I have a 2017 toyota rav4 with 56,582. I noticed the coolant reservoir is almost empty and wondered if i should just top it off or do a flush? The manual says to replace the first time at 100k miles or 120 months. Also which coolant should I use? Do I need to get the toyota dealership coolant or can I use the Prestone platinum red fluid that says its good for toyotas which i already have and use that to top it off? I do not know if mixing different brands of coolant but it have the same type/color is okay to do. I would also like to know if coolant being that low normal? I haven't seen any signs of leaks.
Since the coolant has already been in there for 8 years I would go ahead and change it with Toyota OEM coolant. (10 years is a bit optimistic.) You should be able to find Toyota coolant at sources other than your local dealer for a lower price. You don't want to mix coolants with differing chemistry. The color is just a dye that's added and you cannot depend on it to identify the coolant type.
However if your coolant reservoir is almost empty that implies that you have a leak somewhere. You might want to pressure test your cooling system or use some UV dye to check on that.
Luckily I had the radiator cap off to give the pressure somewhere to go, but in hind sight this is probably another reason to remove the thermostat when flushing a coolant system with pure water. In order to keep the engine temperature well below the boiling point of water.
having the cap off is what caused the boiling , since pressure does the lions share of elevating boiling point. Coolant only adds a few degrees.
The thermostat " controls" whether or not there's going to be pressure from the water pump at the radiator neck
the system is pressurized by the expanding water, not the pump. The thermostat is not a perfect seal. In fact some have a tiny relief hole to allow air to escape and pressure to equalize ("wiggle pin"). Even if it was perfect, the radiator is not sealed at both ends, so the pressure is equal everywhere. On modern system the thermostat is downstream of the radiator, right before the pump. Water pumps are of a centrifugal design and move fluid, not pressurize it.
When the thermostat is closed and the engine is running, you're fine with pouring in coolant
you should never open (or open very carefully) the radiator when the engine is hot.
Once the thermostat starts opening up, the water pump starts pressurizing the coolant in the radiator as well.
Even if your pump is completely failed, the radiator will be pressurized when the engine is hot.
The radiator cap is lower than the overflow and the coolant spilled out everywhere.
This isn't always the case.
That's partly why on the overflow tank, the engine hot and engine cold marks are at different levels.
it's nothing to do with the elevation. pressure moves the coolant to and from the reservoir.
@imperator I know that, by "elevation" I was meaning the difference between the radiator cap and the overflow. The overflow is almost always the highest part of the cooling system as far as under the actual hood. It's not highest absolute point, that's going to be the heater core. I guess I didn't explain it throughly enough. I knew the pressure part as well. I guess I didn't explain that part clearly, either. I actually didn't know that about modern thermostats. I figured they were all up top, because heat rises. My Pontiac and Ranger are all that way, they both lead directly to the water pump.
@imperator Thinking about it again, there's no way you could make a thermostat watertight. The impeller sucks coolant through the radiator's bottom hose, as well as coolant that was already circulating in the water pump itself and pumps it into the block to be heated up. If the thermostat hasn't opened up yet, it bypasses the radiator and goes back into the block in a "shorter" circuit. There would almost be a vacuum if it sucked all of the coolant out of the lower radiator hose and the t-stat were watertight.
I couldn't remember if the coolant expanded significantly while still liquid, or not. I was kinda reaching the end of my easily disposable knowledge (I woke up like 20 minutes before replying). I kinda didn't realize until your response that the hot liquid's expansion is quite significant. Hot liquid+the same space=higher pressure.
I've only ever opened a radiator when the car has sat for a few hours, because subconsciously know the risk of opening one when it's still hot. I tried to imply that in what I wrote earlier, but I never directly stated it. My apologies.
yes liquid which is near it's boiling point wants to expand GREATLY. About 1600x the volume.
the thermostat switches between the bypass circuit and the radiator circuit. I don't think the pump would create a vacuum since it always has water at the input from somewhere. (also omitted from the drawing is the heater circuit, which is another input).
There's a thermodynamic term for any liquid that has reached its boiling point that I forgot until just now, that is a "saturated liquid." It makes sense, too, the water can't absorb anymore thermal energy without boiling, so it would technically be "saturated".
Doing a drain and fill every 5 years or 50,000 miles is much easier than flushing the coolant system.
The coolant type is listed in the owner's manual and you can probably buy it at the dealer for around the same price as Prestone.
I prefer not to mix fluids, especially transmission fluid. The only non-OEM fluid I use is motor oil.
I recently flushed the coolant system on a 2016 Jeep Patriot with 100,000 miles. It was labor intensive because it has two thermostats inside a plastic housing that I dare not take apart so I had to do repeat drain and fills with distilled water until the water ran clear.
Then I had to idle the engine up to temperature so the thermostats opened to circulate the water through the engine block. At one point water boiled out of the radiator and burned me a little because I had the cap off when the thermostats opened and pure water has a lower boiling point than coolant.
I don't recommend letting an engine get much over 180-190°F with pure water, even with the radiator cap on. Once the thermostats open and the water touches the hot engine block it explodes into steam very quickly and over pressurizes the cooling system. Blowing out seals and causing leaks. Luckily I had the radiator cap off to give the pressure somewhere to go, but in hind sight this is probably another reason to remove the thermostat when flushing a coolant system with pure water. In order to keep the engine temperature well below the boiling point of water.
If I were to ever do a coolant flush again I would buy a vacuum purge and refill tool kit that hooks up to an air compressor and sucks all the coolant out of the engine block using vacuum. Then refills the entire system under vacuum so there's no air pockets anywhere.
Moral of the story. Never run pure water in a coolant system, especially with a thermostat installed. The water will explode into steam and over pressurize the system in an instant. I've seen it happen first hand.
Turns out a vacuum purge and refill tool kit can't suck all the coolant out of the engine block like I thought. Putting a liquid under vacuum causes it to boil but doesn't suck it out of the system. https://youtube.com/shorts/CiqITk9fzds I also learned that water has a boiling point of 250°F at 15psi of pressure. So it's probably safe to run pure water in a radiator with the cap on. I'm still nervous about running a Jeep up to temperature with the radiator cap off. My Jeep boiled over on me doing that and I've seen multiple videos of other Jeeps boiling over as well. https://youtube.com/shorts/fJvZp3rY1Js Thermostats that open above boiling temperatures must be a Jeep thing and it wasn't in any of the air bleeding tutorials I watched.
I don't recommend letting an engine get much over 180-190°F with pure water, even with the radiator cap on.
Water boils at 212⁰F under atmospheric pressure. The radiator cap increases the boiling point to around 240-260⁰F. When you took the cap off, you depressurized the system and it flash boiled into steam. I took Thermodynamics a couple years ago in college.
Radiators are pressurized they reach operating temperature. The thermostat " controls" whether or not there's going to be pressure from the water pump at the radiator neck. When the thermostat is closed and the engine is running, you're fine with pouring in coolant because the closed thermostat isolates the two. Once the thermostat starts opening up, the water pump starts pressurizing the coolant in the radiator as well. When there's no radiator cap, the coolant overfills the radiator and gets all over the ground. The radiator was designed to let coolant flow into the overflow tank when it reached operating temperature, but you had the cap off. The radiator cap is lower than the overflow and the coolant spilled out everywhere. That's partly why on the overflow tank, the engine hot and engine cold marks are at different levels.
