K-Seal Coolant Leak

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2008 Mazda5 GT
2008 @ 135K.

Radiator developed a slow but continuous leak, right above the drain plug (near lowest point); pour coolant in, it comes right out in a slow/steady trickle. Thankfully I was able to catch it while I was on the road (thank god for temp gauge) and had to shut it on/off and limp my way home to prevent overheating. Tried a bottle of K-seal and it works even on our plastic radiators. I was concerned it was formulated for meatal radiators b/c the liquid has a metallic/copper-ish sheen to it. It seal up and no leaks and is advertised as permanent fix. Hope this anecdotal feedback can be helpful to someone who might get stuck. Holding strong for the last two weeks and took a few hours long drive. If it can hold till warmer weather, that is a big win so I can address it later.

FWIW, I got the car up to temp before I pour in the k-seal (extra coolant and distilled water on standby). Shake well, pour in, let idle for 15-20 mins. Note this will not fix your head gasket leak, they have a different solution for that.
 
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Sure if you're desperate, it can save the day. But don't think it's a permanent fix.

Modern radiators are plastic and just crack over time so this problem is most likely going to resurface.

I would do a coolant flush and replace your radiator.
 
Update. Sealant was good for about 1.5 month. Leak returned but went from slow trickle to very slow drip when parked/cool. Ran coolant dye and seems the engine oil cooler gasket is also leaking.
 
Thanks for the update.

You need a new radiator. And make sure whoever does the job flushes out the sealant. Radiators are cheap and easy to replace on these cars. These sealant products can cause blockages in other tight areas. I don't think you will ever see anyone that works on cars recommend a leak-stop as anything other than an emergency fix.
 
It is a fantastic emergency fix. From what I observe, it seems to coagulate the leak well when warm. The fact it brought a steady trickle down to a drip (only occurs when coolant is cold overnight) is a big win. Fact it stopped it for over a month is a fantastic win. I’m not going under the car in the March NE weather. This held me over till warmer weather.

Technically, they advertise you can add 2nd another bottle IF one does not seal it completely and I do ‘think’ it can stop the leak. The debate is how long does it actually hold long term. Regarding causing blockages, I personally believe this is anecdotal. I can image folks with old cars that have heavily contaminated coolant/rusted passages run a bottle of sealant and call foul. I flushed my coolant once @ 80K (it was way too early).

TO DO:
-Water pump
-Thermostat
-Radiator
-Oil cooler gasket
-Probably upper&lower rad hose as preventative measure since it’s about that age…

Seal holes up to 0.635mm in diameter.
Seal a slot or crack up to 0.254mm wide by 12.7mm long.
Pass through a mesh of 0.85mm without gumming or gelling together.
 
Small update. Added half of a 2nd bottle about a month ago b/c I didn't have time (or want) to deal with the small leak. It sealed up and the car was usable without any leaks.

Took Sunday to get through the laundry list.

- OEM radiator has a hairline leak along one of the lower fins. Removal was not hard but you do have to take off the bumper to get to the top mounts off. Toughest part is prob getting the clips off the hoses at awaked angels. Fan comes off super easy, AC condenser clips in/out BUT the old age mean the clips were not budging. OEM parts have super tight fitment. Had to beak off clips but putting in new radiator with new clips anyway. (Denso @Rockauto).

- OEM thermostat was easy to replace. It was working fine but replace as preventative. (OEM @Online Mazda dealer)

- OEM waterpump was a PITA, practically fused to engine. PB blaster, pray bar, and couple of hammer whacks got it to move. Remove the two PMM to chassis bolts and you have space to wedge the engine (jack support) over to get the pump out. (NPW @ebay)

- OEM oil cooler gasket has been leaking coolant for a while. Only found out when I used the dye due to raditor leak... Easy to do if you take off oil filter. (Felpro @ amazon)

- All hoses look/feel good so leave them as is.

- Flush and refill. hope the cooling system will be trouble free.
 
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