Should I Use High Mileage Motor Oil?

High mileage motor oil is designed for engines with the kind of wear that often comes with high mileage. It’s available in conventional, synthetic or synthetic blend form. Some manufacturers advertise the need to switch to this type of oil as early as 75,000 miles.

The difference between regular and high mileage oil is in the additives. Many engines with higher miles have minor issues that these additives can help solve. These problems generally involve engine oil use between changes. If you’re not using any oil between changes, going to high mileage oil is of little or no benefit. There are also other products you can use that don’t require changing oil type or brands.

What Additives Are In High Mileage Oil?

To know the exact name of these additives, you have to go to the manufacturer’s website. Then you can follow links to the materials safety data sheets. Once there, you’ll find some big words that I can’t pronounce and don’t care to rewrite.

The point of these additives is to aid in solving the problems caused by engine wear. These additives can’t fix worn metal surfaces, but they can help old seals and gaskets do a better job. They do this by causing them to swell a bit.

The swelling fills the gaps caused by wear, resulting in less oil getting through. This could also help increase oil pressure, and get much-needed oil to vital engine components.

Another goal of these additives is to remove engine sludge. Cold starts, short trips and other factors will cause the sludge to build up overtime. Again, removing the sludge could help increase oil pressure and reduce engine wear.

Am I Solving A Problem With My Vehicle?

Now that we know what the additives are designed to do, you need to decide if you have any of these problems. You really don’t want to cause seals and gaskets that are working as designed and aren’t overly worn to swell. If your engine’s oil dipstick doesn’t show any kind of oil usage between changes, you don’t need to make the switch.

Is your engine leaking any oil? This is easy to detect, especially if you park in the same spot every day. Just check the spot before you park and be sure it’s clear of oil. Then re-examine the spot after you’ve been parked for several hours.

Not only will this tell you if your vehicle is leaking oil, coolant, transmission fluid and other fluid leaks can easily be detected. A major oil leak needs to be dealt with by repairing the failing part, but minor seepage and leaks could be addressed by the additives in high mileage motor oil.

Is your engine burning oil? If oil is leaving your engine and not hitting the ground, it may be leaking into the cylinders. The usual result of this is blue smoke when you accelerate from a stop. It might not be a big plume, but it’s generally noticeable.

Although high mileage oil won’t repair the wear on your engine’s pistons, rings or valves, it can still help. Your valves have seals that could be worn, allowing oil to seep into the combustion chambers. As we’ve already discussed, these valve seals will swell a bit from the additives. Problem solved.

Is engine sludge really a problem? As oil ages in your engine, it can oxidize. Heat and oxygen can turn the oxidation into sludge.

If sludge is built up in oil passages, it could interfere with oil pressure and proper lubrication. Any deposits in the area of the piston rings could also be a problem resulting in that blue smoke we’ve described above.

Today’s standard engine oils already have additives to deal with sludge, but they require an engine to be warmed up to operating temperature to work properly. That’s a big part of why highway driving is so good for your engine.

The high mileage motor oils will certainly do a better job of cleaning out sludge than standard oil. Since it’s designed to go into an already warm engine with some sludge buildup, It should do a better job cleaning it out.

It Won’t Solve Your Problems Overnight. A high mileage engine that’s a candidate for this oil probably has deposits and sludge that will take more that a trip to the park after an oil change to address. Seals and gaskets will slowly swell, develop new wear patterns and perform better within one oil change cycle.

Harder deposits like those found on piston skirts and in ring lands could take a few months of driving to dissolve. After all, you don’t want this stuff to just drop off, then run through your engine for 3,000 miles.

Will it help engine noise? If the noise you’re hearing is a sticky lifter or two, high mileage engine oil may solve the problem. Sludge and buildup are a common cause of sticking lifters, especially in high mileage application.

Other Options?

Maybe you’ve been using the same oil for years, and you don’t want to make a change. There are other options that could easily accomplish the same goals as the high mileage oils. Auto parts stores generally have rows of additive products making all kinds of claims. Keep in mind, we’re looking only for products that solve a problem.

STP High Mileage Oil Treatment And Stop-Leak

STP is a long trusted name, and I’ve used more than one of their products in the past. In fact, I’ve recently used their power steering additive to treat a minor leak in my power steering system. Although the High Mileage Oil Treatment And Stop Leak should perform as advertised, it is a thicker product and will slightly raise the viscosity level of your engine oil.

Sea Foam High Mileage

Sea Foam has been around for years. Mostly used as a fuel system cleaner, Sea Foam High Mileage can also be added to the crankcase. Much like the high mileage oils, it’s a great choice for cleaning built up sludge and deposits.

It’s interesting to note that you don’t add the product with fresh oil. Instead, you add Sea Foam about 300 miles before an oil change. This prevents the opportunity of the dissolved crud to circulate through your engine for a couple thousand miles.

On the down side, there are no additives I can find to address the issue of worn seals and gaskets. Oh, and be sure to use the proper amount in the crankcase. One ounce per quart of oil is all that’s recommended.

Lucas Engine Oil Stop Leak is probably one of the best products out there for treating minor oil leaks. Although it is a thicker product, you’re not going to add it with every change. I’ve used a few of their other products with varying levels of success. Like the STP product, Lucas is also thicker than your motor oil.

These are the three names I’ve used regularly through the years, and have no problem recommending. There are dozens of other products on the market that work in the same way, and I’m sure are just as good. I’ve just not used most of them, so I can’t recommend them.

Keep in mind, if you have any kind of substantial leak, it probably needs to be addressed by replacing the seal or gasket. These products work best when the problem is caught early on.


I did my research for this article because my 07 Chevy Trailblazer has over 170,000 miles on the clock. It’s a daily driver. We also tow our travel trailer with the truck. The truck does have high miles, and that inline 6-cylinder engine earns it’s keep while towing.

The truck has no oil leaks and runs fine, but looking underneath the vehicle, I do see early signs of oil seepage. Not enough to drip on the driveway, but enough to cause the oil pan and surrounding metal surfaces to be damp.

My decision is to make the switch to a high mileage oil. I’ve yet to decide between a synthetic blend and full synthetic, but it will be one of the two. Having tried both full synthetic and synthetic blend in the past, I found the fuel mileage gains identical.

One of the reasons I’m going with the high mileage oil rather than the additive is viscosity. The oil manufacturer has the stated viscosity in mind when the oil and additives are blended. 5w-20 is what the truck originally required and I don’t want to alter that with an additive.

The other reason I’ve made this choice is because of the consistency between oil changes. The high mileage oils aren’t meant for a one time shock treatment or flush out. Rather, they’re intended to do their job over time. They’re designed with the idea that the owner will continue using the same product in the future.