I hear that one should NEVER put a stop leak product in the Coolant, but why? My vehicle has a small water pump leak that is causing the Check Engine Light to come on. I was told by my savvy brother to just put a 1/4 can of some stop leak product in the coolant. Why not do this? He says it is just a tiny bit.

 

Personally, I think "a tiny bit" wouldn't hurt anything. The concern is that too much stop-leak will eventually "stop flow" through the small passages in the heater core. I've seen it too many times on older cars. I had an Alfa Spider with a heater core that was completely blocked by the stuff. The radiator was also JB Welded all across the top seam, too, so that was my first clue to why no heat was coming out! LOL.

 

So, you concur. Thank you!

 

Stop leak is band aid fix not a permanent solution. If the car is your daily driver that you depend on then dont waste you time because eventually the Water pump is going to fail and usually its at the worse possible time. So imo fix it once and fix it right.

 

Granted.
He had the idea to clear the Check Engine Light by doing this temporary band aid in order to see if there's anything else wrong with the car. In particular, do we still have a Map Thermostat issue (does the Map Thermostat code still come up)?

 

Hi, as the other guys have said don't bother with the 'stop-leak' it's only temporary so just fix it right first time.
With the check engine light I very much doubt that the water pump leak would cause this unless it pouring out. More likely a coolant temp sensor or the thermostat it's self.

 

Thank you. There's only a small leak, so what I'm going to do is have the mechanic replace the Thermostat (it's on warranty and throwing a code). At the same time I'll have them replace the water pump.