Written By, Mike McGlothlin
The CAT 3116 engine is one of the smallest diesel engines Caterpillar produced itself (its smallest displacement power plants are built by Perkins or Mitsubishi). The 6.6L (402 ci), dry sleeve, inline-six made its debut in the early 1990s, and it would find a happy home in on-highway, medium duty trucks (think GMC TopKicks and Bluebird buses) as well as marine applications (namely moderate sized trawlers). Most 3116’s were equipped with Caterpillar’s mechanical unit injection system (MUI), but a small run in the late 1990s came with hydraulically actuated electronically controlled unit injection (HEUI). Though a reliable, durable engine, CAT’s 3116 isn’t without its sticking points. From the complex configuration process required to dial in its fuel system to leaking injector cups to cracked aftercoolers, we’ll cover all of this little kitty’s shortcomings below.
HIGHLIGHTS
Most Common Problems:
*Synchronizing The Fuel Rack
*Leaking Injector Cups
*Bad Aftercooler
*Leaking Oil Cooler
Most Expensive Problem:
*Defective Block
*High RPM Failures
Less-Frequent Headaches:
*Blown Fuel Injector O-rings
*Defective Block
*Bad Starter Solenoid
*Failed Fuel Transfer Pump
Problem #1: Synchronizing The Rack
Caterpillar 3116 Diesel Engine Fuel Rack Overhead Valvetrain
Most CAT 3116 engines are 100-percent mechanical, with no ECM or electronic controls to speak of. Prior to the introduction of HEUI (on 8WL versions), these 3116’s utilized MUI, or mechanical unit injection. Within the MUI system, the fuel injectors are actuated by dedicated lobes on the camshaft (as well as the corresponding pushrods). There is a low-pressure fuel transfer pump that feeds the injectors, but no high-pressure injection pump is present. Rather, an internal governor controls the fuel rack, and the fuel rack determines how much fuel flows to each injector.
Why It Can Be A Problem
3116 Cat Rack Synchronization Fuel Injector Tooling Engine Repair
Unfortunately, any time the fuel injectors require servicing or replacement, the rack has to be re-synchronized upon reassembly. This process is often called “running the rack” and it calls for specialized tooling and in-depth experience with this particular injection system in order to get it right. If injector height isn’t adjusted properly and correctly set, injection timing will be thrown off and the engine will never perform like it should. Other issues can include a stuck rack, specifically if the rack isn’t perfectly positioned on the pivot point for the fuel injectors.
Solution(s)
Tool Set Cat 3116 Injector Height Fuel Rack Adjustment Kit
Synching the rack should only be performed by a mechanic familiar with the 3116’s intricate fuel system. Just as important, the rack should only be run (and the injectors only adjusted) using the correct tooling. It’s a tedious, time-consuming process, and a job that must be carefully performed. “Close enough” won’t cut it. Trust us, for ultimate peace of mind it’s worth paying an expert to piece the overhead in your 3116 back together. Correctly performed, the fuel rack and fuel injectors will likely operate flawlessly for years before any owner encounters another reason to dig in beneath the valve cover.
Problem #2: Injector Cups
Cat 3116 Fuel Injector Cup Copper Sleeve Diesel Engine Failure
Within the CAT 3116 cylinder head, the fuel injectors sit in copper sleeves (also known as injector cups). Like a lot of diesel engines, these cups are interference fit into the head. On the 3116, the cups serve to keep coolant separate from the fuel system, and each injector tip actually seals to its corresponding cup. By coolant being present (and circulated) on the other side of them, the cups also help cool the injectors. Unfortunately, old age, extreme heat, and fuel and cooling system neglect can lead to a cup that eventually cracks and leaks.
What Happens
3116 Caterpillar Diesel Engine Cracked Injector Cup
When hairline cracks or pin holes develop in the injector cups, cross contamination between fuel and coolant can occur. And because the fuel system operates at a higher pressure than the cooling system, the cooling system becomes pressurized. In other failures, combustion gases are permitted to infiltrate the fuel system. Cracked injector cups are often misdiagnosed as a blown head gasket or (worse) a hurt cylinder or damaged piston ring. Proper diagnosis is paramount here, and it’s important to remember that injector cup failure is highly common on this engine. Never assume you’ve lost the head gasket or hurt the engine without confirming anything.
Solution(s)
Reaming Injector Sleeve Cat 3116 Diesel Engine Repair Special Tooling
New injector cups or reamed original cups are the only solutions for this rampant 3116 issue. Luckily, the head doesn’t have to be pulled to ream the factory injector cups, which cuts down on repair costs. Whether you’re completely replacing them or reaming them, the task calls for special tooling. A high temperature retaining compound is required for optimum sealing if installing new cups. Keep in mind that injector cup failure forces you into the overhead of the engine, which means you have to reset the fuel rack and reinstall and measure injector height… If you don’t, don’t expect the engine to run well.
