This has been discussed on many Mazda forums in the past. Most people familiar with doing their own mechanic work will suggest that the valve stem seals will need to be changed. On our Mazda trucks (only) this will help some, but unfortunately, it will not cure the large scale white smoking on startup of a cold Mazda engine.
I have rebuilt numerous Mazda B2000, B2200, & B2600i engines over the past 20+ years. I have owned trucks that have had this issue. I can state with near certainty, that the issue that is causing the large scale white smoke on startup......is gunked up piston rings.
The rings in these engines are of a low-tension design and are designed that way to minimize friction in the cylinders which helps fuel mileage. When the engine is in good working order and is clean internally, it works as designed. After the engine get many miles on it and it starts to build up combustion gunk at the top and sides of the pistons, the lighter ring tensions cannot overcome the gunk around the rings, and their ring grooves, when the gunk is COLD in order to SEAL/SEAT the piston rings to the cylinder walls as they should be, in a cleaner engine.
When the piston rings (particularly the OIL CONTROL RING SET) can't seat against the cylinder walls as they should, you will get too much oil blowby around the pistons (hence the smoke) until the heat from the running engine warms the rings, pistons, and the gunk around them.......and the rings will start to overcome the gunk and start doing their job as they should.
Changing the old valve stem seals is a good thing to do, but I would be willing to bet money that it won't provide a noticeable difference in the smoking at startup with a cold engine.
If you do decide to change the valve stem seals first, please report back your findings after you do this. I have said this before.......if you took one of these engines that was doing the smoking on startup, and dismantled it, cleaned the pistons and rings, then put it back together with the same exact old rings (I have always put new rings back in these engines....just makes sense to do so) just to see if it will smoke again.......I would bet that it would NOT smoke after simply cleaning the pistons and rings.
One day I need to do this to prove without a doubt, that the excessive smoking on cold startup is because of the gunked up rings. But for now, it is just my opinion that the dirty piston rings are the cause for the smoking.
Also, keep in mind that overheating the engine can also hurt the piston rings ability to do their job.....even after the usual head gasket and cylinder head refurbishing. Also.......it is very easy (and popular in these trucks) to swap the gauge cluster to either show lower mileage OR change from a regular cluster to a tachometer cluster........so the shown mileage on the gauge cluster may or may not be indicative of the ACTUAL mileage on a trucks engine!
