View Full Version : Leak Down & Pressurized Testing 101 *Approved*

02-05-2007, 02:28 AM
Leak Down & Pressurized Testing 101

* Image: Leak down & pressure testing 101

Learn how to pressure check your engine's combustion, coolant, intake, fuel and oil systems for fun & profit.
Ok, maybe not profit... Or much fun either... But -- it will help you solve an existing problem, or even
prevent a future problem. Read on to learn more about getting the most of out of your leak down tester!

WARNING! This guide is meant to give you some general guidelines to go by, but the techniques and methods I have laid out in this article may not work for everyone or on every motor. You can probably hurt yourself or damage your engine using a leakdown tester (as with any tools in your garage) so please follow all safety instructions and precautions when working on your car. I assume no liability for your actions as a result of reading this guide.

0) Leak Down Tester tool overview. What is this magical device? :confused:
1) Leak Test: Cylinder & Combustion Chamber :hsdance:
2) Leak Test: Intake & Boost system :tweak:
3) Leak Test: Coolant system :eek:
4) Leak Test: Oil system :hahano:
5) Leak Test: Fuel system :)
6) Other uses :naughty:
7) Build your own leakdown tester
8) Resources and external links

Chapter 0) Leak Down Tester tool overview

* Image of my leak down tester tool and spark plug hole adapter hose.

A "Leak Down Tester" (LDT for this article) is a very simple tool used to inflate a supposedly sealed chamber with air. As the chamber fills with pressurized air, you can observe the seals or seams for audible leaks. By spraying the seams with a soapy water solution, you can visually inspect more accurately, seeing very small pinhole leaks with ease.

The tester helps immensely during re-assembly by allowing you to double check the air-tightness of your work. Any leaks can be found now when the car is in your garage on jack stands, instead of driving down the road! While it helps detect existing leaks, it cannot predict future problems. If you have developed a boost, coolant or gasket leak, you can use the tester to help pinpoint the location for quicker repairs.

The LDT physically consists of two 1/4 quick disconnect air hose fittings (inlet & outlet), an adjustable pressure regulator, and one or more pressure gauges. One hose fitting connects to your tank of compressed air (30 to 100psi) while the other fitting connects to an included hose that threads into a spark plug hole. While the device is primarily made for testing cylinders & combustion chambers, it can easily be adapted to diagnose other sealed pressure systems such as intake/boost and cooling.

I've found that this tool can be a tremendous help in a number of situations, and should be included in every DIY-ers garage. While some people only purchase a LDT to use a few times on a potential swap motor, I have found a couple other uses that I think are useful enough to show you here.

* Sorry apartment dwellers... The tool requires a tank of compressed tank (from 30psi to 100+psi).

The pressure regulator adjusts the air flow through the LDT. The first gauge will show the input pressure (tank pressure), and the second gauge shows the sealing percentage of the chamber being tested (80% seal = a 20% leak). When you buy the LDT it may have the gauges mounted so that the pressure gauge monitors the compressed tank pressure. I think this is redundant (tank already has gauge & regulator), plus I would rather see the pressure of the chamber being tested. I removed and reversed my gauges so the pressure gauge shows the pressure of the chamber, not the tank.

Chapter 1) Leak testing: Cylinder & Combustion Chamber

* Image of plug hole adapter hose threaded into RB20DET

Of course one of the top reasons to add a LDT to your arsenal is so you can measure the sealing capability of combustion chambers. With the LDT we can troubleshoot the piston rings, valve seats and the head gasket -- all at the same time. How well an engine seals helps determines it's ability to make power. If your engine leaks fire past a valve or past the rings, you are losing power and fighting a loosing battle.

The LDT helps diagnose cylinder and combustion chamber sealing, giving and indication of three main sealing areas:

Piston & Piston Rings

* Image courtesy of aa1car.com. Hope they don't mind.

Piston & piston rings - The piston rings keep the combustion chamber sealed from the crank case and oil. Leaking rings will allow oil to be burnt, and will allow more exhaust blow-by into the crank case. You will be able to hear excessive leaking past the rings, and will notice on the pressure gauge that the chamber cannot ever achieve a 100% seal.
Valve & Valve Seats

* Image of my RB20DET valves. No wonder cylinder #3 leaked?

