Water/Coolant Flush 1999 Mustang 3.8 V6

Hello All,
I need to flush my Mustang Water/Coolant.

It has been sitting for a while, and when I started it recently, the thermostat did not open.
Luckily, it did not overheat badly, just a little. I turned on my heater vents full blast and the temp went down. Also, the smell was like dirty water. I use regular tap water, which I will changing to distilled water and the correct coolant mixed at the correct ratio from now on.

I changed my thermostat, and that fixed my overheating problem, now I need to change and flush my radiator and reservoir.

I bought sea foam. I know I can use this. I would just like some help, and confirmation. I will be adding sea foam to my gas tank, 1 oz per gal of fuel, and I would also to know how much I should add to my water. I am thinking to flush my radiator multiple times.

I will also be removing my thermostat again, and also my lower radiator hose to flush the ports in my engine, in which the water travels. I am thinking first to change my water out with tap water. And let it idle for a while. Then drain and take apart thermostat and lower hose to flush out the engines’ water ports. I would like to know if there is anything I can add to my water to make the rust come out, and also to clean the walls of the ports. I only have sea foam, but if anyone can recommend anything else, that would be great.

Also, if someone can please point out the screw under my radiator that I have to remove to drain it, that would be great. I’ve done my thermostat and other work on my car, but not a radiator drain. I will be looking at my chilton’s manual and also on other sites for this. But always best to have multiple answers pointing at the same thing, for confirmation.

So yeah, if anyone has done this before and knows a better way than I described, or if you know of something to add to my water to get it to clean the port walls, that would be great.

Thank you

Ford radiators tend to have a white 19mm plastic hex head drain plug. What I just said applies to genuine Motorcraft radiators. Aftermarket radiators may have a drain which looks different, though . . .

auto parts stores usually have chemicals that will do exactly what you just described. They’re usually called radiator flush, cooling system flush, or cooling system rust remover

Prestone and Blue Devil market such products, but there are several to choose from

I assume you’re planning to remove the plugs on the block and drain the coolant out of there, as well. The side that has the starter might be next to impossible to get to, but the other side should not present a problem. Once you unscrew that plug on the block, don’t be surprised if nothing initially comes out. You may have to poke in there with a screwdriver to get it flowing out.


If you can’t open or find the radiator drain plug, you can always remove the bottom hose.


This is the best course of action. It is not uncommon for the drain plug on an old radiator to break when you try to remove it, or even worse, to leak once you reinstall it. Removing the hose is easier and less risky. If it leaks, well then guess what? You needed a new one anyways.

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You can’t smell your coolant, assuming there’s no leak. It sounds like you’re smelling mold, in which case I suggest that you replace your cabin air filter and check the cleanliness of the ductwork as much as you can.

I flush by filling w tap water drive a couple miles let cool drain and repeat twice before filling w proper mix. Has worked well for me but not all agree saying aluninum should never come in contact w plain water. Best way to flush radiator, remove and turn upside down, good time to correct bent fins.

I’m going to assume the coolant he drained smelled like dirty water

That was the case with a used car my brother bought several years ago . . . it was original coolant which was WAY overdue for replacement. It definitely smelled terrible