My brothers Saff 4x4 has a weird issue with his coolant. When he drives the temps of the water are normal, not too high or too low. The system doesn't leak or whatever but after he drove a while and turns of the car the coolant in the reservoir stats to bubble.

How does the air get into the system if it isn't leaking?



It's a bit difficult to explain as I'm not Brittish

 

This is normal, when you turn off the engine when hot, the water still absorbs the heat from the engine, as it is not being circulated through the radiator it continues to get hotter and hotter, this will form air bubbles, and hot spots of water in the system, it's merely this finding it's way into the expansion tank, whereupon it meets cooler water, and air space and so the air comes out of the water, it couldn't before as there was no free space, as water is much denser than air.
Whenever water is spun it causes air bubbles as well, this is why ship propellers erode, due to cavitation caused by spinning propellors, it causes pitting of the blades.
tabetha

 

I haven't noticed it at my 3door but if it's normal then we'll just leave it I guess

Thanks for the awnser.

 

My 4x4 does the same and has never given me any trouble (now touching a large piece of wood!!! ).