Mercury Repair Questions? Ask a Mechanic for Answers ASAP
Hello. My thought is that you are leaking coolant slowly and as you drive it blows away. Do you have access to a pressure tester that you can put on the system and let it be for a while to see if you end up with a puddle? It's most likely leaking from the water pump or the radiator but there are many other places it could be leaking from.
Ok. If the leak is not obvious, then we will need to use a pressure tester to determine where it's leaking from. First, use a flash light and inspect everything very carefully. Something is going to be wet with coolant. Look under the water pump, bottom of the radiator, etc. If you don't find anything, then you can rent a radiator pressure tester from auto zone I believe, and I think they will return the rental fee upon return of the tool. This is the only way to know where that coolant is escaping if it can't be seen otherwise. Again, I see it often where it leaks slowly, usually from the water pump or radiator, so slowly that it only leaks when the system is hot and under pressure and it blows away while driving and you never end up with a puddle. Not until the leak gets bad enough.
Water pump is the most common cause of coolant loss though.
Ok. It's probably the water pump leaking and running down before dripping where you see it, but it could be a freeze plug, coolant hose, etc. It may take a little investigating to find the exact location of the leak, but you will want to locate it and get it fixed before it gets very bad. You don't want to end up over heating and doing engine damage.
The water pump is located in the front, but I have seen many times where the leak presents itself in the rear because the coolant runs down the engine and doesn't drip until it reaches the lowest point which is many times toward the rear of the engine. To determine whether or not that's the case you would have to take a look under the truck at the water pump and see if that's where it's coming from. If not, It could be a freeze plug, or a coolant hose to the heater core, etc.
what we can confidently rule out is a radiator leak
You do have a plastic intake plenum, but coolant does not flow through it on this engine. Here is a diagram of your entire cooling system. The only way to be certain of what it is, is to inspect it good and if necessary, a pressure test will amplify the leak to a point where you should definitely be able to determine the source of the leak.
Did you find the source of your coolant leak?