I bought an Rx-7 FC a while back, blown coolant seals. The white smoke pouring out the tail pipe pretty much confirmed that. After browsing online, and being broke as hell, I found that many people attempted to solve their leak with radiator stop leak.

Anyway, I used some, I know there's some controversy over the effects of this treatment, but it seemed to work. The white smoke stopped, in fact all smoke did. The car still overheated extremely easily, but I drove approximately 20 miles total (I drove for short periods of time after warmup, refilling coolant and adding more stop leak to try and get the "full effect" after this fix before my starter crapped out, and if it isn't my starter, my clutch slave also went out. Either way, no ignition, and the car sat for about 2 months.

I'm coming up on a job opportunity finally, so I'll have some cash to work with, so I decided to start taking things apart. I get the radiator out and a lot of the fluid is still green, but then I notice the tell tale milky brown substance of rust in the mix.

Basically I would just like to know, what are the approximate chances that the inside is going to be completely rusted out? I assumed because I was no longer burning coolant that it was no longer inside the housing. I understand that I won't know till the engine is apart, but nontheless I'm worried and would just like another opinion before wasting a bunch of time tearing apart a rusty engine that I'll have to scrap.

 

It's not likely the engine will be completely rusted out inside. The castings are for the most part very thick (a few exceptions but since block seal stopped the smoke, nothing is cracked). All the rust you are seeing is probably just years of neglect.

The problem with water pumpers is that they overheat constantly which ends up warping irons/housings. And if water ends up on the wrong side of the jacket into the combustion areas, rotors and irons rust.

Really, the only thing to do at this point if you want to rebuild the engine is to pull it apart and inspect the components. It doesn't take too long to tear down a short block and you'll need to pull the engine anyway. Don't hold your breath that anything is usable.

Then before you install a freshly built engine, you need to solve cooling problem. Likely a new radiator, new clutch fan (or e-fan), water pump and thermostat.

 

If you are worried about the coolant passages.....then yes, you cannot see any damage until the engine is apart. Any corrosion or cracks can only be see by cleaning and careful inspection.

On the other hand, if you are concerned about the combustion chambers (rotor/housing): I have taken a couple of engines apart, one that sat for a number of years and found a surprisingly minor amount of surface rust in there and most of that on the easily cleaned faces of the rotors.

There are two places you can look into the engine internals. One is at the leading plug holes. These are tiny holes in awkward positions....unless you have access to a boroscope...about all you can see using a light and mirror is that the visible part of the apex seals are still there!

The other spot is at the exhaust ports. You have to remove a lot of the exhaust stuff to get to the cast iron exhaust manifold (called the reactor by Mazda I think). Remove this and you can see perhaps 70% of the rotor surface (by hand rotating the engine of course).

In any case the engine must come apart then you can be sure of all the rebuild parts you will need,

Good luck,
Dave