1997 Ford Aerostar Engine loosing water, no viable leaks

do you have any water in the oil .. or oil in the water tank !! ant gunky yellow white deposit on oil filler cap !! compression test the cylinders to check the gasket !!

Last week noticed a little bit of white gunk at top of coolant bottle. Haven't done compression test. Even wondering if it will show which head gasket is away.

when you compression test it will tell you which cylinder(s) has LOW compression .. that's the head that the gasket will have blown on !! hope this helps

Just done a compression test, what a beast to work on. All pressures around 150-160. Was told it could be leaking at intake gasket, any ideas?

You said you have to check the coolant level every couple of days so this is quite a significant leak .. I think you would notice some coolant pooling under the vehicle after a run etc. .. but it could be from the manifold .. can you see any coolant around the manifolds !!

Already have changed the manifold gasket, was told it was a problem with 4.0 v6 engine. Already reassembled but now am running off one cylinder. What a headache, you have to strip so much off to see anything.
There were no visible leaks at engine, still in process.