Problem #3: “Soft” Blocks
Cylinder Bores Cat 3116 Diesel Engine New Block Crankcase
Any time engine blocks and cylinder heads are cast, there can be flaws. And if a faulty casting is used on a mass production scale, the problem can multiply very quickly, with an OEM not even discovering the problem until its engines begin to fail in the field. Such was the case with early versions of the CAT 3116, where inferior cast-iron blocks left the assembly line bound for various on-highway, equipment, and marine applications. It’s an issue somewhat reminiscent of the rampant “53” block failures that occurred on many Cummins 5.9L 24-valve ISB engines in 1999 to 2001 model year Dodge Rams.
What Happens
Cat 3116 Medium Duty Diesel Truck Engine Block Failure
Early production 3116 blocks, which were cast in France and came to be known as “French blocks,” were prone to cylinder distortion. It isn’t believed that the casting material itself was to blame, but rather improper heat treating following the casting and machining processes that caused it. These problematic early blocks typically expose themselves by consuming oil. Another common indicator is excessive blowby. Most defective blocks are discovered within the first 500 hours of operation, with many even having significant issues in the first 200-300 hours
Solution(s)
Cat 3116 Short Block Rebuild Replacement Diesel Engine Parts
In short, outside of complete replacement there is no easy or quick solution for these “soft block” 3116’s. Luckily, after being informed of the problem Caterpillar replaced most of the effected blocks under warranty, and it took place many moons ago. In that sense, it’s once again reminiscent of what happened with the ISB 24-valve 5.9L Cummins, which Chrysler/Dodge remedied as best it could back in the early 2000s by replacing its faulty blocks. With CAT’s intervention, the 3116’s soft block issue isn’t much of a concern these days. However, some early blocks may still be out there, and any early, low-hour engine should be treated with suspicion.
Problem #4: Aftercooler Issues (Marine Applications)
Cat 3116 Marine Diesel Engine Trawler Boat New Turbo
Sea-going versions of the CAT 3116 are highly common, with the engine being very well suited for trawler boats, which tend to operate at lower rpm (below 2,500 rpm). An aftercooler is employed on these engines, a heat exchanger which serves to cool down compressed intake air. In turn, the lower temperature, denser intake air allows the 3116 to turn out maximum horsepower for sustained periods of time. On many of these engines, coolant circulates through the aftercooler rather than sea water (i.e. salt water). However, the aftercooler still has its problems.
What Happens
Cat 3116 Aftercooler Diesel Engine Heat Exchanger Cleaning Maintenance
Be it due to age or maintenance neglect, 3116 aftercoolers tend to crack, and when they do water is allowed to leak into the engine. Over time, this causes fouling due to crankcase vapor ingestion. Oftentimes, when the aftercooler cracks it’s due to pin holes developing in the wet exhaust riser. Here, the riser tends to collect and hold salt water. Eventually, this leads to corrosion, followed by the development of holes, and ultimately permits salt water to leak down into the turbocharger. It doesn’t take long after that for the operator to notice a problem.
Solution(s)
3116 Caterpillar Diesel Engine Turbo Aftercooler Replacement Parts
The only permanent solution for a corroded aftercooler is a complete replacement unit, and unfortunately, they don’t usually last more than seven to 10 years. However, preventative maintenance can go a long way in avoiding aftercooler failure in the first place. Regular cleaning, inspection, and even pressure testing of the aftercooler should be performed to keep this vital heat exchanger in proper operating order. This includes disassembly and a careful, thorough look inside the aftercooler’s internal core. Regardless of condition, it’s recommended the aftercooler be replaced every eight to 10 years.
Problem #5: Leaking Oil Cooler
Diesel Engine Oil Cooler Cat 3116 Heat Exchanger Core
An older diesel engine developing an oil leak is nothing new. However, every engine seems to have its location where seepage is bound to occur sooner or later. For the CAT 3116 that spot is at the engine oil cooler. Thousands of heat cycles, exposure to the elements, and regular wear and tear can all take their toll on the oil cooler. When the outer gasket springs a leak, you’ve got oil seeping out from between the plate and cover. When the internal gasket is gone, you’ll have a coolant issue. Either problem warrants a complete reseal.
What Happens
Cat 3116 Diesel Engine Oil Cooler Failure Replacement Part
The oil cooler itself rarely outright fails. Instead, the O-rings fail due to old age, corrosion, and/or becoming brittle. In other cases, when the oil cooler has just been replaced or resealed and an oil leak develops, it’s usually the result of an O-ring becoming twisted or rolled during installation. It’s also not uncommon for a new gasket to become damaged during assembly. More of a nuisance than an end-game type failure, some operators wait until the leak worsens and can no longer be ignored before addressing the issue.
