Written By, Mike McGlothlin
Caterpillar’s 3066 is a dry sleeve, cast-iron block and head, inline-six diesel engine displacing 6.4L that debuted in the early 1990s. Immediately, it became a hit in heavy construction equipment, especially in excavators. The CAT 3066 is renowned for its durability, with many going 15,000 hours before requiring a major overhaul. It was produced by Mitsubishi in Japan, is also identified as a “6K” and “S6K-T” (depending on the specific model), and enjoys worldwide use in the construction, power generation, and marine sectors. Of course, it has its share of shortcomings, too, with overheating, a leaking front cover and rear main seal carrier, and water pump failure topping the list. Less frequent headaches include wet stacking and various fuel system issues. We’ll spell all of them out for you below, as well as provide a permanent remedy for each.
HIGHLIGHTS
Most Common Problems:
*Overheating
*Leaky front cover
*Failed water pump
*Leaking rear main seal carrier
*Bad fuel primer
Most Expensive Problem:
*Overhaul (old age)
*Injection pump replacement
*Injector replacement
Less-Frequent Headaches:
*Wet stacking (generators)
*Fuel injector failure
*Injection pump issues
Problem #1: Overheating
Caterpillar Excavator Coolant Temperature Gauge Engine Overheat
One of the most frequent headaches an operator of a CAT 3066 can experience is overheating. Oftentimes, it’s up to an alert and experienced operator to shut the engine down before coolant is allowed to boil over and potentially cause significant damage. As in many Caterpillar applications, excessive engine coolant temp can lead to head warpage, a blown head gasket or, worse, in-cylinder damage. Unfortunately, with the CAT 3066 primarily being employed in construction equipment—equipment that typically gets worked hard in hot, dusty environments—overheating is the most common problem it faces.
What Happens
Cat 3066 Diesel Engine Radiator Fan Shroud
Especially in aging construction equipment, a plugged radiator is an exceptionally common reason for engine overheating. Any time the radiator core is obstructed or denied the airflow it needs, it doesn’t take long for the engine to run warm. Additionally, an overheating hydraulic system in a piece of heavy equipment can place increased stress on a 3066, causing ECT to rise. Other common culprits behind overheating include a failed (or failing) water pump, a stuck thermostat, an engine fan that fails to engage (or that is installed incorrectly), and low coolant level—be it due to a leak, a blown head gasket, or even a blown freeze plug.
Solution(s)
Cat Extended Life Coolant Diesel Engine Antifreeze
The best medicine here lies in preventative maintenance. Regular inspection and routine cleaning of the radiator, cooling stack, ensuring the engine fan is installed correctly and operating as it should, keeping tabs on coolant level, and looking into the cause of any leak at the time it’s noticed will go a long way in avoiding an overheat scenario. And any time the engine’s water pump gets replaced, take the extra step of starting over with a new thermostat and fresh coolant. Of course, make certain the operator keeps a watchful eye on engine coolant temp in the cab, along with all other vital parameters, and promptly shuts things down if anything gets out of hand.
Problem #2: Leaking Front Cover Gasket
Caterpillar 3066 Heavy Equipment Turbo Diesel Engine
Father Time, and especially thermal cycles, takes its toll here. In that sense, there’s nothing new, as most engines experience a leak or two at some point in their tenure. Add to that the fact that NVH is high on diesel engines, and when you combine constant vibration with aging seals, you’re bound to face fluid loss from somewhere at some point. On the CAT 3066, the place where you’re most likely to encounter a leak is where the front cover mates with the block. Here, a significant oil leak can develop.
What Happens
3066 Cat Diesel Engine Repair Front Cover Oil Leak
After thousands of heat cycles (and thousands of operating hours), CAT’s 3066 tends to develop a leak where the front cover seals to the crankcase. The leak will begin to weep initially and then get progressively worse with time. It’s a problem that can occur as early as the 6,000-hour mark, while other 3066 engines go twice that long before developing a leak. Unfortunately, it’s more of a nuisance or an eyesore than anything else, which means this notorious oil leak often goes unaddressed until it can no longer be ignored.
Solution(s)
Front Cover Gasket Set CAT 3066 Diesel Engine Parts Repair
The severity of the oil leak often dictates exactly when the owner pulls the trigger on performing the front cover gasket repair. However, once the gasket begins weeping, it’s only a matter of time before addressing it becomes mandatory. Depending on the operator’s budget (and possibly the hours on the engine), it may be time to pursue a complete overhaul at the same time. It goes without saying that this trouble area should always be checked any time related repairs force a mechanic to venture inside the front of the engine.
