My 2002 mercury mountaineer shakes when i start it up and over heats and leaks anit freeze

Try not to run it. Antifreeze w oil can ruin berings. Can also bend a rod cause liquids cant b compressd. Get a private mechanic by checkn surecritic.com. keep that old car. New ones too complex

I had a similar problem. It could be as Ian has stated especially with it over heating. I would definitely do a coolant pressure test. However It could be your intake manifold gasket has gone bad and is leaking antifreeze into the cylinder. You may just need to replace the intake manifold gasket. Also the intake manifold is known to fail where the coolant crosses over from one side to the other of the engine. They made this part out of plastic for some reason (made it out of metal in 2003). But the weight of the alternator is also on this plastic and with the heating up and cooling of the engine it could have cracked that coolant passage. Even if it is just the gasket I would replace the manifold with a dorman manifold that has that passage made of metal. I did this and haven't had a problem yet. You obviously have a cylinder missfire (possibly multiple). I would recomend new spark plugs and get you code read for your check engine light that is probably on (this will tell what cylinders are misfiring) and replace the coils on those cylinders as well. Replace spark plugs with OEM or you could risk a spark plug blow out in the engine then you have to get a helicoil. Also on the dorman intake manifold you will see they have a coolant port on the back with a cap on it. Do yourself a favor if you get one take the cap off and run a heater hose off of it and cut into your heat hose return and put a t into it and attach the heater hose from that port onto the other part of the t. I had mine on for a month when the cap blew and I had coolant over everything. I put the t in and ran the hose and had no issue since.

Sounds like a blown headgasket..do a radiator pressure test,then you could either get a mechanic or do it yourself,recheck the torque on some of the cylinder head bolts.back off then retighten to specified torque,see if they go down a lot.try to do the lot starting from the middle and circling outwards