1994 Suzuki Vitara V6 H20A Engine smoking intermittently from exhaust
I have a Mazda which in Australia (here) is called a 323 Astina, overseas a 323f, Familia, etc.
It uses a 2.0L Mazda KF Engine very similar to (in fact co-developed with) the Suzuki H20A engine, except designed to be transverse, variable resonance induction and other different tuning inc. 7000 redline, and probably not as reliable as an H20A.
I've had the engine rebuilt because I want to keep this car for a while and it needed it. Oil slipped past the rings which burned out grooves on one of the exhaust valves on Cyl-6 to the point where that cylinder had no compression...
... but I still get smoke occasionally, as you describe yours except not as often nor on the open road at speed. It happened ever since the first time I changed the oil after the rebuild. The tech who rebuilt it used a grade of oil I couldn't find and, liking synthetics, I used a lighter oil.
About the time you were writing your message, I replaced the rubber intake pipe feeding the throttle body and I noticed the inside of the intake manifold lined liberally with oil. The old pipe had oil only at one end.
The pipe I replaced didn't just go from the air mass sensor on the filter box to the throttle body. There was also a large pipe to an air reservoir (a lengthy pipe sealed at one end so that if you open the throttle quickly, you don't have to wait for more air to be filtered before it enters the engine, supposedly) and a tiny pipe to PCV valve.
It's not a long pipe so it's easy to look inside. The reason I'm boring you with all of that detail is because you'll almost certainly have a different one, but this is still most probably something you'll find feeding your intake manifold a supply of oil. The PCV (Positive Crankcase Ventilation) valve runs from one of the rocker covers (not that we have rockers) into a pipe feeding into this intake pipe. It's supposed to **** air in from the intake pipe due to a vacuum created by another pipe connecting from another part of the crankcase to the intake manifold (after the throttle body so it has a lower pressure than the intake pipe) and that might be happening in my engine but oil is, or was before the rebuild, seeping back into the intake pipe.
Being a transverse version of your engine, the PCV valve is on the front bank and the pipe from it to the intake pipe is quite short. The PCV valve is also situated above (if I remember correctly) a cam lobe so at higher revs, the oil gets flicked up into the PCV valve.
... so use an oil which is thicker at high temperature, do a compression test, or as I'm considering, run the pipe from the PCV valve into a canister to catch the oil before feeding the gasses into the intake manifold. That way less of the thinner oil will be burned off and I'll have a better chance at getting away with using it.
I use 15W40 Oil - viscosity of 15 weight (units?) when hot, 40 in Winter (which the W stands for). I should use 20Wxx, perhaps, to burn less oil.
This engine likes thin oil, it just goes on to liking it enough to inhale it. This engine also likes higher revs.
Hope that helps.