How do I run a leak down test?

chris91LX · 11-23-2001, 06:20 PM

Do I need a special gauge or tester or can I use a regular compression tester? I need to run this before I buy new heads, I might go with the 347 instead if i'm having a problem with compression.

2FastLX · 11-23-2001, 10:54 PM

Pull the plug, insert the compression tester, and with the coil wire disconnected crank the engine. The tester will show you your compression.

A leak down test is to test the coolant system for leaks I believe.

Five0 · 11-23-2001, 11:20 PM

Actually I think there is a way to test the time it takes for the cylinders to loose pressure but I don't know how to do it either.

Anyone else?

robertwigton · 11-24-2001, 06:59 AM

To do a leak down test,you have to have a "leak down"
gauge.It has 2 gauges that are attached to each other,
one tells you the in put pressure(you have to have air comp)
and there is a knob to adjust this in put pressure(I think on mine
you adjust to 90psi)The other gauge will just be a dial broken down in to %s,Instructions should tell you how to "interpret"
resuilts,ie 5% leakage ok etc... also used to find sources of cyl.
pressure lost,ie bad rings,head gaskets,valves etc. Sears has these gauges,or you might be able to get one on loan from Auto parts store...

Five0 · 11-24-2001, 08:38 AM

Cool, thanks for the info!

exgmguy · 11-24-2001, 11:23 AM

Most decent auto parts stores sell leakdown testers for about 80 bucks. You will also need an air compressor to use it.

I recently checked mine and all cylinders were 10-12% leakage. A new just broken in motor usually shows about 5%. I would say if it is 20% or above you have a problem.

Also the testers come with pretty easy instructions.

11-23-2001, 06:20 PM	#1
chris91LX Registered Member Join Date: Oct 1998 Location: Suburban Chicago, Hanover Park Posts: 695	How do I run a leak down test? Do I need a special gauge or tester or can I use a regular compression tester? I need to run this before I buy new heads, I might go with the 347 instead if i'm having a problem with compression. __________________ My Ford Club http://www.midwestfords.org/ Best time N/A 12.9 @ 107 1.711 60' 125 shot - 12.04 @ 113 1.59 60'

11-23-2001, 10:54 PM	#2
2FastLX The Photoshop Guru Join Date: Feb 2001 Location: Mecca, Indiana Posts: 1,419	Pull the plug, insert the compression tester, and with the coil wire disconnected crank the engine. The tester will show you your compression. A leak down test is to test the coolant system for leaks I believe. __________________ Project: 1988 Coupe - EFI 5.8L Twin Turbo with Victor intake, Canfield heads, F303 cam, March aluminum underdrive pulleys, TKO (or T56 if funds permit), PBR twin piston calipers and 13" rotors up front, 94 Cobra rear calipers and 12" rotors on the rear, 3.73's, Griggs K-member, tubular front control arms, torque arm and panhard bar, polished 99 Cobra wheels. "The GR-40 kit installation is now complete, and the humble Fox-chassis car will now out-corner and out-stop a ZR-1 or a Viper, and support massive horsepower additions with perfect balance." Griggs Racing ICQ# 42269241

11-23-2001, 11:20 PM	#3
Five0 Registered Member Join Date: Apr 2000 Location: middleburg, fl, usa Posts: 1,134	Actually I think there is a way to test the time it takes for the cylinders to loose pressure but I don't know how to do it either. Anyone else? __________________ James Cox RHC Member #44 nochevy@hotmail.com 1991 Mustang LX Dart iron eagle block, 4340 28oz 347 crank, 4340 h-beam rods, probe ultra light pistons canfield heads “race ported by Brent Frazier”, solid roller cam and lifters “custom grind”, kooks 1 7/8" race headers, and much more. Engine built by Brent Frazier.

11-24-2001, 06:59 AM	#4
robertwigton Registered Member Join Date: Oct 2001 Location: orlando,fl USA Posts: 44	Leak down test To do a leak down test,you have to have a "leak down" gauge.It has 2 gauges that are attached to each other, one tells you the in put pressure(you have to have air comp) and there is a knob to adjust this in put pressure(I think on mine you adjust to 90psi)The other gauge will just be a dial broken down in to %s,Instructions should tell you how to "interpret" resuilts,ie 5% leakage ok etc... also used to find sources of cyl. pressure lost,ie bad rings,head gaskets,valves etc. Sears has these gauges,or you might be able to get one on loan from Auto parts store... __________________ 89'LX 5.oh.BBK shortys,no cats Flow masters w/Dumps,Crane Cam(Top secert) MSD 6AL,Blaster coil,Motor sport 9mm wires,under drive pulleys,no smog timming @ 16 deg,K&N,70 mm maf, Pro5.0shifter,Home made frame con. south side lift bars,3.73 bald @#! tires(2 on rear!)Sony C-D and Rockford fasgate rear,w/sony explode 5 1/2 in front.

11-24-2001, 08:38 AM	#5
Five0 Registered Member Join Date: Apr 2000 Location: middleburg, fl, usa Posts: 1,134	Cool, thanks for the info! __________________ James Cox RHC Member #44 nochevy@hotmail.com 1991 Mustang LX Dart iron eagle block, 4340 28oz 347 crank, 4340 h-beam rods, probe ultra light pistons canfield heads “race ported by Brent Frazier”, solid roller cam and lifters “custom grind”, kooks 1 7/8" race headers, and much more. Engine built by Brent Frazier.

11-24-2001, 11:23 AM	#6
exgmguy Registered Member Join Date: Feb 1999 Location: Utica, Michigan Posts: 2,631	Most decent auto parts stores sell leakdown testers for about 80 bucks. You will also need an air compressor to use it. I recently checked mine and all cylinders were 10-12% leakage. A new just broken in motor usually shows about 5%. I would say if it is 20% or above you have a problem. Also the testers come with pretty easy instructions. __________________ 1988 Mustang GT stock bottom 302, C4 10.9 @ 128 with 8 psi of Novi 1000 boost!----STOLEN 1989 Mustang notchback Warmed up 306 with a Procharger.

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