Compression Testing Correctly and Cold vs Warm engine - 3000GT/Stealth International Message Center

ProwlerGT · 04-23-2008, 12:36 AM

I have done searches and not seen any real hard data as to the differences in psi observed doing this test COLD vs WARM. I have my engine bay apart tonight and as you could imagine I don't really want to put it all back together to obtain WARM temp to do the test and of course nor do I like working on a hot engine bay for obvious reasons.

So please answer to what you have SEEN cold compression tests show vs warm ones on the SAME ENGINE. This isn't a thread to bicker as I've seen some of the other compression threads do. This is a thread to try and find possibly an established PSI range difference that cold testing would show vs hot testing AS WELL AS TO CLEAR UP HOW COMPRESSION TESTING IS DONE ON OUR CARS for those that need to know.

Kicking questions/comments off right here is the official procedure from the manual (with a few added remarks) and yes I realize it says to test warm so I don't need to hear it. I know everyone isn't testing warm.

Procedure:
Page 11-14 ENGINE - On-vehicle Service
COMPRESSION PRESSURE CHECK

(1) Prior to inspection, check to ensure that the engine oil, starter motor and battery (good charge on it) are in proper condition. Place the vehicle in the following conditions:

Engine coolant temperature: 80-95°C (176-203°F)
Lights, electric cooling fan and accessories: OFF
Transaxle: Neutral (P for A/T)

(2) Remove the spark plug cables.
(3) Remove all of the spark plugs.
(4) Disconnect the crankshaft position sensor connector.
NOTE: By so doing the engine control module stops performing ignition and fuel injection.

(5) Cover the spark plug mounting holes with a shop towel, crank the engine, and then check for foreign substances deposited on the shop towel.

Caution
1. When you crank the engine, keep away from the spark plug mounting holes.
2. If a compression measurement is performed with water, oil, fuel, etc. in the cylinder due to the cracks in the cylinders, these substances heated to a very high temperature will blow off the spark plug mounting holes and could be dangerous.

(6) Install a compression gauge in a spark plug mounting hole.

(7) Set the throttle valve in a fully opened position (unless the plenum is off already), and crank the engine to measure the compression pressure.
Standard value:
Non-Turbo 1,270 kPa (185 psi) [250-400 rpm]
Turbo 1,080 kPa (156 psi) [250-400 rpm]

Limit:
Non-Turbo min. 959 kPa (139 psi) [250-400 rpm]
Turbo min. 792 kPa (115 psi) [250-400 rpm]

(8) Measure the compression pressure in each of the cylinders and check that the difference in compression pressure between the individual cylinders is less than the limit value.

Limit: max. 98 kPa (14 psi)

ZephTheChef · 04-23-2008, 02:32 AM

The difference between cold and warm measurements is going to vary greatly engine to engine, or even cylinder to cylinder...it's not really a good practice to guess at what that difference is.

cbehnken · 04-23-2008, 02:44 AM

Quote:

Originally Posted by ZephTheChef

The difference between cold and warm measurements is going to vary greatly engine to engine, or even cylinder to cylinder...it's not really a good practice to guess at what that difference is.

yep, on my personal car it has varied as much as 15 PSI cold to warm.

There is no accuracy when you check the engine cold, so you may as well not bother. All it will tell you is if your rings are totally shot or not.

oohnoo · 04-23-2008, 06:05 AM

You'll be fine. Should be around 130psi cold. You'll still be able to tell if there's an issue such as a gross compression, valve leak, etc.

SkortchGT · 04-23-2008, 10:04 AM

I had 160 across the board on a semi warm motor on a new shorty

ProwlerGT · 04-24-2008, 09:56 PM

Quote:

Originally Posted by SkortchGT

I had 160 across the board on a semi warm motor on a new shorty

Thats a lil high for a turbo though probably due to mods right?

I'm gonna cold test mine tonight and post the cold vs warm figures for others to have a basis to go off of. I may not do the rear bank warm... depends on how I feel. lol

mike92stealthtt · 04-24-2008, 10:34 PM

I did a cold compression test on my 110K motor after doing my 120K and all the cylinders were between 150-160 psi.

ProwlerGT · 04-25-2008, 05:49 AM

Well, in my case my engine has been sitting for several months with no crank. I don't know if that affects the test or not, but what I do think affects the test is debris inside the spark plug bore where the compression tester fitting/gasket meets with the metal to make a good seal to receive the pressure.

I did each test on a COLD engine and tightened as much as I could and cleaned as best I could first. Here are the results:

Cyl 1: 213 & 169 Cyl 2: 183
Cyl 3: 135 Cyl 4: 139
Cyl 5: 135 Cyl 6: 147

Cylinder 1 had some oil on the plug threads and in the bore before I loosened it. The 2nd test I did on it was done after retightening the fitting for the compression tester. I didn't realize it till later, but that was the bore with the most debris in it hence me needing to tighten it more.

I have reassembled the beast, but I am not starting it up because if things don't run right I'm gonna be HELLA pissed after I spent the entire AM hours till dawn putting her back together. I will do a HOT test on the front bank when I awake later today and if the car is running good I will not do the rear bank. Its just too much to do especially if things are running good.

In any case if I were to go by the cold numbers it looks like I'd have some problems, but this is a good test to show you probably cannot as others have said.

SkortchGT · 04-25-2008, 07:26 AM

Quote:

Originally Posted by ProwlerGT

Thats a lil high for a turbo though probably due to mods right?

I'm gonna cold test mine tonight and post the cold vs warm figures for others to have a basis to go off of. I may not do the rear bank warm... depends on how I feel. lol

Na thats not high, I have a brand new stock short block. The manual calls for 156psi within 14 psi of eachother. It's possible that the head resurfacing might have upped the compression 4psi due to an extremely slight loss in head height, but I doubt it. Everything is just nice, new, and tight like a virgin.

