PPI advice: myths about leakdown/compression test - needed or not?
06-01-2011, 11:01 AM
#16
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From a professional standpoint who has done a hell of a lot of PPI's, I have seen 50k mile motors with 30% leakdown on the cylinders, and 175k motors with less than 5% leakdown. Don't guess by mileage, have at minimum a leakdown test done. I have also seen good compression results with bad leakdown results.
Personally, I would not buy an older 911 without leakdown and compression tests, with the leakdown test IMHO being the most important and where I see the most variations with the 993 motor specifically.
I only advise throwing in new spark plugs on the turbo cars that are single plug, since they will be out for the test. Just costs the price of the plugs. I typically don't do it on the NA's because there are 12 plugs and you are only pulling out 6.
Personally, I would not buy an older 911 without leakdown and compression tests, with the leakdown test IMHO being the most important and where I see the most variations with the 993 motor specifically.
I only advise throwing in new spark plugs on the turbo cars that are single plug, since they will be out for the test. Just costs the price of the plugs. I typically don't do it on the NA's because there are 12 plugs and you are only pulling out 6.
06-01-2011, 11:32 AM
#17
Burning Brakes
I personally wouldn't bother with a compression/leakdown on a low mileage motor that was running perfectly, had service records, etc. 993 motors are pretty damned bulletproof except for valve guide wear, and you can only get a read on that from looking at oil consumption.
A car that has higher mileage, been tracked, modified, chipped, etc, is another story of course. Then it pays to verify.
A car that has higher mileage, been tracked, modified, chipped, etc, is another story of course. Then it pays to verify.
06-01-2011, 12:22 PM
#18
Racer
Hi all,
I was recently advised that if a car is a lower mileage example (<40K miles), in good shape, it's sufficient to gauge the engine's health through the smog results. In other words, the smog reading won't lie, and will tell you if the engine/valves/etc. are working properly.
I was also advised by one shop that if they do a leakdown and compression test, they would need to change the sparkplugs. I'd never heard that before.
-bg
I was recently advised that if a car is a lower mileage example (<40K miles), in good shape, it's sufficient to gauge the engine's health through the smog results. In other words, the smog reading won't lie, and will tell you if the engine/valves/etc. are working properly.
I was also advised by one shop that if they do a leakdown and compression test, they would need to change the sparkplugs. I'd never heard that before.
-bg
As to your question about the smog test... it's not completely reliable as an indicator because the cats will scrub the exhaust... if you had bad cats & o2 sensors, then sure it would be a bad sign...not likely on a low mileage motor that runs fine otherwise.
As far as the plugs, have them changed if it passes w/flying colors, otherwise have them put the old plugs back in. The don't "have" to be changed .
My advice... get the PPI done for peace of mind.
06-01-2011, 01:41 PM
#19
hysterical.
however, given that "static" and "dynamic" are words in the english language, they have meanings aside from compression ratios.
In a leakdown test, the piston is static (i.e. not moving) at TDC while the test is conducted.
In a compression test, by cranking the starter, the piston is moving, the valves are opening/closing, etc.
The tests do tend to give corresponding readings, but it makes no sense to do one without the other.
however, given that "static" and "dynamic" are words in the english language, they have meanings aside from compression ratios.
In a leakdown test, the piston is static (i.e. not moving) at TDC while the test is conducted.
In a compression test, by cranking the starter, the piston is moving, the valves are opening/closing, etc.
The tests do tend to give corresponding readings, but it makes no sense to do one without the other.
Stop the maddness, you're just making up stuff now.
They are different test that will tell you different things but if the first test, ie compression test is okay, it's okay, no need to test further.
06-01-2011, 01:46 PM
#20
seriously, a compression leakdown is a good insurance for someone who is not familar with the car and only spent 15 minutes in the car. These are test to varify a problem, they are not pass fail test on the health of the engine.
06-01-2011, 01:56 PM
#21
Rennlist Member
OP,
Search this forum....this has been covered a 100 times. You can find a bunch of opinions on this particular topic in a few minutes, rather than waiting for responses to this thread. A quick search for:
ppi leakdown compression
returns 6 pages of results. There's your evening's reading...and then some!
Search this forum....this has been covered a 100 times. You can find a bunch of opinions on this particular topic in a few minutes, rather than waiting for responses to this thread. A quick search for:
ppi leakdown compression
returns 6 pages of results. There's your evening's reading...and then some!
who pays when the mechanic inadvertently damages a head during sparkplug re-install?
even if the shop pays all costs, the engine will NEVER be as good as it was prior to the "oh so vital leakdown / compression testing"
a prospective buyer would have to convince me that they are VERY serious before i OK'd the process.
PS i bought my car with ZERO PPI other than putting it up on a lift and poking around and i have ZERO regrets.
good luck.
Craig
06-01-2011, 02:05 PM
#22
I bought mine C4 without out a leak down, the PO did do a compression test but that was for other reasons.
The C2 I did neither and other some oil leaks there has been no problems with that car either. There isn't any reason why I would suspect a bad hole. Starts fine, runs fine, idles fine, ir you know the cars you know when there is a probably that warrents a compression test, and the compression test will tell you if you need to do the leakdown.
