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post #1 of (permalink) Old 03-28-2000, 08:35 PM
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oil blow by into air filter

I just joined this site, wow!! I like it... I'm no mechanic but i like to learn. I have seen a couple of quick fixes for this oil blow by problem. But what is it caused by? Is it as common as it appears from looking at this site. I have an 88 yj, 72,000 miles 258 I6.

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post #2 of (permalink) Old 03-28-2000, 08:47 PM
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Re: oil blow by into air filter

how much oil and how is it getting in? through the pcv filter? i remember this topic brought up before. i am curious to the answer!
steve

post #3 of (permalink) Old 03-28-2000, 09:17 PM
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Re: oil blow by into air filter

sas87yj ----- Any oil in the breather is too much for me. The oil is entering in hose that attaches to the side filter on the breather and the back of the rocker cover. After reading all the old posts on the subject it appears that i may have a ring problem. Is a 258 prone to ring problems? anyone.
Thanks
Jim

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post #4 of (permalink) Old 03-28-2000, 11:09 PM
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Re: oil blow by into air filter

258's....4.2L.... engines like good PCV valves. Valve clogs a little then oil goes to air filter. I keep a couple, one on engine, one in kerosene cleaning and one dried out ready to go. Extremely my $.02 Jimmy Z.

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post #5 of (permalink) Old 03-29-2000, 10:55 AM
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Re: oil blow by into air filter

I just changed the PCV valve, I hope it works,
Thanks.

post #6 of (permalink) Old 03-29-2000, 01:23 PM
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Re: oil blow by into air filter


There was a big discussion about this 2-3 weeks ago so you may want to scroll back a bit or do a search.

Basically, I think... and please notice I am voicing my personal opinion... that when the cylinder walls wear, you have more blow-by past the rings when the piston is on the compression stroke. When the piston moves down in the power stroke, the gases that passed by the rings are now pushed into the crankcase. This gas must now be vented somewhere. The PCV (Positive Crankcase Ventilation) system takes a large part of the gas away. However, as the cylinder walls wear and the pressure inside the crankcase increases, the PCV can't handle all of it. And so the gas vents out the only other hole in the valve cover and that is the one that is connected directly to the air filter housing.

You can buy a oil blow-by filter or a breater filter that will help separate the oil from the vapor and reduce the oil in your housing and keep it from gunking up the air filter. You can do a compresson check to confirm if this is the cause. Hope this makes sense. Good luck.

post #7 of (permalink) Old 03-29-2000, 02:17 PM
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Re: oil blow by into air filter

One of the problems is that the 258 is so reliable and built so well, that it continues to run well into the time that it shouldn't. [img]/wwwthreads_images/icons/smile.gif[/img]. I got about 194,000 out of my first one. I had blow-by so bad that I rigged up a system to catch all the oil, and still vent the valve cover. I went to NAPA, and bought a 90 degree elbow that fit in the rear valve cover grommet, and some heater hose. I ran the heater hose over to behind the windsheild washer bottle (always going downhill), and went to a "T", installed sideways. The downspout of the "T" I put into a quart plastic oil jug, with hose clamps, to catch the oil, and the top of the "T" I put to a breather. It really was amazing how much oil would come out of that motor. [img]/wwwthreads_images/icons/crazy.gif[/img] Being on the highway at high rpms was the worst. I have since put in a rebuilt 258. [img]/wwwthreads_images/icons/smile.gif[/img]

Also, in your PCV line, between the valve and the intake/carb, there are some restrictors - small plastic things with small holes, I guess to reduce the flow of air getting to the pcv. These will clog also, and you'll get no suction to the pcv valve, so watch those.

Good luck
Pete

88YJ,4"susp,33"BFGMT,9kwinch,homemade swingout,258,999,4.10,weber32/36,GMHEI,one moonguy[img]/wwwthreads_images/icons/smile.gif[/img]
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post #8 of (permalink) Old 03-29-2000, 06:08 PM
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Re: oil blow by into air filter

I looked at the old posts and there is mention of a filter made by K&N that will fit into the grommet at the rear of the rocker cover, but I can't find it on the web site that sells K&N air filters, does anyone have a part number for it? Can anyone tell me how and where to find it.
Jim

post #9 of (permalink) Old 03-29-2000, 06:44 PM
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Re: oil blow by into air filter

the little kn air filter is used in cars also. I think they are in summit racing and they are about 10-12 bucks

post #10 of (permalink) Old 04-02-2000, 12:42 PM
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Re: oil blow by into air filter

I read somewhere (I think AllData) that this can happen even when compression is within acceptable limits. If the grommet at the back of the valve cover shrinks due to age it can increase the pressure inside the cover enough to send oil mist up the hose. I just changed mine and will soon see if this is true.

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