Written By, Mike McGlothlin
The smaller sibling of the CAT 3306 engine, the CAT 3304 engine is a highly reliable, fuel-efficient, 7.0L (425 ci) inline-four-cylinder diesel engine born in the 1970s. Immensely popular in the construction and forestry industries (think rollers, dozers, excavators, gen-sets, and skidders), it’s also a proven platform in many marine applications. The very definition of durable, the 3304 can easily go 15,000 hours between overhauls if properly maintained. However, these old-iron gems do have their weak links, some of which can be financially crippling. From the CAT 3304’s common water pump and pre-combustion chamber failures to its pitted liner, oil pump, and overheating issues, we’ll cover this engine’s Top 10 drawbacks below.
HIGHLIGHTS
Most Common Problems:
*Pitted Pre-combustion Chambers
*Water Pump Failure
*Overheating
*Vibration After Rebuild
*Oil Leaks
Most Expensive Problem:
*Catastrophic Engine Failure
*Oil Pump Failure
*Dropped Valve
*Pitted Liner
Less-Frequent Headaches:
*Catastrophic Engine Failure
*Fluctuating RPM
*Corroded Valve Seats
Problem #1: Pre-combustion Chambers
Caterpillar 3304 Diesel Engine Pre Combustion Chambers
In many older, industrial applications, indirect injection versions of the CAT 3304 were used. These early 3304’s utilize what are known as pre-combustion chambers (PC). Within the cylinder head, each fuel injector sits in its own dedicated pre-combustion chamber. The exterior of each pre-combustion chamber is in constant contact with engine coolant, which helps to keep both the fuel injector and the cylinder head cool. They thread into each injector bore within the cylinder head and are also accompanied by glow plugs, for easier starting.
What Happens
Diesel Engine Failure Cat 3304 Pre Combustion Chamber
Most frequently, pre-combustion chambers fail from the outside-in, and namely whenever coolant maintenance is neglected. Coolant with improper additives often contributes to pitting of the pre-combustion chamber, but coolant system leaks that go unaddressed can contribute as well. A third common cause of pre-combustion chamber failure stems from overheating, where the pre-combustion chamber’s seals burn up. The telltale signs that a pre-combustion chamber has failed are: coolant infiltrating the combustion chamber (when the engine is off and the machine has been allowed to sit) and bubbles being observed in the radiator. Upon teardown, cracks are commonly discovered at the bottom (seat) area of the chamber, where it threads into the cylinder head.
Solution
Cat Extended Life Coolant Diesel Engine Antifreeze
As with many engine failures, pre-combustion chamber issues can be avoided with proper cooling system maintenance. That means not only running the correct antifreeze, but one with the right additive package. On top of that, ensuring the 3304’s coolant level never gets low, any leaks are promptly addressed, and that it never sees an overheat goes a long way in preserving the life of the pre-combustion chambers. Do that, and they will last a very long time. But when they do finally need to be replaced, only source genuine replacement chambers from Caterpillar or a highly reputable aftermarket manufacturer.
Problem #2: Pitted Liners
Diesel Engine Rebuild Parts Cat 3304 Wet Sleeve Liners Connecting Rods
Like its big brother, the 3306, CAT’s 3304 employs a wet liner in each cylinder within its cast-iron block. Wet liners, made from ductile iron, keep the sleeve’s exterior in constant contact with engine coolant, which allows for exceptional heat transfer and helps keep the cylinder itself perfectly round. Use of wet sleeves also makes the 3304 rebuildable, one cylinder at a time, with a fresh liner capable of being installed in-frame and in the field. It’s the type of heavy-duty component typically found in heavy-duty inline-six power plants and it enables a properly maintained 3304 to last 15,000 hours or more.
What Happens
Cat 3304 Wet Cylinder Liner Cavitation Engine Part Damage
Not unlike what can happen with the aforementioned pre-combustion chamber failure, lack of a proper additive package within the engine coolant can lead to cavitation/pitting. Extended flush intervals, neglected top-offs, and an incompatible or non-specified coolant can all contribute to pitting of the liners. Once the pinholes develop, there is no turning back. And once one of them penetrates all the way through the ductile iron sleeve, you’ll quickly get cross contamination between fluids and even combustion gases escaping the cylinder. Worse yet, it’s the type of failure that can take a minute to become overtly noticeable to a novice operator.
Solution
Caterpillar 3304 Diesel Engine Rebuild Overhaul Wet Liners PistonsCaterpillar 3304 Diesel Engine Rebuild Overhaul Wet Liners Pistons
As with pre-combustion chamber failure, avoidance is the best medicine for wet liner pitting. Its occurrence can be avoided (or at least put off as long as possible) by simply maintaining the engine’s cooling system. Again, running the proper coolant (which consists of the correct Supplemental Coolant Additives, or SCA’s), quickly remedying coolant leaks any time they arise, and never allowing the engine to overheat will serve to keep the liners in tip-top shape for years. But when a liner does finally fail, there is no other choice other than to rebuild the problematic cylinder.
Problem #3: Foreign Contamination
Cat Bulldozer Heavy Equipment Diesel Smoke Engine Blowby
With the bulk of CAT 3304’s serving time in off-road (and namely construction) equipment, it goes without saying that they operate in harsh conditions. From cradle to grave, they tend to live in very dirty environments, and at high rpm. As you can imagine, prompt engine servicing and maintenance is paramount in keeping a 3304 running at full steam ahead. Unfortunately, air intake and oil contamination is extremely common on this engine, and it’s more likely to occur when maintenance intervals are extended or neglected.