The C2 I did neither and other some oil leaks there has been no problems with that car either. There isn't any reason why I would suspect a bad hole. Starts fine, runs fine, idles fine, ir you know the cars you know when there is a probably that warrents a compression test, and the compression test will tell you if you need to do the leakdown.
06-01-2011, 02:08 PM
#23
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when the time comes to sell my car.................... i will be very resistant to allowing leakdown / compression testing.
who pays when the mechanic inadvertently damages a head during sparkplug re-install?
even if the shop pays all costs, the engine will NEVER be as good as it was prior to the "oh so vital leakdown / compression testing"
a prospective buyer would have to convince me that they are VERY serious before i OK'd the process.
PS i bought my car with ZERO PPI other than putting it up on a lift and poking around and i have ZERO regrets.
good luck.
Craig
who pays when the mechanic inadvertently damages a head during sparkplug re-install?
even if the shop pays all costs, the engine will NEVER be as good as it was prior to the "oh so vital leakdown / compression testing"
a prospective buyer would have to convince me that they are VERY serious before i OK'd the process.
PS i bought my car with ZERO PPI other than putting it up on a lift and poking around and i have ZERO regrets.
good luck.
Craig
No I'm not.....oh sweet jesus are you kidding me? Stripping a spark plug? I'm not saying it couldn't happen, but if you have a shop with even the slightest bit of competence, then it isn't even a factor. You would have to be an absolute idiot to gall the threads in the head, and if that is the case, you shouldn't let that shop so much as change the oil let alone wash the car.
This isn't brain surgery, it is basic mechanics of a car/engine. It may not seem like it to guys that know nothing about engines, but to those of us that do, doing a leakdown test is about as hard as changing the oil, lol.
06-01-2011, 02:11 PM
#24
Rennlist Member
Not true. A smog test wont show a spun bearing, A smog test wont show a broken head stud... There are mechanical items that if are bad wont show up on a smog test.
Lastly, you only need the leakdown if the compression test fails. The compression test will tell you if it leaks or not, the leakdown will tell you where it's leaking and give you an idea how bad it is.
Lastly, you only need the leakdown if the compression test fails. The compression test will tell you if it leaks or not, the leakdown will tell you where it's leaking and give you an idea how bad it is.
I disagree with just about everything you've said.
A good compression test doesn't necessarily mean there is no cylinder leakage because they are different tests. One is static and the other is dynamic for one. Hell compression tests can be swayed by a weak battery as well.
A good compression test doesn't necessarily mean there is no cylinder leakage because they are different tests. One is static and the other is dynamic for one. Hell compression tests can be swayed by a weak battery as well.
You can find a bunch of opinions on this particular topic in a few minutes
06-01-2011, 04:20 PM
#25
Racer
I am speechless.
No I'm not.....oh sweet jesus are you kidding me? Stripping a spark plug? I'm not saying it couldn't happen, but if you have a shop with even the slightest bit of competence, then it isn't even a factor. You would have to be an absolute idiot to gall the threads in the head, and if that is the case, you shouldn't let that shop so much as change the oil let alone wash the car.
This isn't brain surgery, it is basic mechanics of a car/engine. It may not seem like it to guys that know nothing about engines, but to those of us that do, doing a leakdown test is about as hard as changing the oil, lol.
No I'm not.....oh sweet jesus are you kidding me? Stripping a spark plug? I'm not saying it couldn't happen, but if you have a shop with even the slightest bit of competence, then it isn't even a factor. You would have to be an absolute idiot to gall the threads in the head, and if that is the case, you shouldn't let that shop so much as change the oil let alone wash the car.
This isn't brain surgery, it is basic mechanics of a car/engine. It may not seem like it to guys that know nothing about engines, but to those of us that do, doing a leakdown test is about as hard as changing the oil, lol.
If the shop doing your PPI can't R&R spark plugs w/o damaging the heads, then the PPI is truly a waste of time and money because they are incompetent!!!
C'mon guys, let's give the shops a little more credit than this. Potential head damage is not a valid reason for avoiding taking out a spark plug!!!
06-01-2011, 09:43 PM
#26
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I trusted my mechanic to be competent enough to R&R the plugs on the sell of my 993. Duh. Hell he has the code to my storage unit and knows where the keys are. But then again my mechanic is Karl....aka PorscheDoc.
If I had not been in a time squeeze on the purchase of my Targa last week I would have taken Karl to Dallas with me for the PPI. I'm convinced Karl could do a compression and leakdown on jack stands within two hours on the owners driveway with the owner laying right beside him if they felt compelled.
I would never buy any 911 without a PPI. So why in the world would I refuse one when selling.
Oh and off topic. Everything you guys said about leaving the air cooled world for the dark side was right. I love my 997 as a DD but it's a Lexus with a expensive triangle badge pasted to the hood. Of course a 993 would have been ideal, but wanted to try something different. When this matching Targa come up I pounced.
Cheers boys.....I miss the 993 gang. Even goofballdeluxe.
If I had not been in a time squeeze on the purchase of my Targa last week I would have taken Karl to Dallas with me for the PPI. I'm convinced Karl could do a compression and leakdown on jack stands within two hours on the owners driveway with the owner laying right beside him if they felt compelled.
