Kia Rio Coolant Problem

[vulcan42]

The engine coolant doesn't return to the system as it should. This seems to be a fairly common problem but cannot find a solution. We have followed the advice of Kia engineers, changing the radiator cap, the expansion tank, its cap and hose but this has made no difference. The system has ben pressure tested twice for leaks, none found.
Does anybody know a cure for this problem?

[nero2024]

Does the car run ok or over heat?
"The engine coolant doesn't return to the system as it should" ? so is it pouring out somewhere it cant just disappear

[bhg481]

If there is a problem with the cylinder head gasket it can often result in coolant loss; this usually causes running problems with the engine. It would be useful to know how much coolant is being lost - do you have to top it up every time it's used/every few thousand miles?

[nero2024]

look on the inside of your oil filler cap if you have white "mayonnaise"on it your cylinder head gasket has blown and the engine will be rough running

[bhg481]

Mayonnaise in the rocker box can also be caused by using the car for mainly short trips. When you convert petrol or diesel into energy water is produced as a by-product.; the water mixes with the engine oil. Once the engine oil reaches running temperature the water boils out of the oil; too many short runs and this doesn't happen and the mayonnaise appears in the rocker box.

[vulcan42]

Thank you for your answers, the last time I checked there were no replies.
The engine runs fine and the heater works. The coolant fills the expansion bottle and then "disappears" through the overflow hole at the top. The pressure tests discovered no leaks.
No mayonnaise in oil filler cap.
Not sure exactly how much is actually lost as I've bought a small hand operated pump and transfer the coolant back to the radiator when the expansion tank fills up. The experts all agree that the expansion bottle shouldn't fill up and overflow but cannot work out why this is happening.

[davebro]

not very expert "experts" are they!

//The coolant fills the expansion bottle and then "disappears" through the overflow hole at the top.//

Coolant can't just disappear - it goes back into the system or it comes out somewhere. Where does this overflow hole lead to?

[davebro]

You say the engine runs fine - suppose you just ignore the perceived coolant issue and run the car as usual - what would happen?

[bhg481]

I'm not familiar with your particular car, so I might have the geometry wrong, but I assume the pressure cap is on the radiator and the overflow runs to a separate bottle which has a non-pressure cap on it. The tube from the radiator to the overflow bottle is NOT pressurised. If that is the case, as the system heats up, the coolant expands and runs into the overflow bottle. When the system cools again the coolant contracts and should suck coolant from the overflow bottle back into the radiator. If the tube from the radiator to the overflow bottle has a pinhole or is not fixed tightly at both ends then air, not coolant, will be sucked back to the radiator. This tube is OUTSIDE the pressure system, so a pressure check will not show a leak in it. I suggest that you replace the tube connecting the radiator to the overflow bottle, making sure that the connections at both ends are tight.

[vulcan42]

Again, many thanks for your replies.
As I said at the beginning, the radiator cap, expansion tank, its cap and hose have all been replaced. Sorry, I shouldn't have used disappeared. The expansion tank fills up and there is a hole at the top just below and to one side of the cap, which has been molded into it, ie it looks as it's meant to be there, and the excess coolant goes through this hole and out into the engine bay. I assume seeing as how the expansion tank is full all the time and the coolant is going out of the system it will eventually lose all the coolant. For obvious reasons I'm not willing to risk it. As I've said, the Kia engineers know the system isn't working properly but don't know why.

[davebro]

I can only think that the problem lies with the radiator cap or connecting hoses. Is it possible that the replacement cap is also faulty or maybe of a wrong type?

[bhg481]

The expansion tank should only be full when the engine has reached full operating temperature ie, at the end of a good run. As the engine cools the coolant should be sucked back into the engine from the expansion tank, so that the engine is full and the level in the expansion tank is not up to the overflow. When the engine is fully cold you should be able to remove the radiator cap and the radiator should be full; the overflow tank should be not full. If the radiator is full when cold you've nothing to worry about. If it's not the problem must lie in the fact that the coolant is not being sucked back from the expansion tank and there must be an air leak somewhere between the radiator and the expansion tank. You say you've changed both caps, expansion hose and expansion bottle - are you sure the connections at each end of the hose are tight? Is there any possibility of a crack where the expansion tube joins the radiator? I said in an earlier reply that I don't know your particular system so I'm having to think of how it might be set up.

[vulcan42]

davebro, thank you, I will get the radiator cap checked although I was assured all the new items fitted were genuine Kia and correct for this model. At the moment I've started to experiment. I'm recording the mileage, keeping the coolant in the expansion tank at the correct level by pumping out the excess into another container to see exactly how much is leaving the system. this might tell us something, it might not. It's intriguing if nothing else, Thanks for your help.

[vulcan42]

bhg481, thank you, yes that is how the system should operate although the expansion tank has maximum and minimum levels marked and the maximum mark is roughly half way up the tank. The handbook states to check the radiator level and if it needs topping up add the coolant to the expansion tank but as the coolant is not being drawn back into the radiator all it would do is gradually fill the tank. As I've said to davebro, I'm now trying to establish just how much coolant is leaving the system.