Valve & valve seats - The valve seats are the mating surface for the top of the exhaust valve. Each valve has a seat that runs the circumference of the valve surface. Because of their location and purpose in life, nearly all the air entering the cylinder passes by the valve seats. Therefore, the seats can easily become fouled if the combustion process is not clean (too rich and sooty) or the intake tract is dirty (Blown oil seal or no catch can). These deposits over time can build up and eventually cause a small leak each time the valve seats. A bent valve will also display a similar symptom, but I would expect a much more dramatic leak. You will be able to hear the air leaking past the valves and into the intake manifold or exhaust manifold, and should be able to pinpoint exactly which valve(s) are leaking.
Head Gasket

* Image courtesy of Netins.net/web/dkbowers Hope they don't mind.

Head gasket - The almighty head gasket separates the combustion chamber, oil passages and coolant passages from each other. Over time, it's possible for the head gasket to form a leak between two or more systems, causing a variety of combustion problems. Using a LDT you can test the head gasket's ability to seal these pressurized systems from each other. The LDT will audibly indicate most head gasket problems and may show bubbles or overflowing in the cooling system.

Steps to pressure test the cylinder & combustion chamber:

Remove the spark plug wire, or coil pack from the cylinder to be tested.
Remove the spark plug from the cylinder to be tested.
Set the cylinder being tested to top dead center using the timing marks or other method. One quick way to set TDC on any cylinder is to put a long screw driver down the spark plug hole, then rotate the crank with a ratchet and socket while watching the end of the screw driver handle. As the piston approaches TDC the screwdriver handle will reach it's peak height. Rock the crank until you're sure the piston is at exact TDC and both intake and exhaust valves are 100% closed.
* Image of RB20DET exhaust cam lobe position at TDC

You may wish to remove the cam cover, to ensure the cam lobes are pointing away from each other. Remove the screw driver if used to set TDC.

Thread the LDT into the spark plug hole, twisting the hose until the adapter is threaded snugly and the o-ring seals.
Set the compressed air tank regulator to 100psi, connect the hose to the LDT.
Attach the LDT adapter hose to the main LDT.
* Image of ratchet and 27mm socket on crank pulley bolt

** Warning: Hold the crank in position with the ratchet! **

SLOWLY open the LDT regulator by twisting it counter clockwise. As you begin to allow the air to fill the combustion chamber, watch the gauge needles and listen particularly for air leaks from the LDT adapter in the spark plug hole. Continue to slowly build the chamber pressure, while increasing your grip on the ratchet holding the crank. As the combustion chamber pressure climbs towards 100psi, the force on the piston may cause the crank to want to spin one way or the other. You should feel and repel this force on the ratchet, as every millimeter the piston moves will change the cylinder pressure.

Finally open the LDT regulator 100% to fill the chamber will all available air/pressure. Observe the leaking percentage gauge. Does the gauge indicate 80% or better sealing?

Time to diagnose the main leak-risk areas:

Piston rings - Some leaking past the piston rings is normal, especially on a cold engine. Excessive leaking may indicate a ring sealing problem. A leak down test should be performed when the engine is at operating temperature, but that is sometimes not an option (like when you're re-assembling the motor on a stand). You may pour a small amount of engine oil down the spark plug hole to help the piston rings seal. If this improves your leak percentage, it may indicate problems with the rings on that cylinder. Remember, as the engine gets up to operating temperature the metals expand and offer a tighter seal.

Valves - Listen to the intake and exhaust ports; do you hear air escaping from one, or both valves? This may indicate a valve sealing problem, caused by a bent valve stem and/or contaminates on the valve seat. Try rocking the crank very slightly to ensure the valves are 100% seated. Sometimes the cam lobes may be keeping them partially open.

Here is a video of my motor leaking from the cylinder #3 exhaust valves:

Head Gasket - Do you hear any bubbling? Remove the radiator cap or cooling system bleed screw and check for bubbles or leaking fluid. Be sure to listen to the adjacent cylinders for leaking, this can help indicate where a head gasket is blown. If you have good numbers except for two cylinders next to each other, it is very likely that the head gasket between them is blown.

