How to perform leak down test?

[arS6]

Anyone have a good DIY or link to performing a leak down test on the 2.7T? I borrowed the tools.

[Scotty@Advanced]

Anyone have a good DIY or link to performing a leak down test on the 2.7T? I borrowed the tools.

It's pretty simple..

Hook your tester to shop air. The get a reading of air pressure. Make sure cylinder being tested is at TDC. Remove spark plug and screw leak tester into spark plug hole. Open valve allowing shop air to fill cylinder. Take pressure reading. Your leakdown % is the shop air pressure with the valve opened over the shop air pressure with the valve closed.

eg.

82psi (valve opened) /90psi (valve closed) = .911 - 1 = .09 = 9% leakdown (which is alot). You generally want to be under 5% for leakdown values.

Also make sure your compressed air service pressure it consistent as fluctuations in air pressure can indicate false high leak down percentages

If you have a high leakdown percentage, you can listen in the intake tract, exhaust manifold or crankcase for whistling air, this will tell you where the problem is..

Whistling in Exhaust indicated an exhaust valve issue, Noise through the intake is an intake valve issue and air noise through the crankcase will indicate a piston/rings/cylinder issue.

[drdimick]

Since you brought it up, and I am not contesting what you said just asking a question because I am not sure. I have heard 15% is the number to stay above regardless of what kind of engine the test is being performed on. The Matco leakdown tester I have states something like (I dont have it in front of me) 20%, I have also heard 10% is the cut off. Is there a figure stated somewhere?

[drdimick]

And yes Scotty nailed it on the head, not that hard. I also have done them with engine at operating temperature and be aware that the compressed air can push the piston downwards and if you dont notice it can give you a very bad leakdown result.

[Scotty@Advanced]

Since you brought it up, and I am not contesting what you said just asking a question because I am not sure. I have heard 15% is the number to stay above regardless of what kind of engine the test is being performed on. The Matco leakdown tester I have states something like (I dont have it in front of me) 20%, I have also heard 10% is the cut off. Is there a figure stated somewhere?

An excellent engine in perfect condition should have a leak down no less than 5%. However this does not mean if you see 10% it's necessarily bad, generally smaller engines should have less leak down percentages due to tighter clearances.

As drdmick clarified, you want to do this to simulate conditions in which the engine is operating, so doing it at operating temp is preferable, although a bit of a PITA.

[arS6]

So I finally completed the leak down test! All 6 cylinders are perfect with no leaks at all. Unless I performed the test wrong? Set each piston at TDC, turn regulator to about 100 psi and leak gauge at 0 and wait for leak gauge needle to move right? This was done on a hot engine. Towards the end of the test the engine was just warm I assume. I also did a compression check and I got 190+ on all 6 cylinders.

The reason for the tests? I'm losing oil! I have to add about 1 quart a month. Depends on how much I drive of course.

Bringing you guys up to speed...
1. The motor was over heated...bad! Burning oil and coolant!
2. So the motor came out and the heads were removed and completely rebuilt. Bottom end never touched.
3. new turbos are on (I removed the DP to check for oil in the hot side and it's bone dry)
4. No leaks from new valve covers or cam seals
5. no oil drips on the floor
6. I do see some white smoke from the tail pipes when I start the car. After it warms up, no more smoke (no cat)
7. I can see the 3 pistons in bank 1 are wet and black. Looks oily.
8. Most important, the car makes no power! When WOT it feels like I'm gradually giving it gas.
9. I've tried different tunes. Same thing so it's not a tune issue.
10. The car doesnt not make boost all the time. 90% of the time it makes boost just fine. When it does, it makes 23psi and holds it (so no boost leak there). Sometimes It wont make more than 10psi. Hmmmm?


Sounds like a leak in bank 1 cylinders right? Why can I still 190psi on a compressions test and no leaks detected during a leak down test?


Scotty: Good luck with the TDI projects! Can't wait to see the finish product.

[mr.awesome]

I might be misinterpreting this. But in the case scotty provided why would the pressure with the valve be greater than with the valve open, assuming that valve open meant the cylinder was at shop air pressure, then with valve closed some of it leaked out?