Use the pepper or the sealant. Johnm6211 December 4, 2007, 1:13am 11. Radiator “Stop Leak” products do work to a limited extent however: remember, if it stops the leak (clogs up the hole) it is also clogging up something else. I have a 1986 Subaru with a pin hole leak in an original equipment radiator. They want $350 for a new radiator - is The answer to this question is yes, radiator sealants really do work. However, they are not a miracle solution, and are only good for a temporary fix. Even so-called “permanent” sealants will only last for months, not years. A good radiator sealant–also called a stop-leak–can seal all kinds of cooling system leaks. If you’ve ever had an oil leak in your car, you’ve probably used (or were tempted to use) a stop-leak product. But, do they actually work? Do they cause damage to your engine seals? Will they destroy your engine? Read and watch on to find out. Product Description. Lucas Engine Oil Stop Leak is an all-new formulation of Lucas additives and very specific base stocks designed to stop seal leaks in engines! It reduces engine noise and oil consumption, while raising oil pressure and renews worn seals with no risk of damage or eventual corrosion. It is not limited to engines – effective Stop-leak additives are designed to prevent that by reducing the amount of oil getting out of those spaces. Early versions used ‘mechanical’ methods – clogging the holes with (wait for it) nut shell particles suspended in castor oil. Others used sawdust and teeny bits of metals. if it leaks while running: the leak is coming out of the top half of the engine, typically the valve cover, also an easier fix. but if its anything other than valve cover or oil pan, i wouldnt mess with it and just add more oil. perhaps adding some lucas oil additive could slow the process; it doesnt stop leaks, but it might slow them a bit The A/C system is typically a closed system where the refrigerant level stays constant, except in the case of a leak. This is why it makes sense to seal any Turn vehicle off and allow engine to cool. Allow enough time so it is safe to open cap. Top off (fill up) cooling system with water and reinstall radiator cap. Run engine at idle until normal operating temperature is reached. Continue running engine at idle for 15 minutes. Turn vehicle off and allow 45 minutes to cool. 9zIIc.