Over the weekend I took my 2000 Toyota 4Runner to a local shop to get the oil changed. While there they told me I needed to flush the coolant, pulling clear water out of the coolant reservoir. They insisted that the water in the coolant could cause problems for my engine. Also insisting that I couldn't flush it myself because it requires special equipment.

Given that I know antifreeze is in the engine and it was last serviced by the dealer I'm a little perplexed as to how water (or a clear liquid anyway) ended up in the overflow.

My guess is that coolant is low, so the overflow was empty. They added water so they could up-sell me into flushing the coolant system.

Is there any other reasonable explanation for how that could have happened?

(for the record I didn't have them flush the coolant)

  • 2
    I have NEVER seen an automotive engine that was the least bit unhappy with straight water in the cooling loop. The normal cooling fluid is 50% water, 50% coolant. You can buy the coolant and mix it yourself, or you can (if you don't mind spending money for convenience) buy pre-mixed 50/50. That shop was almost certainly lying through their teeth to you (but you know this already). Dec 8, 2015 at 16:32
  • Note: If you run straight water in the loop, you do have to keep a careful eye on the engine temperature, or you may boil over. Mixing in the coolant increases the boiling point of the mixture. Dec 8, 2015 at 16:34

4 Answers 4


Since it's clear the shop was being dishonest, I wouldn't even assume the overflow tank was low. They could have just poured it out or siphoned it off and filled it with water.


To add to R...'s answer, I don't know about your Toyota, but on my buick there's a wingnut on the radiator, once I unscrewed that all the coolant came out (so drip pan was my 'special equipment'), once it stopped I tightened the wingnut and added properly mixed coolant, been running fine ever since.

If you really want a peak at what it will take, here is the repair manual for your car, and this site is offering a download of it, I don't know how legit the download is, but Haynes manuals are pretty accurate from my use.

  • 1
    In fairness, you can't do a real flush without a little bit more equipment; up to half of the coolant will remain in the system depending on your vehicle if you just drain it from the bottom of the radiator. The best method of flushing seems to be to disconnect bottom radiator hose at the thermostat and run water from a garden hose or similar backwards through the radiator, coming out at the thermostat housing. Apr 30, 2013 at 16:01
  • @R.. I think I've heard that before (along the lines of run water into it until it comes out clear), thanks for the info, I probably need to flush mine and will keep that in mind.
    – MDMoore313
    Apr 30, 2013 at 16:29

The only special equipment you'll need to flush your own radiator is a bucket. The fact that they claimed it would take special equipment is just one red flag. I'd be skeptical they even changed the oil. Just google how to flush your Toyota's radiator, you'll see it's super easy. And see if you can warn everyone else in your area about that shop.

  • I disagree. The power flushers that shops use do a much better job than DIY with a bucket. :-) May 1, 2013 at 17:45

Clear water is not a sign of requiring a flush. It might be a sign that you need some anti-freeze...
Brownish water or any other color that is not the normal color of your coolant could potentially benefit from a flush.

Plain water in our engine could potentially cause problems:

  • Water will boil over and not cool the engine sufficiently.
  • Danger of rust if in contact with iron.

You cannot "flush it yourself" because they use a machine to power flush your system.
Although you cannot power flush it yourself, you can use some other methods to flush it. Power flushes are actually potentially damaging to your coolant system, especially if your car or cooling system components are old.
Drain and fill are safest, but sometimes you need to flush a bunch of crap out of the system (if you see a bunch of crap in the coolant).

Are you dead-sure that the dealer service included coolant and they put mixed/colored coolant in? If they didn't put coolant, then are you sure you had mixed/colored coolant in there already?

If there is clear coolant in the overflow tank but colored fluid mixes in after it starts circulating, then it is very clear that the shop added in clear water to the overflow (whether they took some out or not) and you should never go there again.
If there is only clear coolant in your entire coolant system, then someone before them probably put a lot of plain water in your coolant system, whether the dealer or someone else before that.

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