is 13% on cylinder 4 leakdown test cause for concern?

[Rizapta]

Hi all, thanks for reading and any advice/thoughts, really appreciate it..

 

I have my car at a local tuning shop and asked to them to check out the motor, so they ran a compression test and leakdown test. The car has 126,000 miles on it, stock turbo, stock everything except a Grimmspeed TMIC and CAI only for the last 5k miles, and has been running a accessport stage 1 ots tune. I also sent in a sample of my last oil change to Blackstone Labs.

 

The compression was between 136 and 140 on all 4 cylinders.

 

The leakdown test was:

#1 - 4%

#2 - 6%

#3 - 6%

#4 - 13%

 

I asked them to please run the leakdown test again, just to confirm, and they did and they got the same results the second time.

 

The oil report came back from Blackstone with excellent results, saying that the sample looks excellent, all gaskets and seals are doing their jobs, and that I could safely increase oil change intervals based on that sample. The sample was taken at 123,000 miles. The oil had 3200 miles on it and the car had burned right around 1 quart during that 3200 miles.

 

The shop is telling me that the 13% indicates a cracked ringland on the #4 piston and that the motor, while it is ok right now and runs strong, will deteriorate quickly from this point on. They say it could be 20k or 2k miles, and at worst case when the piston breaks apart it will ruin the heads and possibly the turbo, best case is the car slowly keeps burning more and more oil and will misfire/knock badly.

 

So - I wanted to ask some advice from this forum. I have been searching through threads and reading a lot, but just thought I'd ask. Is 13% leak on cylinder 4 a big cause for concern? Should I stop driving the car to save the motor instead of risking further damage by continuing to drive it? How can I have such high compression on cylinder 4 even though leakdown indicates 13% ? Could this be a valve seating problem instead of the piston?

[Rhitter]

Hey, you are local to me. What shop did you take it too? I took my car to LIC in Novato for a compression/ leakdown and mine was really damn obvious. I have heard good things about TD garage in Berkeley, but beyond getting oil changes there I don't have a lot of feedback on them.

http://i.imgur.com/oSBIitk.jpg?1

 

but the next step they were going to perform was a boroscope (wasn't needed because it was so obvious).

 

It could be at the valves or the piston. Did they listen to where the leak was? 13% indicates you have a problem.

[Rizapta]

Hey, good to know another local LGT enthusiast! I have gone to TD Garage in Berkeley for help with bushing installs and other advice - Kea is the guy there and he's been cool. I would consider having him do the motor rebuild if that is indeed what is going to be needed..

 

But for now - my car is at Equilibrium Tuning out in Fairfield - awesome guys, they have some really cool builds out there, far beyond anything I'm going to get into.

 

Back to my issue though - I will ask about the boroscope and if they heard where the leak was coming from. Thanks! Ed at EQ tuning seemed quite sure it was the ringland, especially because he says the #4 piston is usually the most susceptible and he's been looking at these motors for a long time.

[Rhitter]

. Thanks! Ed at EQ tuning seemed quite sure it was the ringland, especially because he says the #4 piston is usually the most susceptible and he's been looking at these motors for a long time.

 

Nothing about what he said is wrong. I would bet money him being right. The compression test doesn't reveal all the issues which is why they perform compression and leakdown.

 

When the experts say ringland it probably is...good luck

[Rizapta]

So what about driving the car in the meantime? Risky and stupid?

 

Where did you rebuild? Did you use forged pistons? get a new shortblock? or take yours to a machine shop?

[Rhitter]

I sent mine to Infamous Performance in SoCal:

 

same old shortblock

CP pistons

King main bearings

King rod bearings

ARP head studs

 

rebuild was done February 2014 so only have 11 months and 7k miles on it.

 

Mostly because Infamous was active on these boards and I knew his deal. I am not too plugged into the local car scene and was more comfortable getting it built down there. I hear great things about FW in Rocklin and a few of the other shops. I just didn't want to investigate them.

[GTEASER]

I wouldn't drive it. At this point there is minimal chance that the cylinder wall is scored, so you may as well save the motor. The cylinders can likely still be honed and rebuilt with new pistons, bearings and rings rather than a whole new shortblock.

 

I have a 2012 LGT engine sitting in my garage with 53k miles on it that was replaced under warranty by the dealer for a cracked ringland. The leakdown showed #4 at 13%, the rest were 2-3%.

[magnusonsubie]

I will second what GTEASER said and not drive it. I actually cut up OB2.5XT's failed pistons and #4 was actually failed quite spectacularly. Even with a 13% leakdown I would suspect a failure even if it is not the the extreme that his was. See my "Material test" link in my signature for pictures and more information if what I found on OB2.5XT's pistons.