Hey guys, this is my first post but I've been lurking for a few years. my wife totaled her rav4...so I'm back to daily driving my 97 blazer that just hit 100k. it needs some love before winter though.

symptoms:
the heater doesn't blow hot, just lukewarm.
heater core is gurgling.
very slow coolant leak that I haven't seen, only smelled and noticed low levels over time.

I already have a thermostat and I'll replace that when I do anything else. the gurgling is just air in the heater core I think. there's no leaking on passenger floorboard btw. the heater core seems time consuming af but not intimidating. and the slow leak makes me think I need to replace the intake manifold gasket. I've also read that if the crap oem gaskets deteriorate they can clog the heater core..?

do these conclusions add up? It seems like I should just do them all in one go and flush the system while swapping out coolant types. I'm on the fence about replacing the heater core(I have seen it takes forever) but doubt its ever been done and figured it might be a good time and the peace of mind sounds comforting. I may just reverse flush it also.

I'm not a real mechanic I just like tinkering and this will be the most in depth thing I've done. I appreciate all the previous posts and have read as many as I could find, most of the links are no longer active though. if you have any tips/tricks/dos/don'ts/links or suggestions I would highly appreciate them!

 

Sounds like you are on track.

Gurgling is low coolant and the no heat may be due to this.

Gasket failure only causes leaks - but that can ruin engine bearings.

195 thermostat (not 180)

Use Felpro rubber/metal intake gaskets (yes they are more expensive). I'm sure there are multiple instructions for intake gaskets on this site. Make sure rotor on distributor goes back in pointing exactly the same position. Use no sandpaper or abrasive disks/pads!!! Use razor blades or sharpened putty knife or a real gasket scraper and carb cleaner and keep the grit out of your engine bearing. Keep scrapings from falling into your engine. Vacuum out anything that does.

I personally would stay with the Dexcool (I did, 60k miles ago).

You can test heater core for plugging by feeling the hoses going to it and comparing to the radiator hose. With the vehicle fully hot (temp gauge around 200), you should not be able to wrap your fingers around either of the heater core hoses near the firewall. If one is hot an one is much colder (or both cold), expect plugging. Otherwise I would leave a heater core alone.

If you do try to flush the heater core, don't put over 16 psi of pressure when back-flushing or you may cause leaks (no house water pressure from garden hose without pressure safety device).

I would do the thermostat and intake gaskets first and re-evaluate heat before worrying about the heater core.

Good luck!