Oil stop leak products — Do they work?

Oil stop leak products work sometimes, but can actually make some leaks worse

Most oil stop leak products are made from one of two base products: heavy naphthenic or glycol ethers.  Heavy naphthenic products soften hardened rubber seals and gaskets, making them more pliable. Glycol ethers, on the other hand, cause rubber

seals and gaskets to soften and swell. That’s how they work; by softening and swelling rubber seals, not by plugging the leak with particles, like most radiator sealing products.

But do they work?

Over time and with heat, neoprene gaskets and seals tend to harden, become brittle, crack, and leak oil. Oil stop leak products work on flat cut neoprene gaskets and seals. The products cause them to soften and swell and that can make neoprene gaskets seal again. However, if the leak is from a round seal on a rotating part, the fix will be temporary since the rotating part will quickly wear out the newly swelled neoprene. So my advice is to avoid using them if you’re leaking oil from a crankshaft or camshaft seal.

Oil stop leak doesn’t work on RTV or silicone gaskets

Most late model engines use RTV instead of gaskets to seal valve covers, oil pan, water pump, and thermostat. RTV and silicone seals and gaskets are highly resistant to the softening and swelling effects of petroleum-based products. Since heavy naphthenic is produced from petroleum, it doesn’t work on silicone seals and gaskets. The same is true with glycol ethers; not very effective on silicone. In other words, if the leak is coming from a component that was sealed with RTV or is made from silicone, don’t even bother trying a stop leak product.

And be aware they can make the leak worse

If the leaking seal or gasket is made from a composite of rubber and cork, these oil stop leak products don’t do a very good job because the chemicals have no effect on the cork components and they can dissolve the binding agents that hold the composite materials together. In other words, adding an oil leak stop product can actually make those leaks worse.

Should you use oil stop leak products in your engine?

If oil is leaking from a neoprene seal or gasket, you may see temporary relief. But in my experience, they don’t stop the leak for very long. It’s a band-aid at best and you’ll still have to fix the leak.

CAUTION: When using a stop leak product, you must follow the dosing instructions on the container. More is NOT better. You can cause expensive seal damage throughout the engine by using too much oil stop leak product

©, 2021 Rick Muscoplat