Air Bubbles in expansion tank


Smile Hello Everybody, I have recently bought a deisel Hi-jet which i knew that had something wrong with it.I have noticed that it starts to overheat after travelling a mile,i then switch off and restart after a minute or so then the the temperature guage is at normal.I have noticed that there are air bubbles going into the expansion tank when the engine is running.I have done the sniffer test which indicated no gasses in the water system; so i think illiminates head Gasket.I also noticed that there was no warm air coming out of the fan until i restarted the engine.Any Ideas please. Thanks,Stotty.


There is only one way air bubbles get into the coolant reservoir and its due to compression gasses being forced into the coolant. Head gasket or cracked cylinder head.
I bet it blows out lots of water/drips from the exhaust when it starts from cold.

Thermostat usually fail in an open mode, so the usual probem is lack of warmth from the heater. Overheating is again a symptom of an air bubble getting into the water-ways within the engine block. Air blocks circulation and the engine rapidly over heats. The air bubbles get forced around with the coolant and escape via the coolant reservoir.

You probably hear a 'gush' when starting the engine from cold.

Get the cylinders pressure tested. A test should record any compression leak.


Could simply be an air lock, bleed the system properly, and if this is not effective, refer to comment from mace.