greenjt

I will be having a PPI done and am curious how to interpret the result of a leakdown once i get it. Any help is appreciated. Thanks.

enthusiast

The test should be performed by personnel who know the proper procedures such that the results are accurate and the engine is not damaged from excessive pressure.

Leak Down. This is a test to determine how well the combustion chamber is sealed. With the valves closed pressure is applied to the chamber through the spark plug hole and the rate of leakage is measured.

Bruce Anderson says that 5% to 15% is acceptable and that a well maintained Porsche engine has a leakage rate of 3% to 5%.

Bill Gregory

Typically, 10% or less is fine.

greenjt

Does consistency of the numbers accross cylinders be another objective in addition to the %?

My understanding is that a leakdown can measure where the leak is coming from. Is this true?

JoeW

Sure, consistency is important .... but don't get too **** on this. If one cylinder is 4% and another is 8% there would be no concern. But if a third cylinder comes in at 40%, a problem is in the works!

Good luck.
Joe

warmfuzzies

Quick question,

should this be done hot or cold? and if so why.........sorry two questions. (My say is on hot.)

kevin

DerkBarrington

can you do a leak down test @ home or do you need specialized equipment? I assume you need an air compressor, adapter for the sparkplug and a gauge.... is it an advanced DIY procedure?

Bill Gregory

On 964 engines, you want to do the leakdown on a warm engine. Remember that 964 cylinders are tapered slightly, so you want the engine warm to accurately reflect it's leakdown. A leakdown on a cold 964 engine can misstate the leakdown numbers.

Bluey964

How much does the leakdown test reflect real world changes in performance or engine stability as the engine wears?

I'm curious as I had a leakdown test done at my last service just to gauge the engine condition - the car runs super smooth, no idle problems or hunting, no smoke on acceleration,no excessive oil consumption but the ranges were as follows:

#1 cylinder 20%
#2 30%
#3 15%
#4 25%
#5 20%
#6 22%

I suspect that it was done when the engine was cold as it was a full service with valves being reset which would account for the higher leakage figures shown that you might otherwise expect. However, the fact that there are no real standout marked differences between the cylinders means this is just normal wear and tear. The specialists were not themselves concerned, indicating that they would only do a rebuild once most of the cylinders were over a 40% leakdown figure. I have not put the car on a dyno to know what HP it is actually putting out, but it doesn't feel unduly down on power when going out for runs with other 964's.

Interested to hear peoples thoughts.

Iain

Dunasso

I've read the responces that you guys have posted on this thread and it has become apparent to me that although some of you know what a leak down test is, and the theory behind it, I do not believe that any of you have adiquately performed one.

I could be wrong, and have been before.

In any case, a leak down test can not be performed with out the specialized equiptment and the knowlege to use it. You WILL need the air compressor and a leakdown manifold ( preferably a quality one ) and the knowlege neccessary to dial in the proper pressures which will inturn give you the percentages upon proper calculation.

Bill Gregory is write the engine should be warm. If read the guages in any other manner they will yeild inconsistant results. Warm is the norm, for any engine, Not hot and not cold. Those pesky little % points ARE exactly what you're looking for.

On the other hand if your engine is NOT hitting on all cylinders and you have ruled out electrical and fuel as the problem, then your next step should be a wet test, NOT A LEAK DOWN test.

The wet test will provide you with the simplest and quickest result. If the result is a negative wet test then you have no choice but to tear down the engine. Again there is knowlege that must be acquired to determine the results of the wet test aswell. Never the less the problem can be discovered with either test, but the wet test IS quicker.

Duncan

DavidI

I'm interested to see answers to this too; my results were 18-23% over all 6.

As an additional question, what would you actually rebuild to improve leakdown results? Valves, guides, piston rings? Or is it a case of if you're going so far you strip the whole thing down and see what you find?

warmfuzzies

By Wet test, do you mean spraying the cylinder walls with fluid before doing a leak down? IIRC this is what we used to do to rule in/out the piston rings out of the equation where I used to work.

kevin.

Texas993

Wow, this makes me feel good. When I had the leakdown test done on my former '92 C2 (sold to my Dad and bought the 993 Targa) all cylinders were less than 5%! Car had 40k miles.

Always knew that car had a strong and tight engine.

Pesty

Leak down results for my car were as follows. at 58k miles

1: 8%
2:12%
3:10%
4:12%
5:10%
6:5%

Dunasso

OK, here we go.

Wet test is used to find an immediate problem with a particular cylinder that has little to no participation with the engine. In other words the engine is missing baddly on one cylinder. Once that cylinder has been isolated, a fuel injector test has shown no negative results and an electrcal test has shown no negative results, then a compression test should be performed. If the compression test results are low or no compression is indicated, the next step would be a wet test.

The wet test is done by disconnecting the compression guage and squirting a light wieght oil into the cylinder and reattaching the guage. Repeating the compression test at this time will yeild different conclusions depending upon the problem that has occured with the engine. If the guage reveals no change do to the added fluid in the cylinder then it is a possibilty that the engine may have (1) tight valve/s, (2) burnt valve, (3) broken/bent valve, (4) broken or worn compression rings, or (5) hole in the piston due to broken/bent valve. On the other hand if the wet test shows an increase in compression upon the repeat, then the rings are in need of replacement. In any case the engine has to come apart, so you might as well start digging deep ($$$$). These are a few problems that could be a result of little or no compression and other indicators may preclude that you may not need a test to determine.

A leakdown test is not ment to be used in determining damage to an engine; it is used to determine performance. If the performace of an engine is lower than one might expect it to be, then a leakdown test can determine how low it is. For example, if two cars are identicle, and both have there engines rebuilt at the same time, by the same person, using the same parts, then one might assume that the engines are the same and would yeild the same performance. This IS NOT true, although the parts and skill it took to rebuild them was the same, there tollerances and temperatures were different. A leakdown test will reveal the difference between the two engines and allow a skilled or trained eye to conclude which engine may yeild the best performance for the longest period of time. However, for the everyday driver and ocassional track racer it will let them know when a refreshment of their engine is neccessary to optimize their engines performance. That's where those pesky little differences in % points come in. If a certain car has an average across the board % of 5-10, then the engine is OK. If it is it higher that 10% then the choce is up to you and your budget. If it is higher than that and still runs good with minimal oil consumption then it will still be a good driver but may need a refresh soon. No need to wait for a major event, although alot of people do, and thats where the wet test and rebulids come in.

Duncan