Hello everyone!

After i cured my internal coolant leak on my 355 (replaced head gasket, no coolant loss since then) im still having some troubles with some oil consumption. Not really excessive but there is consumption, the oil level gets lower and lower.

BUT, i have to say, i drove the car a lot over the summer and since its a driver, i really dont baby my engine.

Im pretty sure that some oil or oil mist is being sucked in by the pcv valve, since the pcv hose is oily inside and my thick heat-insulating gasket under the qjet is wet from oil in the section where the PCV fitting of the carb is entering and the inside of my intake manifold is wet from oil or oil mist right under the carb.

Even, yesterday i put a new PCV valve (AC Delco, stock style like its shown in the CSM) i had lying around in the valve cover, and today after about 1h driving, i pulled it out to check it and the valve was oily again.

BTW, i use stock valve covers, so baffeling shouldnt be the problem, even when revving the engine in neutral, there is no oil splashing around when looking through the pcv grommet.

I also dont think that i have some "excessive blowby/crankcase pressure" that would force too much oil through the pcv. When i plug both valve cover with my thumbs, there is just a really small amount of pressure building up (Not like it was when i had my internal coolant leak where pressure was really whooshing out when letting the thumb off). I also have no symptoms like oil leaks from valve cover or valley end seals or pushed out dipstick.

Maybe someone knows more about this problem.
im close to learn to live with it, since the consumption is not really excessive, but im simply still curious about what can cause this problem.

BTW, this was with 20W-50 oil.

Thanks to all!

 

It won't hut anything to block off the PCV for a while and see if you oil level continues to drop.

 

I will definitely try that out.

But do i really need a tunable wagner pcv valve for 120 $ ?

My engine is a mild build, so i was hoping the stock replacement pcv valve would work right.

I red in a chevy forum that there are some recommendations of a few ac delco pcv valves with different part #'s depending on the spring pressure.

 

The reason most go to the Wagoner valve is because of low vacuum caused by lumpy cams. If yours is mild, no.

 

This is my cam:

Advertised Duration (Int/Exh): 272/276 ;Duration @ .050 (Int/Exh): 217/221 ;Gross Valve Lift (Int/Exh): .485/.485 ;LSA/ICL: 10/104 ;Valve Lash (Int/Exh): Hyd/Hyd ;RPM Range: Idle-5500

not as slow as stock, but not really radical.

 

Same cam in my engine, which idles smoothly and pulls over 16" vacuum (with the proper tuning).

 

Fashion a temporary oil catch can into the PCV line and see how much oil accumulates.

Good luck!!!

 

How much is too much? It would be nice to have a reference to go by. Like how many miles to the quart, It may not be that bad..... Tedd

 

ill try that out, i already ordered a
cheap catch can 👍

 

Leaving it disconnected with the port plugged is as cheap as you can get.

 

I missed to write miles down after a fill-up to full marking on the dipstick, my fault.

Which amount of oil consumption would be "normal" or acceptable?

I know that some engines use more and some less. a big factor is how the engine gets driven and for sure, if its really get used with a lot of WOT and hard acceleration, the consumption of oil will be higher.

I only know that with my stock, un-rebuilt low comp 350, the oil consumption was low enough over the whole summers of driving that someone wouldnt even recognize it.

 

Thats true, but i am curious of how much oil really comes from the PCV line.

 

my idle is really smooth too with this cam, i have to hook up my vacuum gauge again to check how much is pulled exactly.

 

How many miles on the engine? Did you seat the rings? To our current engine builders or anyone else that knows do rings still need to be seated? I haven't replaced rings in a long time.

How much oil consumption is too much? IMO a quart or less per thousand miles is ok. More than that isn't. What say other members?

 

The engine is fairly new. I havent built the short block, my previous owner assembled it. I have speed pro 4.087 flat top forged pistons with moly rings. When i had the heads off to swap the head gaskets i have seen that the bores looked good with crosshatched hone markings.

i run stock baffled valve covers.

When i got the engine, i swapped to a new camshaft because the previous owner had a comp towing cam installed, and what can maybe a reason for my problem too is that i use Lunatis micro-trol lifters because i like the snap ring design of them.

BUT, i also think that these lifters allow more oil up to the top end. Maybe this can be the reason of more oil mist in the valve covers that will get just sucked around the baffles right in the PCV valve 🤔🤨

 

That used to be the rule of thumb back when these engine were new.

 

Do you guys think that the micro trol lifters could be the problem?

Even, for me its kinda difficult to determine if my engine has too much blowby or if its normal.

When i take out the breather and the PCV valve at idle, there are slightly oil fumes coming out. When i plug both valvecover grommets with my thumbs, i cant really feel some real pressure building up, but when i let my thumb off, there is a small whoosh coming out.

A lot less than i had it when my cooling system was "pressurizing" my crankcase, caused by a failed head gasket, but its definitely building up a slight pressure when blocking off the grommets.

But how much is normal and how much not?

Im not really exited to pull the engine again in winter to re - ring the pistons, so i really want to find out if there maybe are some other reasons for my problem 🤔

If its really coming to the point of installing new Piston rings, would you replace all bearings of the crank, rods etc. too? Or just install new Rings and reassemble the engine again? Im thinking about this because this engine is fairly fresh rebuilt.

Thanks for any thoughts, and thanks a lot for your help!

 

Compression and leak down tests could help you determine the condition of the rings

 

X2 @ Cutlass Fan, Do a leak down test before pulling anything apart. Time put into diagnosis is well spent. Confirm through measurements how much oil it is burning, maybe all is well.

If it does prove to use excessive, oil pull the valve covers and check for valve seals that have ridden up too high.

Reuse bearings? Yes if they look good, measure to spec, are quality parts and everything is put back EXACTLY where it was.

I'd also try seating the rings by getting the engine hot and then doing ten cycles of full throttle bursts from 20-50 mph with each burst followed by a 50-20 coast.

 

I did both tests a half year ago, these were the results:

Compression:

#1 171 PSI
#2 182 PSI
#3 180 PSI
#4 180 PSI
#5 171 PSI
#6 182 PSI
#7 185 PSI
#8 183 PSI

Leakdown:

#1: 15%
#2: 14%
#3: 10%
#4: 15%
#5: 25%
#6: 8%
#7: 13%
#8: 10%

I know, those leakdown test numbers arent really good but i was hoping that it will get better, with some driving, maybe the rings will seat a bit better.

But i will so both tests again for comparison.

 

before you rip the heads off, be sure that you don't have the system sealed. pcv sucks air, you need a way for fresh air to go in, an open breather cap not a twist on sealed one