Remove the LDT from the spark plug hole
Replace the spark plug
Replace the plug wire or coil pack
Move on to the next cylinder
Set the cylinder to TDC.

Chapter 2) Leak testing: Intake & Boost system

* Image courtesy of home.pacbell.net/gj_os/, hope they don't mind.

Another popular use for the LDT is to check the intake system for "boost leaks". Any leaks in a pressurized mass-air system will cause combustion problems, typically including backfires, poor performance and excessive exhaust soot. The entire intake system between the turbocharger and the combustion chamber needs to be able to hold more air pressure than you intend to force through it under boost. Most street driven vehicles typically run low to moderate boost levels, from 5 to 16 psi of boost. Pressure checking the intake system to 2 bar (or 30psi) will ensure no leaks for all but the most hard core engines.

While my motor is on the engine stand being re-assembled, I needed to pressure check the various intake manifold gaskets and recent RTV work. I knew I could get the vac hoses sealed off easily enough, but I was more skeptical about the throttle body hole and the injector holes. I ended up making a quick throttle body blockoff plate from some 3/8" thick wood and RTV, and blocked the injectors using rubber stoppers on long lag bolts.

* Image showing my injector block offs - 1/2" rubber stoppers on a lag bolt

By installing a block off plate in place of the throttle body and stoppers in the injector holes, I was able to pressurize the intake manifold through the spark plug hole by allowing only one intake valve to be open. I slowly pressurized the system to 2 bar (30psi), then I went around with soapy water and sprayed all the gaskets and RTV work watching for bubbles.

I found the paper gaskets on the intake manifold allowed a small leak (through the paper fibers, it seemed), so I reassembled the manifolds using RTV on both sides of the gasket, then re-pressure checked. I am confident that the intake system is good to at least 2 bar now, way more boost than I will ever run! Don't forget to spray the bubble mixture around your IACV, PCV vavlve, EGR, etc.. I actually found that my PCV leaks slightly after about 5psi, so I replaced it with a teflon-taped bolt for pressure testing.

* Image of 3" boost leak adapter. Courtesy of TTZed.com, hope they don't mind.

Pressure checking the intake system on a motor installed in car is a little easier, since all the hoses should be hooked up to something. You'll need to buy or make a 2.5" or 3" pressurized tester adapter like the one shown above. You can make your own out of a 3" cap, tire valve, a 3" silicone coupler and some RTV. To use the adapter, remove your turbo outlet "hot pipe" and twist it so you can clamp the adapter on the end. The opposite end of the pipe should still be securely clamped to your intercooler!

Slowly inflate the hotpipe to 2 bar to test the hot pipe, hot pipe->fmic coupler, fmic, fmic->cold pipe coupler, cold pipe, cold pipe-> throttle body coupler, the throttle body and the intake manifolds. The valves can be in just about any position for this to work.

Be sure to double check around the Throttle Body. I found my throttle body shaft seal near the TPS was leaking horribly, which wouldn't let the intake pressurize any more than 10psi. Even at that low level it was leaking quite a bit of air, it was so bad it wouldn't hold anything more than 3-5psi before I could hear it rushing out...

Chapter 3) Leak testing: Coolant system

You can pressure check the coolant system to check for water leaks. I did this with the engine dry on the motor stand, but it's possible with the engine mounted in the car.

Steps to pressure check your coolant system

* Image of test motor waiting patiently on the stand

* Image of test motor coolant hoses connected or blocked
Connect all hoses together. Here you can see I used a length of fuel hose to seal two coolant nipples together. You can also see my use of rubber stopper-on-a-stick to block off a 16mm heater hose fitting. With a little creativity you'll find enough stuff around your garage to block off all openings.

* Image of LDT plug hole adapter clamped to 16mm coolant inlet hose
Clamp 16mm heater core hose onto plug hole adapter with the Teflon tape

* Image of test motor upper and lower water outlets connected with hose
Clamp radiator hose from water outlet to water inlet.