Problem #3: Failed Water Pump
Water Pump Failure Cat 3066 Diesel Engine Coolant Overheat
If you want to see how quick a piece of equipment can overheat, try running it with a non-functioning water pump. A failed water pump is one of the most well documented problems a CAT 3066 can face, and it oftentimes goes unnoticed until coolant level drops or an excessive ECT alert sounds. In its early stages of failure, the water pump will attempt to get the operator’s attention by leaking from the integrated weep hole. If that goes neglected, the water pump can check out in catastrophic fashion.
What Happens
Water Pump Weep Hole Coolant Leak Caterpillar 3066 Diesel Engine
The biggest point of concern on the 3066’s water pump is its impeller breaking down after coming into contact with poor coolant quality. Water pumps equipped with a brass impeller tend to corrode when exposed to coolant with low glycol content. When glycol is inadequate, the corrosion inhibiting quality of the antifreeze is compromised and the brass material of the impeller begins to break down. After being exposed to low glycol coolant for an extended amount of time, significant pitting and even rust can be found on the water pump’s impeller.
Solution(s)
Cat 3066 Replacement Water Pump OEM Diesel Engine Parts
A brand-new water pump, and all the labor that the repair entails, is the only solution for a failed water pump. However, determining the cause of the pump’s failure is of equal importance, so as to keep it from happening again. This means inspecting the impeller on the failed water pump for blade pitting and thinning. New coolant should also be part of any water pump repair on a 3066. Always run the proper, CAT-specified antifreeze to eliminate any issues with glycol levels going forward.
Problem #4: Leaking Rear Main Seal Carrier
Cat 3066 Diesel Engine Oil Rear Main Seal Leak
No different from other aging engines, oil leaks are frequently encountered with the CAT 3066. In particular, rear main seal leaks are nothing new for diesel engines (or front main seals, for that matter). However, oil seepage from the rear main seal is much more common on early versions of the 3066 than on later models. This is due to pre-1998 models utilizing a rear main seal carrier that’s prone to warping. As with all rear main leaks, oil loss only increases as time (and operating hours) passes.
What Happens
Caterpillar Excavator Equipment 3066 Engine Hydraulic Pump Removal
As we alluded to above, early CAT 3066 (and especially 3066T) blocks employ a rear main seal carrier at the rear of the engine. This carrier is made of aluminum and is notorious for warpage. Oil seepage can often be traced back to where the carrier meets the block. It’s sometimes presumed that warpage occurs due to the use of dissimilar metals (aluminum carrier/iron block), which expand and contract at different rates. Regardless of why the carrier becomes deformed, it’s a highly common and well-known problem that many early 3066 owners face.
Solution(s)
Cat 3066 Diesel Engine Replacement Repair Parts Rear Main Seal
Accessing the rear main seal is a laborious task on a 3066 engine installed in a piece of heavy equipment. In excavator applications, the hydraulic pump will have to be disconnected (photo above) and removed first—a time-consuming endeavor all on its own. It’s not uncommon to discover oil everywhere surrounding the flywheel. A rear crankshaft and wear ring installer will be required to tackle the job. And most importantly, the correct retainer must be ordered. Whenever possible, stick with OEM Caterpillar replacement parts, or aftermarket components that meet or exceed factory quality.
Problem #5: Wet Stacking
Wet Stacking Diesel Engine Exhaust Soot
Wet stacking is the phenomenon where unburned fuel makes it past the engine’s exhaust valves and, along with carbon, pools or accumulates in the exhaust system. The exhaust valves, exhaust side of the turbocharger (turbine), and the exhaust system itself will all see accumulation when wet stacking occurs. Neglected long enough, wet stacking can lead to a drop in engine performance, elevated back pressure, and deposits on the turbine wheel that turbocharger efficiency. In addition to a drop in overall engine efficiency, over time the deposits from wet stacking will contaminate the engine oil, potentially decreasing its quality.
When It Happens
Cat 3066 Standby Diesel Generator Power Generation
Wet stacking is most commonly experienced in generator applications where the engine has operated at light load or been allowed to idle for extended periods. These intervals of prolonged low load or no load keep the engine from reaching its optimum operating temperature. Simply put, idling doesn’t generate enough heat during combustion to completely burn off all of the fuel being injected into the cylinder. Wet stacking is especially common in pre-1998 mechanical injection 3066’s. In these early engines, many of which featured a Bosch P7100, injection timing isn’t variable.
