Hey everyone, I recently picked up a 2005 evo with just over 100k on the clock. The car just had a new radiator put in before I purchased it, and I want to make sure the HG didn't pop when that issue took place. I took both cold and normal operating temp compression tests. Cold Test came in at 165, 149, 155, 155. Compression test at normal operating temp came in at 170, 168, 168, and 142. What would cause compression to drop on the #4 cylinder? Could this be a problem with the headgasket? Thoughts on this would be much appreciated. I will post pictures of the compression tests as well.

 

Did you repeat the test to verify, or were these one time numbers? Also, did you crank it until the gauge stopped going up?

 

I bled the gauge and did the readings 3 times. Also, I cranked until the needle would not rise any longer which I would then stop for a few seconds and then crank again a few more times.

 

Oil on the plug threads of no 4?


No, it's not the head gasket.
The headgasket can leak and you still get perfect compression numbers.


So doing a compression test won't usually find a HG problem.


Try retorquing the head?

 

155 is still pretty good id say. Not to different from one another. Doing a leakdown test would be your best bet.

Also a quick way is to add a few tea spoons of oil in low cylinder and see if it rises compression. If so usually indicates a piston ring issue. If readings stay same likely valve issue.

 

It was 155ish when cold but 143ish when hot. The other cylinders were nearly 170 if not 170. No oil on the threads, and the spark plugs that were in there when I swapped them all looked like they were in identical conditions. No smoke when idling/driving. I am going to find a leakdown tester as thats what English Racing recommended I do when I called them today. Car starts with no effort, idles perfectly, and drives/boosts fine.

 

I just did a compression test over the weekend on my car. 180 psi 1,3,4. And cylinder 2 was 160. 152k miles 30 psi e85.

Ima rock it till the rods fall off lol

 

180 is a little high for these cars and I would wonder if there is severe carbon build up on the Pistons or head. 163 is the "normal expected compression" from what I believe. I will try to find the specs for compression that I found while searching earlier. 138 was factory minimum that I remember for sure.

 

E85 usually cleans carbon. I looked with a bore scope look clean. 180 psi was the max it went after cranking for a while. Thats the way i do cr tests. Max compression reached was 180.

For all i know it doesnt have oem pistons.

 

170 to 142 is a pretty large gap. But how does it run? If it runs ok, send it...

 

Everything seems to run fine but it was completely stock and will be getting upgraded across the board before its back on the road. That's why I'm trying to determine the health of the longblock

 

If it runs good, with no smoke. I honestly wouldn't worry about it. You could do a leak down test, see if it's rings, or a valve not sealing properly.

 

I don't know your goals but for 100K this is a good engine.