GM LS guys - catch can questions

rfuerst911sc · 02-10-2025, 05:37 AM

I have a Gen 3 LS 5.3 in my S10 . I did not do the conversion . Had it a year now and it runs great . I have been reading about the potential benefits of adding a catch can .

Some guys are saying the OEM PCV system is weak and allows too much oil to make it to the combustion chamber . And some say it causes buildup on the valves . My engine is a early 2000's model with cable throttle body .

So any of you running a catch can ? How did you plumb it ? How often do you check it or empty it ? Any negatives to running a catch can ? This is just a street driver , zero track time .

RANDY P · RANDY P's Garage

I got one on my LS7 The PO installed. Done 13K miles (car has 26K)- I have never found any meaningful amount of oil in mine. More of a pain to get it out to empty than it's worth.

Given that, on a stock well-running engine I wouldn't waste my time. Such a small amount I highly doubt it affects octane.

Probably more of a need for higher miles car that burns oil or cars with really sketchy tunes highly susceptible to detonation or under extreme use (boost)

rjp

cockerpunk · 02-10-2025, 07:10 AM

my general rule with catch cans, is that they catch was the engine already planned to consume, and thus make you feel like you've done something, but they actually dont do anything.

like all that **** is supposed to get pumped back into the intake and burned off, so like taking it out by hand, doesnt really improve anything lol. there was already a system made to do that for you.

rfuerst911sc · 02-10-2025, 09:24 AM

So in your guys opinions the stock PCV system is sufficient for a stock engine ? The only mods to my knowledge are aftermarket headers and dual exhaust . I think it's a stock cam . I have no knowledge of it having a tune .

pwd72s · 09:54 AM

They're pretty popular in the Mustang world. Since it was an easy plug & play on my'09, I bought one. Theory is it keeps your intake cleaner. Easy to empty the JLT one I bought, simply unscrews. Catches maybe a teaspoon or 2 of oil with each oil change. No negatives I can think of...(edit) Found an old thread on the JLT...a link:
https://www.imboc.com/threads/jlt-oil-separator-issue.204186/

Probably a better thread:
https://www.imboc.com/threads/oil-catch-cans.308033/?post_id=3074785#post-3074785

JackDidley · JackDidley's Garage

If you have crankcase pressure you need a catch can. It will keep out from buliding up on the throttle blades, the intake ports , valves and fowling spark plugs. My C6 has 102k miles and has no crankcase pressure. Never burns or leaks a drop. No catch can needed.

rfuerst911sc · 02-10-2025, 09:47 AM

Quote:

Originally Posted by pwd72s

They're pretty popular in the Mustang world. Since it was an easy plug & play on my'09, I bought one. Theory is it keeps your intake cleaner. Easy to empty the JLT one I bought, simply unscrews. Catches maybe a teaspoon or 2 of oil with each oil change. No negatives I can think of...

Hmmm not sure it's worth it for a teaspoon or two of oil every 3k to 5k oil changes . But there must be some value keeping the oil out of the intake .

pwd72s · 02-10-2025, 10:22 AM

I do look at it as a "Can't hurt, might help" thing. Like I said, on my 4.6 Mustang it was an easy plug & play thing...as simple as replacing the PCV hose using the factory clips...a no tool required thing. Dunno if it would be as easy with your LS. JLT did some good design work.

Alan A · 02-10-2025, 11:59 AM

Don't have one on the LS2 on the Rumf.

rfuerst911sc · 02-10-2025, 12:20 PM

Quote:

Originally Posted by JackDidley

If you have crankcase pressure you need a catch can. It will keep out from buliding up on the throttle blades, the intake ports , valves and fowling spark plugs. My C6 has 102k miles and has no crankcase pressure. Never burns or leaks a drop. No catch can needed.

I will ask a stupid question , how do I know if I have crankcase pressure ? Does that mean one of the valve covers would be vented with a small filter on it ?

cockerpunk · 02-10-2025, 12:34 PM

Quote:

Originally Posted by rfuerst911sc

I will ask a stupid question , how do I know if I have crankcase pressure ? Does that mean one of the valve covers would be vented with a small filter on it ?

you can measure it with a vacuum gauge.

flipper35 · flipper35's Garage

Quote:

Originally Posted by rfuerst911sc

Hmmm not sure it's worth it for a teaspoon or two of oil every 3k to 5k oil changes . But there must be some value keeping the oil out of the intake .

Oil will reduce the octane rating of the fuel, but minute amounts make minute changes.

On my carbed setup I have a catch can because the intake pulls a vacuum on the crank case for better ring seal. At least that is what the builder told me. Also keeps the system closed since tracks don't allow open breathers on the valve covers.

For a modern engine it probably provides no benefit unless the rings are bad.

oldE · 02-10-2025, 01:59 PM

Quote:

Originally Posted by rfuerst911sc

I will ask a stupid question , how do I know if I have crankcase pressure ? Does that mean one of the valve covers would be vented with a small filter on it ?

Quick and dirty way would be to remove the oil fill cap while the engine is running and look for vapors escaping. Or place your hand over the opening to detect escaping gasses. Wear something to protect your hand.

Best
Les

JackDidley · JackDidley's Garage

Quote:

Originally Posted by rfuerst911sc

I will ask a stupid question , how do I know if I have crankcase pressure ? Does that mean one of the valve covers would be vented with a small filter on it ?

Quote:

Originally Posted by oldE

Quick and dirty way would be to remove the oil fill cap while the engine is running and look for vapors escaping. Or place your hand over the opening to detect escaping gasses. Wear something to protect your hand.

Best
Les

Les is correct. Also, if you have an oil film around the filler cap or around the valve covers you may have crankcase pressure. A little is normal on a high mile motor and is not a real problem. If you have a lot of crankcase pressure you will be adding oil often.

rfuerst911sc · 02-10-2025, 04:11 PM

Quote:

Originally Posted by oldE

Quick and dirty way would be to remove the oil fill cap while the engine is running and look for vapors escaping. Or place your hand over the opening to detect escaping gasses. Wear something to protect your hand.

Best
Les

Thank you that is very helpful .

rfuerst911sc · 02-10-2025, 04:14 PM

Quote:

Originally Posted by JackDidley

Les is correct. Also, if you have an oil film around the filler cap or around the valve covers you may have crankcase pressure. A little is normal on a high mile motor and is not a real problem. If you have a lot of crankcase pressure you will be adding oil often.

The engine supposedly only has 30k miles . I am coming up on my 2nd oil change , so far have not had to add any oil . Good info thank you .

JackDidley · JackDidley's Garage

Quote:

Originally Posted by rfuerst911sc

The engine supposedly only has 30k miles . I am coming up on my 2nd oil change , so far have not had to add any oil . Good info thank you .

I'd say you are a long way from needing a catch can.

Arizona_928 · 02-10-2025, 05:02 PM

My understanding it’s for diesels with blow-by.

If you’re still running an egr, it might be beneficial but i highly doubt you still have that bolted up.

Brian 162 · 02-10-2025, 05:22 PM

I have a bone stock LS7 as well. I don’t have a catch can, and I used to track the car. I never thought of getting one.
Saying that on the Corvette Forum some guys have them and there are vendors doing a booming business selling them. The used ones get snapped up as well
There are threads on this topic over there.

rfuerst911sc · 02-11-2025, 10:42 AM

Quote:

Originally Posted by Arizona_928

My understanding it’s for diesels with blow-by.

If you’re still running an egr, it might be beneficial but i highly doubt you still have that bolted up.

I looked the engine over this morning , and you are correct the EGR has been eliminated . I have decided a catch can is not needed .