Hello there,
i put an ST170 Engine in an Super Seven.

I have really annoying Problems, the Coolant is pushed from the lower hose in the expansion tank.
As soon as i start the engine, the coolant Level rises in the Expansion Tank.
For my understanding this is complete wrong.

I think air is pushed trough the small hose in the Thermostat Housing.

When i stop the Engine, i can hear the Air going back to the expansion tank through the small hose.

Sometimes when i rev the engine, i can see air coming in at the lower hose in the expansion tank.

I made a drawing to show you how my coolant circuit is actually routed.
I hope someone here has Tipps for me what can cause my annoying Problem.

I think the pressure at the lower hose must be bigger than at the top hose in the expansion tank. But why?

Maybe if you watch the Video you can see my Problem.

https://vimeo.com/1139690884?fl=pl&fe=sh


Greetings

[Edited on 22/11/25 by Ghostrider1911]

You want the expansion tank bottom hose going to the rad bottom hose.
That way the water (and any air) enter at the top of the expansion tank, and hopefully only water exits at the bottom.

Thank you for your Answer, i rerouted it to the Inlet of the Waterpump (Bottom Radiator Hose), now it works and the fluid is sucked in with the Waterpump.
I really cant believe this makes so much difference, but yes it does.

Greetings