ProwlerGT · 05-01-2008, 04:03 PM

I know proper procedure is to remove ALL plugs before doing testing, but is that just because the manual wants you to test all cylinders or because it changes the pressure results?

I ask cause I'm about to test the front bank after I take the car for a spin and of course I would rather not remove all the junk to test the rear bank again if the car seems to be running fine.

04-23-2008, 02:32 AM	#2 (permalink)
ZephTheChef Forum Member Join Date: Nov 2004 Location: Wichita, KS Drives: Red 1991 VR-4 (#3) Trader Rating: (2)	Re: Compression Testing Correctly and Cold vs Warm engine The difference between cold and warm measurements is going to vary greatly engine to engine, or even cylinder to cylinder...it's not really a good practice to guess at what that difference is. __________________ "why its a tubloidial butt noid!" - Ray Pampena, 2006

04-23-2008, 06:05 AM	#4 (permalink)
oohnoo Verified Seller Join Date: Apr 2003 Location: LI,NY Trader Rating: (146)	Re: Compression Testing Correctly and Cold vs Warm engine You'll be fine. Should be around 130psi cold. You'll still be able to tell if there's an issue such as a gross compression, valve leak, etc. __________________ ----------------[2007 Ride of the Year *"Stroke" her I did.* Retired - TD04 WRX19t's = 513awhp @ 18psi on PUMP

04-23-2008, 10:04 AM	#5 (permalink)
SkortchGT Warning: I'm an asshole Join Date: Jan 2002 Location: Lehigh Valley, PA Drives: 1992 3000GT VR4 Trader Rating: (10)	Re: Compression Testing Correctly and Cold vs Warm engine I had 160 across the board on a semi warm motor on a new shorty __________________ 1992 3000GT VR4 --Completely rebuilt 5/06-4/07. Everything new. For a list see: http://www.3si.org/forum/showthread.php?t=372579 --First time on dyno: 364AWHP@16psi with a 10.3AFR (now tuned at 11.4-11.6 with timing control, time for another dyno run soon) --Mods: DR Stage I heads, 3rd gen lifters, TD04L 13Gs, DSM SMICs, PTE 550s, Apexi SAFC, Apexi SITC, Walbro FP, IPO hotwire, Robbeck adapter & AEM FPR, 3SX underhood fuel gauge, 3SX fuel rail loop, DN Y-pipe, HKS SSQ BOV, K&N FIPK, Greddy Profec Spec S, AEM WB02, Autometer C2 boost, egt, oil press & water temp gauges, MSD wires, NGK BCP7ES's, TEIN FLEX coilovers, Maximal performance control arms, solid engine mounts & powdercoating, RPS Streetmax Clutch, RPS Flywheel, NBT Tranny (cryotreated OS, shift forks & rails), updated speedo gear, solid shifter bushings, full 2nd gen brake conversion, 3SX SS brake & clutch lines, Carbotech Panther+ pads in the front & Bob Cats in the rear, 3SX clutch vac delete, EGR delete, vac reduction, Ebay DP, gutted pre cats, Bronze FN01RCs 5Zigen 18x8.5 + 30 offset, Pirelli P-Zeros, engine dress up kit, Bigtyla ground wire kit. --Daily Driver: 98 Malibu, 4cyl, auto

04-24-2008, 10:34 PM	#7 (permalink)
mike92stealthtt Pearl White 92 Stealth TT Join Date: Feb 2006 Location: Philly Suburbs/ PSU Drives: 100+ IDC's Trader Rating: (12)	Re: Compression Testing Correctly and Cold vs Warm engine I did a cold compression test on my 110K motor after doing my 120K and all the cylinders were between 150-160 psi.

04-25-2008, 05:49 AM	#8 (permalink)
ProwlerGT King Detail Join Date: Oct 2003 Location: New Orleans area Drives: 95 3000GT Base DOHC Trader Rating: (11)	Re: Compression Testing Correctly and Cold vs Warm engine Well, in my case my engine has been sitting for several months with no crank. I don't know if that affects the test or not, but what I do think affects the test is debris inside the spark plug bore where the compression tester fitting/gasket meets with the metal to make a good seal to receive the pressure. I did each test on a COLD engine and tightened as much as I could and cleaned as best I could first. Here are the results: Cyl 1: 213 & 169 Cyl 2: 183 Cyl 3: 135 Cyl 4: 139 Cyl 5: 135 Cyl 6: 147 Cylinder 1 had some oil on the plug threads and in the bore before I loosened it. The 2nd test I did on it was done after retightening the fitting for the compression tester. I didn't realize it till later, but that was the bore with the most debris in it hence me needing to tighten it more. I have reassembled the beast, but I am not starting it up because if things don't run right I'm gonna be HELLA pissed after I spent the entire AM hours till dawn putting her back together. I will do a HOT test on the front bank when I awake later today and if the car is running good I will not do the rear bank. Its just too much to do especially if things are running good. In any case if I were to go by the cold numbers it looks like I'd have some problems, but this is a good test to show you probably cannot as others have said.

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05-01-2008, 04:03 PM	#10 (permalink)
ProwlerGT King Detail Join Date: Oct 2003 Location: New Orleans area Drives: 95 3000GT Base DOHC Trader Rating: (11)	Re: Compression Testing Correctly and Cold vs Warm engine I know proper procedure is to remove ALL plugs before doing testing, but is that just because the manual wants you to test all cylinders or because it changes the pressure results? I ask cause I'm about to test the front bank after I take the car for a spin and of course I would rather not remove all the junk to test the rear bank again if the car seems to be running fine.