Do you recommend “leak-stopping” products?

December 1, 2011 | By Richard Prince


As an owner of an old truck I am used to seeing leaks of one sort or another under my vehicle that were not there before. After I have tracked down the source of the various leaks I am sometimes faced with having to repair or replace an expensive component. In my case at the moment that’s the automatic transmission.

This brings me to my question about products I see at local auto parts stores that promise to fix leaks of all sorts, such as automatic transmission, power steering, radiator, etc. leaks.

I know the proper answer is to go ahead and fix the actual problem, but I can’t help wonder if those products really work or would help me limp along until I could afford to fix the problem at a later date. Could you discuss your experience with leak-stop products and tell us if they work or make things worse?


In most situations products designed to cure leaks are like drugs insofar as there are almost always unintended and/or unwanted side effects.

A substance designed to plug an opening doesn’t know the difference between a good opening and a bad one and while it may stop the unwanted leak it may also prevent or restrict the flow of fluid to places where you want it to go.

Sometimes, leak “cures” are little more than thickening agents that increase the viscosity of the fluid that’s leaking out and in so doing they slow down or eliminate the leak if the fluid gets too thick to fit through the breach. Thicker fluid can, however, strain the pump that’s moving it, not reach areas with very tight tolerances that it’s supposed to reach, react to changes more slowly than it’s supposed to, and so on.

So, as you can deduce by now, I’m not a fan of products that promise to fix leaks with minimal effort.

Having said that, in some instances if you’re faced with the choice of a complete rebuild/major teardown or a quick fix out of a can or packet there is usually little or no immediate harm in trying the quick fix. In most cases, however, I wouldn’t even try it because I assume there could be unwanted side effects.

Let’s say, for example, that your power steering pump’s front seal is leaking and you pour a product advertised to cure the leak into the pump’s reservoir. That product will obviously be pumped throughout the system so you end up with it in the steering box, hoses, control valve, etc.

Will it harm any of these parts? I don’t know but I’d rather put in the extra time and effort to change the pump seal with the secure knowledge that the problem will surely be solved and there will definitely be no collateral damage to other parts of the power steering system.