Slowly pressurize the cooling system. You're going to want to test the system to a little over what your radiator cap is rated for. On a stock radiator, the cap opens around .5 bar (7 psi). Many people upgrade their radiator cap to a higher pressure cap, which opens from .9 to 1.3 bar (13 psi to 19 psi). Personally I would make sure your cooling system can withhold at least 25% more pressure than what your radiator cap is rated at. For instance, I am running an ARC 1.3 Bar cap, which means I should pressure test to about 1.6 Bar (a little over 23 psi).

Listen for air leaks. As the system is pressurizing, move around the various fittings and connections to listen for air being leaked. If you have no leaks at all, you will barely be able to hear the air rushing into the engine... But if you hear a loud "whooshing" noise, you need to investigate further if you're not able to obtain the minimum test PSI!

Click here for a video of my water pump's RTV leaking:

* Image of soapy water being sprayed on coolant temperate sensors
Now that you have solved some of the minor leaks by tightening the hose clamps and blocking off missed openings, you can test the actual gaskets. This is done by using a small squirt bottle filled with some soapy water. Simply spray the mixture on any pressurized connection and observe the fluid as it runs down the seal. If there are any pinhole leaks, you will see small bubbles forming! Don't forget to check around your sensors and auxiliary connections, such as the heater core, turbo banjo bolts, etc.

Remove LDT after diagnosing any leaks

* Image of radiator pressure test kit

To test a cooling system on a motor already installed into a vehicle, you may wish to pick up a radiator pressure test kit. It's basically a radiator cap with a nipple on it that you install in place of your existing pressure cap. You then pressurize the cooling system through the nipple, but be sure to not exceed the pressure rating of your regular radiator cap. For instance, if you're running a 1.3 bar cap, you should only pressure test to 25psi or so. This is because the stock cap works like a blow off valve, dumping excess pressure to the coolant overflow tank. If you exceed the rating of your normal cap, you may "find" a leak by blowing out a seal somewhere.

Chapter 4) Leak testing: Oil System

Install an oil filter
RTV the oil pan on
Torque the cam covers down
Place cap on oil dipstick tube
Disconnect and block off PCV hoses
Install LDT onto PCV tube
Use 10-20psi tank pressure. Note: I would suggest using low pressure here, since the valve covers are not normally pressurized. The turbo should be able to handle the same pressure as the pump would generate, but I would keep the pressure low here just in case.

Pressurize and listen for leaks/use soapy water on:

Oil filter
Oil pan
Cam covers
Oil pump
Banjo bolt on block
Banjo bolt on turbo
Drain on turbo
Drain fitting on block
Turbo oil seal - listen to turbo inlet, outlet and turbine side

Here's a video of my turbo oil seal leaking, and a quick overview of how I hooked up the LDT:

Chapter 5) Leak testing: Fuel System

Remove fuel inlet hose
Install hose with inflation adapter onto fuel inlet hose
Use 40-60psi tank pressure.
Pressurize and listen for leaks

Fuel injectors
Fuel pressure regulator
Fuel hose & fittings
Fuel pressure gauge/sender & fittings

Stock fuel pressure is 43.6 psi. You should be able to hear your FPR open up at ~45 psi and start venting back to the tank.

This is also an adequate way to preset your Nismo or Adjustable Fuel Pressure Regulator before firing up the engine for the first time. Simply pressurize the fuel rail to ~50psi then loosen the lock nut and adjust the bolt on the FPR until your fuel pressure gauge reads 3bar (43.5psi)! I ran a 1.5" VDO fuel pressure gauge on a 3/8" tee in the fuel hose before the fuel rail.

Chapter 6) Other Uses?

It should be possible to pressure check the exhaust system (muffler, cat, down pipe, dump pipe, turbo gasket, manifold gasket) for leaks by using a block off plate installed on the muffler tip, or bolted in place of the catback, cat, downpipe, etc.

As I find useful ways to test other various systems I'll update the guide.

