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Engine coolant

Can you tell me how many drain plugs are on a 2003 mercury grand marquis and where they are located & is it necessary to flush the engine before installing new coolant?

Most of todays cars cooling systems are sealed systems. This means there’s no pressure cap on the radiator but instead it’s located on the coolant reservior. These type of cooling systems usually don’t provide a means of draining the radiator except by removing the lower radiator hose. The engine block does have a drain plug located on it. But most times this plug is inaccessible because of a component being in the way. So replacing the coolant on these sealed systems can become a messy, time consuming affair.

This is why I recommend that the coolant be exchanged with coolant exchange machine. This is connected into the loop of the cooling system and exchanges 100% of the coolant. And while this being done, the cooling system can be checked for leaks. However, if you decide to go this route, refuse any kind of cooling system cleaning agent. Just tell them you want a coolant exchange only. Nothing else.


If you cannot find or access the drain in the block, which should be a 3/8" to 1/2" opening of some kind in the block, a few inches above the oil pan, then remember that it is not critical that you get out every drop of old coolant. Your primary goal is to get fresh corrosion inhibitor in there. What I do in that situation is:

Find out how much total capacity the system has.
Buy antifreeze and a couple of extra gallons of distilled water.
Drain it at the lower hose.
Refill with water and warm up the car until water circulates (top hose gets warm).
Drain again.
Repeat if you only got a gallon or so out.

When you have pretty much pure distilled water in the system, drain it again, add enough pure antifreeze to make a 50/50 mix (or whatever mix you are shooting for).
Then top off with distilled water.

This won’t work if you buy premixed antifreeze.

“This won’t work with pre-mixed anti-freeze”, because about a gallon of pure water was left in the engine after the last pure water flush. You want to put about a gallon of pure (100%) anti-freeze into the engine to mix with that pure water. One gallon of water plus one gallon of anti-freeze equals a fifty fifty mix in the engine. Then, if there is room, add pre-mixed anti-freeze untl the engine is full.

Use G05 coolant or old-fashioned green. Ford says both were used in early 2003 ( , but I think that the yellow was rare. I think that the G05 is better stuff. You can either it at a Ford dealer or use Zerex available at NAPA. The radiator has a drain in it. You can get out about two gallons by draining which is half the volume. Drain, refill and start the engine. Run water into the coolant reservoir with a hose and open the drain. Flush until the draining fluid is clear or stops changing shade/color.

Drain and fill with distilled or deionized water. Warm up and circulate the coolant, repeat. Repeat again if you have hard water. Drain, measuring the volume of what you drain with a marked bucket. Squeeze the big hoses to get a little more out if you can. Fill with G05 coolant. After you warm it up, check to see if you need to add more coolant. Check again after you drive it for a couple of days.