Not a vehicle I familiar with but you may have a bad head gasket or a cracked head. The quick test for a gasket and is to start it stone cold rev up and then see if pressure is in rad. There should be none. Another test is replace a cap with a radiator tester. Pump up to 15psi and leave on overnight. Lower press in morning will indicate a leak somewhere.
Heads may crack near those hard exhaust seats. This may allow coolant to get into combustion chamber or crankcases (or both). The later contaminates the oil. The former may, but not always, create white smoke out tail pipe. My 90 Ranger had a cracked head at 100K. Used 1qt /moth for all of 5 years. Never smoked, oil was OK. Ran another 100,000 miles fine this way. At 200K there was a sudden increase in coolant use, to 1 gal every few days. That was a problem. I now had more white smoke(some normal in this time of year -Feb-, however the white smoke now in puffs every RPM) . The oil quickly formed very thick sludge on cool valve covers(inside). The concern was the stuff would move and clog the oil pickup. 20 years ago I had heard of a product called Moroso Ceramic seal. They have 2 products. On used in anti-freeze, a second,a better product, used with water in cooling system(10-15$). The label said a race care block sealer but can be used in you tow rig....The inst was to remove anti-freeze, add water, add goop, drive around for 24Hr, drain, leave empty 24 hrs, fill with anti-freeze. Well I'm not a big believer in miracles in a can, but holy smokes- it stopped -ALL- coolant usage, even a leaking head gasket(external leak only, been leaving a few drops on ground (once and a while) since I got truck, and a small thermostat housing leak. That was a contrast. It always used some. It ran another 100,000 hard miles, often towing a 5K-6K trailer cross country, never used any coolant. The 2.9 Ford had some history of common head cracks, cracks between the 2 seats. I might also point out that most head design has a lot of cooling around the exhaust seat/port. Someone said a truck rad sealer was similar-K/W sealer(Kenworth?). The coolant may have damaged cam bearings causing a huge loss of oil pressure. Amazingly it still ran fine, Engine was replaced/retired 100 K later, at 300K, due to a pending heavy CC transport (R4360). It had many issues at this time but the real concern was that the original hand sized clutch disk w/300K was just fried moving a neighbor's camper off road in snow. No coolant use even at that 2.9's end.
Anyways, Moroso Ceramic Seal, should anyone have a cracked head /bad head gasket.
Wayne
