So I have a 1996 civic its been over heating with this hot weather , it only over heats after about 70 miles , my coolant burns away because I don't see no leak and sometimes coolant stays at perfect levels but still over heats.. What can be my issue? No clicking or white smoke, does get sluggish after a bit and rpms drop and raises like crazy while I warm it up at first start ..

 

Buy/borrow/rent a block tester, and a compression tester. Use them both. Give us the results. Coolant doesn't just magically disappear.

 

The black sludge wasn't from the coolant burning, that was from other bad maintenance habits.

 

Black sludge within a motor is from bad oil, over-used oil, bad oil filters, over-used oil filters, or occasionally mixing different types of non-compatible coolant. If anything, burning coolant would have steam cleaned certain parts of your engine, not caused black sludge.

You also don't need to keep putting those lines between the quote and your post. It makes it look like a signature.

 

Sorry, I've been rebuilding engines since 1974. I happen to know that black sludge in a crankcase has several possible causes, including "contamination by coolant." Coolant contains 50% water. Coolant (water) in the oil WILL cause black sludge formation.

 

Heavy sludge means one of two things. Either shitty oil/filter/maintenance, or you drove knowing the head gasket was failed, for a long period of time, which would also fit under shitty maintenance. It doesn't just suddenly appear.

 

I don't particularly give a damn how long you've been building engines. Different engines have different issues and different peculiarities. If you really have been building engines "since 1974", you would know this. What you are describing simply won't happen to a Honda motor, unless it has been woefully neglected.