Blow By Issues (Compression + Leakdown Results)
10-18-2018, 05:59 AM
#1
Teching In
Thread Starter
Blow By Issues (Compression + Leakdown Results) I've been running a rebuilt engine this year (LS3 - stock build). On the first event I found lots of oil in the catch can and have been trying to diagnose what's up.
From my understanding it's being caused by blow by, the question is rings or valve guides (as far as I understand it). I've done compression and leak down tests (engine hot - results below). For the compression test I see that there are a couple of methods out there: run for 5 bumps or; run until the needle stops. I did the latter so hopefully it still makes sense (it was at least consistent as I went round twice).
The one thing I have found is that on all of the leak down testing, all of the leaking air is being pushed out of the passenger valve cover breather line. Does this make sense? Is this because the drivers side has a PCV valve in the valve cover?
Compression Test:
1 - 174
2 - 175
3 - 180
4 - 183
5 - 182
6 - 191
7 - 181
8 - 185
Leak down
1 - 11%
2 - 5%
3 - 11%
4 - 7%
5 - 5%
6 - 5%
7 - 11%
8 - 10%
Still learning so would love to try and understand what's happening. I appreciate it could mean new rings but I'm not sure I fully understand why all of the air is coming out of the passenger side valley cover? If it was going past the rings, would it then try and find the path of least resistance - which in this case does that mean going back up the passenger side and into that valley cover (due to the previously mentioned PCV in the drivers side)?
I'm pumping a qt of oil in a 30 minute session so would love to reduce that! Appreciate any thoughts/suggestions.
From my understanding it's being caused by blow by, the question is rings or valve guides (as far as I understand it). I've done compression and leak down tests (engine hot - results below). For the compression test I see that there are a couple of methods out there: run for 5 bumps or; run until the needle stops. I did the latter so hopefully it still makes sense (it was at least consistent as I went round twice).
The one thing I have found is that on all of the leak down testing, all of the leaking air is being pushed out of the passenger valve cover breather line. Does this make sense? Is this because the drivers side has a PCV valve in the valve cover?
Compression Test:
1 - 174
2 - 175
3 - 180
4 - 183
5 - 182
6 - 191
7 - 181
8 - 185
Leak down
1 - 11%
2 - 5%
3 - 11%
4 - 7%
5 - 5%
6 - 5%
7 - 11%
8 - 10%
Still learning so would love to try and understand what's happening. I appreciate it could mean new rings but I'm not sure I fully understand why all of the air is coming out of the passenger side valley cover? If it was going past the rings, would it then try and find the path of least resistance - which in this case does that mean going back up the passenger side and into that valley cover (due to the previously mentioned PCV in the drivers side)?
I'm pumping a qt of oil in a 30 minute session so would love to reduce that! Appreciate any thoughts/suggestions.
10-18-2018, 09:27 AM
#2
ModSquad
iTrader: (6)
Can you post up a diagram of your hose routing for the catch can? What can are you using?
10-18-2018, 10:51 AM
#3
Teching In
Thread Starter
I don’t have a way to post a diagram this morning but the routing is simple. Passenger valve cover is T’d into valley cover and goes straight into the catch can. Drivers side goes directly to catchcan. It’s a custom aluminum can.
I’ve been reading this morning about vacuum pumps helping with blow by. I’m wondering if the mistake we have made is by putting the valley cover into the can. Looking at other diagrams this alsways gets plumbed into the intake. Am I right in thinking that the reason this is done is to apply a vacuum to the crankcase to reduce blow by?
I’ve been reading this morning about vacuum pumps helping with blow by. I’m wondering if the mistake we have made is by putting the valley cover into the can. Looking at other diagrams this alsways gets plumbed into the intake. Am I right in thinking that the reason this is done is to apply a vacuum to the crankcase to reduce blow by?
10-18-2018, 04:37 PM
#4
ModSquad
iTrader: (6)
There’s a sticky, over in the gen3 external section regarding catch can setups.
10-18-2018, 09:09 PM
#5
I think Che70velle is on the right track in suspecting the catch can routing. Your compression test looks pretty good so the normal minimal blow by shouldn’t cause what your seeing. And a stock LS3 really shouldn’t need a vacuum pump to evacuate the crankcase if the PCV is setup correctly.