Chapter 7) Build your own leakdown tester

[i]* Image courtesy of Mike Nixon (xs11.com hotlinked for now)

More to come in this section. For now if you're interested in building your own leakdown tester, check out these resources:

Hotrodders.com thread discussing two DIY testers (http://www.hotrodders.com/forum/make-your-own-leak-down-tester-81646.html)
Mike Nixon's DIY leakdown tester write up (http://www.xs11.com/tips/misc/misc3.shtml)
Bob Bertaut Sr's DIY leakdown tester write up (http://www.650motorcycles.com/LeakDownTester.html)

Chapter 8) Resources & External Links

* Image of a LDT available from Summit Racing

There are many different leak down testers on ebay, selling from about $50 to over $100 each. Summit Racing also sells the exact tester I own.

Ebay Leak Down Tester link (http://search.ebay.com/search/search.dll?query=LEAK+TESTER&MfcISAPICommand=GetResult&ht=1&ebaytag1=ebayreg&srchdesc=n&maxRecordsReturned=300&maxRecordsPerPage=50&SortProperty=MetaEndSort)
Summit Racing's line of leak down testers (http://store.summitracing.com/egnsearch.asp?N=700+115+%2D112449&D=%2D112449)

02-05-2007, 02:43 AM
this would really help me allot. once i see how it is done i will help you by adding my own imput and testing on my sr20

02-05-2007, 02:56 AM
Cool I hope it's useful for you and other people.

Here is why I decided to put this together..

First off I my tester told me that a few cylinders, but esp. cyl #3 had leaky exhaust valves. I had a 3 angle valve job done based on these results -- after the head job, the tester confirmed the leaks went away 100%.

Another day, I tested the intake system for leaks. The tester showed me that the paper upper to lower intake manifold gaskets leaked... Took apart the manifolds, and used RTV on both sides. Retested, and now the manifolds are good to 2 bar/30psi no leaks.

Just now, I finished getting the coolant lines ran and the turbo plumbed so I tested the coolant system. The tester showed me a tremendous, monstrous, stupidly huge leak on the water pump's RTV. That would have really pissed me off filling the motor with water if I didn't catch this one. I'm taking the timing belt off again to reinstall the water pump.

Anyway, after today's testing, I decided that since the LDT has saved my ass three times, I should write this up! Somehow I think the LDT will help me down the road with the FMIC also :). It is definitely a useful and flexible tool that everyone should have. It's not just for testing to see if a swap motor is in good condition!

02-10-2007, 05:06 PM
Added oil system testing instructions and uploaded oil system video... More work to come on oil system instructions..

Just used the LDT to confirm that the turbo oil seal is BLOWN... I already suspected it was blown due to the oil in the outlet pipe & turbo blades when I recevied and tore down the motor. This is just another confirmation that it'll smoke and fill the fmic with oil..........

02-11-2007, 10:40 AM
Damn, very good thread. Thanks man.

02-11-2007, 01:05 PM
Thanks, lmk if u have any suggestions or input

Revised a few areas this morning.

02-15-2007, 09:15 PM
Added some notes on fuel system pressure checking

02-21-2007, 07:09 PM
Fantastic write-up! Very detailed.

02-28-2007, 11:03 AM
:bow: Dōmo arigatō dude.. hope it helps you track a leak down someday

03-05-2007, 02:41 PM
The first video link didnt work for me, but once I tried the next one I found the first, might want to check it.
5 stars!

03-05-2007, 04:06 PM
Fixed that link.. idk what happened there

Thanks glad you enjoyed it.

03-26-2007, 06:36 AM

This is pretty much what I'm using as a baseline for most desirable FAQ type thread.

Just get those leeched images hosted on a stable host!!

07-25-2007, 03:40 PM
Went thru and revised all the images, watermarked with either a copyright or a source. Made some cool chapter images & revised the main header image. Rehosted all images on Flickr... I think I might go back and re-write the section on boost testing to include a little portion or at least a link to DIY boost testers... Enjoy

07-26-2007, 03:17 PM
damn, this is a killer writeup, very detailed

07-26-2007, 04:50 PM
thanks! any suggestions? I saw a couple areas I want to clean up when I was rereading it the other day.


10-20-2007, 04:46 PM
Great thread.

One question though: Can you list the parts needed ot create your own Leakdown tester?

Since no one in town knows what a leakdown tester is, let alone sell one, I went ahead a purchased a bunch of 1/4 brass fittings and a couple of pressure gauges.

