Caterpillar 3126 Engine Problems, Reliability, and Reviews
Good engines have bad moments. No matter how well an engine is made, there can always be some minor or major flaw that ruins its reputation. You won’t get 100% performance, reliability, or longevity out of the best motors all the time. There will be those few that slip[p through the cracks and give their owners fits.
There have been major problems like dropped valves and cracked blocks but for the most part, RV owners have been able to avoid facing those problems. Caterpillar did take care of those early problems and the 3126 should last you a long time with relatively few issues to deal with.
To learn more about this problem just continue to read our article. It goes through those problems and lets you know how reliable this engine really is. The 3126 should be a reliable engine for most RV owners and replacing the engine any time soon should not be on your schedule.
Cat 3126 Engine Problems
What is a 3126 Cat Engine?
This is a diesel motor that is a bit of a workhorse. However, it is built for medium and light-duty, not heavy-duty applications. The owners that do use this motor for heavy-duty will experience far more problems than the owners who do not.
The 3126 is a 7.2 Liter that produces 330 HP at 2200 RPM. It comes with the early edition of ACERT which is a fuel/air management system. Also, it is an inline 6-cylinder motor that also produced 420 lb-ft @ 1440 RPM of torque.
The early versions were not as powerful as they only produced 175 HP at 2400 RPM. This engine was first introduced in 1997 with the 3126B coming out in 19989 and the 3126E upgrade was introduced in 2002.
This motor was often coupled with the Allison 2000 or 3000 transmission and as new models came out Caterpillar made upgrades to solve many of the problems that existed in the original version of this motor.
While you can get upgrades to tow more weight, this motor was designed to tow up to 9000 pounds. The owners with the most problem with this engine were those who owned boats and engaged them in heavy-duty activities.
Is a Cat 3126 a C7?
It depends on how you look at it. The C7 was developed and released in 2003 and only lasted till 2009. It was more of a replacement for the 3126 than an upgrade to that motor.
This was more of a heavy-duty motor that shared the same configuration as the 3126 but its upgrades made it a different motor. This newer motor came with the HEUI fuel injection system that made multiple injections at metered rates.
Other upgrades helped to reduce emissions. This motor was released just before the new regulations took effect in 2004. Also, the valve train is different in the C7 than in the 3126.
Then gears in the front gear train had fewer teeth but made stronger than the 3126. Then the oil pump and water pump are larger in the C7 than in the 3126. These changes were made so that the 3126 and the C7 engine parts could not be interchanged.
There were other changes made so technically, you cannot call these two engines the same. They are different motors with the C7 supposed to be the best engine in Caterpillar’s lineup.
That did not work out as production stopped in 2009. The biggest problem with this engine was that 50% of the engines built were not going to function after 500,000 miles without a rebuild.
Is a Cat 3126 a Good Engine?
In spite of its reputation and all the bad mouthing going on about this motor, this is a very good engine to have in your RV. Despite all the complaints, there are still tens of thousands or more on the road doing the job they were designed to do.
Yes, the 3126 is a good engine but that does not mean everyone is going to get a perfect motor. Some owners who used their 3126 for heavy-duty applications have faced a lot of problems and have been outspoken about those problems.
But this motor is designed for medium and light use. Over the history of this motor, only 1 RV owner had to have their engine replaced at 69,000 miles. The reason behind the bad mouthing is that the 3126 was based on the 3116 which did have its share of problems.
Many of the complaints were attributed to the 3126 but that motor did not create the problem. Caterpillar did fix the drop valve issue and the weak block problem in later versions of the 3126.
But again, too many owners put the engine into heavy-duty tasks which the 3126 was not prepared to handle nor had the power to handle those duties. We have not come across many complaints made by RV owners who have this engine in their RVs.
Caterpillar 3126 Engine Problems
In the beginning, the 3126 had a cracked block and dropped valve problem. Since the engine was still under warranty, the company recalled the motors and fixed the problem. Later editions of the 3126 did not have these two issues to deal with.
1. Cylinders- this engine came with machined into the block. This is not the wet sleeve style and this caused a lot of problems as you had to remove the engine to work on those cylinders.
Once you did that, you had to bore out the cylinders, then have the new sleeves pressed in.
2. HEUI Fuel System- this is called a minor issue and it revolves around the oil pressure. The 3126 had dual oil pumps to keep the oil pressure at 1500+ and this feature helped you get better cold starts, the engine ran quieter, produce better fuel efficiency, more power, and fewer emissions.
However, if you did not keep the oil pressure up then the HEUI system would act up and problems would ensue.
3. The ECM- this is the computer monitoring system and like all other parts in an RV, it can fail on you. The cost of repair can run you about $3200 or more depending on your mechanic.
But a rebuilt ECM only costs about $1000 and you can replace it yourself. One other problem you may face eventually is that these engines may lonely last to about 200,000 miles before needing to be rebuilt.
That may be a high figure for some RV owners as they do not use their RV that much. But for those that do, those 200,000 miles can come quickly and along with it, a high repair bill.
Cat 3126 Engine Reviews
You are going to find that most of the negative complaints will be coming from the marine and heavy equipment industries and not the medium or light-duty industries.
The reason for this is that many boat owners, where many of these engines went, used to push their 3126 to 2800+ RPM. That is well over the 2200 red line. Those boat owners did this to get their boats up on a plane and this was not the intended duty of the 3126.
Many heavy truck or equipment operators did something similar but their activities just put the 3126 into applications it was not suited for. Also, you will hear about the bad blocks in the early versions but actually, those bad blocks belonged to the 3116.
