How much does coolant mix with the overflow?

[Nick1994]

This is for my Jeep. I flushed the cooling system out and replaced the radiator, cap, and thermostat. I refilled with 50/50 green coolant and distilled water. Well, I was in a big hurry a little over a month ago before heading out of town and went to top off the washer fluid and for whatever reason poured it into the coolant overflow bottle. I then unbolted it and poured it into a gallon jug and filled it up with water, I didn’t have any coolant with me at the time. I’ve put about 1,000 miles on it since then, including highway at 75 mph, hard off-road driving, and traffic. So it’s been up to temp. My question is, shouldn’t the radiator cap be letting some coolant into the overflow bottle? And then sucking it out? Because what’s in the overflow is still crystal clear and if it was mixing it would be very obvious since it’s vibrant green in the radiator. The radiator cap was from O’Reilly’s and looks like it was made out of a tin can, I really don’t like it. Just wondering if maybe my cap is bad? Thanks.

 

[69GTX]

It depends on the system. Some flow into the bottle as the car is running at temp, and other systems (usually older) draw/supply via the reservoir to move a small amount of makeup or expansion fluid. I don't have a radiator cap on one of my cars as it has a separate high point vent plug. The "reservoir" (pressurized degas bottle) sits lower. So that exchanges a lot more fluid than my 1999 GM where the radiator sits higher than the reservoir and the reservoir is not pressurized. If your reservoir gets quite hot, it's probably exchanging considerable fluid. So what's in washer fluid that cause issues with engine coolant? Consumer advocacy groups and auto enthusiasts believe that the alcohols and solvents present in some, but not all, windshield washer fluid can damage the vehicle. These critics point to the corrosive effects of ethanol, methanol, and other components on paint, rubber, car wax, and plastics, and groups propose various alternatives and homemade recipes[specify] to protect the finish and mechanics of the motor vehicle. You're not the first one to ever do this. If you google it I'd bet you'd find many interesting anecdotes and findings. Bloggy

 

[dlundblad]

So you caught the issue right when you did it? If that's the case, zero washer fluid mixed with your coolant. This isn't your concern right? Assuming you don't have any obvious issues such as collapsed hoses or overheating, I would say your cap is just fine. I like to think of radiator caps as an oil filter bypass. Who really knows how often they open. The cap has a warranty right? Swap it out if you're really worried.

 

[Nick1994]

Originally Posted By: 69GTX

It depends on the system. Some flow into the bottle as the car is running at temp, and other systems (usually older) draw/supply via the reservoir to move a small amount of makeup or expansion fluid. I don't have a radiator cap on one of my cars as it has a separate high point vent plug. The "reservoir" (pressurized degas bottle) sits lower. So that exchanges a lot more fluid than my 1999 GM where the radiator sits higher than the reservoir and the reservoir is not pressurized. If your reservoir gets quite hot, it's probably exchanging considerable fluid. So what's in washer fluid that cause issues with engine coolant? Consumer advocacy groups and auto enthusiasts believe that the alcohols and solvents present in some, but not all, windshield washer fluid can damage the vehicle. These critics point to the corrosive effects of ethanol, methanol, and other components on paint, rubber, car wax, and plastics, and groups propose various alternatives and homemade recipes[specify] to protect the finish and mechanics of the motor vehicle. You're not the first one to ever do this. If you google it I'd bet you'd find many interesting anecdotes and findings. Bloggy

I wasn’t sure if it would hurt it, I was about to put 300 miles on it and was in a hurry and didn’t want to risk t so I poured out the overflow and filled with water.

Originally Posted By: dlundblad

So you caught the issue right when you did it? If that's the case, zero washer fluid mixed with your coolant. This isn't your concern right? Assuming you don't have any obvious issues such as collapsed hoses or overheating, I would say your cap is just fine. I like to think of radiator caps as an oil filter bypass. Who really knows how often they open. The cap has a warranty right? Swap it out if you're really worried.

Not concerned about the washer fluid in the reservoir, that’s why I dumped it out and refilled with just water. The Jeep does run a bit hotter in the summer than I’d like, wondering if this is the cause. I’m going to get one from the dealer either way, this Murray cap’s build quality is like someone formed it out of an aluminum can. Just wondering if anyone thinks the coolant will then flow.

 

[ecotourist]

Are you saying you emptied the overflow (because of the mix-up) right after you changed the coolant, and there still isn't any fluid in the overflow tank? If that's what you're saying, the reason may be that there isn't any overflow. The cooling system could a little short of coolant, as it often is after changing. Seems you don't get all of the air out of the system and it takes a while for it to "burp out". That air "burped out" is replaced by fluid from the overflow, but your overflow has been empty because you didn't have any extra coolant to fill it. In that case you need to put some premixed coolant into the overflow and likely add a bit more over the next few days until you get the cooling system full of coolant again.

 

[Superflan]

I think the system maybe sucked water because he put back the reservoir with water. No big deal for the quantity. On my Yaris qqun the level in the overflow reservoir went down only to replace air that may have been left in the circuit after flushing. Then I went changing the color to see if it mixes up sometimes. Blue instead of red. It only turned dark after being stuck in traffic in a hot sunny day

 

[SilverFusion2010]

I'd put some straight coolant into the overflow if there is room. Otherwise don't worry about it. You can have the cap tested to make sure it is holding the correct pressure

 

[eljefino]

The methanol from the washer fluid would have boiled off if it got in the real radiator which I doubt it did in any real quantity. No worries.