I drive my old dent around town and for short stints on the highway almost everyday with out issue, however, if I'm cruising on the interstate at speed for any length of time, I get a billow of smoke out of the engine. All I do is pull over for a minute and all is well again.

I'm thinking maybe the valve seals are shot and the increased load to maintain 65mph is making the problem show up? I can't imagine 65 is putting un due strain on that motor.

Your thoughts?

 

White smoke or black smoke? When you say "billow of smoke out of the engine", yer talkin out of the exhaust, right?

White smoke could indicate a cooling, tranny, or oil leak. Black/blue is typically a fuel issue. What does it smell like? Burnt? Sweet?

 

ooh good question. I'm thinking it was white, there was the distinct burning oil smell. Thats what got me thinking the seals. It does leak a little oil, but it always does but doesn't always smoke.

 

Got an automatic? I've heard of tranny modulators going out and fluid getting sucked into the intake stream.

If the valve seals/guides are bad, you'd have a noticeable billow when it is first fired up and then only maybe a little while it is running. Generally, it's not noticeable.

Are you/the rig doing anything specific when the smoke show begins? Like accelerating or decelerating or does it do it whenever it feels like it?

 

No, I've only ever noticed it if I push the truck to between 65-70 mph for any length of time. If I keep it 60-65, nothing. In short bursts I have not noticed it. I've considered that maybe the RPMs are higher than I think due to running 33's. Would that be plausible?

There is a VERY little bit of smoke at start up, but only for maybe a split second.

Just for info,
360
C6
4wd
Stock gears (i'm pretty sure)
33" tires

 

I'm stumped. Strange that it occurs only at higher RPM/highway speeds and otherwise not RPM sensitive. I mean, ya'd think revving the engine could reproduce the symptom.

Could the rig be burping coolant and the coolant spray is getting onto the headers or exhaust manifold?

 

Beats me! All I know is that it stops if I pull over for a minute, let it sit, and then take off again. There is definitely an oil component involved because it is thick smoke. Maybe once I get the wheels re-mounted, I cruise a bit and see if I can make it happen again. It's only showed up when I've driven for a few hours straight, so not really a common problem, just something that's got me stumped.

I'm not exaggerating when I say it is a cloud. It looks like something Q would mount to 007's car!

 

Here's one possible scenario. The oil returns in the heads are partly blocked, and the extended period of holding the RPM up causes the oil to pool in the head/valve covers until it gets deep enough to get sucked past the valve guides. Pulling over allows the oil to drain back into the pan, therefor the issue goes away.
The slight smoking on start up can also be from the same thing. I had a 71 with a 360, and it smoked on start up *unless* it was parked nose down on a hill. It would also smoke after running for a while, again the smoke would go away if it was parked or driven in a nose down manner. It really smoked bad on long uphill pulls. I pulled the valve covers, and used a wire to poke out the oil drains, and the rear drain was totally plugged on one side (by #4). I knew which side was the main culprit after installing dual exhaust, but I still made sure all 4 drains were cleaned out good.
Never smoked again. Leaked a little oil at the valve covers, as I didn't have new gaskets when I did the wire trick, but less than 1/2 qt between changes, so I never bothered to replace the gaskets. It was much less oil loss than before I unstopped the drains. Besides, I kept thinking I would get around to pulling the heads for a valve job, since #6 exhaust valve was burnt......

 

Hmmm, that sounds like what mine is doing and a simple thing to try. Now i'll just have to talk myself in to pulling the covers AGAIN!

 

I had the exact same problem you had about a year ago. My problem was a bad intake gasket. On FE motors like ours if they start leaking they will draw oil right from the valley right into the intake port on the cylinder head. This will also make them lean when they arent getting any oil since its basically drawing air after the carb. I'd bet you even have a little bit of a pinging issue when its smoking. This was very noticeable for me on the highway with puffs of smoke like you said or on any kind of incline when the oil in the valley of the intake would run towards the back.

 

As a matter of fact, I do have a bit of pinging. I assume you're referring to the gasket between the carb and the block?

 

I figured you would. I'm talking about the intake gaskets that are between the cylinder heads and the intake that your cab sits on. I have some pictures I can post then if that helps.

 

That would help. Definitely a noob with engine related bits.

 

Here is what you will be looking at there will be gaskets on both sides where the intake meets the heads.

 

Thanks, I appreciate the help.