How Many Miles Will A Rebuilt Engine Last?


Rebuilding an engine is a labor of love if you do the work yourself or even part of it. You choose the pistons that you want, find all the right valve train parts, and consider performance upgrades along the path. Just how long that newly rebuilt engine will last is also important and requires a bit of conversation below.

How Many Miles Will A Rebuilt Engine Last?

A fully rebuilt engine can last millions of miles if you ensure optimal maintenance and run it on full synthetic motor oil. However, it is critical that you change the motor oil when you feel it degrading and that you also replace the filter, preferably with a performance style filter.

If you’ve had to rebuild your engine after a catastrophic failure, you need to be careful about keeping up optimal maintenance on your new engine. A newly rebuilt engine is a big investment and can pay off for a lifetime if you take good care of it. Researchers have run engines over a million miles on full synthetic motor oil with no measurable wear, and so can you.

How Many Miles Can You Really Run a Rebuilt Engine?

You can absolutely run that engine for an unlimited number of miles, provided that you ensure that it is well lubricated and properly maintained. Depending on the type of engine that you own, it may have some inherent manufacturing weaknesses that limit the chances of reaching 200,000 miles, let alone a million.

Some engines are designed with planned obsolescence and will self-destruct due to minor tweaks in the design. This may be attributable to leaner parts, less durable metals, or an Achille’s Heel hidden somewhere. 

Volkswagen is well known for building planned obsolescence into its engines. The infamous 1.8T engines were designed with an oil pan that was much too small and an ultrafine oil-pickup screen. 

This design flaw inherently overheated the oil and caused coking. Coking is a hardening of the oil particles into a carbon material that literally chokes off oil flow in oil cooler hoses and that ultrafine mesh of the pickup screen. 

And the bearings weren’t very sturdy in these engines either. As a result, you would burn out the bearings and would be left with a five-hundred-pound piece of jewelry. It’s nice if you want to make some of that retro furniture but not a lot of fun if you need wheels to get around.

Honda, on the other hand, is known for building ultradurable, precision engines. Honda was always very careful to ensure that the tolerances of the engines they manufacture are within slim margins. For this reason, they developed quite a cult following for the quality and durability of their engines.

Honda engines were among the first to reach a quarter million miles or more, long before the days of synthetic lubricants. So, again, the durability of it has a lot to do with the brand of the engine and the specific model.

The Advent of Synthetic Lubricants

It was a BMW 3-Series that was run by the Mobil 1 labcoats on a dyno for a full million miles with negligible wear. Considering that they ran it in a lab at 85 mph, it probably surpassed the duty cycles and burdens that an engine may face in the real world.

Of course, they were constantly checking the quality of the oil in the lab and flushing it out whenever it was showing any signs of wear.

Nevertheless, if you have run a premium full synthetic oil, like Mobil 1 or Royal Purple, in your vehicle, you probably noticed a major difference. Of course, that is assuming that the other systems in your vehicle were rebuilt and operating like new.

When you use a full synthetic oil and a premium filter, such as K&N, it can transform an old beater into a brand-new car. You would be simply amazed at the volume of linear power at the pedal and how quickly it climbs through the power range without any flat spots if you use a premium oil, such as Elf.

And because the motor oils these days have lots of conditioners to rejuvenate the seals and to clean up the carbon, the engines are being coddled in this golden basket of limitless lubrication. You can literally feel the bearings gliding, so healthy and happy as you accelerate.

However, if you don’t change the oil after about 5k of hard driving, you will definitely feel it returning to the sluggish paperweight it was before. But this is just a reminder to go ahead and change the oil and filter again.

The reason why full synthetic lubricants are such a darling for any engine is the fact that they are pure. A fossil lubricant, that nasty dino oil they used to run, is full of paraffin waxes, contaminants, and chemicals. In fact, it is typically a blend of numerous oils having different molecular weights and properties. 

A true synthetic lubricant is made in a lab and is comprised of homogeneous particles and lots of detergents and other additives. In fact, motor oil isn’t really that much oil at all. About thirty percent of any motor oil is actually made up of an additive package to do all of the following:

  • Increase pourability at cold temperatures
  • Absorb acids produced by combustion
  • Reduce ash
  • Prevent oxidation
  • Enhance lubrication during heavy duty cycles
  • Reduce volatility

Truly, heat is the destroyer of engines and transmissions. And the uneven heating that occurs in the heterogenous dino-oil mixtures wreaks havoc on the metal parts. It creates hotspots that expand the metal beyond other parts and increase fatigue.

Let’s not forget that the pistons in an engine are practically at their boiling point when the engine is running full steam at operating temperature. Adding in the variable of hotspots is a certain recipe for disaster on a minute scale.

Cold starts are the second biggest enemy of engines. Your engine is facing premature wear every time you start it because the cylinder walls have very little lubricant and incur lots of frictional erosion when they are run from a cold start. 

Once the engine runs a bit, and the engine warms up, the oil pressure also increases and squirts out of the ports and bathes the metal surfaces with lubricant. The lubricant reduces friction heat and the wear that it causes. 

Using the right weight of oil during the winter, a thinner oil, perhaps a 0W 40, will help to reduce the frictional erosion from cold starts. This is another reason to invest in good oil if you want your engine to keep running like new for a long time.

Choosing the Right Oil Filters

The filter is nearly as important as the oil. If you use a filter that is too small, you run the risk of clogs and the oil overheating. 

If you run a cheap filter, such as Fram, it can burn out your bearings entirely. This is because Fram oil filters do not have a bypass valve. While a bypass valve is not something that you want to use, it is there as last resort protection, if the filter clogs, to sustain oil pressure.

Using an OEM (Original Equipment Manufacturer) oil filter or a performance filter, such as those made by K&N, add considerable value to your engine’s performance and life. 

Always be wary of quick lube shops that are selling a discount rate on oil changes. They may use the cheapest filters and the cheapest oils around at their base rate. They generally have some upgraded oil change package for the oil connoisseurs, but it is still better to bring your own.

Other Aspects of Engine Maintenance

Some other key factors that affect your engine are misfires. There are lots of sensors on your engine that keep it running in tune. However, the coolant temperature sensors and knock sensors, inter alia, may develop an undetectable amount of internal resistance. 

As a result, you can develop overheating and excessive knock from misfires if you do not test and, if necessary, replace these sensors every few years. This usually requires a multimeter and an ohm reading to check the internal resistance against factory specifications, a simple job if you have the right manual.

Fuel injectors can also clog up and leak. This will dilute the oil and reduce its ability to lubricate. It also wastes fuel and reduces performance. Ensuring that everything is properly maintained all helps because every little bit counts. 

Kern Campbell

I've had a passion for four-wheel-drive vehicles since I was a kid riding in the back seat of my Grandfather's Jeep Grand Wagoneer. I have owned a lot of vehicles over the years. They each have their pros and cons and I look forward to sharing my knowledge with you so you can find the vehicle that's just right for your needs.

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