So if im getting coolant through the over flow...

[bastianshaw]

my head gasket is blown?
im talking about the little hose for the overflow return?

[dnguyen1963]

If your engine is pumping air into the coolant then the answer is yes.

[bastianshaw]

No air just coolant but someone very knowledgeable posted and I wanted to confirm

[jlevie]

Assuming the cap is good, the only reason for coolant to vent out the of the overflow is excessive pressure in the cooling system. And the only way that can happen is if the engine has overheated to the boiling point of the coolant or if air is being pumped into the cooling system from a head gasket failure or a cracked head.

[bastianshaw]

this is happening w the cap off on a late model

[bastianshaw]

what if the heater core is leaking could air be entering the system from there and causing excessive pressure? also if air is entering the system wouldn't that be evident when bleeding?

[dnguyen1963]

If the heater core is leaking then you would see coolant inside your car first. As the car cools down, it can suck air into the system. But coolant leak must first be seen.

[TurboJake]

So you have the cap off, and coolant is just creeping up and coming out of the coolant reservoir as the car heats up?

If so, that's normal. Liquid expands when heated.

Air cannot enter the system where there is a hole, without coolant leaking out and you being able to find it visually. The only exception to this is the headgasket into the cylinder, because the coolant is going into the cylinder and eventually out the tailpipe (Unless it's pooling in the cylinder and the engine hydrolocks).

Also, for air to get into the system, coolant has to drain. From what you have said it isn't draining. Just overflowing. Assuming you have the cap on and are allowing pressure in the system to build, this can only happen from an overheating situation, a bad reservoir cap that isn't holding pressure, a headgasket failure (causing your pistons to pressurize the system), or you just simply have it filled too much.

You'd notice the air in bleeding the system, yes. But the easier way is to just look at the reservoir. It isn't just an overflow. The cap is a one way valve. If coolant is leaving the system, it will allow air into the res allowing coolant to remain in the engine.


So, does the system hold pressure?
If so, pay attention to the level in the reservoir.
If it gets lower you have a leak somewhere.

If it doesn't hold pressure. Test the cap. Replace if necessary.
If the cap tests good, you have a leak somewhere. If you cannot see it find it for the life of you, it could be headgasket.
Check oil for milk.
If oil is good, could be leaking into the cylinder.
If oil is milky, coolant is leaking into the oil.

[bastianshaw]

not venting fluid out of the system but a stream is returning to the coolant overflow tank

[chriswin3]

That is normal, that's what the overflow bottle it for. It will push coolant out of the overflow bottle into the engine bay if the headgasket is blown and pressurizing the cooling system. The little coolant tube that returns to the top of the overflow bottle is part of the cooling system.

[bastianshaw]

so if im getting an intermittent stream from that little return hose does that mean there is air in the system?
Does the system bleed itself if you have the cap off?