I would never buy any 911 without a PPI. So why in the world would I refuse one when selling.
Oh and off topic. Everything you guys said about leaving the air cooled world for the dark side was right. I love my 997 as a DD but it's a Lexus with a expensive triangle badge pasted to the hood. Of course a 993 would have been ideal, but wanted to try something different. When this matching Targa come up I pounced.
Cheers boys.....I miss the 993 gang. Even goofballdeluxe.
06-01-2011, 10:53 PM
#27
Congrats on the g50 Targa, Mark! Good to see you back.
Here's a different perspective from someone who does all their own maintenance/repairs:
As a seller, I would be loath to trust a technician to perform these types of tests simply because I would probably not be familiar with the technician's skill level. Unless I knew and trusted the tech, there's no way I'm letting him touch my car in anything but the most superfical way.
Fortunately, this should never be a problem for me as I'll hopefully never need to sell the 993 I've had for 13 years now.......
Here's a different perspective from someone who does all their own maintenance/repairs:
As a seller, I would be loath to trust a technician to perform these types of tests simply because I would probably not be familiar with the technician's skill level. Unless I knew and trusted the tech, there's no way I'm letting him touch my car in anything but the most superfical way.
Fortunately, this should never be a problem for me as I'll hopefully never need to sell the 993 I've had for 13 years now.......
06-02-2011, 05:21 PM
#28
Rennlist Member
I am speechless.
No I'm not.....oh sweet jesus are you kidding me? Stripping a spark plug? I'm not saying it couldn't happen, but if you have a shop with even the slightest bit of competence, then it isn't even a factor. You would have to be an absolute idiot to gall the threads in the head, and if that is the case, you shouldn't let that shop so much as change the oil let alone wash the car.
This isn't brain surgery, it is basic mechanics of a car/engine. It may not seem like it to guys that know nothing about engines, but to those of us that do, doing a leakdown test is about as hard as changing the oil, lol.
No I'm not.....oh sweet jesus are you kidding me? Stripping a spark plug? I'm not saying it couldn't happen, but if you have a shop with even the slightest bit of competence, then it isn't even a factor. You would have to be an absolute idiot to gall the threads in the head, and if that is the case, you shouldn't let that shop so much as change the oil let alone wash the car.
This isn't brain surgery, it is basic mechanics of a car/engine. It may not seem like it to guys that know nothing about engines, but to those of us that do, doing a leakdown test is about as hard as changing the oil, lol.
I do agree when you say "You would have to be an absolute idiot to gall the threads in the head," since i've seen the results of just this occurrence done by a pro mechanic who made a mistake.
As a seller, I would be loath to trust a technician to perform these types of tests simply because I would probably not be familiar with the technician's skill level. Unless I knew and trusted the tech, there's no way I'm letting him touch my car in anything but the most superfical way.
and we agree.
cheers
Craig
06-02-2011, 07:50 PM
#29
Racer
Quote:
Originally Posted by PNogC2S
+1
Potential head damage is not a valid reason for avoiding taking out a spark plug!!!
"we disagree"
So wouldn't the logical extension of that statement be that unless you can change your own plugs, you should never have your plugs changed because a mechanic can't be trusted to do it w/o damaging the heads??? I do my own work, so I know how easy it is to change plugs on these cars w/o wreaking havoc. (yes one plug in particular is a pain, but they're all quite doable)
The only point I was trying to make was that one should be able to trust a competent professional mechanic to perform a task as simple as changing out plugs. So as long as one agrees to a PPI by a shop that is reputable, a leakdown and/or compression test should not be an issue. It's not like you are asking to open up the engine to check the valve guides...it's just spark plugs (and only the easy 6 at that)
Originally Posted by PNogC2S
+1
Potential head damage is not a valid reason for avoiding taking out a spark plug!!!
"we disagree"
So wouldn't the logical extension of that statement be that unless you can change your own plugs, you should never have your plugs changed because a mechanic can't be trusted to do it w/o damaging the heads??? I do my own work, so I know how easy it is to change plugs on these cars w/o wreaking havoc. (yes one plug in particular is a pain, but they're all quite doable)
The only point I was trying to make was that one should be able to trust a competent professional mechanic to perform a task as simple as changing out plugs. So as long as one agrees to a PPI by a shop that is reputable, a leakdown and/or compression test should not be an issue. It's not like you are asking to open up the engine to check the valve guides...it's just spark plugs (and only the easy 6 at that)
06-02-2011, 10:10 PM
#30
Rennlist Member
Thread Starter
All,
I appreciate the responses and dialogue. I will do the leakdown and compression tests, but I'm not sure where to go in light of conflicting advice I've received from two shops (and frankly, one shop's unresponsiveness). Can you all recommend shops that are within 15-20 miles of Hollywood?
Bobby
I appreciate the responses and dialogue. I will do the leakdown and compression tests, but I'm not sure where to go in light of conflicting advice I've received from two shops (and frankly, one shop's unresponsiveness). Can you all recommend shops that are within 15-20 miles of Hollywood?
Bobby