10-19-2018, 12:02 PM
#6
Hello,
Is no one else concerned with the leak down numbers here? (This is a genuine question, not a condescending statement)
Numbers mentioned in OP's post:
Leak down
1 - 11%
2 - 5%
3 - 11%
4 - 7%
5 - 5%
6 - 5%
7 - 11%
8 - 10%
I have always thought that the general rule of thumb is: If the leak down results in 10% or more loss in pressure, that cylinder needs to be looked at/inspected/re-ringed or "fixed" in some fashion. Is this not true? aren't there legitimate concerns to be had by the difference in pressure leakage from cylinder to cylinder? Say Cylinder 2 (5%) vs something like cylinder 3 (11%)?
Are you saying that in a driving session of about 30 minutes, you're losing a full quart of oil? (Technically this is considered a loss, in your situation it just happens to get caught in the catch can, and oil that's in the catch can, is oil that's not being used by the oil pan/engine/pump)
Thanks,
Andy
Is no one else concerned with the leak down numbers here? (This is a genuine question, not a condescending statement)
Numbers mentioned in OP's post:
Leak down
1 - 11%
2 - 5%
3 - 11%
4 - 7%
5 - 5%
6 - 5%
7 - 11%
8 - 10%
I have always thought that the general rule of thumb is: If the leak down results in 10% or more loss in pressure, that cylinder needs to be looked at/inspected/re-ringed or "fixed" in some fashion. Is this not true? aren't there legitimate concerns to be had by the difference in pressure leakage from cylinder to cylinder? Say Cylinder 2 (5%) vs something like cylinder 3 (11%)?
Thanks,
Andy
Last edited by AndyTA; 10-19-2018 at 12:15 PM.
10-19-2018, 12:33 PM
#7
Teching In
Thread Starter
Are you saying that in a driving session of about 30 minutes, you're losing a full quart of oil? (Technically this is considered a loss, in your situation it just happens to get caught in the catch can, and oil that's in the catch can, is oil that's not being used by the oil pan/engine/pump)
Thanks,
Andy
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10-19-2018, 12:40 PM
#9
My thought on the leak by numbers is that yes they are borderline high on some cylinders. But if you have good compression (no misfires) and you’re not BURNING oil you should be ok. The OP mentioned a rebuild but I didn’t see how many miles are on it since the rebuild...? If it’s a fresh hone and new rings I might be concerned about possibly unseated/glazed rings but if the engine is running good I wouldn’t lose sleep over it with those leak down numbers.
First thing that that needs to be addressed is the catch can routing. Hopefully that stops moving the oil around. Once that is verified, you can see if there are other symptoms to worry about.
First thing that that needs to be addressed is the catch can routing. Hopefully that stops moving the oil around. Once that is verified, you can see if there are other symptoms to worry about.
10-19-2018, 12:45 PM
#10
Teching In
Thread Starter
10-19-2018, 12:46 PM
#11
My thought on the leak by numbers is that yes they are borderline high on some cylinders. But if you have good compression (no misfires) and you’re not BURNING oil you should be ok. The OP mentioned a rebuild but I didn’t see how many miles are on it since the rebuild...? If it’s a fresh hone and new rings I might be concerned about possibly unseated/glazed rings but if the engine is running good I wouldn’t lose sleep over it with those leak down numbers.
First thing that that needs to be addressed is the catch can routing. Hopefully that stops moving the oil around. Once that is verified, you can see if there are other symptoms to worry about.
First thing that that needs to be addressed is the catch can routing. Hopefully that stops moving the oil around. Once that is verified, you can see if there are other symptoms to worry about.
Geiko,
When you did the compression/leak down test, did you take spark plug readings? (As in, inspect them and identify their color/health)? What did they look like? Were any of the spark plugs smothered in oil through the threads?
Do you see smoke out of your pipes when you give it throttle?
Basic questions, I know. But important none-the-less.
