Coolant leak

[Subru]

For a while now I have been losing a little bit of coolant out of the milk bottle reservoir, I top it up to above the full line and have to check it every two or three weeks. Mechanic did a leak test and head gasket test and both came up with no leaks/blown head gaskets, the mechanic said coolant could be seeping through the radiator cap so I brought the proper sti one but its still losing coolant somehow. Does it matter if I fill up the bottle above the full line as im sure the first drive after I top it up there is a noticeable difference in the level...

[IZichard]

16 minutes ago, Subru said:

For a while now I have been losing a little bit of coolant out of the milk bottle reservoir, I top it up to above the full line and have to check it every two or three weeks. Mechanic did a leak test and head gasket test and both came up with no leaks/blown head gaskets, the mechanic said coolant could be seeping through the radiator cap so I brought the proper sti one but its still losing coolant somehow. Does it matter if I fill up the bottle above the full line as im sure the first drive after I top it up there is a noticeable difference in the level...

During normal operation the level should move up and down between the L and F marks. The radiator cap will open and close to let coolant in and out of the system as the temperature changes.

 

Are you checking it when it is at the same temperature each time?

 

Was the radiator cap you bought brand new? What pressure is it rated to? I think the STI caps are 1.1bar instead of the usual 0.9bar but i'm not 100%

 

You shouldn't fill it above the full line, there is deliberately room left in the top of the overflow bottle so that the coolant can "overflow" into it as it expands in the cooling system.

 

It would be a good idea to check that the front passenger carpet is dry under the dash. It could also be an air bubble in the system somewhere allowing coolant to boil off.

 

Do you hear a quiet gurgle under the dash when you first start the car?

[Subru]

Generally I check just after a drive but definitely has a decrease over few weeks however maybe this is because i overfilled it. I never let it get even close to the 'low' marking. I might not fill it up unless it gets really low and see if it still leeks. Yes brand new 1.1bar. I dont recall hearing a gurgle under the dash so ill have to listen out for it next time.

Could bleed it again to get air bubbles out.

[IZichard]

4 minutes ago, Subru said:

Generally I check just after a drive but definitely has a decrease over few weeks however maybe this is because i overfilled it. I never let it get even close to the 'low' marking. I might not fill it up unless it gets really low and see if it still leeks. Yes brand new 1.1bar. I dont recall hearing a gurgle under the dash so ill have to listen out for it next time.

Could bleed it again to get air bubbles out.

Just keep driving it and checking it. Don't fill it up unless it is at or below the L mark and see what happens. If it keeps dropping below the L try bleeding it again.

 

If the car is warm the level in the overflow will be higher and if the car is cold the level will be lower, just so you better understand what you are looking at.

[calebwrx]

Have a good look under the intake manifold, your crossover pipe o-rings could be leaking a little like mine are. 

[boostin]

Check it cold. Make sure the radiator is full and the bottle is on the full mark. Check it next time the same way, always at dead cold.

[Ross]

Had the same issue with my gtb, my issue was the plastic petcock at the bottom of the radiator, very miniscule amount of coolant but frustrating! bit of silicone on the thread fixed it