Coolant Boiling Normal?

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Avoidin Deer

Central Virginia
Contributor
V
2019 CX-5 Reserve
The small rubber hose from escape outlet on the radiator filler neck through overflow reservior cap have to be long enough to be submerged under the coolant to absorb the coolant back into the radiator.
Are you saying the converse to this is that the reservoir has to have enough liquid in it to keep the end of the hose submerged so that the system will work properly?

(I'm not challenging, just pointing out the need to check the reservoir level the same as you would check the oil.)
 
V
2010 Mazda 5 Sport
Are you saying the converse to this is that the reservoir has to have enough liquid in it to keep the end of the hose submerged so that the system will work properly?

(I'm not challenging, just pointing out the need to check the reservoir level the same as you would check the oil.)
Kind of, yeah. You should have some coolant in there when the engine is cold. But if not...it's not a huge deal as the system will pressurize with a bit less than it should have. As long as there is no over heating, it's fine. If, though you keep adding coolant to the overflow tank...and it keeps going empty...you should investigate. My 4Runner always runs out of coolant after a while in the reservoir but the radiator has a small leak. She's due for a T-Belt...so that will get taken care of then. Otherwise she drives fine.
 
V
2010 Mazda 5 Sport
Never paid attention to the radiator set-up in Mazda, always thought it was the same as our other car. Took a peek under the hood and yeah, I'm sorry for my confusion!
I think all cars have had this since 1980. Your other car must be pretty old!
 
V
2016.5 CX-5 GT AWD titanium/black 2016 Miata Club ST MT white
Never paid attention to the radiator set-up in Mazda, always thought it was the same as our other car. Took a peek under the hood and yeah, I'm sorry for my confusion!
Don't know what your other car is but every car that I've had since at least the year 1979 has had this same setup.
 
I checked under the hood and checked the coolant level while the car had time to settle down throughout the day. I noticed the coolant was filled above the Full line from dealer so not sure if that poses any issues. The hose inside the reservoir is submerged below the filled coolant as well. I'll also check the radiator cap today once it's cooled down. Haven't had time to schedule a visit to the dealer but as my trip is in mid November I'm going to schedule something soon. I unfortunately wasn't able to record a video of this when it occurred.
 
V
2019 CX5 Signature
The outlet for overflow tank is in the radiator neck above where the cap seats.

See it stick out to the right in this pic:

And what happens when the car overheats is that the seal inside the radiator cap gets pushed up. Once it gets pushed up higher than the overflow outlet coolant escapes and travels into the overflow tank. When the car cools back down the rubber seal extends back down into the radiator neck and closes the overflow vent sealing up the system.
 

madar

Contributor
V
2016.5 CX 5 Touring AWD, 2015 SCION XB
Could be a weak or faulty radiator cap, or as some one pointed out- not on all the way. The boiling point rises 3 degrees for every pound of pressure the cap has, a weak cap would lower your boiling point.
 
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yugrus

Contributor
V
CX-5 GT
'14 Tahoe. The expansion tank is pressurized. I've never paid attention to Mazda setup, sorry guys...
 
V
2010 Mazda 5 Sport
'14 Tahoe. The expansion tank is pressurized. I've never paid attention to Mazda setup, sorry guys...
I looked it up...yep pressurized to 20 psi. Unbelievable. Thanks Chevy for making it hard to add coolant.
 

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