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Discussion Starter #1
Hi all
I have a 1966 Mustang gt 289 it burns a little bit of oil. I did a compression test all cylinders were right around 170 lbs varying by a few lbs 1-4 with a cold engine no oil added so that seems good could it be valve seals worn cam lobes stretched timing chain a combination of all of that? I only notice a small puff of some when starting it after the engine is already hot no other smoke or could it be the timing I have it set at 6btbc that's what the Hanes manual said it should be buy it sometimes diesels when I shut it off. Any help would be appreciated.
Jason
 

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Goodafternoon.. Your problem could be many tings.. The dieseling could be from carbon build up in the cyl's. A good run at hwy. speeds just might burn some of the carbon away. Change the oil and filter along with a new set of spark plugs just might help...
 

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If compression is good on all cylinders then valve seals would be the most likely cause. They are likely original and worn out. Often, burning oil is from one of these causes: worn rings, worn seals, or a damaged/scratched cylinder wall. Since compression seems good seals would be the likely cause.
 

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I agree that the dieseling is not likely related to your oil usage. One thing we don't know is what you define as a 'little bit' of oil usage. A quart every 3,000 miles or every 300 miles?

The original valve stem 'seals' were just little umbrellas on the valve stems and were not a true seal in a modern sense. Those will never reduce oil consumption to what a modern lip seal can do. But then, oil is fairly cheap and was even cheaper in 1966. But when new those umbrella seals can give you 3,000+ miles per quart of oil with a decent set of oil rings.

Since your compression is good, if you are getting 1000+ miles per quart of oil and its causing no other problems its likely not worth doing anything other than watching your oil level. However, it is fairly easy to change those umbrella seals if you want to try a 'fix'.
 

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Do you notice smoke at any particular time? Mine was using oil and I noyiced that I would see some smoke on decel, like getting off the freeway. As in your case compression was fine. I immediately thought it was guides or stem seals, however the engine was relatively new after a complete rebuild.
After many sleepless nights I flashed on it. When I rebuilt the engine I put new fancy schmancy valve covers on it. The covers didn't have a baffle plate blocking the oil fill hole OR the pcv valve hole. Built a baffle for both holes and problem gone. Turned out that the pcv was sucking oil into the carb on decel (high vacuum).
Sometimes the problem is an easy fix.
Good luck.
 

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hello

how many miles on the engine and heads?


since it diesels with only 6 degrees of advance, some other possible causes are, timing mark has moved, very hot engine or very high compression or running octane that is too low for your engine. try some higher octane, its an easy test.

worn cam, lifters or "stretched" timing chain will not cause it.

if the seals are in tact they are likely not leaKING OIL WHICH MEANS IT COULD BE EXCESSIVELY WORN VALVE GUIDES. EITHER WAY, YOU CAN REPLACE THE SEALS IN THE CAR. you can get seals that push onto the valve guide and seal on the stem. these types are the best for keeping oil put of the cylinder. they are cheap and easy to find. they must be the rubber type, not the hard plastic type.

below are the most common types. the left one will not work. the 2nd and 4th are basically the same and will seal the best.

.
 

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Discussion Starter #7
Thanks for all of the replies, I have changed the oil because it was due but I also changed the plugs trying to fix a miss fire that comes and goes... I have also driven at 70mph for about 10 minutes and it seems to diesel less it will only diesel if I lug along like parking in a driveway. However it's seems to diesel less after the highway speeds "clearing it out" I guess. It used about a quart of oil in about 600 miles but seems to not use as much now like a quart in 800 miles. The car has 133000 miles on it but was rebuild in the 90s or so I was told. So I think I'm just going to learn how to do valve seals or the push on one's they are interesting. Oh and I almost forgot I have put on aftermarket valve covers and I didn't notice if they had baffles because I was about 14 when I put them on and didn't know much about cars but they don't leak haha. I have noticed oil all around the pvc valve and I am wondering if it's just sucking oil the covers have a metal strip that is supposed to keep oil in the engine will those be adequate? Also I will run 93 octane to see if the dieseling improves instead of 89
 

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Do you notice smoke at any particular time? Mine was using oil and I noyiced that I would see some smoke on decel, like getting off the freeway. As in your case compression was fine. I immediately thought it was guides or stem seals, however the engine was relatively new after a complete rebuild.
After many sleepless nights I flashed on it. When I rebuilt the engine I put new fancy schmancy valve covers on it. The covers didn't have a baffle plate blocking the oil fill hole OR the pcv valve hole. Built a baffle for both holes and problem gone. Turned out that the pcv was sucking oil into the carb on decel (high vacuum).
Sometimes the problem is an easy fix.
Good luck.
This is something that should be looked into further. No baffles would indeed make it easy for the PCV valve to ingest oil. You'll have the valve covers off when you do the seals so just make a note of whether baffles are there or not. If not, do as printman did or just buy new valve covers with baffles.
 
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