Blowing white smoke
People use products such as silverseal, Barsleak, K&W Block Seal, etc. in an attempt to solve these issues.
Rent / buy a block tester and see if you have exhaust gases in your coolant. Very simple to do and cheap. You can rent them from some of the auto parts stores like Orielly and / or Auto Zone. Here is a Youtube vid that shows the test being done. I think it was about $10 for a bottle of the fluid, and you'll get your money back on the rental tool as long as you return it undamaged. There are better vids about this, but this shows what you are looking for quickly
Check your oil. Is it clean, or as mentioned above a milky color? Is it over the full mark like antifreeze has added to the volume?
Are you sure it's white smoke? Do you have a sweet smell from the exhaust?
What do your plugs look like? Do any of them show an indication of coolant in the combustion process?
If the smoking is as bad as you say, it seems unlikely that an additive was masking that. More than likely it's coincidence in the timing of changing your fluids.
Let us know what you find out on the items above.
Adam
Last edited by AdamMeh; Dec 18, 2014 at 07:40 AM.
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If you don't have oil in the water or water in the oil I would suspect the valve seals.
Just out of curiosity what weight oil did you put in? ( old engines like straight 30)

I believe some pieces are missing from this puzzle,
While a 150 miles screams rebuild time to some, if the engine was maintained well it could still have many more miles of life as a fun driver,
I have seen people use all kinds of "engine honey" but never seen it get rid of 100% of the smoke,

The OP says the car ran fine and while I wonder why fix what isn't broken he did a tune up and oil change,
When I read that my first thought was what did the owner do to cause this,
Like TEXASDESERTVETTE says and I agree it doesn't mean yet the engine is toast toss it out it could be some silly little something.

Start with a compression check, if that checks out then you likely just mucked up something when you tuned it....


