Solution(s)
Cat 3116 Oil Cooler Gasket Kit Diesel Engine Repair Seals
A reseal will cure most leaky oil coolers on the CAT 3116, but when the job is undertaken the oil cooler’s internal core should be given a thorough once over. Aftermarket oil cooler gasket kits can be had for less than $40 and should include both the outer and internal gasket, as well as all required O-rings. A complete replacement oil cooler can be obtained for $120 to $400, depending on where it’s sourced (and who it’s sourced from). Although take-off, secondhand oil coolers can be found on the cheap, there is no guarantee how long they will last. Buy at your own risk.
Problem #6: Injector Tip O-rings
Fuel Injector Nozzle O-ring Failure Cat 3116 Diesel Engine
There are two locations for O-ring seals on mechanical versions of the 3116’s fuel injectors. They are labeled and known as “upper” and “lower.” While the upper O-ring is a permanent seal, the lower (a Viton rubber O-ring) serves as a carbon dam. Its purpose is to provide a seal during initial break-in that lasts long enough for a carbon dam to be established at the tip of the injector. It’s expected to deteriorate, but by the time it does an efficient seal is presumed to have been established within the injector tip bore.
What Happens
Cat 3116 Fuel Injector Nozzle O-ring Deterioration Combustion Leak
Although it’s expected that the lower O-ring will deteriorate, CAT didn’t count on it causing problems. And while lower injector O-rings don’t always cause trouble, when they do the operator knows it immediately. When this failure strikes, combustion gases can escape and enter the injector bore. Hard starting and excessive smoke are well-documented indicators that a lower injector O-ring has allowed combustion to escape a cylinder. That means you’re pulling the injector(s), solving the problem, and then re-running the injector height process—as well as re-synching the fuel rack—before it’s all said and done.
Solution(s)
MUI Mechanical Unit Injection Cat 3116 Fuel Injector Replacement
Depending on the engine you’re dealing with and, more importantly, which era (and type) of injector cup you’re working with, more than one solution exists. For starters, there are updated injectors which don’t require the lower O-ring and allow for more accurate torquing of the injector (i.e. less chance of combustion gases getting into the fuel rail). Then there are special injector cup reaming and seating tools, which can rule out the need for the lower O-ring at all. Just don’t forget that, on top of that, an injector tip bore cleaning tool should also be used any time an injector-related issue arises (and the injector has to be removed).
Problem #7: High RPM
Chevrolet Kodiak Truck Tachometer Gauge Cat 3116 Diesel Engine
In general, most diesel engines don’t enjoy (or even thrive) at high engine speed. In fact, in addition to their low-rpm operation producing the kind of torque we need to move heavy loads it’s their sub-2,500 rpm operation that helps keep them alive for so long. That, and most compression ignition power plants are equipped with heavy, forged-steel components that don’t particularly like to spin fast. Without a doubt, torque production is what the working class needs from a diesel engine, not high rpm or horsepower.
What (Often) Happens
Connecting Rod Failure Piston Cat 3116 Diesel Engine Damage
Though it can effect on-highway engines that see elevated rpm, most high-rpm problems associated with the CAT 3116 come from the marine sector. In sea-going vessels, and especially higher horsepower versions (ex: 350 hp vs. 300 hp), 3116’s are sometimes subjected to 2,600 rpm or more. High rpm failures and issues related to an engine living at elevated rpm are rarely minor headaches. Valvetrain issues and spun main or rod bearings can be the result in a high operating hour 3116 that’s seen regular operation at high speed.
Solution(s)
Trawler Boat Cat Diesel Power 3116 Engine Marine Vessel
Avoiding high rpm is the best way to dodge engine-related failures on the CAT 3116. More specifically, keeping the tachometer at 2,300 rpm or lower will go a long way in ensuring the engine returns the type of durability you’re after. Throw in regular oil and filter changes (oil, fuel, and air), along with all other maintenance the book calls for, and the 3116 will be highly reliable. Especially in marine applications, the 3116 should never be used to win any races. This is a workhorse engine, not a thoroughbred.
Problem #8: Fuel Shutoff Solenoid
Caterpillar 3116 Fuel Shutoff Solenoid Power Terminals
Old-school, mechanical diesel engines such as most CAT 3116’s make use of a fuel shutoff solenoid. This simple part is used to both start the engine as well as shut it down. On the 3116, the fuel shutoff solenoid is located at the fuel transfer pump. It’s equipped with a power terminal and a ground terminal. With the ignition keyed on and 12-volt power being supplied to the shutoff solenoid, the coil is energized, and fuel is allowed to flow. Turn the ignition off and the coil is de-energized, stopping fuel flow, and killing the engine.
