Compression Test With Warm Engine

TorchRed04GT · January 5th, 2012, 11:47 PM

I'm thinking of doing a compression test on my engine. I've read that you have to do it when the engine is warm to get the best readings. Will pulling the plugs out while the engine is warm mess up the threads on the heads? I want to avoid any possible damage.

number1gt · January 6th, 2012, 12:03 AM

It should make it easier to get the plugs out

Shaun03GT · January 6th, 2012, 12:09 AM

The heads are aluminum, I was always told to wait because the threads can easily strip out. So not exactly sure.

Nitmare67 · January 6th, 2012, 12:29 AM

I've pulled them HOT, COLD, WARM at least 40 times on the worst series motor built. The windsor 4.6. Never had a plug problem even with 150hp wet kit and 12lbs of boost. The key to survival is correct plug torque and anti-seize. 156in/lbs final torque with anti-seize and your golden.

tbirdscwd · January 6th, 2012, 12:30 AM

If the engine is at normal operating temp, it is fine to pull the plugs. If the engine is HOT, then wait til it cools down. Upon re-install, use anti-seize on the spark plug threads and actually torque them down.

cliffyk · January 6th, 2012, 06:05 AM

Originally Posted by tbirdscwd

If the engine is at normal operating temp, it is fine to pull the plugs. If the engine is HOT, then wait til it cools down. Upon re-install, use anti-seize on the spark plug threads and actually torque them down.

Torque to 11 to 15 lb-ft (132 to 180 lb-in). The shop manual says 11 to 13 lb-ft, however I have been torquing them to 15 lb-ft (with a known accurate wrench) for over 5 years with no problems.

Also it is best to use a 1/4" drive torque wrench as you will be operating at the top end of it's range. A 3/8" drive wrench is OK, sort of. Using a 1/2" drive wrench is generally not possible because most of them have a range that starts out at 20 lb-ft.

Here is an alternative I have been using for a while now, a torque limiting spark plug socket:

Read more about this here...

99GT35thLE · January 6th, 2012, 06:09 AM

CliffyK your link isn't working!

cliffyk · January 6th, 2012, 06:11 AM

Working on it right now...

[edit]
Got it, the blog index was corrupted...
[/edit]

TorchRed04GT · January 6th, 2012, 03:57 PM

Last time I changed the plugs I used anti sieze and torqued them to 13 lb-ft. I will let the engine warm up just enought for the fan to kick on then I will pull them and do a compression test. Does the throttle body have to be at WOT for the readings to be correct?

cliffyk · January 6th, 2012, 04:59 PM

Originally Posted by TorchRed04GT

Last time I changed the plugs I used anti sieze and torqued them to 13 lb-ft. I will let the engine warm up just enought for the fan to kick on then I will pull them and do a compression test. Does the throttle body have to be at WOT for the readings to be correct?

Yes, it does not have to be ALL the way open but at least 1/3 to 1/2 open--also remove all eight plugs before conducting the test...

January 5th, 2012, 11:47 PM	#1
TorchRed04GT Regular Join Date: May 2009 Posts: 66 iTrader: 0 reviews	Compression Test With Warm Engine I'm thinking of doing a compression test on my engine. I've read that you have to do it when the engine is warm to get the best readings. Will pulling the plugs out while the engine is warm mess up the threads on the heads? I want to avoid any possible damage. __________________ 04' GT - Vortech & Meth

January 6th, 2012, 12:03 AM	#2
number1gt Hardcore Enthusiast 2002 mustang gt Join Date: Jan 2010 Posts: 1,896 iTrader: 1 reviews	It should make it easier to get the plugs out __________________ Rock stock

January 6th, 2012, 12:09 AM	#3
Shaun03GT I Post Entirely Way Too Much 2003 Mustang GT 1/8 - 7.92 @ 91.13mph 1/4 - 12.21 @ 115.84mph Join Date: Sep 2009 Location: Weymouth, MA Posts: 13,442 iTrader: 12 reviews	The heads are aluminum, I was always told to wait because the threads can easily strip out. So not exactly sure. __________________ Vortech V1 Intercooled @ 11psi 394rwhp/392rwtq @ 9.5psi 415rwhp/400rwtq @ 11psi on Methanol Tuned By: Pete @ Performance Dyno Affordable Supercharger Build Guide Supercharger Info for Noobs

January 6th, 2012, 12:29 AM	#4
Nitmare67 Hardcore Enthusiast Join Date: Feb 2010 Posts: 1,391 iTrader: 0 reviews	I've pulled them HOT, COLD, WARM at least 40 times on the worst series motor built. The windsor 4.6. Never had a plug problem even with 150hp wet kit and 12lbs of boost. The key to survival is correct plug torque and anti-seize. 156in/lbs final torque with anti-seize and your golden. __________________ 99 Mustang GT 446rwhp, Vortech Aftercooled, Killer Chiller @12lbs, HPX, 3.73s, MGW, Battery Relocation, Intercooler Tank Relocated, CF DF clutch, Steeda Quick Release Quadrant, 75mm TB, Ported C&L Plenum, Stock PI Cams Advance 4 degrees, Pro Chamber

January 6th, 2012, 12:30 AM	#5
tbirdscwd MM Fanatic 2004 Mustang GT 12.88 @ 109.45 N/A Join Date: Feb 2010 Location: Davis, CA Posts: 3,417 iTrader: -1 reviews	If the engine is at normal operating temp, it is fine to pull the plugs. If the engine is HOT, then wait til it cools down. Upon re-install, use anti-seize on the spark plug threads and actually torque them down. __________________ Fun: 2004 Mustang GT DD: 1994 Ram 2500 Cummins 4x4 Borla "Stinger" Exhaust Vids

January 6th, 2012, 06:09 AM	#7
99GT35thLE Hardcore Enthusiast 1999 GT 35th LE Join Date: Dec 2009 Location: Jacksonville, Florida Posts: 1,428 iTrader: 0 reviews	CliffyK your link isn't working! __________________ Drive it like you stole it

January 6th, 2012, 06:11 AM	#8
cliffyk Hardcore Enthusiast Join Date: Feb 2007 Location: Saint Augustine, FL Posts: 1,805 iTrader: 1 reviews	Working on it right now... [edit] Got it, the blog index was corrupted... [/edit] __________________ -cliff knight- My Mustang 2003 GT, UPR X, 24lb/h injectors, Magnaflow, 180° stat, PP 70mm TB & plenum, DF Commando, Steeda UDPs, Ralco RZ_flywheel, RAM HDX clutch, WX EFX COPs 3.73s, 262 rwHP/305 lb-ft. Flex-fuel: burns gas and rubber...

January 6th, 2012, 03:57 PM	#9
TorchRed04GT Regular Join Date: May 2009 Posts: 66 iTrader: 0 reviews	Last time I changed the plugs I used anti sieze and torqued them to 13 lb-ft. I will let the engine warm up just enought for the fan to kick on then I will pull them and do a compression test. Does the throttle body have to be at WOT for the readings to be correct? __________________ 04' GT - Vortech & Meth

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