I have a slow leak in my car’s radiator. Does that crap they sell for radiator leaks at Wal-Mart etc. really work or should I take it to the mechanic?
It depends. How slow is the leak? If it is a dribble, and you only need to add water every few days or so, then you can probably get the aluminum-based stop leak to work just fine. I have done so myself, and been able to delay the fixing or replacement of a radiator - possibly for a year or so if you are fortunate. But normally, after time, it becomes a recurring problem, and mandates radiator replacement or major repair. Try it and see - you won’t be out much money.
Typically at this point I would recommend that one get the radiator fixed, or else a new radiator. Experience has shown me, however, that when I do so people will jump in and complain that I am telling people to “waste money”. So I won’t suggest that.
What type of car?
If you have a slow leak in your radiator you have the option of picking the time to get it repaired or replaced. If you delay the repair or replacement by adding the stop leak gunk you might have to replace it at a time that is not convenient to you.
Somewhat tangetially, I offer this advice: Never buy a car with a can of stop-leak in the glove-box. I did that once, after crawling underneath and finding no apparent leaks. The leak, I found out, was between the radiator and its internal transmission cooler. I found that out after the anti-freeze had eaten all of the transmission’s clutch parts. Expensive lesson.
I have used the stuff with success for a permanent repair. I have heard it can mess up your water pump, but I never had a problem.