test and it came back all cylinders between 130 - 135psi which is all nice and even but seems quite low to me. Just wondering if the series 2 engines ran lower compression or can anyone shed any light on this? The only other thing I can think of is the mechanic's compression gauge is reading low, I would of thought if the engine had lost 25-30psi of compression during it's lifetime that there would far more variation across the cylinders.
Figures are a bit low for TT; anything below 127 is considered a "fail". That said things like gauge calibration, throttle bodies open/closed, balance tube on/off, whether it was tested with all plugs removed, how healthy the batter is etc etc are all going to play on the final result. The important thing is that the readings are all very close.
Re: Compression Figures A TT engine in excellent condition with low kilometres will read at the high end of the specification chart. An engine in poor condition that has done high kilometres, or has been poorly maintained will read at the low end of the chart. The compression specifications are the same for all TT's regardless of year of manufacture & are 171psi down to 128psi. The maximum allowable difference between cylinders is 14psi. The engine you are looking at based on the test would indicate this is a high milage engine approaching the end of its life. It is possible it is in fact a low milage engine that has been 'dusted'. That is an engine that has inhaled dirt/dust particles causing severe wear. This type of wear is normally caused by not using intake air filters, or filters of poor quality. I don't understand how WazTTed could claim "That's a healthy engine dude !!" The test figures clearly indicate otherwise. If the mechanic you used to do the test is a real mechanic, you would expect that he would know how to test an engine. He would also realise the consequences of performing tests with defective test equipment. The test figures indicate the engine has lost between 36 & 41psi in compression, not 25 to 30psi.
I think that waz's comment was made on the assumption that such wear of 36+ psi equally across all 6 pots was highly unusual, and a good way to consider compression tests is the variance between the pots due to the inconsistencies of test equipment, (DIY test equipment in particular).
I understand what you're saying Andy. I based my comments on the information supplied. If the test procedure, or the equipment used is suspect, then a second compression test by another mechanic using different equipment should be considered. Then again, if the results don't match, which mechanic is correct?
Compression tests are merely an indication of engine condition. If you require an accurate assesssment, then a leak down test should be performed. The downside of a leak down test is, it is more complicated & time consuming to perform & if you are paying someone else to do it, it will be more expensive. As far as compression tests being a wank, if you were looking at purchasing a TT Z32 & the choice was narrowed down to two vehicles at the same price, identical in all aspects except one had engine compression of 135psi across all cylinders & the other had 165psi across all cylinders. Which would you purchase? Obviously you would choose the one with the lower compression, because you only need 70psi in your rotary.
Nah compression tests are important, I remember when I bought the bull, basically flicked through all the PPI documents to the compression test. 162-168 on all 12 cylinders. Wouldn't have bothered reading the rest if it wasn't solid. Saying that the car only had 20,000k's on it, so it had better have been good.
Rotaries require a special type of tester cant remember exactly why but I do remember they dont read right on a normal one. Been 20 years since I did a compression test on a rotary engine
My engine was freshly rebuilt and run in when I bought it and it tests within close to 170 across all 6 when cold
Right on the money Stu. The Nissan data indicates a TT would have compression in the order of 171psi. Whereas an NA would have 186psi.
Updated test info. So I got back to the owner and said that something was not right with those test results. He then spoke with the manager at Auto Masters who spoke with the young guy who performed the test. Result was he only cranked the engine 4 times on each cylinder, the battery was not fully charged and sounds like he only removed one plug at a time, end result a completely inaccurate test. The manger did the test again correctly free of charge. Results are No 1 - 153, No's 2 - 6 all 150. Great results for a 177,000km engine I think. Glad to confirm that my gut feeling proved to be right. And no, I won't be getting any work done at that particular branch of Auto Masters.
So many bad tests I have seen have pointed to a stuffed engine but have in fact been either faulty technique in testing or faulty compression tester. I saw a good engine junked because some knob tested with a Chinese compression tester which read 40 PSI lower than actual....
yep if all numbers are within spec of each other then there is always a chance its the tester. its not usual for all 6 cylinders to lose the same amount of compression/seal over the years. Normally 1 or 2 cylinders can be low on compression and even if all are there is more variation than 5-10 psi. So if a compression test show 6 cylinders all ~120 I would suggest trying a different tester but if 4 are 150 and 2 are 120 then I would blame the engine (after a second check to rule out user error)
