I'm trying to use a stop-leak solution to fix a leak in the radiator, but I'm stuck in a catch-22.

The stop-leak instructions say to flush the coolant system if it is dirty or clogged. I don't know if it is, but I figured it couldn't hurt, and the flush+cleaner was cheap, so I got it. The problem is that the flush+cleaner instructions say to pour it into the radiator and run the car for a while.

This doesn't make sense. I have to flush the radiator before I use the stop-leak, but if I pour the flush+cleaner into the radiator, it will just pour out the bottom if I don't use the stop-leak first.

What should I do to get out of this infinite loop?

  • Is the leak in the radiator itself, or is it just a hose hanging off? I'd recommend NOT using a stop-leak as I've never got them to work for me. As for how to use it, literally the flush+clean and run the engine. Whether or not it drains out doesn't matter too much so long as it's in there long enough to allow the engine to run ten minutes. If it's gonna empty before ten minutes pass, I'd not bother with stop-leak and go for a new radiator. – yollooool Jan 26 '18 at 19:33
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    Agree with @yollooool here ... stop-leak is just a band-aid. Figure out what the real issue is (if you don't know already) and get it fixed. I've never really had good luck with stop-leak either, and I've tried many different brands/types. You know what the definition of insanity is, right? Doing the same thing over again expecting different results. If so, I'm completely nuts. – Pᴀᴜʟsᴛᴇʀ2 Jan 26 '18 at 21:01
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    They say run the car for a while as the sealer needs to be heated to coagulate and stick, then eventually seal the hole... If the leak you are trying to fix is larger than a pin-hole then it won't work... You need to do the job properly.. Mind you I did see a tractor radiator with a branch hammered into it once... – Solar Mike Jan 26 '18 at 21:21
  • @SolarMike Going full RoyalNavalRepairs there, lol. That's actually how the UK Royal Navy repair their ships upon being damaged by missiles; chunks of wood hammered into the damage. That being said, that's against saltwater that's cold, not hot, coolant-containing water. :P The stop-leak, as you say, would only work on tiny, tiny leaks. It may be worth chucking one in to repair any other damage throughout the rest of the system, but if the radiator is leaking so fast that 10 minutes depletes enough to stop you running the engine, there's a serious problem that needs fixing FAST. – yollooool Jan 26 '18 at 22:16
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    If it is leaking so bad that it is visibly pouring out then "stop leak" isn't going to fix it. – agentp Jan 27 '18 at 1:53

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