The blocks for that engine were produced by a French factory and there was a problem with their casting. As for the good reviews, most reviewers were not over-excited about the performance of this engine but they had solid positive comments about the 3126.
They were all happy with the performance they got and said that if you did proper maintenance there should be little to no problems. Many of these owners have had the 3126 for years and did not experience any major issues with their motor.
Caterpillar 3126 Engine Reliability
The word is that this is a very good and reliable engine IF, you do not put it to work in the wrong application. What that means for RV owners is that if you do not have a lead foot, your motor should perform well and last a long time for you.
The key is to make sure you do proper maintenance and keep the oil pressure up above that 1500 PSI level. This should not be a problem for most RV owners. Freightliner has said that the early HEUI system was much better than the newer system so be careful with that.
Except for the heavy-duty applications, we have not come across any engine in an RV that has not been reliable-- save for one. There will be individual motors that may have a flaw in them but that one bad apple does not spoil all the rest.
One RV owner replaced his engine before it got to 70,000 miles. But that was an exception as tens of thousands of RV owners with this engine have had little to no problem with the motor.
If you take care of the engine and do not push it beyond its capabilities, then you should have no problem for a long time.
How Many Miles is a Cat 3126 Good For?
When compared to its competitors, the 200,000-mile lifespan is relatively short. But both the 3116 nor 3126 do not have a greater lifespan than this. You may find individual motors going beyond the 200,000-mile mark.
But that will be due to the good maintenance program and the fact that those engines were kept in their medium to light duty range.
You may hear stories about these engines not lasting that long but the owners most likely wanted a certain level of performance which the engine was not made to do.
In other words, user error was the main problem with these engines. This is a common problem no matter which engine you own. If you make the engine perform above its capacity, then you can expect it to quit on you sooner than its life expectancy says.
That 200,000-mile life expectancy is a good number for many part-time RVer owners. They do not go out that much and having the engine last a long time for them make their RV experience more enjoyable.
For those who use their RVs full-time and drive all over the country, that 200,000-mile mark may come too soon. Once it does you have to watch out for when the motor says it is time to rebuild it.
There may not be a warranty available to cover the high cost of repair.
Does a Cat 3126 Have Liners?
According to our research, no the 3126 does not have any liners. The cylinders are machined into the block which makes them difficult to repair. With normal wet sleeves, these can be pressed out, and then a new liner can be pressed in without too much trouble.
Because the cylinders are machined in, you have to remove the engine from the vehicle and then bore the cylinders out before inserting new sleeves. Caterpillar does make a kit to help you with this change over but you still have to remove the engine from the vehicle.
This design has created a large repair bill when you want to rebuild your engine. While you may not have to face this as an RV owner, if you put a lot of miles on each year, then you will need to set aside some money to cover the repair.
If you had a problem with your cylinders, then the source is generally poor oiling. Some owners do not keep up with the maintenance which can then lead to parts wearing down faster than they should. Watch your oil and make sure the pressure stays high and above 1500 PSI.
Cat 3126 Dimensions
The dimensions for the 3126B are as follows: 42.5 inches long by 31.4 inches wide at its widest point by 34 inches high. It held roughly 4.75 gallons or roughly 19 liters of oil.
Its bore was 4.33 inches and its stroke was 5 inches. Its compression ratio was 16:1 and the HP ranged between 175 to 330 at 2200 RPM. Then the cooling system needed 3.5 gallons of coolant to function correctly.
Those are the basic specs for this motor. The motor was designed for RV, ambulances, buses, marine applications as well as construction and agriculture. These are usually medium to light-duty applications and should not be used in any heavy-duty performance tasks.
Some other problems that different owners experienced are as follows-- including cracked cylinder heads (mostly CAT 3116 models), crankshaft failures, over-fueling, lack of oil pressure, and scored pistons/liners.
You may run across other complaints but those may be individual issues and not common ones. Different owners will experience different issues depending on their driving and maintenance habits.
Keep in mind, the 3126 was the replacement for the 3116 and has more in
common with that engine than with the C7.
How Much Does a Cat 3126 Weigh?
According to the manual for the 3126B, this engine weighed 1295 pounds. That weight included the fly wheel. The 3116 weighed 1500 pounds so you gained some advantage by going with the 3126.
As for maintenance, some 3126 engines took 22 quarts of oil and this oil should have been changed every 6000 miles or every 6 months. The fuel filter needed to be changed every 15,000 miles or every 6 months.
The coolant gave you a little more breathing space as it only needed to be changed every 200,000 miles or 2 years. Finally, the transmission fluid and filter should be changed every 30,000 miles.
To keep up the maintenance on this engine, you can create a schedule so you can keep track of the last time you replaced all the fluids and filters. The schedule should help you find the perfect time to make these changes.
There should be some leeway in the mileage or time requirements. You may be able to do it a little later and a little sooner than those amounts say. But not too much difference. Play it by ear and pick the best times for you and your location.
Some Final Words
The 3126 did have some faults but many of those problems were inherited from the 3116. In fact, the 3126 is not guilty of many of the problems it has been accused of having.
This is a solid engine that was well-built. The many thousands of engines still on the road today are physical evidence for that statement. If the engine was bad, Caterpillar would have recalled them all and you would see a broader negative review response than just the marine industry.
Just take care of your 3126 and you should not experience many of the problems that other owners have experienced. With a good maintenance program, your 3126 may last for 300,000 miles.
