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ajszig

Blow By On Cold Start

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It's a 1991 with 100K on the odometer. Gets blow by on a cold start - regularly. No oil burning after car runs for a few minutes. Local mechanic thinks it's seals - anyone else a thought? Oil has been regularly changed every 3K miles.

Passed Georgia emissions test the other day!

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Please more explanation.. What do you mean by "Blow-By.??

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I'm with Lou... What is it doing when cold, and how do you measure it? If it passes emissions, it can't be burining much oil.

Alan

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I-m sorry that I wasn't clear...there's smoke from burnt oil out of the exhaust pipes...only after a cold start...mechanic seems to think that the rubber valvecseals, now about 20 years old, are worn and only after the engine warms up do they expand and prevent oil from seeping

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Hi,

That is exactly my diagnosis.. When the V6 gets over 100K, you can usually look forward to a blue puff when it starts.

You can pull both heads and do a valve job ~ But ~ The increased vacuum created in the combustion chamber, by the nice tight valve job, can often cause the oil to be sucked past the rings, and it will still smoke a little.. But it may not..

I have driven these 3.0-V6 engines with over 200k mi. and altho they were very well maintained they had the same puff of blue on start-up, ran very well, never used any measurable oil between changes (some 3,000 & some 4,000 mi.).

I suggest; unless the oil use was worse than you describe, I would leave it alone till it did. And it probably never will. Good Luck, Lou

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The 3.0 V6 in the very early 90's was known to start blowing oil past the valve guides at 30,000 miles. They were also bad about pushing out the cam seals at the end of the heads. The tranny behind the V6 was also not known for longevity. All these problems were addressed by Chrysler to the dealer in TSA's, but not published to the public.

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My 1990 135k miles TC have the same symptoms. It smokes usually in low RPM (stop light or traffic) and/or worm weather. I am using high mileage oil and changing every 3000 miles. It all disappears in higher RPM or driving in free ways. I tent to leave it as is but it is still annoying, some mechanics suggest replacing a gasket.

Any comments? Thanks.

Shay

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Hey Guys, especially Lit Muse,

Be sure to clean out the PCV system = hoses, pcv valve, engine inlet breather. The engine crankcase must breathe, and it must be held in a partial vacuum. (vacuum is highest at idle).. Good Luck, Lou

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Hi Lou,

Appreciate your knowledge. Can you elaborate a bit.

Were are these units located? Do you happen to have a pic.

Thx.

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Now you worry me,

A PCV (positive crankcase ventilation) valve is a very common and simple system. If you don't know what it is I hesitate suggesting you touch it. With that stage of overall knowledge considered I would suggest you have a Mechanic/Tech inspect it. I will explain it and I will show it if I can find a picture. ~ But ~ I fear you would not know what to look for, or what you were seeing if you looked. Please give me year + engine, and trans. type. Thanks, Lou

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It is 1990 3.0l 4 gear automatic.

I am not touching anything if I don't understand what I am doing. I have an idea where things are located but want to make sure. No need to worry.

Thanks,

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OK, The PCV valve is located in the front valve cover or valley behind the cover on the right side looking over the radiator facing the engine..

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There is a formed hose on the right side of the front valve cover, the other end of this hose is attached to the PCV valve, which is screwed into the block below the throttle body. Generally speaking, if you remove the PCV valve and it rattles freely it is OK. Most problems occur when the valve sticks and does not allow the passage of gasses.

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The hoses also degrade from the inside out, if it seems to be gummy at all then it is time to replace. Use hose that can stand up to fuel and oil rather than a standard type vacuum hose.

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How about just disconnecting the hose from the PCV? Let it vent to the atmosphere. And what's the other hose on the engine backside that goes from the intake manifold to a fitting on the air intake, does that have a separate PCV too?

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Don't do that. The PVC system sucks out contaminated gasses fron the crankcase and feeds them into the combustion chamber for burning. If you leave off the hose these gasses will vent to the atmosphere and most likely also cause a big stink around your car.

The hose on the backside is the fresh air feed to the crankcase. Fresh air passes through a coarse sponge filter in the air box and into the combustion chamber, from there they are sucked out the PVC system to the combustion chamber. In all it is a sealed system and should remain that way. There is NO advantage of disconnecting the system.

Remember the 'old' days when a metal hose ran from the top pan to below the engine and in most older cars, this pipe smoked, this is the contamination that the PVC system replaces.

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