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How To How to do a leak down test on R56 Mini Cooper S

How To How to do a leak down test on R56 Mini Cooper S

Old 05-10-2017, 08:25 AM
Lex2008 is offline
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How to do a leak down test on R56 Mini Cooper S

I just did a leak down test on my 2008 Cooper S and I thought I'd post some basic instructions. I'm no expert so feel free to add value here.

You can do this alone with my instructions but helping hands are always appreciated.

YOU NEED AN AIR COMPRESSOR TO DO A CYLINDER LEAKAGE TEST, a.k.a "a leak down test".You need an air compressor because youre going to pressurize the cylinders with air when the 4 valves are closed and watch for leaks from the combustion chamber from bad valve seals (intake or exhaust), blown head gaskets or failing piston rings.

My engine was cold when I did this test. Does it matter? It might if you have a minor leak, as a warm engine might give a better result.

I finished doing a compression test (https://www.northamericanmotoring.co...56-cooper.html) and while I was at it I wanted to try a leak down test as well to get to use my new kit for the first time. Usually you use a leak down test to pinpoint the cause of poor compression. So first you do the compression test. If the test shows bad compression in one or more cylinders you move to a leak down test to find the cause.

I used OTC's Cylinder Leakage kit 5609 which is OK but not without some issues:


-Jack up front of car. Take off passenger side wheel.

-Take out all 4 ignition coils and spark plugs.

-Remove the coolant bottle cap and oil filler cap on the valve cover.

-You can do this alone using a couple of long (1.5 feet or so total) of 1/2 inch extensions and a ratcheting breaker bar or a regular 1/2 inch ratchet with a pipe extension on the end, which you use to crank on the crank shaft bolt (CLOCKWISE ONLY) to move the pistons up and down. I think its a 22mm....cant remember at the moment. You need enough extension to clear the fender so you can articulate the breaker bar while holding the leakage tester in your other hand.

As so:

See the breaker bar?: I have this bar:
https://www.amazon.com/gp/product/B003U4YWCK/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 https://www.amazon.com/gp/product/B003U4YWCK/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

Now you have to find TDC (TOP DEAD CENTER) on any one of the pistons, so you can do the air leakage test. Its easy.

You install the M12 spark plug hole adapter from the kit and screw it in place until the rubber o-ring is snug.

In our case this is easy because its an inline 4 cylinder and the car is small so everything is within easy reach. They sell a TDC whistle
https://www.amazon.com/gp/product/B000TQ16HG/ref=ox_sc_sfl_title_3?ie=UTF8&psc=1&smid=ATVPDKIKX0DER https://www.amazon.com/gp/product/B000TQ16HG/ref=ox_sc_sfl_title_3?ie=UTF8&psc=1&smid=ATVPDKIKX0DER
but you dont need it for the Mini because you can crank the motor while you feel for air escaping the end of the hose that screws into the spark plug hole which is part of the OTC kit.

So you crank the motor with the LONG ratcheting breaker bar while you keep your finger over the end of the hose screwed into the spark plug hole. When you feel a puff of air you know the cylinder has sealed its exhaust and intake valves and you can commence the test.

If you pass TDC, just keep cranking till the engine cycles back to that cylinder. It can be a lot of cranking so be patient. DONT CRANK THE ENGINE BACKWARDS!!! ONLY crank clockwise. That's typical for most engines. See Bentley manual:

In my case I used the long metal tube extension that came with the OTC 5605 Deluxe Compression Tester Kit but in theory you don't need it. You just use the rubber hose from the leak down test kit and the correct spark plug hole adapter. Of course trying to screw a wobbly rubber hose into a cylinder hole is kind of silly but apparently it seals well enough.

Here you see the rubber hose and I have the metal extension tube in cylinder 1 from OTC's 5605 Deluxe Compression Tester Kit.

If you do happen to have OTC's 5605 Deluxe Compression Tester Kit, remember to unscrew the valve out of the end of the long metal extension tube using a valve removal tool or some needle nose pliers. You dont want a valve in the system for a leak down test. Like so:

I digress. Back to the test.

So you use the OTC dual gauge manifold and hook the left side to your air compressor and right side to the rubber hose that goes into the cylinder. As you can see in the pic I used a section of rubber air hose and some fittings as an extension between the leakage gauge and the metal tube in the cylinder. Without it I wouldn't have had the space/height to hook the gauge manifold to the air compressor because of the length of the fittings in my garage. Yours may be different. I was decreasing from 3/8 to 1/4 so I had to rig up that mess of connectors.

If you don't use the metal extension tube from the OTC Deluxe Compression Test kit you should not need to make up an extension, as the kit's black rubber hose will offer the flexibility you need.

WHILE HOLDING THE RATCHETING BREAKER BAR FIRMLY you start opening the valve on the compression tester (the black **** on the tester manifold). If it doesnt turn, pull it towards you to unlock it, then turn it.

As the cylinder starts to fill with pressurized air, the cylinder will want to move down so you must resist that motion with the breaker bar. You slowly increase pressure up to 100 psi and then look for a loss in pressure (LEAKAGE) on the right side gauge. If you see pressure decreasing you then start looking and listening for the causes (air/bubbles from coolant bottle, air from oil filler hole in valve cover, air from muffler). The bar will be pushing back at you really hard at 100 psi, beware.

Then you repeat for the next 3 cylinders. If you have some air pressure loss/leakage, make sure youre truly at TDC. You can crank the engine every so slightly while you have the cylinder pressurized and you'll know when the valves open because you'll start to lose pressure very quickly.

Here my gauges held steady at 100psi into the gauge manifold and holding 100 psi in the cylinder. Therefore, I have no leakage in that cylinder.


One problem with the OTC kits (both compression and leak down) is that they use adapters for different size spark plug holes which screw in the same direction as the tester extensions so when you unscrew the tester from the spark plug hole it can leave the adapter in that deep spark plug hole!

That's kinda scary. So make so you tighten the little adapter REAL tight and only lightly snug down the entire assemble into the cylinder. Or use some Loctite BLUE threadlocker on the adapter's threads before hand and let it set a few hours before using it.

Also, have a long needle nose pliers on hand just in case the adapter gets stuck in the cylinder so you can try and unscrew it.

It happened to me despite my precautions. Rememeber, it doesn't need to be in very tight to the cylinder to seal the rubber o-ring.

The adapters I refer to are in the black OTC box on the left side:


Last edited by Lex2008; 05-11-2017 at 12:49 PM.
Old 05-10-2017, 08:54 PM
squawSkiBum is offline
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Great How To, thanks for posting!
Old 05-11-2017, 10:54 AM
Lex2008 is offline
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Hope it helps a few of you guys out.

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