10-19-2018, 12:52 PM
#12
Teching In
Thread Starter
It’s a racecar. I don’t have a mileage readout on the dash but it’s bad perhaps 40 sessions on the track (20-30 minutes in length).
I’m putting 410HP to the wheels. Trying to go for reliability vs peak power.
The colour of the plugs look good and the AFR logs are all within are tune Spec (running Speed Density).
Now you mention it there was oil around the threads (but at the end furthest away from the spark). I figured I might have put some anti seize on the threads during the build and it had become discolored. Is this a symptom of something (I’m going to search right now!)
No-one has mentioned smoke and when a team mate has been out on track I’ve never seen any. The only time I notice anything is in wet conditions when it’s idling in the pits. With all of the moisture around it’s pretty normal to see that.
I’m putting 410HP to the wheels. Trying to go for reliability vs peak power.
The colour of the plugs look good and the AFR logs are all within are tune Spec (running Speed Density).
Now you mention it there was oil around the threads (but at the end furthest away from the spark). I figured I might have put some anti seize on the threads during the build and it had become discolored. Is this a symptom of something (I’m going to search right now!)
No-one has mentioned smoke and when a team mate has been out on track I’ve never seen any. The only time I notice anything is in wet conditions when it’s idling in the pits. With all of the moisture around it’s pretty normal to see that.
10-19-2018, 01:01 PM
#13
It’s a racecar. I don’t have a mileage readout on the dash but it’s bad perhaps 40 sessions on the track (20-30 minutes in length).
I’m putting 410HP to the wheels. Trying to go for reliability vs peak power.
The colour of the plugs look good and the AFR logs are all within are tune Spec (running Speed Density).
Now you mention it there was oil around the threads (but at the end furthest away from the spark). I figured I might have put some anti seize on the threads during the build and it had become discolored. Is this a symptom of something (I’m going to search right now!)
No-one has mentioned smoke and when a team mate has been out on track I’ve never seen any. The only time I notice anything is in wet conditions when it’s idling in the pits. With all of the moisture around it’s pretty normal to see that.
I’m putting 410HP to the wheels. Trying to go for reliability vs peak power.
The colour of the plugs look good and the AFR logs are all within are tune Spec (running Speed Density).
Now you mention it there was oil around the threads (but at the end furthest away from the spark). I figured I might have put some anti seize on the threads during the build and it had become discolored. Is this a symptom of something (I’m going to search right now!)
No-one has mentioned smoke and when a team mate has been out on track I’ve never seen any. The only time I notice anything is in wet conditions when it’s idling in the pits. With all of the moisture around it’s pretty normal to see that.
Oil on the threads is a symptom of excessive blow-by. If you have oil on the threads of your spark plug that is *furthest* from the spark itself (or any where on the thread, really) it means that there is oil that's finding its' way in to the combustion chamber, and finding its' way on to your spark plugs.
Someone please correct me if I'm wrong here. If you couple that information with the fact he's got around 11% of leakage in some cylinders, I believe the LEAST OP should do, is remove those valve covers and see what's going on. That is just my opinion, and not some sort of fear-tactic. Trust me, it SUCKS being in this position, I know.
With all that being said, I'm surprised you don't notice blue smoke from your exhaust when you open the throttle, I would expect this to be the case given the situation. However, I could be totally off-base here. I apologize in advance if any information I'm giving you is inaccurate, but I'm giving it to you based off of past experiences.
10-19-2018, 01:04 PM
#14
Teching In
Thread Starter
Geiko,
Oil on the threads is a symptom of excessive blow-by. If you have oil on the threads of your spark plug that is *furthest* from the spark itself (or any where on the thread, really) it means that there is oil that's finding its' way in to the combustion chamber, and finding its' way on to your spark plugs.
Someone please correct me if I'm wrong here. If you couple that information with the fact he's got around 11% of leakage in some cylinders, I believe the LEAST OP should do, is remove those valve covers and see what's going on. That is just my opinion, and not some sort of fear-tactic. Trust me, it SUCKS being in this position, I know.
With all that being said, I'm surprised you don't notice blue smoke from your exhaust when you open the throttle, I would expect this to be the case given the situation. However, I could be totally off-base here. I apologize in advance if any information I'm giving you is inaccurate, but I'm giving it to you based off of past experiences.
