View Full Version : Insane amount of blowby with great compression


samson_420
06-25-2010, 05:58 PM
This is not a LSx engine, but it is still a standard issue GM engine.




I tested the compression and the #'s are great across all cylinders. Yet this thing breaths oil. I mean it flows that shit like there is no tomorrow out of any orifice.


My internal engine knowledge is good to excellent, so I thought.

But, this just makes no sense.

WTF?

71novaguy
06-25-2010, 07:33 PM
I had a 307 that ran great but used a shit ton of oil. Had two pistons with broken oil ringlands

samson_420
06-25-2010, 08:06 PM
I had a 307 that ran great but used a shit ton of oil. Had two pistons with broken oil ringlands



Wow, weird shit. . . . . .


But, compression numbers can't lie. . . . . And it sounds totally fine, no knock or anything of the sort.

blitzace12
06-25-2010, 09:18 PM
valve guides? i was told in class that 85% of all oil consumption is head related.

samson_420
06-25-2010, 09:32 PM
I've seen some so bad they had good compression because so much oil was getting by.


That is too funny, but is actually possible.


This is a straight six in a Jeep.


It does not burn oil worth a crap, just feels like half of it's compression is going in the oil pan.


It's so fricking weird. . . . If I cared more I would tear into it just to see WTF is inside this thing.

01ssreda4
06-26-2010, 01:19 AM
Not LSx :lock:


:jest: had to

samson_420
06-26-2010, 01:49 AM
Not LSx :lock:


:jest: had to


Sho ain't. . . . But this is a place with the most automotive knowlegable people I have seen.

Saturn5
06-26-2010, 12:28 PM
Valve guides/seals would be my first guess.

LS6427
06-26-2010, 12:55 PM
Maybe a badly scored/grooved cylinder wall. During the compression test if the score/groove is below the piston it won't effect the compression test.

.

samson_420
06-26-2010, 07:58 PM
I bet it is the valve guides. . . And this so called blowby is exhaust gas pouring through the crank case.

I knew this motor had to be fucked. . . . It has not ran for 10 years then was driven on no oil for a 1,000 miles.


Oh well, at least it still runs. . . . . . Badly:mullet:



P.S. The crank case pressure is so high it shoots oil everywhere. I carry a gallon oil jug. The last one lasted about 500 miles. . . .


I think it will still run for a bit since my oil pressure is still real good along with the compression.

LS6427
06-26-2010, 09:07 PM
I bet it is the valve guides. . . And this so called blowby is exhaust gas pouring through the crank case.



Bad valve seals can't cause high crankcase pressures, they have no route to the crankcase....just to the cylinders. If you have high crankcase pressures it can only get that way if the cylinder pressure is getting by the rings, through a crack in a piston or a crack in a cylinder wall.

The only thing that can go through bad valve seals is oil....getting sucked through by the downstroke of the cylinder(s).

Unless you have an intake/exhaust valve that is not closing and on the upstroke or exhaust stroke its pushing cylinder pressure back up through the head and through the valve seal into the valve cover.....bent valve stem maybe......fuck man I don't know. Wierd.

If you really have high crankcase pressure I'd say its a crack somewhere, maybe down low in a cylinder...so the compression check still checks out good. Or piston.

.

samson_420
06-27-2010, 12:25 AM
Well, fuck. . . . it started over heating on my last run into the desert.

I made it home, but it started warming up to boil slowly.


I have been thinking about it a bit. I am thinking worn to shit exhaust valve guides. When exhaust is starting to to enter past the valve it shoots into the valve cover which of course is connected to the crank case.


I would also consider lower engine damage. But, fuck a compression test would catch that shit.


Or maybe so sort of crazy ass valve float at higher RPM caused by who knows what.


The oil pressure is still real good untill it gets very hot.

LS6427
06-27-2010, 12:36 AM
I made it home, but it started warming up to boil slowly.

One thing is for sure...if coolant boils over....you are getting air in the system. Blown head gasket or a small tiny leak somewhere. If its a tiny leak it will piss coolant out very slowly while driving or after shutdown when the heat and pressure rise for a little while before cooling and you'll probably never find it, but when you shut down and it cools it will suck in air. Then later on as that air bubble grows, the boiling point decreases, then you get boiling.


I have been thinking about it a bit. I am thinking worn to shit exhaust valve guides. When exhaust is starting to to enter past the valve it shoots into the valve cover which of course is connected to the crank case.

I think a leakdown check will find bad valve seals or valves not sealing in the heads....no?

I would also consider lower engine damage. But, fuck a compression test would catch that shit.

Compression check won't identify any internal damage, except rings or pistons. Nothing lower end though.

01ssreda4
06-27-2010, 12:46 AM
Motor's fucked. My .02

samson_420
06-27-2010, 02:54 PM
Motor's fucked. My .02



Agreed



This motor is toast. It needs a full reman or another complete donor.

If it was to be remaned it needs to be dissmantled and fluxed to see if the head or the block have any cracks. It might have some hair line cracks in the head since the oil was so low when it was ran before. You know the top end had to be dry for a bit.


I really did not expect much, it was in really bad shape. It went about 1,500 miles before it came down to this.



Oh well. . . . I had fun with it . . . . for a little while.:nod:

fuseone
06-27-2010, 09:04 PM
Did you try a running compression test?

samson_420
06-27-2010, 09:26 PM
Did you try a running compression test?




Hmmmm, what is a running compression test?

blitzace12
07-01-2010, 08:01 PM
is that the one where its hooked up to the computer and it tested while running? Those are cool but i hear its not as accurate. Got a 10k computer handy =)

blitzace12
07-01-2010, 08:03 PM
if you have good compression tho you could have the guides replaced. I would have it fluxed and see how much a good shop is going to charge to change the guides, and i bet they know a whole lot more than me!!

samson_420
07-02-2010, 09:24 AM
Well, I don't have the title to this POS and now I have no interest to get it. I am letting this Jeep die + I don't have the funds to tear into this big of a project.

I am trying to buy a house right now, that seems a bit more important then getting a 4th running vehicle right now. Would be a cool project though.

SparkyJJO
07-02-2010, 04:03 PM
It would be interesting to take it apart just to find out what is wrong inside. Just for curiosity's sake.