How much blow by is too much?

[metalmonkey47]

I've noticed ever since I got my truck that I've had a little seepage from the valve cover vent. HRH's recent thread reminded me about this.

 

It's been more or less minimal, but I decided to put a breather filter on instead of routing it back to in filter. (Don't need to blow oil into the carb.)

 

I drive it very easy and usually piss people off. No one really expects to see a straight-piped Datsun pull in front of them and go slow. lol

 

 

 

 

Yesterday I noticed that my breather filter has literally started to seep oil down the valve cover from the amount of oil collecting. It has plenty of power, doesn't blow smoke at all! I'm a little concerned that this may be a sign of problems yet to come. The trucks been well maintained. It's been owned by Ratsun members for several years and I was told had a fresh top end rebuild about 7K miles ago (rough estimate) and looks to be in great health.

 

I haven't done a compression test yet, but sheer curiosity has me to that point. I'll be doing on in the next few days.

Edited December 18, 2011 by metalmonkey47

[I'm BLUE]

Check/Replace PCV valve ,,, cheap ones are shit too ! lol

[metalmonkey47]

Check/Replace PCV valve ,,, cheap ones are shit too ! lol

 

Forgot to mention above, I already replaced it :( I was hoping that would be a good solution.

[I'm BLUE]

compression and ,,, leakdown test ,,, yo !!!

 

Top end Rebuilds ,,, tend to put more pressure on bottom ends ,,, that are not touched

 

Bottom End Rebuilds ,,, tend to put more pressure on top ends ,,, that are not touched

 

ya dig ?

[metalmonkey47]

^^Yup, that's exactly what I figured someone was gonna say :P

 

I figure with as much oil I see in the crankcase vent, I would see even a tiny bit of smoke or evidence of it. I don't have ANY smoke at all. Not in the cold, or anything. No carbon in the tailpipe, the truck just runs perfect.

[I'm BLUE]

Yo dawg we heard you like anticipation ,,, I anticipated your anticipation ,,, and replied back to you ,,,, so you can anticipate what Ima saying ,,, while I anticipate what your saying !!! ( insert x-zibit face here in your head with big smile )

 

How much oil do you "lose" over course of miles/changes ? ( I know you said you don't "burn" any ,,, )

 

If not much ,,, or any at all ,,, I really wouldn't worry about it ,,, build a catch can ,,,

 

Yo dawg ,,, do a GOSH DAMN compression check ,,, or ima YO yo yo yo yo dawg you until you do !!!

[Guest 510kamikazifreak]

Yo dawg we heard you like anticipation ,,, I anticipated your anticipation ,,, and replied back to you ,,,, so you can anticipate what Ima saying ,,, while I anticipate what your saying !!! ( insert x-zibit face here in your head with big smile )

 

How much oil do you "lose" over course of miles/changes ? ( I know you said you don't "burn" any ,,, )

 

If not much ,,, or any at all ,,, I really wouldn't worry about it ,,, build a catch can ,,,

 

Yo dawg ,,, do a GOSH DAMN compression check ,,, or ima YO yo yo yo yo dawg you until you do !!!

 

 

^ YO Word

[datsunaholic]

I have an engine that burns a quart every 100-150 miles. Plumb wore out. No smoke. No blowby out the top vent either.

 

Anything out the top vent is too much.I suppose you could at least check to see if your valve cover has a baffle. I recall one engine that was pumping half a quart out the top vent every 50 miles... no baffle in the valve cover, so the cam lobes were simply throwing oil up into the vent, and the blowby pushed it out. The baffle won't stop it since there's misted oil up there, but it does slow it down.

[ggzilla]

How much blow by is too much?

 

ANY that you can see is too much. It means your rings are not sealing correctly (or that your crankcase ventilation is blocked).

 

If you can't see vapor come out of the valve cover vent, and don't see smoke out the tailpipe when you rap it to 4000 RPM three times, then it's good.

 

You can use a compression test to confirm.

[yello620]

Check/Replace PCV valve ,,, cheap ones are shit too ! lol

 

 

Forgot to mention above, I already replaced it :( I was hoping that would be a good solution.

 

Ya, we know where you work. ;)

[Skib]

^ YO Word

 

 

[wayno]

My brand new LZ23 has blow-by at an idle with the oil cap off, but when I gave it the gas, it would go away, I guess this is normal.

Before I put that new engine in, if I removed the oil filler cap on the old L20b engine, it would soak the bottom of the hood.

I was also rolling the dice on every long trip, I figured on one of those trips, it would run out of oil before it ran out of gas, normally I had to dump 3+ quarts of oil for evey tank of gas, it was to the point that I didn't change the oil anymore, I just changed the oil filter every once in a while.

I was also blowing out the seals in the engine also, I changed that oilpan gasket more than once.

If any of this sounds familiar, try changing all the leaky gaskets once, if they start leaking again, maybe it is time for a complete rebuild.

My engine blew white smoke in the morning when cold, after it warmed up that went away.

