My 1994 Splash was overheating and blow back into the antifreeze overflow container. I changed the fan clutch, radiator cap and flushed radiator but still getting blow back (gurgles when warm) back to resivor. However, temp gauge still in safe zone and does not overheat now. Perhaps water pump blades are broken and needs to be replaced? Any reason why I should continue to get blow back. Circulation problem??? Thanks

 

Welcome to the forum

Engine size?

Cooling systems with overflow tanks release pressure above Rad cap rating, say it is a 14lbs rad cap, at 15lbs internal pressure, larger valve in rad cap opens and allows what ever is at the TOP of the radiator to flow out to the overflow tank.
Now that should be warm coolant flowing out to overflow tank.
If there is air at the top of the radiator then the air will come out and Bubble up to the top of the overflow tank.

The pressure IN the cooling system comes from engine heating up the coolant, any liquid EXPANDS when heated, so as the coolant expands in volume the pressure in the system goes up.
After engine is shut off coolant cools down and SHRINKS back to cold volume so pressure drops, if any coolant was sent over to overflow tank then pressure drops below 0psi to -1 psi, and the smaller valve in rad cap opens and SUCKS coolant from overflow tank back into rad.
This system purges air, and replaces it with coolant each time engine is warmed up and cools down.

If you constantly have air in the system then you may have a leak that is sucking air in after engine is shut off.
OR..........the start of a cracked head or head gasket leak.

Bubbles in the overflow tank are rarely related to circulation, running warmer than usual is a circulation issue, but that wouldn't cause bubbles in overflow.
Bubbles can come from super-heated coolant(above 265degF) that forms steam bubbles, but temp gauge would be spiked high at that point.


Simple test for cracked head or head gasket leak is the Glove Test, it is free and definitive.
Cold engine
remove rad cap
remove overflow hose
plug overflow hose outlet on rad cap opening
Put a Latex Glove over rad cap opening, seal it with rubber band or zip tie or ??, you can also use a balloon or even a condom will work.

Disconnect coil pack wires, you want a no start

Crank engine and watch glove
If glove just lays there then head gasket is fine.

If glove bounces in time with engine turning then you do have a leak.
Remove 1 spark plug at a time and crank engine
When glove stops bouncing then last spark plug removed is the cylinder with the leak
Put it back in and crank again to confirm.