What Happens
Replacement Fuel Shutoff Solenoid Cat 3116
On the 3116, the fuel shutoff solenoid is notorious for failure. Oftentimes, the plunger seizes up, usually in the closed or off position. When this happens, no fuel is supplied to the engine, and it won’t run as a result. Other times, the shutoff solenoid no longer receives power, be it due to the solenoid failing, a coil issue, or a poor connection. In this scenario, the shutoff solenoid will default into the closed position and wont’ permit fuel to flow to the engine. Shutoff solenoid issues are an all-or-nothing proposition. It either works or it doesn’t—and you’ll know immediately when it stops functioning.
Solution(s)
Cat 3116 Diesel Engine Fuel Shutoff Solenoid Terminal Spanner Wrench
After locating it, a failing fuel shutoff solenoid can be replaced fairly easily. But before your fork over the money for a brand-new unit, it pays to perform a proper diagnosis on the piece. Ensure the wiring is in good shape and verify that the solenoid is still receiving 12-volt power. Once it’s confirmed dead, a replacement can be sourced for between $60 and $200 in the aftermarket. Just make sure you source the part from a reputable supplier. Of course, grabbing one from the local CAT dealer will cost more, but you can rest assured that it will be a genuine replacement component.
Problem #9: Dropped Valves
Cat 3116 Diesel Engine Piston Carnage Dropped Valve Top End Failure
Few top-end engine failures can spell disaster quite like a dropped valve can. When the valve seat (or valve itself) falls into the cylinder below it with the engine running (i.e. the crankshaft still forcing the connecting rod and piston assemblies up and down within their respective cylinders), you’re going to get piston-to-valve contact. It typically obliterates the valve, damages the head enough to force significant repair or even replacement, and can even crack the piston that received the metal-on-metal contact. Unfortunately, there is no heads-up on a failure like this. By the time it happens, it’s usually too late to avoid a major repair.
Why It Can Happen
Cracked Cylinder Head Cat 3116 Diesel Engine Problem Repair
Cracked valve seats and dropped valves aren’t every CAT 3116’s fate, but if the engine is abused, namely in the form of high rpm operation, the chances of it occurring increase. Other notorious contributors are blown head gaskets and overheating, which can cause hairline cracks to develop in the cylinder head. Like most inline-six engines, cylinder number 6 is the furthest away from fresh air and the last to receive coolant. Guess which cylinder sees the most dropped valve scenarios… A maintenance neglected 3116 that’s regularly treated to elevated rpm is most likely to experience this type of failure.
Solution(s)
Cat 3116 Short Block Rebuild Replacement Diesel Engine Parts
As mentioned, there are no warning signs prior to a dropped valve scenario unfolding. There is no way to tell if a hairline crack is present in the cylinder head, or if one is protruding into the valve seat area(s), and there is no way to know if the excessive coolant temp you just saw damaged anything. However, you can avoid this as best as possible if you make certain your 3116 never experiences an overheat, its operating rpm is limited to 2,500 – 2,600 rpm or less, and that it’s subjected to regular maintenance and inspections.
Problem #10: Fuel Transfer Pump
Used Transfer Pump Caterpillar 3116 Diesel Engine Component
Due to utilizing camshaft-driven, mechanical unit injection (MUI), the 3116 doesn’t have a traditional high-pressure injection pump. However, it does have a transfer pump, which effectively supplies low pressure diesel to the fuel injectors. The pump is mechanically driven via the governor drive on the front of the engine and is actually integrated into the governor housing itself. In good working order, the fuel transfer pump produces roughly 20 psi at idle, and more than 50 psi at operating rpm. The pump itself is usually pretty reliable, but unfortunately every part has a lifespan.
What Happens
Cat 3116 Fuel Transfer Pump Governor Housing
A myriad of problems can stem from the transfer pump and its surrounding lines, fittings, and O-rings. As for the pump itself, a weak internal spring can cause a drop in fuel pressure and rough running conditions. Excessively worn check valves, suction side air leaks, and return side air leaks can all bring about the same symptoms. On Chevrolet Kodiak and GMC TopKick applications specifically, the fuel lines spanning from the tank and that tie into the lines at the engine are notorious for O-ring failure within the plastic fittings they reside in. A failure here will allow air to enter the fuel supply system.
Solution(s)
Aftermarket CAT 3116 Replacement Diesel Fuel Transfer Pump
Proper diagnosis is important with any issue believed to be transfer pump related. On the 3116, it pays to start by changing fuel filters. From there, the suction side of the fuel system should be inspected for air leaks, followed by the return side for the same issue. Then the check valves should be ruled out prior to moving on to the transfer pump itself. As for the latter, it can be rebuilt by sourcing an aftermarket repair kit and performing the work yourself. These kits typically retail between $100 and $150. The other option is to start over with a new transfer pump, which could run you $235 to $580.