Solution(s)
CAT Heavy Machinery Equipment Pyrometer EGT gauge
In generator applications, wet stacking can be avoided by ensuring the engine is kept under load in a way that achieves optimal EGT and operating conditions at all times. Specific solutions for eliminating or vastly reducing wet stacking include the implementation of automatic auxiliary loading, use of a facility manual load bank, or employment of a portable load bank. The goal is to keep the engine running in a range where complete combustion takes place. Timely maintenance intervals also play a role in reducing wet stacking, and many generators are serviced according to contracted planned maintenance programs.
Problem #6: Fuel Injector issues
Cat 3066 Replacement Diesel Engine Fuel Injector
Fuel injector issues not only rob a machine of its ability to perform at its peak, but they can also increase operating costs due to excess fuel consumption. Even on early CAT 3066 engines, where the entire fuel injection system is of the old-school, mechanical variety, injector problems can surface from time to time. Decreased engine performance, rough idle, increased smoke levels, and a drop in fuel efficiency are key indicators that a fuel injector is headed south. Of course, proper diagnosis, performed by a trained professional, is always the best method of confirming you have a faulty injector.
What Happens
Used Fuel Injectors Cat 3066 Diesel Engine Parts
A host of contributing factors can damage the 3066’s fuel injectors. Chiefly among them is lack of maintenance. Extended or neglected fuel filter and water separator replacement and poor fuel quality (or contaminated diesel) can cause irreparable damage to the internal components of an injector. Worn nozzle needles and sealing surfaces allow fuel to leave the injector when it’s supposed to be off, weak springs can allow fuel to be forced through the nozzle prematurely and worn, blown or damaged injector O-rings can produce the same symptoms, which is most notably excessive smoke leaving the exhaust system.
Solution(s)
Caterpillar 3066 New Mechanical Fuel Injector Set
As with any problem, avoidance begins with a sound maintenance regimen. A complete fuel system inspection is recommended for the CAT 3066 every 3,000 hours. This includes the injectors, fuel lines and pump, as well as checking all connection points for fuel leaks, corrosion, or loose fittings that may allow air to infiltrate the fuel system. If a bad injector is diagnosed, the owner has the option of replacing that unit alone or replacing the entire set. It's important to note here that fuel injectors perform best when balanced as a complete set.
Problem #7: Fuel Primer
Failed Fuel Primer Pump With Gasket Cat 3066 Diesel Engine Parts
Air infiltration can hinder the performance of any engine, and a bad fuel priming prime is a common source for this on the CAT 3066. When this manual, hand-pump fuel primer fails, the operator is usually faced with a hard-starting engine or one that won’t start at all. And while a lot of fuel supply issues can be tricky to diagnose, this one is about as straightforward as they come. A bad fuel primer is often noticed after a fuel filter service, when the system doesn’t seem to want to reprime. Other times, it’s discovered after a hard cold start.
What (Often) Happens
Cat 3066 Diesel Engine Fuel Primer Pump Assembly
In most cases, the fuel primer pump’s internal seal for the plunger cup fails. In less frequent instances, a bad check valve is the cause. A telltale sign the fuel primer pump is failing is usually denoted by a “cushy” feeling when the handle is compressed inward, but it can also be noticed by the sound of air being forced out of the pump when it’s compressed. No matter what, a leak at the fuel primer will make engine startup more difficult. If these hard starts are ignored, you’ll eventually end up with a fuel system no longer capable of holding prime—and an engine that won’t start or stay running.
Solution(s)
Manual Fuel Primer Hand Pump Caterpillar 3066 Diesel Engine
A failing fuel primer can easily be replaced in most 3066 applications. And luckily, several reputable aftermarket fuel priming pumps can be obtained for $100 or less. Couple that with minimal labor—thanks to both the primer pump’s location and the lack of difficulty in swapping it out—and you’ve got a repair that most novice mechanics can handle in a matter of only a few minutes. Due to their relatively low cost, ease of replacement, and the fact that they fail with regularity, many 3066 owners keep a spare fuel priming pump on hand.
Problem #8: Injection Pump (P7100)
Bosch P7100 Fuel Injection Pump Cat 3066 Diesel Engine
CAT 3066 engines fitted with a Bosch P7100 injection pump enjoy solid reliability, as this is one of the most robust plunger pumps ever produced and that has been widely used throughout the globe. However, with age—and the inevitable wear and tear that comes with it—these inline pumps end up requiring some TLC. Of course, if subjected to poor fuel quality, debris, or other forms of contamination the internal components within the P7100 can become damaged prematurely. Hard starting or long crank, no start scenarios, rough idle, and excessive smoke are key symptoms of an failing P7100.
