Need advice - 1999 F-150 4.6 modular SOHC V8 smoking

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I inherited a 1999 4.6 V8 F-150. It has 283,000 miles on the engine. It was smoking big time on start up. After starting it up and the massive smoke cloud blew out, the smoking almost went away, there may have been some slight smoke still while running but it was too close to tell for sure. So, my father and I took the valve covers off and changed the valve stem seals. Those original valve seals were utterly worn out. There is now very little smoke on start up, far less than before the valve steam seal change, but there is still some smoke on start up. The color of the smoke is kind of whiteish, same as before the stem seal change. However now after start up there is definitely no smoke at all when running.

My question is this - if there is still smoke on start up but zero smoke when running, does that mean the piston rings are burnt? The truck still has good power, I can light up the wheels from a dead stop, and the gas mileage is about right for a V8. IF the piston rings are burnt, will running full synthetic oil "restore" the rings or help them out and reduce the smoking even further? The guy who had it before foolishly only ever ran conventional. IF the rings are not burnt, what could still be causing the smoking given that I changed the valve stem seals already?

Thanks in advance.

EDIT - Actually, the truck now only smokes on start up if it sits for awhile, like if it sits a few days and I start it up, it blows off a little smoke still and then completely stops smoking. However if I run it and then crank it up again two hours later, there is no smoke on start up or at all. If the rings were burnt, wouldn't it constantly smoke?
 
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JRed

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The 4.6 had problems with the intake manifold gaskets failing and leaking coolant into the cylinders.

Does this white smoke happen to smell like coolant?
 

taurus3.5v6

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The 4.6 had problems with the intake manifold gaskets failing and leaking coolant into the cylinders.

Does this white smoke happen to smell like coolant?
No, I changed the intake manifold and valve cover gaskets when I also changed the valve stem seals.
 

Astro14

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Well, at 283,000 miles, a lot of things are possible.

You may have new seals, that are wrapped around very worn valve stems that still allow some oil to leak. The smoke on start-up, worse after sitting, indicates oil leaking around valve stems into the combustion chambers. New seals made that better.

May not have fixed it completely, though, and in that case, I would live with it.
 

taurus3.5v6

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Well, at 283,000 miles, a lot of things are possible.

You may have new seals, that are wrapped around very worn valve stems that still allow some oil to leak. The smoke on start-up, worse after sitting, indicates oil leaking around valve stems into the combustion chambers. New seals made that better.

May not have fixed it completely, though, and in that case, I would live with it.
Damit, I should have replaced the valve stems. Ghat probably would have required removing the camshafts and the timing chain, no?
 
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Damit, I should have replaced the valve stems. Ghat probably would have required removing the camshafts and the timing chain, no?


The valve stem is a portion of the valve. It is not replaceable separately. The guide is in the head. You would have to remove the heads and have them rebuilt by someone with the correct tools. At that mileage, best to live with it or commit to a complete rebuild.
 
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It's common on these engines. I don't mean to be flippant, but don't worry too much about it. It is still likely to be the valve stem seals. The way the oil sits in the head, it finds it's way down the valves and smokes on startup. Mine made it to just shy of 400K miles before the 2nd transmission gave out and the truck was given away. Depending on local conditions, you might consider a more viscous oil.

It is not at all unusual for these engines to make 500K miles with regular service.

By the way, the truck version (that you have) of the 4.6L, has full floating connecting rods, better quality pistons, rods, pins, better rings and so on. They are very well built.
 
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I also wanted to add that the valves sit directly under the camshaft and under the rockers in this design. Oil that is on those parts finds its way down. Even with good seals. My '98 F150 did this occasionally, from about 30,000 miles on, especially when cold outside and sitting overnight. It was embarrassing.
 

taurus3.5v6

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Have to ask.... what brand/type/grade of oil are you consistently using?

And, post a video of the cloud of smoke on startup.
My dad used the cheapest conventional oil. He is a tight coonass. He couldn't spend 12 dollars on antifreeze, he filled the radiator with straight water and let it rust for years. I'm draining the rust out right now.
The 4.6 had problems with the intake manifold gaskets failing and leaking coolant into the cylinders.

Does this white smoke happen to smell like coolant?
Hasn't had coolant in it in years, my dad filled up the radiator with straight water. He is a cheap coonass.
 

taurus3.5v6

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The valve stem is a portion of the valve. It is not replaceable separately. The guide is in the head. You would have to remove the heads and have them rebuilt by someone with the correct tools. At that mileage, best to live with it or commit to a complete rebuild.
How much would a complete rebuild cost?
 

Astro14

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How much would a complete rebuild cost?
More than the truck is worth. Honestly, if the truck has 283,000 miles on it, and it runs well, it's worth keeping, but it's not worth sinking big money into it. Oil is cheap, keep it topped off, drive it, enjoy it. I would leave it at that.
 
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