My vehicle is a 1999 Saturn SC2 with a coolant capacity of 7 liters.

I attempted to start flushing my coolant before changing the water pump. I drained the coolant from the bottom of the radiation. Then I closed petcock and put in some radiator flush and cleaner into the reservoir then topped it off with distilled water. I now realize that I don't think I drained all of the coolant since I only put in about half a gallon of fluid. I can't remove the thermostat because the bolts got stripped when I changed it a few months ago. I noticed a build up of some sort of mineral solid when I replaced the thermostat so that is when I figured a coolant flush would be good. How can I fix any possible problems I may have caused? How do I get the coolant back to the proper concentration?

I was letting the car run and was monitoring the reservoir level to add more water when I noticed that the reservoir was bubbling. I quickly turned it off, any help is appreciated. I had checked it at about 5 minutes and the reservoir had dropped a tad, at ten minutes and it dropped a bit more then at 20 minutes was when it was boiling.

The reservoir was about empty and it took 1/3 of a gallon of distilled water to fill up.

3 Answers 3


Some vehicles don't have any other means of draining other than the petcock, and given your problem with the thermostat housing, you should probably leave that alone unless you want to replace it, which might be a good idea if it has mineral build up.

It would be better to drain from the radiator, and fill with the correct coolant over several times. If its a DIY, you could do it over a few weekends. You will gradually reach a point where the coolant is clean and not contaminated by the flushing product.

If you are set on doing it in one go, it is a bit more difficult and messy. You could remove all the easily accessible hoses and flush using a hosepipe with fresh water. Try to get the heater core hoses and the lower radiator hose. In this case, you will have filled the system with tap water, you should then fill with concentrated coolant to achieve the correct ratio. (don't use ready-mix if you have introduced water). Also, if you have hard tap water, you might want to avoid this method.

The best solution would be to use a combination of the above methods, that's what I did when I had used the wrong coolant. Flush as much as possible with the hosepipe and drain/refill over a few weeks.


To drain the coolant fully you will need to both open the drain (probably the petcock, but check for something around the lower radiator hose as well) and open the cap so that you allow air in. You could also pull off the bottom radiator hose. Be sure to catch the coolant as it comes out, many are both attractive and toxic to animals.

If for some reason that does't work you can get simple testers for coolant concentration. But since you put in the flush "stuff" it is probably a good idea to make sure that you completely drain and refill.

You should be able to accomplish all of this without having to deal with the stripped bolt (heads I assume) on the thermostat housing, but you want to deal with them sooner rather than later (when you need to deal with them). A pair of vice grips, and undersized socket, or a speciality "rounded bolt head" socket will help you get the bolts out. A decent hardware store should have suitable replacements. Do them one at a time and you probably won't loose much coolant.


I just replaced basically my entire cooling system on my 01 SC2. when you drain, you want to first open up the drain cock on the radiator (don't remove it completely if you have a little downward facing hole, that's where it will come out), then take the cap off the top tank. remember, once you release that cap it will start draining a lot faster so get your container ready! as the radiator is draining, there is also a bolt that is connected to the block of the engine. This bolt allows for the coolant to drain out of the engine and not just the radiator. You wanna CAREFULLY remove it and let all the coolant from both the engine and radiator drain out. When it is finished, close everything back up, and with the bolt be careful, lightly snug it up. It doesn't have to be super tight. At this point you are definitely going to want to change that thermostat because the mineral build up you're seeing is not good and it could also get inside the small spaces and jam up it up. With hopefully a new thermostat on and torqued to correct specifications, re connect all hoses except for the upper radiator hose. Have that hose disconnected from the radiator, now is where you must get a little crafty. Either buy a funnel that has a flexible tube on it, or tape a small tube to the bottom half of the funnel. you wanna run the tube slightly into the radiator to the point that it passes the bend. have someone hold up your funnel as you pour in distilled water. keep pouring in the water until water starts coming out of the radiator, this means its full. The reason I fill the radiator first is because the coolant tank runs straight into the engine and not to the radiator, so the radiator doesn't get filled unless you fill the tank, and turn the engine on and let it suck through. this method though is scarier because you have to keep continuously and quickly add coolant to the tank as it sucks it all in, and you never really know if the radiator is completely full, because ive used this way to fill it up, and it did not take 7 quarts!! so after you fill up that radiator with DISTILLED or de ionized (preferably de ionized to prevent any mineral build up) you want to put the hose back on and tighten the clamp so you cant just pull off the hose. then add the radiator flush liquid (I used Blue Devil radiator flush, it works great) to the tank and fill the tank with more water as it goes down the tube. when you fill it up to the "max cool" line, go ahead and start up the engine with the cap OFF and make sure the level stays at that same line. fill it up accordingly. when there are no more bubbles happening in the tank, be sure to check all your hoses, drain cock and engine drain plug for any leaks. let the water and chemical radiator flush circulate through the engine for at least 15 minutes (or whatever your chemical flush instructions say). after that time, shut off the engine and let it cool back down. after its cooled again, drain everything out the exact same way. fill the system up all over again with ONLY water this time and run it for 15 minutes, repeating the same steps as I said before. after letting the water circulate and the engine is cooled off yet again. drain out all the water, if its all clean water, you're ready to move on but if its still dirty, just run the water though again until its clean. After the water comes out clean, you're ready to start adding the coolant. Now before you do this you want to double check your hoses, drain cock and engine drain for being lose or leaking. I everything looks good, make sure you have the correct coolant and start filling that radiator with your funnel. Once you fill up your radiator, secure and tighten the hose, and start filling up that tank. once again, turn on the engine after you filled the coolant to the "Max cool" line and then observe all hoses, drain cock and again the engine drain for any type of leakage. after checking for leaks you want to also be sure your tank stays filled up to the line, after you turn the engine on, like before, it is likely is will suck the coolant down into the engine, so you want to be sure you keep the tank filled. Keep an eye on all the places it could leak out, and the tank. (when you go and purchase a new thermostat, just grab a new "radiator cap" or the cap on your tank.) with your new cap, put it on the tank tightly and continue observing all the leak points I mentioned. If there are no leaks, you're all good and your flush was a success. Also though, be sure to check your coolant tank level again (with the car COMPLETELY cooled off) by opening up the cap, and adding more fluid accordingly the the "Max cool". I hope this helps even though it was awhile ago

  • Hi Noah, welcome to the site. Could you please edit this to add in some paragraph breaks? At the moment it's a "wall of words" and very hard to read.
    – Nick C
    Oct 22, 2018 at 13:55

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