Recently, on my 04 disco, the coolant tank will be full to correct fill level at start but after driving, expansion tank looks empty. Engine temps stay perfectly normal. No visible leaks or smell of coolant, no white smoke. When I open the full cap on the expansion tank, fluid then fills from the lower hose on the tank - like it’s under a vacuum.
It feels like I have air trapped in the lines but when I open up the bleeder valve, I get coolant coming out immediately.
Any ideas what’s going on?

 

[QUOTE=Frank Gordella;744433]Recently, on my 04 disco, the coolant tank will be full to correct fill level at start but after driving, expansion tank looks empty. Engine temps stay perfectly normal. No visible leaks or smell of coolant, no white smoke. When I open the full cap on the expansion tank, fluid then fills from the lower hose on the tank - like it’s under a vacuum.
It feels like I have air trapped in the lines but when I open up the bleeder valve, I get coolant coming out immediately.
Any ideas what’s going on?


Here’s the setup. Inline thermostat was installed by previous owner. I’ve never had any issue with it, so far.