Cummins M11 Life Expectancy: Is The M11 Cummins a Good Motor?

Engine longevity is a must. No one wants to pay a large sum of money only to have the engine fail within the first year. To reach that long lifespan, you do need to maintain your new engine and make sure it is treated properly over the years you own it.

The life expectancy of this motor is roughly 850,000 miles. That is if you take good care of it. Plus, the M-11’s reputation is that it is one of the best made by Cummins in a long time. You shouldn’t go wrong when you buy an RV with an M-11 under the hood.

To learn more about this motor, just continue to read our article. It has the information you want to know about so you can make an informed decision the next time you are in the market for a good engine. Take a few minutes to see how this content can help you.

Cummins M11 Life Expectancy


When it comes to motors, longevity can be hit and miss. There will be times when a previous owner got the best of its life and then sold it. The next owner may get all the problems.

Usually, you are looking at getting 800,000 to 900,000 miles out of an M11 engine. But as we said, that is hit and miss due to so many mitigating factors. Some people bought a used one at 650,000 and then doubled that amount during their ownership.

Others have given up the ghost well before the minimum 800,000-mile mark. Part of that lack of life is due to bad maintenance habits, faulty parts, or it slipped through quality control unnoticed.

Chances are that if you take good care of this motor you may be able to reach the 1,000,000-mile mark without too much going wrong. Make sure not to overload your RV so it does not have to work too hard throughout its lifetime.

Taking care of an engine is more than just changing the oil and filter every so often. You have to look at the indirect factors as well to make sure your M11 lasts.

Is The M11 Cummins a Good Motor?

That is the reputation. One owner called it one of the best engines made by Cummins. Judging from the reports we read, it seems to be just that. It has its flaws but overall you can count on this motor for at least 800,000 miles.

A few other owners said that it was slightly underpowered when given too much weight to haul. But that flaw did not stop the M11 from being reliable. It never left owners stranded when going over steep mountain passes with a full load. It may have been a slow climb but it made it over every time.

Other owners called it a very sound engine and that is what you want under the hood. You want an engine that does not give up on you or you to have to worry about every mile of the road.

The M11 should take those worries away as long as you take good care of it. Plus, it will pull 80,000 pounds but it is better at 70,000 or less. Even if it has been ‘in-framed’ it should be as good as it was before that repair work.

It is worth checking out and taking it for a test drive.

When Did The Cummins M11 Come Out?


This motor was the successor to the L10 engine Cummins produced. We do not have an exact year right now but it is said that this engine was first made in the mid-80s and production stopped in the late 90s.

The design of this motor is an 11 liter, 6 cylinders inline model that seems to have all the best parts put into it. This engine is so good that there are companies that are built around rebuilding, or as they say remanufacturing, these motors and making them useful again.

From what we have read, rebuilt M11s are as good as the original motor and parts. They seem to last a long time with many reaching that 1,000,000-mile mark.

The key is not when they came out but how long they will last. It is an older motor proving that age does not mean a lack of skills. It is all in how you take care of the motor that counts.

Make sure to check to see if any rebuilding has been done or not. That will give you an idea of when or if you may have to do it yourself.

Common Cummins M11 Problems

One of these problems may be that no codes can be found or that the data ports do not respond when connected to the scanner. This problem may be due to loose connections or wiring, broken wires, or a failed part.

It showed up when the motor started to skip and blow white smoke out of the exhaust system. It is not sure what caused the second problem. That problem may be caused by over-fueling.

Another issue is that the wire harness may need replacing at some point in time. It does wear out especially going over 600,000 miles. Replacing the wire harness can get expensive. Some people are looking at paying over $600 to repair theirs.

Replacing the wire harness is expensive as there are a lot of wires involved, plus those wires hold other wires so it can take between 6 to 8 hours to do the replacement work.

A less expensive repair may be the injectors. They can go bad on you over time. It may also be easier and faster to fix than the wire harness. Also check the O-rings on the filter to see if one is missing, gone bad or there is one too many.

That can cause you some problems as well. Another easy repair job and not as costly. Sometimes you just have to look at the simple sources first to make sure you do not overspend on repairing the motor.

Checking the simple sources first may save you a lot of time as well. You will be back on the road before you know it.

Cummins M11 Reviews


We have checked RV discussion forums, heavy-duty equipment discussion forums and trucker forums, and more. So far not one person or owner has said that the M11 is a bad motor or junk and to stay away from it. There are no blatant negative reviews that we were able to find.

We also checked the Cummins Dodge discussion forum and again, not one severely bad word about the motors. The worst that anyone said was that it was a small motor that could not handle 80,000 pounds at highway speeds.

The positive reviews were ‘it is a good little engine’, ‘it is a sound engine’, ‘a great little motor’, ‘reliable’, and ‘sound’. That is good news as no one is over-selling the motor. They know it is not a perfect engine and it has its share of flaws. But those flaws do not overshadow all the positive aspects.

One fleet owner said all their trucks at one time had the M11 and they all went over1,000,000 before needing to be rebuilt. He also said that they were the best engines they had owned for fuel efficiency as well as easy to work on and get parts.

That is another key to helping your motor last a long time. When it is easy to work on and get parts for you should be able to keep the motor at optimum levels all the time.

It is just that some parts are more complicated than others and can cost a lot to replace because the replacement takes a lot of time to get it correct.

Complete Cummins M11 Specs

We took the following information from two different sources with one being a manual for the M11. You can find this information here and here.

