I am going to flush cooling system and replace coolant in my car in near future and was planning on using a radiator cleaner product from Liqui-Moly. The place where I do my DIY auto work like this is about a 25-minute drive by highway. I thought it might make sense to add cleaner to radiator and then drive there, i.e. car would be operating at speed and typical driving temperature for the ~<30 mins or so the product recommends, and I wouldn't then have to wait an hour or so for engine to cool down to be able to add it just to then have to bring it back up to operating temperature and let it sit for ~20 mins.

So question: is there any concern about actually driving car (as opposed to letting it sit idling at same temp) for this amount of time while product is in system? I wouldn't think so but figured it wouldn't hurt to ask...

edit to add some info re: Liqui-Moly Radiator Cleaner product


Add contents to the cooling water. Turn the heating to maximum and let the engine run on idle for 10 - 30 minutes depending on the degree of contamination. Drain the coolant and flush the cooling system with water. Fill the cooling system according to the manufacturers instructions. Contents (300 mL) is sufficient for 4–10 Liters (1 gal. to 2.6 gal.) coolant water.

Full reference here: Liqui-Moly Radiator Cleaner

  • What are the instructions for the cleaner? How many minutes or what have you? Can you spell it out for us? Edit your question and insert it there, if you would please. Commented Sep 19, 2023 at 22:04
  • @Paulster2: done.
    – AA040371
    Commented Sep 19, 2023 at 22:45

1 Answer 1


Everything I'm reading about doing an engine flush states it should not be left in longer than six hours. If you go past that point, do so only at low engine power. That last bit is what is catching me. It means to me that before that time, using it at a reasonable power level would not cause issues. Because of this, I'm going to tell you, running your engine down the highway for under 30 minutes should not be an issue. I would suggest you put the cleaner in your very cool coolant, then straight away drive it to your destination. The hardest part will probably be keeping the heat on during the trip.

Once you get to where you are going, ensure you quickly and cleaning get to getting on with draining the coolant and then flushing. Flushing is very important. The cleaner is caustic and will continue to work on engine and cooling system parts. Make sure you are wearing your PPE (glasses and gloves) while using the stuff, because I'll bet it would chemically burn you.

Also, while not the same, this question and answer may be of help to you.

  • Yep...all makes sense, and jibes with what my instincts were suggesting. When I do a serious flush, as in this case, I typically drain from radiator as well as at the engine block drain plug, and then run two full fills of distilled water through (as in wash, rinse, rinse again) at which point I am usually getting clear or almost clear water out, and then refill with manufacture's recommended coolant mixture.
    – AA040371
    Commented Sep 19, 2023 at 23:48
  • And I note that this particular product indicates it "does not contain acids or alkali", so while I always work safe ("Safety Third!", as Mike Rowe instructs), I am not overly worried about the incidental splash or skin contact...and we keep a sink nearby for anything that may require fresh or running water. As alwasys, Thanks...
    – AA040371
    Commented Sep 19, 2023 at 23:49
  • 1
    @AA040371 According to the MSDS, the cleaner is basically a mix of detergents. So indeed no acids or alkali, likely won't corrode metals, but you don't want it on your skin for very long (or in your eyes at all).
    – TooTea
    Commented Sep 20, 2023 at 9:21
  • 1
    The one thing I would be concerned about would be if the process of cleaning causes a leak. You wouldn't want this to happen on the highway.
    – HandyHowie
    Commented Sep 20, 2023 at 9:48
  • @HandyHowie: yes...good thought. I'll definitely keep an eye on temp gage while heading over. Of course if the product causes a leak of any kind, before or after, I'll be pretty upset! I actually tried to Google for/find occurrences of this happening a week or so ago before purchasing (similar to some old engines experiencing trouble after owner applying and "engine cleaner" product in with oil change) but didn't see anything that applied...have you ever experienced anything like this? Or have direct knowledge of...?
    – AA040371
    Commented Sep 20, 2023 at 13:31

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