Stop Leak Oil Additives and Synthetic Oils:A Perfect Match or a Risky Combination?

If you want your car to really last for a long time, regular oil changes and a maintenance routine that you actually stick to are paramount. By now anyone who owns a car should know these two things can make a world of difference in maintaining your car.

The problem is, with so many different kinds of oil on the market today, it can get really confusing on which one is best to use in your car unless you have some sort of engineering degree or something.
But that’s why we’re here, to hopefully make things a little clearer for you and help you decide which type of oil would be best to use for your specific car and also your driving conditions.

For now though, it’s important to understand the two types we’ll be looking at, synthetic oils and stop leak oils. Although both can achieve the same thing, lubricating your car’s engine, that doesn’t mean they are similar in makeup or compatibility.

In fact, when it comes to older cars, leak oil additives combined with normal non-synthetic oils are most often the best bet. This is because older engines were designed for natural petroleum based oils, and the stop leak additives are a way to boost the oils efficiency by helping to keep your engines non-metallic parts in good working order. So together, you have a ‘new’ high tech option, but with liquids that are meant for your older car.

On the other hand, if you have a newer or high performance engine, you’ll want to use synthetic oils rather than the old standard petroleum types. These newer oil replacements are actually chemical compounds that are manufactured for the newer engines that are far more demanding than the older cars were. And since they are actually chemicals, they simply don’t break down at the same rate as the older oils do, and they can be combined with additives during manufacturing.

In the following sections, we’ll go into a lot more detail about each type and what you need to be aware of in order to make a more ‘scientific’ choice about what to use in your car.

Overview of Leak Oil Additives

The first oil we’ll go over is leak oil additives or stop-leak additives, they mean the same thing. These are the best option when it comes to older cars for a few different reasons. First, they’re made to be combined with petroleum based oils which is what most older car engines were designed to use. But as you probably know, as cars get older, so do their parts. And the interior parts of your engine age just like the rest of your car.

So in time your gaskets and seals start to get brittle and dry out, leaving tiny gaps between them and the engine which in turn results in small pin sized leaks. These leaks can steadily get bigger over time and is a sure sign that it’s time to add something to help out with the problem.

These stop leak oil additives can sometimes completely repair these tiny leaks by rejuvenating your o-rings, seals and gaskets the way that facial cream rejuvenates the cells of your face. The seals ‘take in’ some of the polymer in the additive and become subtler and start to conform back to their original shapes by swelling and expanding the seals so there are no more gaps, thus stopping the leaks.

And while these types of additives can definitely help and even sometimes completely solve the problem, it doesn’t mean there aren’t risks involved if you decide to go with them. And again, this is pertaining mostly to older cars.

See, one of the biggest problems is the polymers can sometimes gunk up and cause clogging problems, especially if there are already problems to begin with. But how would you know what’s going on inside the engine, so it’s not always obvious what you’re doing can potentially cause more problems than it’s solving.
But just because there are risks doesn’t mean there aren’t a lot of benefits as well.

One monetary benefit is when these do work, they’re a low cost and easy fix for small oil leaks, especially for older cars with worn out or cracking gaskets and seals. This really helps you keep an older car going without the costs or hassles of having to have the entire engine taken apart just to replace all of the non-metal parts in your engine.

This makes people who don’t have a clue which end of a wrench is a way to actually fix their car’s problems without necessarily knowing anything about engines.

But even with all of these benefits, one thing you really do need to clearly understand is that most of these types of low cost and easy fixes are not at all permanent. They are just ways to extend the amount of time you have before the problem needs to be addressed by a professional mechanic.

Your seals and gaskets are never going to be new again until you actually replace them, so don’t expect these oil additives to be little miracle workers!

And as a side note, sometimes using stop leak oil additives can even mask the actual root cause of your engine’s problems which can sometimes be far more severe than you think. So don’t put off taking your car into the shop for too long!

One last benefit that most people don’t think about is oil pressure. You see, when you do plug up any ‘holes’ in your system, you are also adding pressure to the system which is a good thing, and the way your system was originally designed to work.

So you just need to decide what you are using them for and if they’re worth the risks involved. If you know it’s a temporary fix and you plan to have everything professional looked at and the work done, then you should be fine.

Overview of Synthetic Oils

Synthetic oils are a lot different than the petroleum based oils you probably grew up with.These synthetically made oils aren’t based off crude oil, but rather are chemical compounds that often perform much better than any ‘natural’ oil could ever dream of.

That means they take a lot longer to break down, even under extreme temperatures, heavy loads, or prolonged use so even though they may cost more, since they do last longer the cost is almost a wash.

This makes them the best of both worlds as they last a lot longer and work a lot better than any traditional oil could.

