Interesting... mystery smoke from tailpipe

[Kermit]

Hey gang... Here's an interesting one... 99 expy, 180k-ish miles, 100k tune up done by previous owners , 4.6 motor, runs strong and smooth but with a little vibration at startup idle. Most of my trips are shorter jaunts, 20-ish miles at 45-55 mph on rural routes but occasional highway jaunts, same distance obviously higher mph, 65-75 mph... This is where my issue comes in is highway driving.

So this problem is intermittent, doesn't happen every time I drive the highway and has never happened at the lower speed trips on the route drives. What happens is after I accelerate to get on the highway, get to cruising speed and set the cruise I get intermittent white puffs of smoke from my tailpipe. Some bigger, some barely noticeable which is why it has taken me this long to figure out it was actually me and not small fog banks... Its happened about 5 times over ten last 3 months so its not even happening evrytime im on the highway.

Scenario... Last trip to tractor supply , get on the highway, set the cruise at 75, go about 5 miles, notice the first puff of smoke... Engine running smooth, no smell of burning oil, no smell of the exhauast being too rich or lean... Go another mile or 2, another puff of smoke... And so on... Drop my speed down to 70, no difference... Drop my speed to 65, no difference... Drop to 60... No difference... Get to my exit and get off t go to tsc and see no more smoke below 50 mph. Get to tsc leave the truck running, gun it a few times, no smoke, smooth idle... Get out check the pipe... Good air flow and clear, no bad smells...no smoke, no dripping, nothing that would lead you to believe there is a problem.

So turn the truck off, do my shopping, maybe a half hour and leave. Get back on the highway, set cruise at 65, no smoke. Go almost all the way home, set cruise at 70, no smoke... Go a couple miles bump it up to 75, and get my first puff of smoke... Get off my exit... Have about 5 miles of route driving at 60 with cruise on, no smoke at all the rest of my trip home.

This has happened With cruise off and on, recently replaced the clock spring but it had done it once or twice before it was replaced as well. My check engine light is currently on, my guess is O2 sensor but have to get the code cecked, Again, doesnt do the smoking every highway trip, just occasionally. My lovely lil gremlin...

Sooo thoughts?

 

[FordandPolaris]

Sounds like you are leaking coolant into the cylinders. Probably bad head gasket. Check your coolant tank and see if the coolant is low, make sure the truck is cold when you do it though.

 

[Kermit]

If it was a coolant leak wouldn't that be constant/consistent every time it was driven at those speeds?

 

[FordandPolaris]

Kind of depends on the size of the coolant leak. There might not be a lot missing or leaking . Draw a line with a marker where the coolant is and watch it over a week's time and see if it changes.

You didn't sea foam the intake lately did you? Coolant and sea foam are the only two things I know of that cause white puffy smoke.


Sent from the Pocket Computer

 

[Kermit]

No seafoam but there was Marvel's mystery oil in the gas for that tank of gas.

 

[FordandPolaris]

No idea what that is but it could be a possibility if that is some kind of fuel stabilizer you chose to add.


Sent from the Pocket Computer

 

[Kermit]

My bad, that's Marvel's mystery oil

::Marvel Mystery Oil::

 

[Yudaman]

Beins it is a '99 with a 4.6, I would lay money that you have a head gasket problem.
My last '99 blew the head gasket at about 120k. That era of engines had a major head gasket problems.

 

[Kermit]

Again tho wouldn't it be consistent/constant if it were a head gasket issue, and wouldn't there be other indicators like loss of power, rough running, etc? Cat that had the truck before me who practically rebuilt the motor said all new gaskets, all new seals, there's no indicator of leaks when looking at the motor.

One other maintenance thing we recently did, changed air filter from the beat to death p.o.s one that was in there to a new Fram filter. That was done a couple weeks before this last incident.

 

[Yudaman]

White smoke would indicate water. The only way for water to enter the exhaust system is by it entering the combustion chamber,
As for all the time, not necessarily. It could be that the head gasket is sealing good enough during low RPM's/speeds. Once you start pushing the engine a little harder, by accelerating to highway speeds, you could be putting enough force on the gaskets for them to start leaking.
Toss a heavy trailer on the back and make it work a little. I would bet that you get quite a bit of smoke out of it.
For your sake, I sure hope that it isn't a head gasket. But with my experience with a '99 that had a 4.6 I doubt that I am wrong.