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King Detail
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Discussion Starter #1
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.
<img border="0" src="http://www.3si.org/forum/attachment.php?attachmentid=70714">
(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.
<img border="0" src="http://www.3si.org/forum/attachment.php?attachmentid=70715">
(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)
 

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Premium Member
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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.
 
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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.
 

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King Detail
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Discussion Starter #6
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
 

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King Detail
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Discussion Starter #8
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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Retired
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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. :)
 

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King Detail
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Discussion Starter #10
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.
 

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King Detail
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Discussion Starter #11
BUMP - No one knows the answer on this?
 

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Keep'n 'em spooled
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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.
The plugs are all removed so that the starter motor is only having to compress the air in one cylinder. The engine will turn over slower with some of the plugs installed, so the readings will be slightly lower.
 

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King Detail
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Discussion Starter #13
The plugs are all removed so that the starter motor is only having to compress the air in one cylinder. The engine will turn over slower with some of the plugs installed, so the readings will be slightly lower.
Thank you. So when ya say "slightly" do ya think thats like maybe 5 psi lower? lol - I know I know.... i should just do it right, but it really would just be only for the sake of the test cause I "think" the engine is running right.
 

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King Detail
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Discussion Starter #15
Just do the test already, it's only a compression test.
I know I know huh? lol ok ok - I just didn't want anything all skewed to happen.
 

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I was just wondering this SAME exact question, how convenient lol

Anyhow, we tested the compression on the VR4 that hasn't ran in a few weeks (so it's obviously cold and no oil pressure). Most cylinders were around 115 and one was slightly lower (5-10psi off). I was hoping the warm figures would be a decent amount higher since these are kind of low (service limit).

How are you guys getting 150psi cold!? lol

From my research it seems that from warm to cold there is a difference of around 10-15 psi but I have no hard proof, just from what I've read.
 

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King Detail
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Discussion Starter #17
Did the warm compression test earlier on the front bank:

Cylinder 1: 184
Cylinder 3: 180
Cylinder 5: 179

Will post the remaining bank later.

As you can see so far testing warm vs cold can variate greatly and really doesn't show a pattern (refer to post#8 for cold test #s). The idea that it'll only be 15lbs difference or any set psi difference is just false. Just gotta do the test correctly. I wasn't even comfortable doing the test warm without the 3 rear plugs out, instead I just removed all front plugs.

I'm probably going to retest again all 6 once all plugs are out and its warm. Would've done it all at once earlier, but had a friend stop by and supper and tonight the NEW ORLEANS HORNETS are playing in the semi-finals so car will sit !!!! lol
 

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King Detail
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Discussion Starter #19
See, nothing to be afraid of........Great results. :)
LOL - I just hope the rear bank is just as good and I have a hunch it will be.
 
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