4.3 smokes on startup.

[Brownsquare]

I recently noticed that I'm getting blue smoke from the tailpipe of my 4.3 V6 '87 GMC when I start it for the first time for the day. After a moment it disappears. The truck runs excellent and isn't fouling plugs. Wondering if maybe the valve guides are shot? It has 105K miles on it, just getting ideas on where to investigate first. I would think if the rings were shot or it needed to be rebuilt it would be fouling up plugs left and right. Any suggestions would be very much appreciated! Thank you!

 

[78C10BigTen]

The 4.3 in my s10 does this also but every start up.

 

[Rickf]

Valve guides.

 

[RetroC10Sport]

Given the mileage, valve seals is more likely than guides. GM did not put an umbrella seal on the exhaust side, it had a small o-ring instead and they do break down over time. I would do seals, which is super easy on these even without removing the heads and I'd put umbrella seals on both intake and exhaust.

 

[RecklessWOT]

Given the mileage, valve seals is more likely than guides. GM did not put an umbrella seal on the exhaust side, it had a small o-ring instead and they do break down over time. I would do seals, which is super easy on these even without removing the heads and I'd put umbrella seals on both intake and exhaust.

this. Almost every GM engine from this period has the same issue. I've personally never cared because it doesn't affect much, but yeah if you want to do things the right way you should technically fix it. Do the seals first, that's almost always what it is unless we're talking like 200+K miles. As stated, super easy to change the factory exhaust valve seals, or like what RetroC10Sport said just doing umbrella seals all around sounds like an even better idea and can't be much harder

 

[PrairieDrifter]

this. Almost every GM engine from this period has the same issue. I've personally never cared because it doesn't affect much, but yeah if you want to do things the right way you should technically fix it. Do the seals first, that's almost always what it is unless we're talking like 200+K miles. As stated, super easy to change the factory exhaust valve seals, or like what RetroC10Sport said just doing umbrella seals all around sounds like an even better idea and can't be much harder

I'd say it's worth it, especially long term. I've seen some crazy carbon and oil buildup on the head side of the valves, that's a lot of weight and can also cause the valves not to seat properly.

 

[JoeR Jr]

As others have stated, almost certainly valve seals. They are cheap and easy to do though,. If you're mechanically inclined, and have some spare time, give it a go. Don't be heartbroken if it doesn't change too much. Those heads do a crummy job with oil control.
Joe

 

[Brownsquare]

Thanks guys! The truck will be stored all winter, so I think I'll limp her for now and go through the heads in the down time. She needs a pan reseal too, might as well do it all at once.