Civic VTEC EJ6 - 1996 losing coolant

As mentioned, I have actually checked phsically that there is no leak- my coolant is dark green and could easily be seen. Except for the engine block, the rediator was pressure tested and water submerged for leak. All OK. I have checked the oil, I'd never seen any sign of contemination or milky stuffs so far. It's still new and dark brownish like original. Unfortunately I wanted to pressure test the engine block, but none of the mechanic in my region has this facility. Yes, I do have slight overheating but not up to 100%, it may go up to 75% and eventually will return to normal and this only happen on a hot day and long journey.(By then my radiator level could have been low)
I am not too sure what is "Tranny fluid is pinkish". Can you elaborate so that I know what to check. Thanks.

Regards,
Vincent

I am not too sure if coolant can mix with the tranny fluid for my Honda Civic 1996 EJ6. I realized that my coolant reservoir level can rise up to 50mm above the "full" making when engine is hot after a 20km journey. The level will very quickly return to the "full" mark or few mm below after 1 hour rest. I saw some coolant spill mark on the reservoir tank. Could this be the cause of my losing coolant after frequent driving where I run and stop the car? Is there any clue what can caused this? I have checked my other two cars and the reservoir level only rise up about 15mm above "full" mark when engine is hot and if I do a bubble check by sticking the reservoir hose in a water filled bottle, there is no bubble unlike this Civic which keep bubbling every few seconds when engine is running.

These engines have a problem with cracking blocks between the water jacket and cylinder. Bubbles in the radiator would be a good symptom. Get you cooling system tested for exhaust gas presence with a Tee Kay tester. I have done a few of these engines with this problem
Regards
Peter

Thanks Peter, that being the case, the way forward would be to change the engine block? I really do not know where can I get a Tee Kay tester to confirm this. I think getting a half cut engine and put in would we cheaper option. Your opinion.

Regards,
Vincent