cylinder leak test question

jteam · Feb 24, 2014

Has anyone out there ever performed a cylinder leak down test on a used engine while it is cold?

I bought a used 112k mile engine and want to check the health of it before swapping it into my truck, but I am concerned that the test will not be a reliable indicator. So I was curious if anyone else has done it on a dead cold engine (it is sitting on my trailer) and gotten reliable results.

I am thinking the readings will show way too much leakage since nothing (rings, pistons, block etc) is expanded from heat like it would be at operating temp.

m j · Feb 26, 2014

it will tell you if it has a dead hole pretty fast

Gary · Feb 27, 2014

I use to build a lot of engines for a living and would do cylinder leakage test on every cylinder when the engine was on the stand, I have never did a CLT on a warm engine. Just get each cylinder on TDC and do it.

jteam · Feb 27, 2014

Gary, would you normally see a higher percentage of leakage or generally an acceptable number? I've tried on mine and saw moderately high numbers with it dead cold. I was going to just do a long block swap but now I'm debating. I may try using the block heater and see if there are changes

Sent from my iPhone using Tapatalk

mondtster · Feb 27, 2014

I think I can count on one hand how many times I've done a CLT on a warm engine. We almost always do them cold.

One word of warning - your leakage numbers will vary depending on how large the orifice is that is in the tester. I'd take the numbers with a grain of salt, they don't mean much in my book.

jteam · Mar 1, 2014

Thanks for the replies guys, posted the same at the "org" and "nation", and not one reply.

Sent from my iPhone using Tapatalk

jteam · Mar 1, 2014

The numbers I got cold were all over the place using a harbor freight leak tester. I'm going to go back over the adapter I made from a grease whip and make sure there's no leak. My numbers were in the 50,60,70, percent. At least one sounded like an exhaust valve and several sound like a faulty injector seal in the cup. Looks like my long block swap will be cylinder head pulls at a minimum. Hopefully I won't discover anything major.

I bought it in hopes to just do a long block swap and get the truck on the road. If it weren't for bad luck...........

Sent from my iPhone using Tapatalk

mondtster · Mar 1, 2014

Do you really have any reason to question the integrity of the motor? In some cases you're best off just leaving it alone. If it were mine and it came out of a running truck I'd just put it in and see how it runs.

FWIW, engines will run and make rated power even with differential compression numbers that are close to zero. Some OEMs will tell you to continue running them that way.

jteam · Mar 2, 2014

I've not heard it run, can only go on the word of the seller (112k) The intake boot on the turbo wasn't in the greatest condition so the fins have a few nicks in them. However, the fins aren't "rounded off" like my engine which is apparently "dusted " (238k) with all the crankcase pressure I have. Mine blows oil out the dipstick tube.

The one I bought is a 1997 and it's going in a 2002 so I'll have to swap everything over. Which means if it doesn't work , I'll just be out the gaskets and labor.

Sent from my iPhone using Tapatalk

Gary · Mar 18, 2014

jteam said:
The numbers I got cold were all over the place using a harbor freight leak tester. I'm going to go back over the adapter I made from a grease whip and make sure there's no leak. My numbers were in the 50,60,70, percent. At least one sounded like an exhaust valve and several sound like a faulty injector seal in the cup. Looks like my long block swap will be cylinder head pulls at a minimum. Hopefully I won't discover anything major.

I bought it in hopes to just do a long block swap and get the truck on the road. If it weren't for bad luck...........

Sent from my iPhone using Tapatalk

The numbers you are getting can't be right. To get good results, get the cylinder on TDC, remove the rocker arms, pressurize the cylinder with the tester, then tap the valve stems with a mallet. That's the way I would do it on a engine stand, I know it kind of a PITA, but that's the way.
It sound like you were probably getting leakage out the valves.

Arisley · Mar 18, 2014

Gary said:
The numbers you are getting can't be right. To get good results, get the cylinder on TDC, remove the rocker arms, pressurize the cylinder with the tester, then tap the valve stems with a mallet. That's the way I would do it on a engine stand, I know it kind of a PITA, but that's the way.
It sound like you were probably getting leakage out the valves.

If you pull the rocker arms, you can have the piston in any position. If it leaks down when the piston is at the bottom but not when it is at the top, you have a hole in the cylinder wall.

jteam · Mar 25, 2014

Gary and Arisley,

both very good points! Thanks for the tips guys. I'll have to give it another try when I get a free day with decent weather.

Sent from my iPhone using Tapatalk

Gary · Mar 26, 2014

Arisley said:
If you pull the rocker arms, you can have the piston in any position. If it leaks down when the piston is at the bottom but not when it is at the top, you have a hole in the cylinder wall.

I use to build prototype engines and work in the dyno labs at Ford and that's the way we did it when it was first build and when we tore them down after durability testing for inspection. Then to test head gaskets we put 1000 psi of nitrogen in the cylinder and look for bubbles in the coolant. Now when I'm looking for a hole in a cylinder wall, I pull the crank, rods and pistons out, bolt the heads back down with fresh gaskets. Then I block off the water pump inlet, heater hose nipples, and I made cap for the upper hose with a schrader valve, then fill the system with water and put the air pressure to it. I have had some blocks that needed 100 psi and I had to heat the block with a rose bud to get them to leak. Usually them old 6.9's and 7.3's it was #8 everytime