Blow by

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vacuum_6

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If an engine is sucking oil thru the PCV (assume the PCV system is operating fine) due to blow-by. Is it better to retain the stock system and use a catch can or move the PCV system to the valve cover or it does not matter?

If the PCV system is no longer sucking oil then does the engine begin to burn it instead?
 
If this is related to your glazed cylinder wall issue (subsequently leads to excessive oil burning), again you need to pursue that direction (of tearing down the engine and inspect) of inspecting the cyl wall honing/cross-hatch pattern, for glazed wall and/or rings orientation (yes, compression rings as well as upper & lower oil control rings have orientations to minimize blowby).

Q.
 
Originally Posted By: vacuum_6
If an engine is sucking oil thru the PCV (assume the PCV system is operating fine) due to blow-by. Is it better to retain the stock system and use a catch can or move the PCV system to the valve cover or it does not matter?


The PCV system should already be connected to the valve cover in at least one place. A catch can is a very good idea though and I can tell you how to make one pretty cheap.
 
Originally Posted By: Quest
If this is related to your glazed cylinder wall issue (subsequently leads to excessive oil burning), again you need to pursue that direction (of tearing down the engine and inspect) of inspecting the cyl wall honing/cross-hatch pattern, for glazed wall and/or rings orientation (yes, compression rings as well as upper & lower oil control rings have orientations to minimize blowby).

Q.


Nope, if it was I would have referenced that thread.
 
Originally Posted By: vacuum_6
If an engine is sucking oil thru the PCV (assume the PCV system is operating fine) due to blow-by. Is it better to retain the stock system and use a catch can or move the PCV system to the valve cover or it does not matter?

If the PCV system is no longer sucking oil then does the engine begin to burn it instead?


I'm trying to understand what happens to the blow-by oil if a catch-can is not used. Does it get burned? Is it better to catch it and then pour it back inon the engine? I understand that all engines have some blow-up but I'm talking about excessive blow-by.
 
It runs down the intake manifold and into the cylinders eventually. Its better to catch it and dump it in the trash when you check your oil since its been contaminated and will be very runny.
 
Thx for the note vacuum_6.

Blowby usually contains unburnt gasoline fumes, all kinds of nasty gas like CO, etc. laden with moisture and such. Unless you can guarantee your system's cleanliness and operational conditions such as clean, dust-free operating environment and consistent normal engine operating temperature to chase away the unburned gas, solvents, and moisture, etc. otherwise, a catchcan may help.

Excessive blowby is usually considered a severe mechanical problem and it may overwhelm your PCV system due to excess pressure difference. If that is that case, nothing, not even a catchcan or so would help but to sort out the blowby issue(s) first. Fix the excessive blowby first before you consider anything....


Q.
 
I have a catch can on my Datsun 510. I have no idea if it is effective but the stuff it catches is nasty looking. I just think the engine is better off burning gasoline and not this stuff. I have also put in an adjustable pcv valve and have carefully guessed at the adjustment I'm now using.
 
Originally Posted By: Quest
Excessive blowby is usually considered a severe mechanical problem and it may overwhelm your PCV system due to excess pressure difference. If that is that case, nothing, not even a catchcan or so would help but to sort out the blowby issue(s) first. Fix the excessive blowby first before you consider anything....


The catch can doesnt fix the blow by though, it just filters it so it doesnt blow all the contaminated [censored] back into the intake.
 
Make your own. Heck, just adapt to a larger hose and coil it up like a snake. Let it drain back when you shut down.
 
Originally Posted By: vacuum_6
Who sells a cost effective catch can? I prefer not to spend $100+.


Make your own at Home Depot or Autozone. All you need is an air tool filter, two barbed 3/8" hose fittings (your size may vary) and maybe a foot of extra hose.
 
I wonder if my Aerostar 3.0 is doing this. It uses a quart about every 1300 miles, but no blue smoke. Engine has good power, so I doubt the rings are bad. There is no PCV filter on it either. Closed system or something weird like that.

So what do you do, just put a big canister in the PCV hose so the velocity is slowed and [censored] drops out into the can?

Which hose?

Where am I to find space for a can under the hood of an Aerostar?
 
Thats why I like the air tool filter. Mine just drops down behind an injector and pops outs when I need to check the level (clear plastic bottle) and dump it (it unscrews from the actual filter). Your van does list a PCV valve so you might want to double check that.
 
Last edited:
Yes, there is a PCV valve, but no filter in the airbox. My F150 has the valve and a filter in the air box. Guess the Aerostar just feed back in some other location.
 
Originally Posted By: vacuum_6
Originally Posted By: vacuum_6
If an engine is sucking oil thru the PCV (assume the PCV system is operating fine) due to blow-by. Is it better to retain the stock system and use a catch can or move the PCV system to the valve cover or it does not matter?

If the PCV system is no longer sucking oil then does the engine begin to burn it instead?


I'm trying to understand what happens to the blow-by oil if a catch-can is not used. Does it get burned? Is it better to catch it and then pour it back inon the engine? I understand that all engines have some blow-up but I'm talking about excessive blow-by.


A PCV system forces an engine to "eat" all of its blow by. It is a means of pollution control. In the old days before emissions and polution control, the blow by was just vented to atmosphere outside the engine.
 
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