Ford Falcon: Blown gasket

Is there water in the engine oil when you remove the dipstick? If there is you could have a blown head gasket. If you did, however, I would expect the engine to be running poorly. Another check you could do is to remove the spark plugs and check for signs of water on them. A blown head gasket would cost around $700-$1000 to fix depending on the condition of the cylinder head. If you’re concerned about oil in the water, that is, in the radiator it could be that you have a problem with the auto transmission cooler. The coolers are a known problem with Falcons, and when they fail water gets into the auto transmission and eventually causes that to fail.