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where is my oil going?
#557948
12/19/09 03:52 PM
12/19/09 03:52 PM
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Joined: Jul 2006
Posts: 4,179
California
mickm
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my engine still uses a lot of oil, quart or so every 100+ miles. haven't checked it exactly, but it's a lot.
brief history. after i got it took the heads off, and found that the intake was very loose and sucking oil. it was bad, the gaskets were wet along the bottom for all the ports. thought i found the problem, all else looked in good shape, so just did a re-gasket, (and cam, new intake), and put it back together. better, but still sucked oil.
leak down showed 8-10% for all cylinders, compression test good, (forget the numbers, but all very close). was sure it was the guides/seals. took the heads off again for this reason, (but also to have them ported), and found it was again leaking through the intake, (i didn't know these had to be sealed with gunk).
so here i am now.
- guides were fine, new seals.
- sealed intake.
- cylinder walls looked good, nice crosshatch still visible.
- plugs do not show signs of oil consumption, (maybe very minor, but i have nice tan insulators, with the slightest bit of soot around the rim, don't know if it's oil or slightly rich mixture).
- leak down and compression tests were a few thousand miles ago, so things could have changed.
- q-tip in pcv port at carb came out grayish, but certainly not what i would expect if it was sucking that much oil through there.
does blow a little blue smoke when starting it up after cold and sitting for a while, but not bad.
if i have been driving normal for a bit, and then nail it, it does blow a big one time puff of smoke out the back, but it's hard to tell the color from looking back. seems that clearing that once or twice is fine, then no more smoke on nailing it.
does not seem to smoke any other times but those two.
so where do i go from here? is it possible that my oil rings are in that bad a shape? engine probably has 6-7k miles on it.
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Re: where is my oil going?
[Re: dodgeboy11]
#557950
12/19/09 04:03 PM
12/19/09 04:03 PM
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Joined: Jul 2006
Posts: 4,179
California
mickm
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Quote:
Is there a baffle under the pcv valve in the valve cover? They'll suck a lot of oil if there isn't one there.
I'd personally toss the pcv valve and run another breather.
there is a baffle. there seemed to be a lot of oil on the outside of the neck that the pcv pushes down onto. was suspicious of that, which led me to check the inside of the hose and connection at the carb.
what other type of breather setup would you use?
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Re: where is my oil going?
[Re: dodgeboy11]
#557953
12/19/09 04:13 PM
12/19/09 04:13 PM
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Joined: Jul 2006
Posts: 4,179
California
mickm
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Quote:
I'd just run another breather like you have on the other valve cover. That it has that much oil around the grommet makes me wonder if the one breather is enough. Does it seem to have a lot of oil residue around the breather and other areas? Reason I'm asking is I've seen some motors glaze the cylinders from improper break-in, but the leak down test kinda rules that out. Where was the piston when you did the leak down? TDC or BDC? Not that it matters, just thinking maybe the rings are sealing where it was tested and not elsewhere. Does it seem to have excessive blowby?
pistons were at TDC. haven't really looked for excessive blowby, although you would think that would have occurred to me me by now 
i'll check that out next time i fire it up.
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Re: where is my oil going?
[Re: mickm]
#557955
12/19/09 04:17 PM
12/19/09 04:17 PM
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Joined: Feb 2007
Posts: 1,025
Las Vegas, NV
dodgeboy11
super stock
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super stock
Joined: Feb 2007
Posts: 1,025
Las Vegas, NV
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Quote:
pistons were at TDC. haven't really looked for excessive blowby, although you would think that would have occurred to me me by now
i'll check that out next time i fire it up.
I can't tell you how many times I've had something stare me in the face and it's taken someone else to bring it to my attention. Part of the fun right? 
Hopefully the problem is simple, like breathers or something along those lines. I highly doubt it's rings. It'd be burning oil on acceleration and the way you're describing it is sounds like it's drawing oil in under vacuum conditions only and once it's cleared out it's fine. Good luck with it.
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Re: where is my oil going?
[Re: dodgeboy11]
#557956
12/19/09 04:22 PM
12/19/09 04:22 PM
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Joined: Jul 2006
Posts: 4,179
California
mickm
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Quote:
I can't tell you how many times I've had something stare me in the face and it's taken someone else to bring it to my attention. Part of the fun right?
yup, know exactly what you mean
Quote:
Hopefully the problem is simple, like breathers or something along those lines. I highly doubt it's rings. It'd be burning oil on acceleration and the way you're describing it is sounds like it's drawing oil in under vacuum conditions only and once it's cleared out it's fine. Good luck with it.
that's what i've thought, too much checks out ok for it to be something major, but who knows.
i'll give this a shot and see where it goes from there.
thanks 
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Re: where is my oil going?
[Re: dodgeboy11]
#557957
12/19/09 06:34 PM
12/19/09 06:34 PM
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Joined: Aug 2003
Posts: 8,716
Baltimore/Denver
64Post
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Quote:
Yes that is correct. PCV is simply a smog deal. But on bigger engines you need enough breather to allow the crankcase to breath and sometimes one breather with a PCV isn't enough.
