Coolant overflow doesn't drain back to rad.

[jux]

The last few days, my radiator will be like a quart low, and my reservoir will be full above the cold fill line. It is not draining back into the radiator for some reason.

Anyone ever had this problem? I just got finished replacing the radiator cap and making sure the line from reserve to rad is clear and free of debris to make sure it wasn't that.

Thanks

More info: My oil is not milky, coolant is clear, and no bubbles while running so i don't think it's head gasket related.

 

[austinado16]

The replacement cap may be the wrong version, or defective. Or the flange on the radiator is bent or damaged, preventing an air tight seal. Or, there's a leak in the system somewhere, so the radiator sucks air in through that leak area, rather than sucking on the coolant reserve tank.

You need a coolant recovery style cap, not just a standard pressure holding cap.

 

[jux]

The problem happened with the old stock cap. Earlier today I replaced with the same style (cap with spring and seal, twist on). I'm not yet sure if the problem is fixed but i will know soon.

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This is the stock style, as well as what I replaced it with. Is it what you're talking about?

Thanks

 

[DoubleDingo]

I had the same problem in my jeep recently, and the hose was plugged. I replaced the hose, and fixed a small crack in the bottle and now it works. When I used the blow nozzle from the compressor on the radiator end of the hose, the hose bulged out because of the blockage. Who knows what was in there but it was black. I am thinking it was just the hose had disintegrated in that area and closed on itself.

 

[DoubleDingo]

As Austin said, there may be a crack in the bottle or leak so it is sucking air. I recommend removing the bottle and fixing any and all cracks with permatex plastic weld. Easy to use, and while the bottle is out, replace the hose. For the plastic weld and new hose, it may cost $7.

 

[89Suburban]

It must be drawing air in somewhere when the engine is cooling down. You don't see any leaks at all anywhere?

 

[jux]

No, I see no leaks whatsoever. When I disconnected the reservoir hose from the neck of the rad and held it a few inches lower in elevation, coolant flowed through it easily. So I don't suspect a clogged line.

It seems that any coolant I add to the radiator just ends up in the reservoir, leaving the rad a little low again and again. This is happening with the new cap too now. I got another hose, so I'll replace that. The reservoir seems tight, I have repaired it a few years ago due to a crack. If I had a crack somewhere now, it would either leak, or it wouldn't matter because it's above the water line.

This has me stumped, thanks so far for the help!

 

[austinado16]

It wouldn't matter if the reservoir was cracked. The res is open to the air. It's the radiator and entire cooling system that has to be air tight in order for a vacuum to be formed as the coolant physically contracts.

I believe a coolant recovery cap will have a rubber gasket up under the cap, as well as a rubber gasket on the spring loaded pressure relief "door."

 

[jux]

It wouldn't matter if the reservoir was cracked. The res is open to the air. It's the radiator and entire cooling system that has to be air tight in order for a vacuum to be formed as the coolant physically contracts.

I believe a coolant recovery cap will have a rubber gasket up under the cap, as well as a rubber gasket on the spring loaded pressure relief "door."

That's why I said it would either leak if it was low enough, of wouldn't matter if it was above the water line.

That's the cap I got, two gaskets and a spring. I just finished replacing the reservoir hose. The old one didn't look bad at all, so I have a feeling I'll be back to the drawing board. I'll be driving it tonight to work, so we shall see.

 

[89Suburban]

You need to get your hands on a pressure tester and pressure test the cooling system. You can probably rent one at Autozone. Also pull the carpet up on the pass side and make sure the floor is dry. Just fold it down from under the heater box. Also check and tighten all your hose clamps just as a precaution. Might be a very slight leak that is hiding it's trace. I hope it is not a head gasket starting to go or a crack in a head.

 

[DoubleDingo]

And I have a pressure tester in my possession right now. With the attachment to test the cap too.

 

[89Suburban]

And I have a pressure tester in my possession right now. With the attachment to test the cap too.

Me too

 

[chengny]

The last few days, my radiator will be like a quart low, and my reservoir will be full above the cold fill line. It is not draining back into the radiator for some reason.


One quart low? Don't get stressed about this. You are jamming more coolant into the radiator than it can handle - or that the coolant system requires. Just pick a point on the side of the expansion tank, mark it with a Sharpie and monitor that level.

The radiator requires an ullage space (distance from the liquid level to the top of the tank). This is to allow for expansion of the coolant that occurs with the rise in temperature during operation. Excessive coolant in the system will increase the pressure under the cap as the engine heats up to operating temp. When the pressure rises above (what - 14 psia?) it overcomes the spring in the cap and allows some coolant to be dumped up into the expansion tank.

When sufficient coolant has been released, the spring then closes off the outlet valve and the system again returns to a "closed" condition.

Leaving an air space at the top of the radiator allows the coolant to expand and contract with changes in temperature without popping the radiator cap's outlet valve.

You will notice a larger air gap as the weather changes and ambient temperatures drop. The reason for that is beyond the scope of this explanation.

But you can rest easy; as long as the top row of tubes remains covered with coolant, there will not be any appreciable loss of cooling capacity. When necessary due to normal losses, the radiator cap will open it's inlet valve and allow coolant to be drawn in from the tank.

 

[89Suburban]

I respectfully disagree with that. If there is an overflow tank on a properly operating cooling system there should be no way that an air pocket should be forming in the top of a radiator. I he fills the radiator and the overflow tank it should purge any air out after a few heating and cooling cycles.

 

[jux]

Ok, between the new cap and new hose, it is all functioning normally now. Thanks guys. I'm guessing the cap, because it was a bit rusty and the rubber appears to have deteriorated a bit.