Hi. Thanks for using JA! I will try and help you out.
Could you get me your engine serial number? If not, that is OK. I just want to make sure you have an ACERT engine with 2 turbos.
yes it is a twin turbo
Thanks for the information.
I must say that I have not seen heard of a C15 that sucks the reservoir dry and when the cap is loosened, the tank refills.
However, I have seen several C15 ACERT engines with twin turbos push coolant out of the over flow under load. Many times when this happens most techs are quick to blame the head gasket for the engine pushing out coolant. But on twin turbo engines, there is another item that can push coolant out, and it will only do it under load.
It is a failed Jacket Water Pre cooler. JWPC. It is a cooler on the outlet of the turbos to cool the air before going into the air to air core. Basically what is happening is when the engine is under load and making alot of boost, there is a small hole or crack in the cooler and boost pressure goes into the cooling system and pushes out coolant from the over flow.
You should be able to remove the piping from the JWPC and see evidence of coolant in the piping.