What Often Fails
Bosch P7100 Diesel Injection Pump Overflow Valve
Despite what is believed by many to be a simple pump, the P7100 features a host of moving parts—all of which can become damaged or worn. Governor issues, stuck or damaged plungers and barrels, a leaking throttle lever, problems stemming from the AFC (air fuel control) housing, and even fuel leaks can all surface. However, the most common failure associated with the P7100 exists in its overflow valve. A weak or broken internal spring in the overflow valve lowers the amount of fuel pressure being delivered to the pump itself. This frequently results in hard-starting, reduced power, or a low rpm miss. A worn check ball seat will also allow excess fuel to return to the tank rather than supply the P7100.
Solution(s)
Bosch P7100 Fuel Bench Test Cat 3066 Diesel Engine Pump
Depending on the type of failure and the age of the ailing P7100, many operators opt for a complete rebuild. This is especially true when leaks are discovered (as they do eventually require a re-seal). Most reputable injection pump shops are well-versed in the P7100 and should have no issue overhauling the unit, as well as bench testing it once it’s complete. Other options include the purchase of a remanufactured pump or addressing the single component diagnosed as the problem child (such as the aforementioned overflow valve). Regardless which solution you choose, it’s wise to always make sure the pump is benched and properly timed before installing it on your 3066.
Problem #9: Availability
Cat 3066 Diesel Engine Heavy Machinery Equipment
There is a common misconception that CAT’s 3066 has availability issues. As a global engine in every sense of the word, we can assure you that that isn’t the case. Depending on your budget, a replacement 3066 from your CAT dealer might not be feasible, but these engines are still widely available. Additional sources of engines and parts include third party aftermarket suppliers, as well as aftermarket engine manufacturers. We at Big Bear Engines offer 3066 long blocks that’ve been remanufactured to OEM specs using factory processes. Inspection, machining, assembly, and testing all take place under the same roof here at Big Bear.
Why Some Parts Can Be Hard To Find
Cat 3066 Engine Overhaul Kit Dry Sleeves Gaskets
Some replacement parts can be difficult to source, at times, through Caterpillar. However, many owners turn to aftermarket suppliers for quality, OEM-like components in these instances. From our perspective, Big Bear Engine’s 3066 long blocks are built using a mix of new OEM parts and high-quality aftermarket replacement components, when available. This allows us to rebuild a customer’s engine back to OEM specs and get their equipment operational again—and this is accomplished for a fraction of the cost of what an engine would cost from the dealer.
Solution(s)
CAT 3066 Remanufactured Diesel Crate Engine
Rather than sourcing one of our used Cummins engines, such as the 3066, where the engine’s history is often a mystery, a remanufactured 3066 is a great solution. Not only is it financially advantageous, but receiving a remanufactured engine—complete with a warranty and after-the-sale support—offers immense peace of mind. Of course, by using your engine’s core components as the basis of the build, (engine block, crankshaft, connecting rods, cylinder heads, etc.) a large portion of money is saved over what would be spent on a complete, new version sourced from a dealer.
Problem #10: Old Age
Cat 3066 Diesel Engine Rebuild Block On Hoist
It may seem obvious that old age will take an engine out of commission, but in the case of the 3066 many of these power plants are more than 30 years old. Others are at least 20 years of age. For these engines, and the equipment they’re powering, this means breakdowns are inevitable at some point, and for varying reasons. One bit of confidence the 3066 offers its owners is its proven track record for longevity. When properly maintained, CAT’s 3066 will last 12,000 to 15,000 hours before a major overhaul is required.
What Tends To Happen
Cat 3066 Cylinder Head Removal Head Gasket Diesel Engine Rebuild
From pesky headaches to game-ending hard part failures, old age brings a host of issues with it. For the CAT 3066, this often includes oil or coolant leaks, exhaust leaks, rusted exhaust manifolds and/or bolts, turbo failure (if equipped), blown head gaskets, corroded fuel lines, and a myriad of other fuel system problems (from the tank all the way to the injectors). Of course, a sudden lack of oil pressure can lead to a cataclysmic chain of events for any 3066, sometimes with a rod or main bearing failure bringing things to a violent halt.
Solution(s)
Caterpillar 3066 Cylinder Block Piston Replacement Diesel Engine Repair
Luckily, solid support can still be found for the CAT 3066, both at the dealership level and in the aftermarket. Between the two, there are easily enough resources to get your 3066 repaired, rebuilt, or keep it well maintained and running. A joint venture between CAT and Mitsubishi Heavy Industries (MHI), the 3066 pairs Japanese precision with Caterpillar’s global parts supply chain. Thanks to being a rock-solid reliable engine platform, having been produced in mass quantities, and enjoying a vast replacement component network, the 3066 will continue to be a heavy favorite among operators and equipment owners for years to come.
