Overheated on track - now what?

[vex]

Originally Posted by infernosg

How does an engine coked in oil look normal?! 105k miles is also hardly what I consider a "long life engine". Hell, I've only put 5k miles on it in nearly two years of ownership. This also isn't a show car. As long as it (was) running I didn't really care how clean it was inside or out.

Tongue, meet cheek.

[infernosg]

Originally Posted by vex

Tongue, meet cheek.

Don't you have a RX-7 to work on?

Anyhow, started pulling the engine apart today. Only got to the intermediate iron before I decided to stop so I could clean the garage to better organize parts. Only thing I found I can't explain is pictured below:



Any explanation? Aside from that everything looks good - really good, but soaked in oil...

[RETed]

That's typical.
It's actually aluminum oxide.
It's galvanic corrosion due to having two dissimilar metals (steel side irons + aluminum rotor housings) and an electrolyte (coolant) - that's basically a battery.


-Ted

[infernosg]

Originally Posted by RETed

That's typical.
It's actually aluminum oxide.
It's galvanic corrosion due to having two dissimilar metals (steel side irons + aluminum rotor housings) and an electrolyte (coolant) - that's basically a battery.


-Ted

Gah, of course! In my search to find something I've managed to forget even the most basic material science. So what exactly should I be looking for given the circumstances? I have a couple other pictures of the rear iron and rotor housing but nothing looks out of the ordinary (to me).

[RETed]

Check the inner water jacket o-ring.
Look for discoloration or distortion.
Check the area of the side iron on both sides of the water jacket o-ring groove - look for discoloration.
The inside (toward the combustion chamber) edge area should be a uniform black - if there is a "clean" area, that could be signs of water leaking into the engine.


-Ted

[infernosg]

Tyler already knows about this but I figured I'd update the thread with the conclusions. FINALLY tore the engine down completely last night. Go figure the failed part is the last exposed. Failed coolant seal like I suspected on the front iron although the extent of the damage is more than I ever expected. Looks like I have a junk iron now...



A closer look:



I'm unsure whether this is the cause of the effect of the overheating event. I plan on returning to the track after the rebuild but I'm now worried about overheating. An upgraded radiator and all new hoses will be installed and I'm also removing heater core so there's no place for the coolant to go except the engine or the radiator. I'd love to underdrive the water pump but there's no way to do that without also underdriving the alternator.