Radiator Stop Leak Additives

radiator stop leak additiveHello I have a Mercury Topaz and its been leaking and thermostat has almost entered the red spot or hot spot, I did take it to a mechanic and he said it was the seals close to the water pump but it wasn’t the water pump.

He said it would cost about $260 to replace and I don’t have that kind of money at this time, I’ve tried , I know not wise , but old stop leak, I had for a year never opened, anyway, is there a temporary solution of a stop leak till my next payday, about a week Or the best brand of stop leak, thank you

Hello there

Those stop leak additives just don’t work very well on seals and rubber parts. They do seem to work a little for METAL radiator leaks (most cars use a plastic and aluminum radiator), but I don’t think you have an alternative…except stop often and refill with water so it does not over heat.

For a METAL radiator “pin hole” sized leak I would recommend BARS Leak Stop additive you can buy from any auto parts store.  You can buy an aftermarket radiator really cheap these days from your auto parts store, so honestly I would just replace the radiator and be done with it.

In your case, since the mechanic doesn’t really sound all that confident as to where the coolant leak is coming from I would get a second opinion from another mechanic and have them do a cooling system pressure test first to help locate the source of the leak.

Many times you can have a small coolant leak at the top of the engine, like from a heater hose, that will slowly run down the sides, back and front of the engine and can be fool you into thinking the leak is coming from something lower on the engine (water pump) than it really is.

For a head gasket leak I would recommend the sealer I talked about in my video above

This is an interesting video about radiator stop leak additives as well, take a watch

I personally have not used the AlumAseal additive but wanted to give you more options. Check it out, let us know if any of these helped out.

Please share this with your friends,

Austin Davis

Posted in: Fluid Leaks

10 Comments on "Radiator Stop Leak Additives"

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  1. Carl says:

    I do agree that Bar’s leak seems to work well on older radiators that are made of real metal, but have not had much luck on the newer plastic and aluminum radiators using it.

  2. Carol W says:

    I am assuming I can use the K&W head gasket sealer you were talking about on another article will also be a good option for a radiator leak?

    • By Austin Davis says:

      No, I would not recommend the block sealer for a radiator leak. Actually these days most radiators are plastic and aluminum and the only real fix is to replace it. I personally have not found a sealer to stop a radiator leak.

  3. Peter says:

    Will the K&W Block sealer additive you talk about on your headgasket leak articles work for radiator leaks as well?

    • By Austin Davis says:

      No, it will not. If you have a plastic radiator like you see on just about all newer vehicles then you will need to replace the radiator. If you have an older vehicle with an all metal radiator (“tanks” on the sides of the radiator are metal) then Barrs Leak Stop additive MIGHT help. You might still be able to find a radiator repair shop in your area that can re-weld or replace the side tanks for you.

  4. Helmut says:

    Barrs leak does work great on older metal radiators. Had not had much luck on a newer plastic one though.

  5. Tex says:

    You’re so interesting! I don’t think I’ve truly read anything like this before. So wonderful to find somebody with a few unique thoughts on this issue. Really.. thank you for starting this up. This site is something that is required on the internet, someone with a little originality!

  6. Cecil says:


    We have had a steady and slow leak in our radiator, and we decided to try Bars Heavy Duty Stop Leak. We have already put the product into the coolant resouvior of our 2006 Volvo. I think we were supposed to put it directly into the radiator. What do you think will happen? Will the pellets pass thru to the radiator from the resouviour?


    • admin says:

      Yes the pellets will dissolve and make their way through the cooling system. I have not had much luck with additives on LEAKS but have had success with radiator additives on SEAPS. Its worth a try but you will probably need to replace the radiator.

  7. Mullet says:

    i’ve got a leak in a water pump seal on my 89 ranger with 300k miles on it. it seriously leaks like a siv. due to the lack of time to fix it myself, i’ve just been adding water every day. i made a quick $20 scrap run yesterday and went to the local autozone to look for a temporary stop leak solution. paid around $7 something for a bottle of the radiator stop leak with the aluminum flakes that was supposedly good for seals too. followed the directions and it said to add half a bottle for 4cyl engines without a/c and treat engines up to 4 gallons. well, i have a 4cyl with a/c and looked it up in my haynes manual and it said that my engine holds 7.2 quarts of coolant with the 2.3l and a/c – which is just short of 2 US gallons (4qts to a gallon, 3.78lt per gallon). so i added just over half the bottle (there’s about a third of the bottle left), filled the radiator to full and let it run for a little over 20 mins, even though it said run it for 10 to 20 mins. after about 8 minutes the leak in the water pump stopped dripping and it was holding water in the overflow. i’ll probably add the rest of the bottle later this week just to be sure. i think it’s a great temporary fix, won’t know until i start driving my truck tomorrow.

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