The thing ran great the whole time, I beat the shit out of that engine everyday, pulling a trailer, and massive weight on the flatbed(it's a dually with overload airbags), it just got tired, as we all will get one day.

[I'm BLUE]

Ya, we know where you work. ;)

 

 

:lol: ... :D

[ggzilla]

Wayne, that is not normal. There should be zero blow-by at idle with the oil cap off. What you might see is some oil splashing out (L-series do that heavily), but that is different from blow-by.

 

Or, if a new engine hasn't had the 100 mile run-in yet, the rings may still not be seated.

 

The way to check for blow-by is to crimp the lower block ventilation hose (which leads to the PCV valve). Crimp this lightly with vice-grips, but only if the hose is soft. Then remove the oil cap and cup your hand behind the opening so that you can see if any opaque vapor is coming out. The reason for crimping the hose is that small amounts of blow-by are caught by the PCV valve. But when crimped on a good engine, there should be zero, nada, none. Most engines start showing some around 150,000 miles, then a couple years later are smoking out the tailpipe too.

[hogboy52]

The valve cover is the fresh air inlet. Nothing should be coming out. Air enters the top and is drawn out the bottom into the intake manifold.

 

That's why it's called ventilation.

[datzenmike]

There is always going to be some blow-by past the rings. It increases the harder you drive it and is less at light throttle. The PCV can only absorb a metered amount through the opening in it, AND only at low throttle when the intake vacuum is high. During heavy throttle and low manifold vacuum, the blow-by will over power the PCV valve and the excess is forced out the valve cover vent.

 

 

 

If worried about the oil dripping on the valve cover simply connect it back the way the factory designed it to work. Any small amount will be sucked into and burnt by the motor. If there is enough oil to seriously affect the carb operation you have bigger problems.

Try a catch can mounted on the firewall or fender and empty the oil back into the motor... :lol: Oil loss solved.

 

Try driving slower or rev the engine less. The crank will whip the oil spray into a fine fog of droplets, almost a mist. This will find it's way up from the oil pan past the timing chain to the valve cover. Excess blow by will push it out... :lol:

[wayno]

Wayne, that is not normal. There should be zero blow-by at idle with the oil cap off. What you might see is some oil splashing out (L-series do that heavily), but that is different from blow-by.

 

Or, if a new engine hasn't had the 100 mile run-in yet, the rings may still not be seated.

 

The way to check for blow-by is to crimp the lower block ventilation hose (which leads to the PCV valve). Crimp this lightly with vice-grips, but only if the hose is soft. Then remove the oil cap and cup your hand behind the opening so that you can see if any opaque vapor is coming out. The reason for crimping the hose is that small amounts of blow-by are caught by the PCV valve. But when crimped on a good engine, there should be zero, nada, none. Most engines start showing some around 150,000 miles, then a couple years later are smoking out the tailpipe too.

 

 

Yes ggzilla, it had 0 miles on it when I made that observation, and when I touched the throddle it actually tried sucking my hand onto the valve cover hole. My old engine was like a steam locomotive, blowing air out so fast, it would soak the bottom of the hood.

[Laecaon]

Me gots lots of blow by. White smoke galore when cold (its not coolant, nor smell sweet), and blue smoke when warm and heavy acceleration. Though any constant rpm has no smoke (yes I am probably still burning).

[metalmonkey47]

Sorry guys, been delayed getting back to you on this. Gonna try and find some time for a compression test tomorrow.

 

 

Anyways, I don't see a lot of oil loss. I've only lost about 1/2 quart within the last 3K miles :rofl: It just seems like lately it's been pushing a little more oil. 29 degrees this morning and still doesn't blow even the slightest bit of smoke.

 

 

What I may do is set up a cheap catch can temporarily.

Edited December 20, 2011 by metalmonkey47

[metalmonkey47]

Figured it out I believe.

 

 

Pulled the block vent and have NO air circulation @ the vent. I covered the valve cover vent to see if that would give me any circulation at the block vent and I had zero. it just pressurized the engine.

 

I'm going to say quite confidently that I believe the block vent tube is clogged. So whats my next step??

 

 

 

http://www.youtube.com/watch?v=UT1BbqENoEQ&feature=youtu.be

 

[Eagle_Adam]

unclog it :P

[ggzilla]

Yep. Either the Tube is clogged, or the filter screen is clogged. Let's hope it is the tube, because to replace the filter you need to drop the oil pan.

[metalmonkey47]

Yep. Either the Tube is clogged, or the filter screen is clogged. Let's hope it is the tube, because to replace the filter you need to drop the oil pan.

 

Well damn. lol I really hope it's clogged in the tube..

 

is there any way to pull the tube from the block without pulling the intake? I only pulled the rubber hose off of it

[daf]

In the case of my Integra, when I was destroying oil pan gaskets, that as too much. Had to get a vented valve cover and catch can to run on 16psi.

[datzenmike]

The L20B pulls straight up and out, the L16/18 pulls out to the side. It's possible it's the pipe that is plugged. Warm vapors will condense on the pipe if you drive short distances. May have built up.