Does Stop-Leak/Stop-Slip Actually Work?

It’s Monday morning, and you’re running out the door for work – but when you get out to your car, you are greeted by a shiny puddle slithering out from underneath your car.

Uh oh.

Or, maybe you got out on your morning drive to work, and all of a sudden, your car isn’t accelerating normally – the revs are going up more than the car is moving forward.

If you have ever had issues with your transmission slipping or fluids leaking, you may have been tempted to use stop-leak or stop-slip products. While you may think these products will save you time and money vs. a repair, they could end up being more costly in the long run when used improperly.

Let’s talk about that.

What is Stop-Leak/Stop-Slip?

Stop-leak and stop-slip are fluid additives that are designed to improve the performance of your transmission fluid, oil, or coolant and prevent leaks and slipping, due to advanced wear and tear  on internal parts. These fluids are additives, that are injected into the system with the goal of temporarily solving oil leaks, coolant leaks, and transmissions slipping out of gear.


Stop-leak is commonly used to prevent or stop a current leak in the oil or coolant system of your  vehicle. The products are generally made up of fluids containing particles of ceramic, metal, or other substances that attach themselves to metal. These particles flow through the coolant or oil system, attaching themselves to any non-smooth surface within the engine or radiator to try and seal leaks along the way. 


Stop-slip fluid is most commonly used in worn-out transmissions to remedy issues with transmission slipping, hesitation, rough shifting, or fluid leaks. In addition, some fluids claim to repair shudder, chatter, and whining. The fluid is added to the existing transmission fluid, with the goal of lowering the operating temperature and interaction between the internal moving parts in the transmission. 

The Affordable Solution to A Common Problem?

Unfortunately, oil, coolant, and transmission leaks are some of the more common auto repair concerns in Muskegon. Because of the temperature changes throughout the year, transmission seals wear out over time – and slipping in & out of traction during the winter doesn’t help the situation. 

Common transmission wear and tear symptoms include: 

  • Slipping
  • Shaking or shuddering
  • Jerking
  • Leaking
  • Delayed shift or hesitation
  • Whining, clunking, or grinding 
  • Strange smells

Some common causes of an oil leak can include: 

  • Damaged valve cover or head gasket(s)
  • Crankcase ventilation due to too much oil in the system
  • Damaged valves
  • Leaking oil cooler (if your vehicle has one)
  • Loose or damaged oil drain plug
  • Loose or damaged oil filter/oil filter housing

Some common causes of a coolant leak can include: 

  • Damage to the radiator
  • Damage to the radiator cap
  • Damaged head gasket(s)
  • Failed water pump
  • Damaged expansion tank

When faced with any one of these concerns, stop-slip fluids may sound like an attractive option,  due to their inexpensive nature compared to actual repairs. However, they may not be all they are advertised to be. 


Stop-leak fluids can be temporarily effective on leaks that are caused by normal wear on the seals inside the engine, transmission, radiator, or crankcase; but it won’t just stop the leak. 

The fluid’s contents impact all of the seals within the system, including the undamaged seals. This means that swelling may occur in areas that were previously undamaged, causing the potential for new leaks to arise. In addition, the results usually don’t last very long, especially compared with an actual repair.  

Pre-Existing Damage

If a leak is caused by rips, tears, or other damage, stop-leak or stop-slip fluid usually won’t be able to actually repair that damage. In some cases, it may push the damaged part of the seal against the mating surface to temporarily slow or stop the leak. However, the damage will still be present, and need to be diagnosed and repaired accordingly. 


Stop-leak/stop-slip fluid is not a permanent solution to your vehicle’s problems. On the contrary, it is a temporary solution that may buy you time to properly diagnose and repair the issue.

Is Stop-Leak/Stop-Slip Effective?

At the end of the day, stop-leak/stop-slip fluid is only effective in momentarily reducing symptoms caused by normal engine, radiator & transmission wear and tear, and should not be used as a long-term solution. In some cases, using stop-leak/stop-slip fluids can actually cause additional damage to the transmission, which could make repairs more costly down the line.

We’ve repeated ourselves here a few times, but it’s critical for you to understand; trying to fix a damaged seal or transmission with these products is like trying to fix a broken arm with a band-aid. 

In addition, using a stop-leak fluid additive with larger particles (like the pellets or ‘sand’ in stop leak), has the potential to clog up very small coolant & oil passages within the engine itself.  

When To Use Stop-Leak/Stop-Slip

There may be times when the use of stop-leak/stop-slip could be appropriate, but it is vital to know the full impact it can have on your vehicle before using it. While we do not recommend using these products, they can give you a little more life out of your vehicle; if you just need it to last JUST long enough to replace the afflicted parts. 

It is essential to understand that using these products improperly often leads to further, more serious damage. In addition, if the products are used to make the car last until a proper repair can be performed, the entire fluid system will need to be flushed before operating the vehicle after the repair. 

A Smarter Alternative

If you are experiencing issues with your transmission slipping, making noises, or leaking, it is best to bring it into a Muskegon auto repair shop for a diagnosis. At The Garage MKG, we can replace transmissions, and perform basic service and repairs like transmission flushes, transmission filters, and gasket/seal replacements, but we do not currently offer internal transmission repair or rebuilds. But don’t worry – we know many reputable transmission repair shops in the Lakeshore area, and can make you an honest recommendation.


The Garage MKG

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