I'll type a long story for the benefit of a complete history (please be patient ..
Ive just bought a 1995 Honda Legend Coupe (bought at 103,000kms) about 6 months ago - its been a very expensive relationship already, but Ive always lusted after one for a few years now! Ive had the timing belt and WP done (and other stuff like MC), and recently I had a scary episode where my plastic top tank cracked from overheating, and coolant spilled out.
I want to a proper dealer and got a quote to fix it, but it was too expensive (they wanted A$750 just to fix it). So I went to a cheapo radiator guy. He repaired the top tank - but said the thermostat was okay (I think cos he coudnt get the part quickly enough). I trusted him - that was mistake 1. Predictably, heating problem came back - luckily I caught it overheating again before more damage was done - I also noticed surging in the overflow tank, which didnt go down when it cooled.
This time I did it properly : thermostat replaced and chemical/compression test for the dreaded BHG (luckily passed..for now)- car went okay for around 800kms, but then i noticed overflow tank levels increasing again. I started noticing temp gauge getting a bit unsteady at startup, and heater would take a longtime to kick in when engine was supposed to be warm. Then it started overheating again..stopped car..waited..restarted and temp was steady again. WEIRD. Is this a AIRPOCKET problem in radiator..is that whats causing overflow reservoir levels to go up (now levels are way over MAX levels). I can still drive it for long distances, but I put heater on max just in case. Should I replace the radiator cap? cos isnt it supposed to maintain pressure to suck coolant back in to avoid airpockets? How do I bleed system - using valve or open cap method/rev?
I dont think its BHG..cos no smoke at exhaust and no oil in coolant, or milky oil (I check this obsessively now!). Is it related to my using 98 Octane gas (too much combustion in chambers?) HELP! I have already spent a lot of money and dont wanna spend anymore but I wanna keep my car!