Rick's Free Auto Repair Advice

Engine oil stop leak products

Do engine oil stop leak products work?

I’ll save us both a lot of time; engine oil stop leak products work in some cases when used according to the directions. However, they can also cause the leak to worsen. It all depends on the type of stop leak product and which type of gasket or seal is leaking. Here’s how engine oil stop leak products work and where they don’t work.

How do engine oil stop leak products work?

Engine oil stop leak main ingredients

Oil stop leak products operate by causing rubber components to soften and swell. The stop leak product must mix well with engine oil so it circulates throughout the engine to reach all gaskets and seals. Keep that in mind because it doesn’t swell just the leaking gasket or seal, it swells all the rubber gaskets and seals in the entire engine. That’s an important factor to consider BEFORE you use a stop leak product.

Also, carmakers used to basic types of rubber gaskets and seals; Polyacrylate elastomers and nitrile elastomers. A stop leak seal swelling agent affects these two types of seals differently.

I’ve pulled up the material safety and data sheet for one commercial seal swelling agent to show just how much the product softens and swells the two types of rubber (elastomeric) products used in engine gaskets and seals. The results shown are for adding 3% of the seal swell agent to Group II engine oil. As you can see, the swelling is much higher (60%) on polyacrylate elastomers (synthetic rubber) and 29.4% on nitrile seals.

engine oil stop leak products

As you can see, this particular seal swelling agent works well to soften synthetic parts and swells them by 60% but does nothing to soften nitrile parts and only swells nitrile parts by 29.4%.

Types of gasket and seal materials used in engines

Polyacrylate elastomers

Polyacrylate elastomers are widely used in the automotive industry because they have excellent resistance to transmission and hydraulic fluids. They’re used in transmission and power steering seals, O-rings and radiator and fuel hoses.

• They have high resistance to oxidation and ozone
• Better compatibility with high temperatures compared to nitrile (operating range -40°F to 300°F)
• However, they have poor compression set characteristics.

Nitrile elastomers

Nitrile is the most popular material for automotive seals. It’s a mixture of two synthetic rubbers, Buna and Acrylonitrile polymers. Synthetic lip materials are bonded to the metal case to prevent leakage between the sealing lip and the shell. Different properties are obtained by changing the percentage of each polymer used in the mixture.

• Good oil/grease compatibility
• Abrasion resistance
• Good low temperature and swell characteristics
• But they aren’t as compatible with synthetic oils

How to use engine stop leak products

The most common mistake DIYers make when using an engine oil stop leak product is to not follow the manufacturers directions. More is NOT better. In fact, adding too much can cause complete gasket and seal failure, resulting in more oil leakage.

Which types of gaskets and seals are candidates for engine oil stop leak products

Flat gaskets like valve cover and oil pan gaskets are a prime candidate for stop leak products. The swelling usually stops the oil leak.

However, leaking rotating shaft seals (axle shaft and rear main seals) are usually NOT good candidates for stop leak products.

©, 2020 Rick Muscoplat


Posted on by Rick Muscoplat

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