First link: No. of cylinders 6 Displacement 10.8 l Layout Inline

Tier Min. Tier 2 Tier Max. Tier 3 Bore 125 mm Stroke 147 mm

Second link:

Dimensions approx: Length 1290 mm Width 973 mm Height 1142 mm

Weight approx: 940 kg

Compression ratio commonly at: 15.9:1 - 16.0:1 but varies with CPL

Displacement: 10.8 liter, 661 CID

Bore: 4.921 in, 125 mm

Stroke: 5.787 in, 147 mm

Arrangement: 6 Cyl In-Line, naturally aspirated and turbocharged

Power: 280-330 hp @ 1800-2000 rpm

Cummins M11 Main Bearing Bolt torque

Step 1 = 68 Nm, 50 lb.ft

Step 2 = 142 Nm, 105 lb.ft

Step 3 = 210 Nm, 155 lb.ft

Step 4 Loosen all;

Step 5 = 68 Nm, 50 lb.ft

Step 6 = 142 Nm, 105 lb.ft

Step 7 = 210 Nm, 155 lb.ft

Cummins M11 Cylinder Head Bolt torque

32 Bolts

Step 1 = 136 Nm

Step 2 = 217 Nm

Step 3 = +90 degrees

7 Bolts (fuel pump side)

Step 1 = 47 Nm

Cummins M11 Connecting Rod Bolt torque

N.B. Same as for Main Bearing Bolts

Step 1 = 68 Nm, 50 lb.ft

Step 2 = 142 Nm, 105 lb.ft

Step 3 = 210 Nm, 155 lb.ft

Step 4 Loosen all;

Step 5 = 68 Nm, 50 lb.ft

Step 6 = 142 Nm, 105 lb.ft

Step 7 = 210 Nm, 155 lb.ft

You can read the manual at the second link or download it. But you have to sign in first to gain access to it. Also, you will find some nice diagrams of the engine and the cylinder head on the second website.

Cummins M11 Dimensions


As you can see by the dimensions above, the listed size is in the metric system and say Length 1290 mm by Width 973 mm by Height 1142 mm. These numbers translate into 51 inches in length approx. or 50.787401575 specifically.

For the width, you are looking at 38 inches approx. or 38.307086614 specifically. Finally, the height is 45 inches approx., or 44.960629921 specifically.

It will be up to you to use the appropriate size if you are installing an M11 inside your engine compartment. Rounding up is when the numeral is 5 or over and rounding down takes place when the numeral is 4 or lower.

This is a good-sized motor that should last you a long time when you take care of it. We know we keep saying that but we want to drive home the point that taking care of your engine is vital. It will help you determine how long it will last and what you can expect down the road when it gets even older.

How Many HP is M11 Cummins?

There is enough HP in this engine to get you where you are going. Depending on the model number you can expect to see 280 to 330 HP @ 1800 to 2000 RPM. It should be enough power to get your RV over steep mountain passes without any difficulty.

This motor is also said to be underpowered if you are trying to haul 80,000 pounds over those same mountain roads. It will get you over the peak eventually but it may take some time as you will not be going that fast.

However, if your load is at least 10,000 pounds lighter, you should have a better and faster time over those steep roads. Most RVs do not get that heavy so you should do fine when you are not traveling through the midwestern states like Kansas.

At any rate, this is a sound engine or a great little engine that does provide good fuel economy. What you lose out in power you should make up in mpg.

How Much Does a Cummins M11 Engine Weigh?


Again, as you can see by the information above, the weight is given in metric measurements. This is not hard to figure out as 2.2 pounds equals 1 kilogram. The total weight in kilos is 940.

That figure translates to 2072.345 pounds. It is not a lightweight at all and you will need lots of help and heavy chains to lift this motor out of the engine compartment to work on it.

According to Cummins, this motor should be able to haul up to 80,000 pounds and still maintain a speed of 62 mph. However, Cummins makes many versions of the M11 and you should look at the specs on all of them to make sure you are getting the best option available.

This link gives you an idea of what you should expect from the different M11 engines. It is from Cummins and it lays out more specs that help you make an informed choice when looking at an RV with this motor inside.

Cummins M11 Rebuild Cost

One thing is for sure, your bank account will take a hit when you go to rebuild this motor. One estimate that we saw was over $13,000. The same company posted a $14,500. Just look up the Big Bear Engine Company to get the total costs and all that is involved in their rebuilding options.

ATL Diesel has rebuild kits for a lot less. These kits range in price from $1295 to just over $5000. HD Kits are going to be in the same price range but the most expensive we saw was priced at $2500. There may be other kits beyond the landing page which may cost more or less.

There are many other companies doing this type of work and a good internet search will help you find a good company near you. Keep in mind that if you want Cummins parts, you are going to spend a lot more money than those kits sell for.

You are looking at paying between $8000 and at least $12,000. No matter if you are doing it yourself or you have a trained mechanic do it at his shop, it will take a long time to do this project.

The wiring harness alone takes between 6 to 8 hours to get it done right. This gives you an idea of how long it will take you to complete the job. The exact time frame depends on many factors including how much spare time you have or how busy the mechanic is.

Some Final Words

When you buy an RV with an M11 engine inside, you are getting a good motor that is reliable, sound, and perfect for most RVs. That is if the previous owner took care of it.

If they didn’t, it is still a good motor but you will have to pay a lot of money to return it to top shape and perform like you expect it to perform. The key will be that you take care of it so you can pass that 1,000,000-mile mark without major repairs.