Blow by at high speeds - JeepForum.com
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post #1 of 13 Old 03-30-2020, 11:33 PM Thread Starter
Azhunter1
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Blow by at high speeds

So this weekend we went for a ride about 100 mile away from home. Drove over on little 2 lanes going 55-60, coming back we hopped on the interstate and did 65-70. We got home and a little bit later noticed oil under the jeep (88 wrangler with a 258 about 20000 on a reman motor from PO). I crawled under it and notice the intake covered in oil. I pulled the air cleaner off the weber (soon to be changed out with a 2100) and notice it covered in oil. My buddy had mention that when I would let off the gas it would puff a little smoke and then when I hit the gas it would puff again. I pulled the valve cover and all the seals are up around the top of the stems. Is this normal I thought they are supposed to be at the bottom of the stems covering the guides? Thanks in advance Chris

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post #2 of 13 Old 03-31-2020, 08:08 AM
Wabatuckian
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Dumb question:

Is your PCV system hooked up correctly? How new is the PCV valve?

Josh
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post #3 of 13 Old 03-31-2020, 02:21 PM Thread Starter
Azhunter1
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Yes PCV is hooked up right to the base of the carb. When it running there is good suction on the end of the valve.
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post #4 of 13 Old 03-31-2020, 02:21 PM Thread Starter
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Maybe a year old.
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post #5 of 13 Old 03-31-2020, 04:35 PM
fishadventure
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How much oil is missing from the crankcase?

I’d also suggest going through a compression test and then a leak down test. See if the rings are bad.

The puffs of smoke are generally indicative of valve seals and from your description it should puff a little. But those won’t put oil in your intake. And even /without/ seals valve guides in good condition stop 99% of valve stem oil deep but even a little bit if oil will make a blue puff.

The leak down test will tell you if the rings are letting cylinder pressure into the crankcase.
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[size=3]Shackles & D-rings are different things.
Cranking IS turning over
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post #6 of 13 Old 03-31-2020, 08:23 PM Thread Starter
Azhunter1
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There is no oil in the intake just on the base of the air cleaner on the weber. The oil looks like its coming up through fresh air hose that connects to the back port on the valve cover. No oil seems to be missing from the crankcase.
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post #7 of 13 Old 04-01-2020, 05:21 AM
fishadventure
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Then I would say you are fine, that’s normal. A common thing on vehicles from paleontology artifact vehicles like ours. I am suspicious that the check valve isn’t functioning completely.

FYI the exhaust puffs at throttle release because of the sudden vacuum event that sucks a smidge of oil down the intake valve guides. Very worn guides will smoke continuously off-throttle.

Upthrottle puff is often rings where they readjust in worn lands and you get an on-throttle puff.

Bad, broken, or frozen rings or very worn exhaust valve guides will smoke all the time. Bad rings can lead to A LOT of oil on the motor from valve rocker cover etc.

I’d leak-down test it myself and at the least you’ll have a baseline.
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[size=3]Shackles & D-rings are different things.
Cranking IS turning over
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post #8 of 13 Old 04-01-2020, 07:14 AM
RockWoRM
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Quote:
Originally Posted by fishadventure View Post
A common thing on vehicles from paleontology artifact vehicles like ours. .
Ah ha! I knew there was a connection when my YJ blew up in Moab a few years ago. (There's a lot of that paleontology stuff going on in Moab, ya know. )

'05 LJR, 6sp, RC long arm w/MC 6" coils, 5.13 D44's w/chromo shafts, MetalCloak fenders/sliders/body armor, 37x12.50 MTR's, Warn 9.5, RockHard swing out w/full spare. <><
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post #9 of 13 Old 04-01-2020, 09:56 AM
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These engines are prone to vaporizing oil in the air cleaner housing. Guys have rigged up all kinds of things to improve the situation, like catch bottles and such.

I've tried a couple of things.

First I put some skotchbrite in the hose to help coalesce the oil, hoping it would run back to the valve cover. It helped, but the stock hose is almost horizontal so some of it still ended up in the filter, due to gravity and air flow. So I got rid of that.

Then I pulled that short hose out and used a long piece of hose with a loop in it. This has worked great. The oil vapor has a longer path to travel just to reach the apex of the loop, and then the elevation allows gravity to overcome air flow and the oil drains back to the valve cover. You can see the loop of hose in the pic below. No more oil on my air filter.

In your case I have to wonder about one thing you mentioned. The bonnet seals on the valve stems are supposed to be down on the guides. Why are they all lifted? It doesn't seem feasible that valve guide blow-by lifted them, but it is possible that oil is being sprayed a little more than designed. Or maybe some PO just didn't know how to install them??? Possibly unrelated to the specific issue of oil vaporization, but an odd coincidence.


Bill
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1988 Wrangler,4.2L I-6, Howell EFI JP-1,CRT HEI Ign,AX15 ext slave conversion, Zone 2" lift + 1" BL + 1/2" booms, BFG 31 x 10.5, Bestop.
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post #10 of 13 Old 04-01-2020, 11:48 AM
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@bpounds interesting- so a coiled piece of copper tubing may condense even better and stop his issue?

[size=3]Shackles & D-rings are different things.
Cranking IS turning over
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post #11 of 13 Old 04-01-2020, 12:08 PM
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I think the idea is to increase the distance that vaporized oil has to travel is the key to that oil coalescing, and the elevation does a couple of things. First is simply that gravity will drain any oil that coalesces in the first half of the hose back to the engine, and second is that the oil will coalesce easier when it impinges on the hose surface due to change in direction. All that compared to just a shorter hose with almost no change in elevation.

As far as a copper tube, I don't think temperature has much to do with it, and the oil is not condensing, it is coalescing. Condensing is the change from a gas to a liquid. Coalescing is droplets of oil rejoining into larger droplets, but the oil has not changed to or from a gas. So I assume copper would work about the same as rubber hose, if you had some preference for that.

Bill
Recently discovered I am bi-flexual.
1988 Wrangler,4.2L I-6, Howell EFI JP-1,CRT HEI Ign,AX15 ext slave conversion, Zone 2" lift + 1" BL + 1/2" booms, BFG 31 x 10.5, Bestop.
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post #12 of 13 Old 04-01-2020, 12:11 PM
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Also, that's basically how catchment bottles would work. The vaporized oil just flows into a bottle, but it has to make a sudden 180 change in direction, which makes the oil droplets fall out.

I don't even think vapor is the correct term, since vapor implies a gas. More like atomized maybe? Or just entrained oil? Not sure what the science would say about that.

Bill
Recently discovered I am bi-flexual.
1988 Wrangler,4.2L I-6, Howell EFI JP-1,CRT HEI Ign,AX15 ext slave conversion, Zone 2" lift + 1" BL + 1/2" booms, BFG 31 x 10.5, Bestop.
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post #13 of 13 Old 04-01-2020, 04:47 PM
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I think science would say air is theoretically ‘liquid’ and that tiny oil droplets were suspended in it

[size=3]Shackles & D-rings are different things.
Cranking IS turning over
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