Coolant not staying in radiator - dumps back into reservoir

Amiguel6

New Member
So, my coolant wont stay in my radiator. When I fill up the radiator with coolant, a few days later, all of the coolant that was put into the radiator will be sitting the reservoir. Its almost as if the radiator is spitting the coolant back into the reservoir when I fill it up. All hoses are good and there are no leaks. I just replaced the radiator cap as well and the problem continues. I use the 50/50 coolant.

The car never overheats (the temp gauge does work), its always a little before the halfway mark on the gauge. My fans turn on as well. There is no coolant being lost, the coolant just dumps into the reservoir. There are no unusual scents either. The car or the engine never smokes or smells burnt. Im stumped on this one.

One thing that I think may work, Is replacing the thermostat and bleeding the system. But, im not positive that will be the solution. Ive gotten mixed answers online as to what the problem may be. The car runs perfect and idles normally. This issue has been going on for some time now.

Any help is appreciated.

Thanks.
 

DonJulio

Reppin' tha NW
Get a oem thermostat.

Are you bleeding while the car is running, engine warm, with the heater on high?

Usually people bleed their coolant without the heater on and the trapped air is inside the heater core.
 

TegSox

Super Duper Moderator
My '05 Civic EX is doing the exact same thing as your car. Coolant moving to the reservoir, not losing any coolant, exhaust is normal. Get yourself a Lisle (brand name) funnel, the yellow one, it attatches to the radiator. You put it on when the car's cold (or cold enough to take the radiator cap off anyway), fill about halfway with coolant, then run the car until it's hot and the fan comes on, and all the air in the system will eventually bubble out the funnel during this time. And yes, make sure you run the heater while doing this to get all the air out of the heater core too.
 


Ganyon

Active Member
My car was doing the same thing. My grandfather poured over a cup of water in the radiator and it would never fill up. Long story short, I had a blown head gasket.
 


Amiguel6

New Member
see when I pour the fluid in the radiator, it will fill up and stay at the top. Then a few days later it will mostly all be in the reservoir
 

Excitable Kid

New Member
Miguel, did the bleed the bloody cooling system? Try do the easy things first.


Don't mean to scare you...it's probably blown headgasket. Probably.... I experienced one quite recently. Only way to find out is a compression test, leak down test, or a block tester

Possible reason why you're reservoir is overflowing is combustion gas.

There are coolant passages that go between the cylinder head and the engine block. There is a leak in the cylinder head gasket between one of these coolant passages and a cylinder.

When the piston is in the compression stroke or if this cylinder fires the pressure in the cylinder will leak from this blown gasket into the coolant passages. This pressure far exceeds the relatively low cooling system pressure which is around 15 PSI.
The volume of this gas needs to go someplace so coolant is rapidly pushed out of the cooling system to make room for this gas.

If you're super lucky, I'd say rad cap, but you already replaced it.
 

Amiguel6

New Member
Car is not running hot at all. Its running a normal temperature. There is also no fluids/vapors coming out of the exhaust. The cooling system hasn't been bled, but im pretty sure the thermostat has never been replaced either. The previous owner never did a thing of maintenance to it. He basically just did oil changes.

EDIT: Im not quite yet convinced that its a blown head gasket. Reason is because most of the signs for one, I haven't yet experienced.
 
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