Some synthetics also have a very low friction coefficient that makes them beneficial in colder weather where starting an engine can be difficult. Since the synthetics are thinner until they warm up, there is less force on the engine and the starter and your vehicle can start easier.

Synthetics also have the added benefit of not oxidizing like traditional oils, this means there are less impurities in these types of oils and less sludge or other types of oil build up over time. This also helps fight against rust and other forms of corrosion.

And like we mentioned before, the biggest drawback is definitely the cost. Synthetics are always more expensive than the traditional oils, but for the added properties these have, it really can be worth the added costs.

Plus since these oils typically take a lot longer to break down and need changing, the added time that you don’t need to do oil changes can cancel out the added costs when you look at it from a time perspective and how often you’d need to change your oil if you were to choose non-synthetic oil for your car.
So even though some car owners may shy away from the higher price tag of synthetic oils, compared to conventional mineral oils, synthetic oils provide better fuel efficiency, increased engine protection, and reduced oil consumption.

And because these oils are literally manufactured from chemicals and compounds, they don’t have the impurities that natural crude oil has and needs to be filtered out. These oils are clean right from the manufacturer.

One thing to note though, not all vehicles can run on synthetic oils. Especially when you’re talking about older cars that weren’t designed for these types of oils and have seals and rings that can end up springing leaks if they’re used. Or even reverse and shrink the non-metallic parts again causing leaks. So you’ll need to look at your specific car model and year to determine if they’re the right choice.

So yes, synthetic oils are the future and most cars designed today are designed for synthetics and not traditional engine oils. It’s when you have an older car that you need to decipher if these types of oils are going to do more harm than good.

And if you’re still unsure whether to use them or not, our best advice is to simply ask your mechanic or someone that is well versed in the area of synthetic oils.

Combining Synthetic Oils and Leak Oil Additives

Combining synthetic oils and leak oil additives can be a way for car owners to get the best worlds of each product while improving your car’s overall performance. But usually people use petroleum based oils with oil additives and not synthetic oils because there can be certain problems when you combine them, especially in older cars.

But there is definitely a time and place to use them together. And when you do, you can be certain that you’re using the very best defense against all sorts of problems resulting from poor engine oil performance or other engine lubrication problems.

This comes down to synthetic oils being far superior than their petroleum based counterparts and they do an exceptional job at keeping your engine performing at optimal levels. Combined with leak oil additives they can be a full maintenance program for older cars by giving you the best lubrication properties while also conditioning any non-metallic parts and keeping them like new so they don’t end up drying out and leaking.

But combine both of these products in the wrong circumstances and it can lad to more damage than if you didn’t use anything at all. This is because not all synthetic oils are formulated to be combined with oil leak products. Each brand and type has different properties and are specially formulated for different types of vehicles and driving conditions. So always be sure your oil is indeed compatible with a leak oil additive before just adding one thinking you’re doing the right thing!

Another thing to be aware of is using too much of an additive. There’s such a thing of having too much of a good thing, especially when you’re mixing random chemical compounds together. Too much oil or a mixture can cause too much pressure on your seals and O-rings, causing leaks when your whole intention was to avoid them. So never add too much of anything as your vehicle is designed for a certain amount and a specific amount of pressure. Anything more creates a lot more problems.

The last thing I want you to be aware of is for those of you with older cars. Synthetic oils were never designed for older cars and vice versa. Synthetics have different lubrication properties and newer cars are specifically designed to run perfectly using them. Older cars were not. So sometimes using a synthetic oil or a mix with stop leak additives, you can end up dissolving your seals rather than helping them. So ask your mechanic if you want to use these or consult your driver’s manual.

Overall the combination of synthetic oils and leak oil additives can be a smart move and can help you extend the life of an engine, but only under the right circumstances!


Combining synthetic oils and leak oil additives can be both beneficial to your engine, or the cause of a lot of problems, it all depends on how you use these compounds and in what vehicle and if the engine is made for a combination like this.

If you are lucky enough to have a car that was designed to use synthetic oils, you really are getting the best oil there is. And if you do have an older car that can use both synthetic oils and stop leak oil additives, you really can’t do anything more than that for any engine. It’s the perfect match.

It all comes down to knowing the products you’re using and if they are compatible with each other, if your engine can use these chemicals without them causing further damage, and knowing when and how much to use each. After reading this very long article, I hope you have a clearer understanding of all of it.


As a user of The Automotive Men (, please note that we participate in the Amazon Associates Program. This means that “As an Amazon Associate, I earn from qualifying purchases.” We are not directly sponsored or endorsed by Amazon, but our website may contain affiliate links that provide us with a commission when you make a purchase through them. Thank you