Point taken, but adding another breather if ring seal is going away doesn't fix the problem, it only hides it.
Mick, next time you have the intake off look at the ports and valves for excess oil build up.
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Re: where is my oil going?
[Re: 64Post]
#557958
12/19/09 06:45 PM
12/19/09 06:45 PM
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Joined: Jul 2006
Posts: 4,179
California
mickm
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Quote:
Mick, next time you have the intake off look at the ports and valves for excess oil build up.
i can do that by taking one of the carbs off. clean shot down into the port, and valve as well. i can get a long swab down in there and see what's there, so i'll do that.
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Re: where is my oil going?
[Re: mickm]
#557959
12/19/09 06:58 PM
12/19/09 06:58 PM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
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Put a pressure gauge on the valve cover(inches of water or a 5 psi) and measure the crank case pressure.... should be near 0, you would love to see it negative but if it shows near 0 check the intake again(use clay to check the gap) 
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Re: where is my oil going?
[Re: mickm]
#557960
12/19/09 07:36 PM
12/19/09 07:36 PM
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Joined: Jan 2003
Posts: 4,084
Indiana
W5Duster436
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I had the same problem with my Cuda when I first got it fired up. No smoke whatsoever but ate 6 quarts of oil after about 500 miles.
It was sucking the oil into the intake ports from under the intake due to poor alignment and not enough sealant. I think it only had the valley pan initially and I ended up having to add the thin gaskets as well with that special gasket sealant.
'70 Duster - SDSS 436 W5 4spd (Gone)
'71 Dodge D100
'70 Dodge W100
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Re: where is my oil going?
[Re: MR_P_BODY]
#557962
12/19/09 08:55 PM
12/19/09 08:55 PM
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Joined: Jul 2006
Posts: 4,179
California
mickm
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Quote:
Put a pressure gauge on the valve cover(inches of water
or a 5 psi) and measure the crank case pressure....
should be near 0, you would love to see it negative
but if it shows near 0 check the intake again(use
clay to check the gap)
is that with one side blocked off? or does the pressure gauge go on the breather side with the pcv still attached?
so there is some blowby in any engine, if not the rings would be 100% sealed. that blowby creates pressure that must escape somehow, in this case through the pcv and breather. so for there to be negative pressure that would mean that the vacuum from the engine, via the pcv, is creating something of a vacuum in the crankcase, correct?
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Re: where is my oil going?
[Re: Big B]
#557963
12/19/09 09:09 PM
12/19/09 09:09 PM
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Joined: Aug 2003
Posts: 8,716
Baltimore/Denver
64Post
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Quote:
My guess would be at full throttle the pcv valve is closing
And the crankcase is pressurizing. The other breather can't keep up.
When the crankcase pressurizes it pushes oil up into the cylinders.
I agree. How much blow by is considered normal? And how much can one breather handle?
I found I have the same blow by problem:
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Re: where is my oil going?
[Re: 64Post]
#557964
12/19/09 09:42 PM
12/19/09 09:42 PM
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Joined: Jul 2006
Posts: 4,179
California
mickm
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ok, i'm finding i need more and more clarification as this post goes on.
here is what i understand to be going on here:
combustion gasses slip by the rings, and so fill the crankcase. those gasses obviously have to be evacuated from the crankcase, or they would build up pressure that would force the gasses, (and oil as someone posted earlier), back into the cylinders.
in my case, the vacuum from the engine opens the check valve in the pcv, which then draws these crankcase gasses into the engine to be burned again.
the air flow goes from the breather on the opposite valve cover, through the crankcase, through the pcv valve and into the carburetor.
if there was no pcv valve, there would be one breather on each valve cover, and the gasses would just escape by being pressurized out of the breathers, (more like exhalers at this point).
so if my issue is there, then the pcv valve is closed when it shouldn't be, which gives the engine only one breather to evacuate the crankcase from. if this isn't enough, the pressure is forcing gases and oil back into the cylinders, hence the burning oil.
so right now i can do 2 things:
1) check the pressure in the crankcase, (do i do that just at idle, all the way through the rpm range???), and
2) just get rid of the pcv, plug the port on the carburetor, and put another breather in the valve cover where the pcv was.
am i on track with this???
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Re: where is my oil going?
[Re: Big B]
#557965
12/19/09 10:26 PM
12/19/09 10:26 PM
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Joined: Oct 2005
Posts: 4,939
WI
Dcuda69
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Quote:
My guess would be at full throttle the pcv valve is closing
And the crankcase is pressurizing. The other breather can't keep up.
When the crankcase pressurizes it pushes oil up into the cylinders.
Your best bet would be to install a vacuum pump.
Gzmotorsports, Jonesracing, and Product Engineering all have
Street vacuum pumps for continuous duty.
A good PCV valve should not close under WOT/heavy load.
When man vac. is high(idle,cruise,light load) the PCV valve restricts flow to maintain a balanced air-fuel mix.It also prevents drawing oil out of the crankcase because of high manifold vac. At WOT,low vac,heavy load the valve OPENS to allow airflow through the crankcase.
This is right out of a textbook. A PCV valve is more than just a check valve. 
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