Oil on the threads is a symptom of excessive blow-by. If you have oil on the threads of your spark plug that is *furthest* from the spark itself (or any where on the thread, really) it means that there is oil that's finding its' way in to the combustion chamber, and finding its' way on to your spark plugs.
Someone please correct me if I'm wrong here. If you couple that information with the fact he's got around 11% of leakage in some cylinders, I believe the LEAST OP should do, is remove those valve covers and see what's going on. That is just my opinion, and not some sort of fear-tactic. Trust me, it SUCKS being in this position, I know.
With all that being said, I'm surprised you don't notice blue smoke from your exhaust when you open the throttle, I would expect this to be the case given the situation. However, I could be totally off-base here. I apologize in advance if any information I'm giving you is inaccurate, but I'm giving it to you based off of past experiences.
I’ve just found the threads relating to oil on the plugs. Looks like there can be many causes but those valve covers are coming off ASAP!
10-19-2018, 02:28 PM
#16
Teching In
Thread Starter
I’d have to go back to the original specs on the clearances but I am using a Melling 10296. I was worried about this earlier in the year and have been told it’s recommended for the heavy track use.
10-19-2018, 02:40 PM
#17
TECH Addict
40 sessions is actually a fair number for a v8 used on track.
On the fleet I took care of we did rings every season, typically 25 to 30 sessions..
Sprint engine got rings 4 times a year, but thats 800 HP at 10.5K rpm..
On the fleet I took care of we did rings every season, typically 25 to 30 sessions..
Sprint engine got rings 4 times a year, but thats 800 HP at 10.5K rpm..
10-19-2018, 02:47 PM
#18
I suspected that you were using a high volume pump well before you said so. That is causing most of your issue.
You dont have a use for it so why use it? Where do you think that extra volume goes when there is no need for it?
Ive literally been preaching this for the past year or more.
DO NOT USE HIGH VOLUME PUMPS ON LS ENGINES.
The only ones that MAY need them are ones with oil accumulators or very large oil coolers or vvt/afm. Otherwise you do not need it and it will cause problems.
You dont have a use for it so why use it? Where do you think that extra volume goes when there is no need for it?
Ive literally been preaching this for the past year or more.
DO NOT USE HIGH VOLUME PUMPS ON LS ENGINES.
The only ones that MAY need them are ones with oil accumulators or very large oil coolers or vvt/afm. Otherwise you do not need it and it will cause problems.
10-19-2018, 03:05 PM
#19
Leak down numbers by themselves are simply a number that can be used for suspicion only. You would need to have leak down numbers from the build when it was new to really use them as a comparison or to determine the health of an engine. Ring gap, hone/cylinder finish, temperature, etc. all effect the leak down number.
Also, the best way to find where the air from the leak down test is going is to use a stethoscope and listen to the exhaust (exhaust valves), throttle body (intake valves) and oil fill (rings).
Just some ideas.
Also, the best way to find where the air from the leak down test is going is to use a stethoscope and listen to the exhaust (exhaust valves), throttle body (intake valves) and oil fill (rings).
Just some ideas.
10-19-2018, 03:07 PM
#20
I suspected that you were using a high volume pump well before you said so. That is causing most of your issue.
You dont have a use for it so why use it? Where do you think that extra volume goes when there is no need for it?
Ive literally been preaching this for the past year or more.
DO NOT USE HIGH VOLUME PUMPS ON LS ENGINES.
The only ones that MAY need them are ones with oil accumulators or very large oil coolers or vvt/afm. Otherwise you do not need it and it will cause problems.
You dont have a use for it so why use it? Where do you think that extra volume goes when there is no need for it?
Ive literally been preaching this for the past year or more.
DO NOT USE HIGH VOLUME PUMPS ON LS ENGINES.
The only ones that MAY need them are ones with oil accumulators or very large oil coolers or vvt/afm. Otherwise you do not need it and it will cause problems.
Would you say the same applies to Pump: Melling 10295? That's currently what I'm running in my LS 427.
Thanks,
Andy