The only thing I'm stuck on is the middle pipe that connects the two pressure gauges. The only online instructions I was able to find mentioned that this middle pipe needed to have some kind of constriction in order for the second gauge to give an accurate reading?

What should I use for this restrictor.

I'll post some pictures of all the parts I have so far and what I still need later on, if needed.

10-21-2007, 03:39 AM
Thanks.. No I've never built my own, but that would be a nice project & a good addition to this write up.

What instructions did you find? Here's two I found quickly that seem to answer the middle pipe question, plus both have parts lists.

http://www.xs11.com/tips/misc/leakdn2.gif (http://www.xs11.com/tips/misc/misc3.shtml)


http://www.650motorcycles.com/LeakTester2.jpg (http://www.650motorcycles.com/LeakDownTester.html)

The only thing I'm stuck on is the middle pipe that connects the two pressure gauges. The only online instructions I was able to find mentioned that this middle pipe needed to have some kind of constriction in order for the second gauge to give an accurate reading?

The damper valve
This necessary part is merely a restriction between the regulator and the gauge. The easiest way is to plug the middle pipe with epoxy and afterward drill a 0.040" (#60 or 1mm drillbit) hole.

Here's another explanation (http://www.hotrodders.com/forum/make-your-own-leak-down-tester-81646.html) of the middle pipe:

I assume the sized restriction in between the gauges the is the benchmark against which the leak(s) in the cylinder are measured. With out the sized orifice I don't think I would trust the regulator to stay consistent with varying flows. It would appear that the amount of air allowed to pass through the .040 restriction is the maximum allowable to leak past the rings,valves,etc. Any more air that is allowed to pass will show up as a pressure drop that can be measured.

Post pics of what you've got.. or what you end up with! :)

10-21-2007, 03:00 PM
Oh, my bad, I thought you had built your own LDT.

Basically, my problem is that every parts store I go to has no clue what a damper valve is.

So, I could fill the middle pipe with epoxy and drill a hole through it - but I'm not quite sure where the number .040" comes from. Why exactly does this hole need to be .040"?

Anyway, I'm going to experiment around and I'll let everybody know what I find out.

Thanks for the reply.

10-22-2007, 02:43 PM
Read the quotes in my previous post. My understanding is that the .040" opening only allows a very small amount of air to enter the chamber, then the leak percentage gauge shows what percentage of that volume of air is leaking. If you're not using a leak % gauge then it's probably not as useful, I think it just helps prevent the chamber from pressurizing too quickly and also stabilizes the reading on the psi gauge.

I bought my LDT off ebay. IIRC it was less than $40 shipped, I'm sure you could build one for half that amount. If you have other DIY-LDT links please post them up and I'll put them to the "build your own" chapter.. thx & gl :)

10-23-2007, 04:31 PM
I'm gonna start working on a "Make Your Own LDT".

It'll probably take me a little while. I'll post up the results when I'm done.

10-24-2007, 12:48 AM
If you do a write up I'll add a link to it from mine. Sounds like a cool idea, good luck with it.

Also try not to think of a LDT as just a "leak down" tester, it's much more powerful than that and really useful as a generic pressurizer/pressure tester. Like I said in an earlier reply I don't even use the leak % gauge anymore, I just use my LDT to pressurize whatever I don't want leaking fluid/gas.. As long as you know aprox how much pressure is ran in the chamber stock you can check lots of things before the motor is even fired up.

10-24-2007, 06:06 PM
very good thread.
A+ thank you repped!

12-15-2007, 12:34 PM
NICE!!!!! +rep for you

12-25-2007, 10:49 PM
Hadn't noticed this thread before. Freakin' awesome. I'll be doing this to the SOHC I have sitting in order to see what condition it's in :D

+rep to you.

12-25-2007, 10:52 PM
oh and quick question, this can be done while engine is still installed right? because I wouldn't mind doing this on my daily driver as well.

01-22-2008, 03:13 AM
haha thanks. i spent a while reading it over and over to make sure i understood it. learn something new everyday. excellent help.

01-29-2008, 03:47 AM
thanks for Great thread.