I can't understand my car (coolant levels)
 

2 years ago, I checked under the hood, and noticed the the reservoir tank was dry.. It drove fine, and I didn't think anything of it, but decided to buy Dexcool since the coolant was orange before it got low.. I filled it to the max line, checked it for weeks to make sure it stayed at the correct line, which it did. But about 2 months later the coolant went up very far past the max line almost to the top of the reservoir. My first thought was that I over filled it, and it actually had the right amount even when the tank was very low. Why would it stay at max level for so long, then go all the way up to over filled? It is repeating the same thing now, low coolant level with no coolant leaks. I'm not for sure if it overflowed because I added too much a couple of years ago, or its doing the same thing it did before I added too much. Is it normal for the coolant to disappear from the max line in the tank, then return to normal levels?

Sometimes you wont see a leak....until its too late and it just busts open more at the worst times. I would change the radiator and thermostat and put some fresh fluid and inspect the hoses while i'm there ......if your doing the work yourself, this is like 120$ job with all the parts and all..... cars over ten years old maybe its time, good luck.

One question? does your heat work? If so good, maybe you filled it up past the max line. The engine usually adds about half an inch of coolant to the tank normally during driving. So the level will go up, now if it goes up more than that then that might be a problem. But it adds coolant in the tank and when the car gets turned off for a while the 1.5 inches gets sucked back into the radiator.

Yes the heat works, also the coolant level didn't drop very low until after I started using the heat a couple of weeks ago. When I thought it needed more in 2017, it stayed to the max line until about 6-7 months later, it jumped all the way to the top, and stayed that way hot or cold until just recently.

I filled it back to the max line, still checking it daily to see if it goes higher or lower. Thanks

It sucked in air. You have a leak somewhere.

I agree, replace the radiator before it blows up. Even if low miles the plastic is just brittle.

The radiator was replaced 35 thousand miles ago. The plastic container is cheaply made, I just don't notice any other flaws, when I open the radiator cap, i can hear it release pressure. I recently had a problem with one of my cooling fans not working, could that have caused a problem with my radiator?

Smell the overflow bottle. Does it smell like coolant or fuel/exhaust?

This is weird. Seems like the coolant would without fail return to the engine upon cycle cooling and not max out the overflow.

Doesn't smell around around the bottle, but I did spill a little while topping off the radiator, so I slightly smelled coolant around there for about a day.

It is, I'm confused over this. This was a problem that I thought worked itself out somehow over 2 years ago. But it's reapeating it now, and at the moment the coolant is still at the proper level, not sure if it would go back up

First of all, calling the plastic container on the fender an overflow tank is incorrect. It is an expansion tank, one of the many things added to cars with the myriad of all all the pollution laws.

When the car/engine is working properly, the engine warming up also warms up the coolant. The coolant expands when warm and is channeled into the expansion tank. When the engine cools off, the coolant contracts and creates a vacuum in the engine. This vacuum will suck the coolant out of the expansion tank and back into the engine.

To set the coolant levels properly, you start with the engine cold. Remove the radiator cap, fill the radiator all the way to the top and put the radiator cap back on. Then for the expansion tank, fill it to the MIN level.

The level of the coolant in the expansion tank will vary between when the engine is cold compared to the engine being being hot. I don't know exactly how much coolant gets transferred back and forth, but I doubt that it is even as much as a pint.

You cannot cause the engine to overheat by adding too much coolant to the expansion tank. If the expansion tank suddenly becomes full, the engine was on the verge of overheating. Lots of reasons for that. But when the engine cools off, the coolant (or most of it) should be sucked back into the engine by the vacuum created when the coolant cools and contracts. If the coolant remains in the overflow tank, then the vacuum in the engine was able to suck in air instead of the coolant in the expansion tank.

First of all, start by checking the coolant level in the engine/radiator when the engine is cold. I suspect that it will be low. The two most likely causes would be the radiator cap or the the hose that runs between the radiator and the expansion tank.