Cylinder Leakdown Test - Expectations

[ZeroH]

Hi All,

I'm having the coils and sparks done today by my local opc on my 03MY 996tt x50, and have requested a cylinder leakdown test at the same time.

Can anyone advise what are decent pressure loss figures that I should be looking for, and has anyone done a similar test and can post numbers so I have something to compare against.

I wanted to get a snapshot of my engines health before deciding to tune it (currently car is stock with 33k miles)

Thanks v much !!

[svansyoc]

I would generaly like to see under 5% on a leak down test, but would not get to excided until reaching the 15 to 20% range, sometimes the accuracy of the gauge being used is somewhat in question, the gauge must be adjustable to compensate for the shop compressor air pressure. Even a slight amount of carbon on a valve can cause a valve not to fully seat fully. A burn't valve or bad rings would generally run higher than 50%. s van syoc

[White987S]

I agree with the <5%.

Also look for consistency among the 6 cylinders.

[ZeroH]

I would generaly like to see under 5% on a leak down test, but would not get to excided until reaching the 15 to 20% range, sometimes the accuracy of the gauge being used is somewhat in question, the gauge must be adjustable to compensate for the shop compressor air pressure. Even a slight amount of carbon on a valve can cause a valve not to fully seat fully. A burn't valve or bad rings would generally run higher than 50%. s van syoc

Thanks v much !

I understand also that its important for consistency across the figures, i.e. you want them to be as close as possible to each other ?

[ZeroH]

I agree with the <5%.

Also look for consistency among the 6 cylinders.

ha... you beat me to it !! Thx !

[ZeroH]

OK so just had my values back, 4%, 5%, 0%, 7%, 12%, 10%.

OPC advises that these numbers are fine (only >30% should I be worried they say !) and no issues to worry about. Clearly I have a few values >5% however, so do you think that this is still acceptable / healthy ?

Seperately I'm advised that I have "idle loss adaption" of 199% (value should be 4%) so air is leaking from somewhere... this needs investigation !

[White987S]

ZeroH, if I were buying your car, and did a PPI, and got those leak-down values, I would probably take a pass on the car. There are a ton of 996 TT's for sale, and prices are dropping like a rock. But, this is not the case. You are not selling the car.

You should invest the money now, or set aside for later, to have the necessary repairs done to this great car in the future.

[svansyoc]

I would not be that concerned with those numbers, the only thing I personally would recomend is adding a fuel cleaning additive such as bg 44k that has a high amount of the chemical techron in it to help clean carbon from back side of valves and combustion chamber, do the tune up and recheck the next time plugs are replaced. Even a slightly loose hose or old o-ring on cylinder leak down tester can give you slight variances in your readings. svansyoc.

[ZeroH]

ZeroH, if I were buying your car, and did a PPI, and got those leak-down values, I would probably take a pass on the car. There are a ton of 996 TT's for sale, and prices are dropping like a rock. But, this is not the case. You are not selling the car.

You should invest the money now, or set aside for later, to have the necessary repairs done to this great car in the future.

Not quite sure what you are saying here... you think I need to set money aside because you think these numbers are so bad I'm looking at some serious engine work down the road ?? Do you have any experience of these numbers leading to such an outcome ?

[White987S]

ZeroH, if I were buying your car, and did a PPI, and got those leak-down values, I would probably take a pass on the car. There are a ton of 996 TT's for sale, and prices are dropping like a rock. But, this is not the case. You are not selling the car.

You should invest the money now, or set aside for later, to have the necessary repairs done to this great car in the future.

Not quite sure what you are saying here... you think I need to set money aside because you think these numbers are so bad I'm looking at some serious engine work down the road ?? Do you have any experience of these numbers leading to such an outcome ?

I think you are fine, but what happens when you "start tuning the car" and put the engine under additional stress? What happends to those leakdown values then?

All I was saying, is if I were looking to buy a car, and did a PPI and got your values, I'd take a pass and look for another car with a narrower range from the leakdown values.

[ZeroH]

ZeroH, if I were buying your car, and did a PPI, and got those leak-down values, I would probably take a pass on the car. There are a ton of 996 TT's for sale, and prices are dropping like a rock. But, this is not the case. You are not selling the car.

You should invest the money now, or set aside for later, to have the necessary repairs done to this great car in the future.

Not quite sure what you are saying here... you think I need to set money aside because you think these numbers are so bad I'm looking at some serious engine work down the road ?? Do you have any experience of these numbers leading to such an outcome ?

I think you are fine, but what happens when you "start tuning the car" and put the engine under additional stress? What happends to those leakdown values then?

All I was saying, is if I were looking to buy a car, and did a PPI and got your values, I'd take a pass and look for another car with a narrower range from the leakdown values.

OK right, so all you wanted to say is that you wouldnt buy my car based on its leakdown values !!

Thanks, i'll take you off my buyers list then... :rolleyes:

Seriously though, I have spoken to someone who is mechanically minded who says that if you split the left cylinder bank, 4/5/0, you get a max difference of 5%, and on the right bank 7/12/10, a max difference of 5% ... Hence there is at least consistency here and nothing to be worried about.

[ZeroH]

Just digging this thread up again as today I had another cylinder leakdown test done on my car before I have it tuned.

Given that the opc in January gave me such high readings I wanted to double check them before mapping it.

The test was done by a well known porsche specialist and the results they got were cyl 1 3%, cyl 2 2% cyl 3 4% cyl 4 2% cyl 5 2% cyl 6 2%.... these compare to results of up to 12% gained by the opc in January.

Assuming that the specialist results are correct, would you consider that these differences are within an acceptable tolerance? r would you say that more likely the opc results are null and void and maybe have a word with them about how they obtained their results ??

[Macster]

ZeroH, if I were buying your car, and did a PPI, and got those leak-down values, I would probably take a pass on the car. There are a ton of 996 TT's for sale, and prices are dropping like a rock. But, this is not the case. You are not selling the car.

You should invest the money now, or set aside for later, to have the necessary repairs done to this great car in the future.

Not quite sure what you are saying here... you think I need to set money aside because you think these numbers are so bad I'm looking at some serious engine work down the road ?? Do you have any experience of these numbers leading to such an outcome ?

I think you are fine, but what happens when you "start tuning the car" and put the engine under additional stress? What happends to those leakdown values then?

All I was saying, is if I were looking to buy a car, and did a PPI and got your values, I'd take a pass and look for another car with a narrower range from the leakdown values.

I think you'd be looking for a car for a long time. Leak down test results are not very definitive unless compression test finds a low cylinder. Then leak down test is used to ID probable cause of low compression.

With these engines oil jets squirt oil onto backside of piston and this oil will work to help seal piston and cylinder. Some cylinders, the good ones, got a good shot of oil, the lower ones not so good. But once running everything will be ok.

As long as compression test finds no out of spec cylinder leak down test waste of time and money.

Sincerely,

Macster.

[Luke T]

Can somebody tell me what the compression should be on a 2004 996 TT pls? i am getting 160  - 190 in Australia. The car runs even with the 15% difference in values. Should i be concerned?