Air in Coolant system

So I bought Cooling System Test and Refill Kit (harborfreight.com) - coolant vacuum kit from Harbor Freight recently, finally put it up to the test today. The vacuum is supposed to evacuate all air from the system, and then that same vacuum will suck coolant from a container into the system, ostensibly filling it without any possibility of air pockets.

Worked well from what I can tell - to test for leaks, you hold it at max negative PSI for 30 seconds once its stabilizes, and then watch it for 1-2 minutes with the valves closed to check for leaks / gauge dropping. Watching my vacuum, I could tell that air slowly leaked in from somewhere, at the rate of ~1psi reduction in vacuum per 50-60 seconds, this coming down from a max vacuum pressure of -25psi. This doesn't seem to scream massive overheating-levels of compromise to the system's pressure integrity, but what do I know. I couldn't hear from anywhere that it was sucking air into the system, in a totally silent garage.

On the plus side after doing this, my heat is finally blowing hot, which it wasn't before.

At this point, I am basically narrowed down to 2 options, let me know if it sounds feasible:

• Water Pump
• Blockage in the radiator / system somewhere (at this point the system has had the coolant changed out ~3 times, plus the vacuum treatment today)

The car idles up to temperature very slowly, on a drive it will go up in fits and starts, at times sitting at different temperatures for 10-15 seconds as it climbs through to operating temp. It also doesn't cool down when the fans kick on, might drop from 219 to 217 for a bit, but won't drop below that when at idle. This is what prompted me changing the thermostat yet again to no avail a few weeks ago.

Curious about what I should try next.

 

Did you go with an OE or aftermarket thermostat? I recently had an issue where I bought an aftermarket thermostat and it stuck closed causing the engine to overheat as it didnt open fully.

Turns out there is a difference in thermostat length which kept it bound up. I used an Air Lift like you used and had checked it a second time with the same tool. OE left, Aftermarket right



You will see a drop in vacuum when using the tool even if you dont have a leak. It isnt an AC system which uses hard lines and crimped connections. You will get some bleed off from the rubber hoses and clamps. But if you're maintaining vacuum in the system for a few minutes chances are you dont have a leak.

 

This time when I switched thermostats, the previous was an OEM, and the new one is a Gates. I'm not convinced it is the thermostat since the behavior is identical before and after. But I guess anything is a possibility with these stupid pieces of cheaply made crap - should I try yet another thermostat?

 

Yes get an OE thermostat.

 

Really don't want to do it a 4th time, but I guess at this point I can do it in under 30 minutes. Worst part is just cleaning up the coolant that spills out.

Edit: What are the odds my OE thermostat goes bad, followed by my replacement being bad straight from the factory?

 

Once I put an OE thermostat in the temps went back to normal and I haven't had the issue since. What you are dealing with is exactly what I dealt with.

Get one directly from Mazda, compare the two and if it looks like the one in the picture I attached, install the Mazda one.

 

I'm on it. Did you get yours from a site like realmazdaparts or something?

 

I just called my local Mazda dealer, gave them my VIN, told them what I wanted and they ordered the part.

 

Well, it looks like the thermostat did the trick. Swapped in the new OEM earlier in the week, didn't have a chance to work out the air as well before I had to leave it alone. The vacuum bleeder for some reason wasn't dropping vacuum as easily as it had in my first attempt, and even after it was filled I had massive burps coming out for quite some time.

Took it out for a drive today, temp went up, I got pissed, took it back, and let it idle out for a while, watching it bubble down and down for a good while. I think my luck with stubborn air pockets is just awful. After that, I let it sit for 2.5 hours while we finished the Mandalorian, and lo and behold, came back out, reservoir empty, topped it off, and away we go. Temps were consistent and reliable yet again.

I'll test it again tomorrow and confirm, but it looks like when in doubt, just don't be a dumbass and change the thermostat again.