What Happens
Cat 3304 Diesel Engine Short Block Rebuild Connecting Rods Caps Wet Liners Pistons
Overlooked or disregarded air filter changes (or cleanings) are the leading cause of foreign contaminants entering a 3304 engine. It’s no surprise that this is also the leading cause of “dusting” a turbo. But dust, dirt, and (worse) sand ingestion doesn’t stop at the turbocharger. This kind of debris can work its way into the engine via the intake manifold and head—also contaminating the engine oil. That means the oil’s lubrication properties are diminished and that main and rod bearings can become damaged. Over time, lack of maintenance will force a complete engine rebuild.
Solution(s)
Diesel Engine Teardown Overhaul Cat 3208 Repair
A clean air filter, routine oil and filter changes, and regular oil analyses are the best preventative measures for guarding against foreign contamination. But once it’s time for a rebuild, most mechanics familiar with the 3304 will tell you it isn’t difficult to overhaul. Many operators, with ample wrenching experience (of course), have even rebuilt their own 3304’s. A word of advice: when rebuilding the 3304—especially one that does its business amid dusty or dirty conditions—make sure the cooling system is completely overhauled, too. On top of that, ensure the engine oil cooler is replaced, or (at the very least) thoroughly cleaned.
Problem #4: Vibration After Rebuild
Old Cat Bulldozer Construction Heavy Equipment 3304 Diesel Engine
There is nothing worse than performing a full-on rebuild of a CAT 3304 only to have it run rough or unbalanced once it’s completely back together. After spending thousands of dollars to restore your workhorse engine to its former glory, it can be demoralizing to have an issue immediately upon startup. Unfortunately, this is a common result in many DIY engine overhauls. Oftentimes, it’s misdiagnosed as a faulty fuel injector. In other cases, it’s believed to be incorrect injection timing or some other fueling related issue. Nine times out of 10, it’s neither of those things
What Happens
Cat 3304 Diesel Engine Balance Shaft Internal Part
What often happens boils down to a timing issue, but not an injection timing issue. Rather, the problem lies with the balance shafts. The CAT 3304 incorporates two balance shafts, and they must be correctly timed when the oil pump is installed. For the do-it-yourselfer or the engine builder who hasn’t conducted the proper research, it’s a highly common oversight. It’s frequent enough that many experienced 3304 mechanics know exactly what the problem is without even having seen the machine in person. They simply show up, pull the oil pan, and set to work retiming the balancers.
Solution(s)
Cat 3304 Diesel Engine Crankcase Balance Shafts Short Block
Correctly timing the balance shafts should be left to someone familiar with the CAT 3304 or, at a minimum, a well-versed mechanic who possesses experience with balance shaft engines. Regardless of who performs the work, the trick to correctly timing the 3304’s balance shafts is fairly simple: Don’t install the timing bolts in the balance shaft bolt holes until the oil pump has been bolted into place. This is because, when the oil pump goes in, it rotates the balancing shafts ever so slightly. By having the oil pump fastened in place first, the balance shafts won’t turn.
Problem #5: Overheating
Water Temperature Engine Coolant Mechanical Analog Gauge
An engine that runs warm is worrisome. An engine that overheats is a major problem. Nothing stifles workday productivity quite like an overheating engine does. Not only can it leave your operator glued to the water temperature gauge, but if temps boil over it can cause significant damage to the engine. We’re talking a warped cylinder head, a blown head gasket, or (worse), a cracked head or piston. Unfortunately, one overheat is all it takes sometimes to lead to any of the latter engine failures.
What Can Cause It
Coolant In Cylinder Blown Head Gasket Antifreeze Cat 3304 Failure
The most common drivers of overheating in a CAT 3304 are stuck thermostats and/or a plugged oil cooler. Symptoms for each of these issues are similar, but be forewarned that the 3304’s oil cooler is prone to plugging up, and when it does coolant flow is severely restricted (if not cut off completely), allowing coolant temp to skyrocket in short order. A plugged radiator can also lead to excessive coolant temps, so it pays to ensure it’s treated to regular visual inspections and (if required) cleanings.
Solution(s)
Replacement Engine Oil Cooler Cat 3304 Heat Exchanger
Depending on the cause of the overheat and the extent of the damage done, solutions vary from engine to engine. If it’s a stuck thermostat or plugged oil cooler the fix is easy (and affordable) enough, but if it’s a blown head gasket you’re looking at considerable downtime along with a thorough inspection once the head is pulled. Hairline cracks within the head, valve seat issues, warpage of the block, damage to the wet liners, and any hot spots or cracks in the pistons should all be looked for.
Problem #6: Failed Water Pump
Water Pump Failure Caterpillar 3304 Diesel Engine
Another cause of elevated coolant temperature, as well as a common occurrence in the 3304, is water pump failure. The 3304 is not alone here, with many CAT engines prone to suffering premature water pump failures. The water pump is gear driven on the 3304, which is ideal, but unfortunately it has a tendency to die quicker in this application than comparable engine. As a natural wear item, it’s a problem that can’t be completely ruled out or eliminated, although sound cooling system maintenance and checks can contribute to the longest life possible for this vital cooling system component.
What Happens
3304 Cat Diesel Engine New Water Pump Installed
Outside of impeller, bearing, or shaft failure, most CAT 3304 water pumps meet their fate when the pump’s seal gives way. Typically, a water pump failure can be identified by a coolant leak from the unit’s weep hole. However, this isn’t always as cut-and-dried as it should be. Particularly in off-road equipment used for work in dusty conditions, the weep hole is sometimes plugged, making immediate diagnosis more difficult. Occasionally, spotting a leak around the water pump is misdiagnosed as a bad pump when in reality the plate behind the water pump, which is known to accumulate coolant, is slowly leaking coolant.
Solution(s)
Replacement Water Pump Caterpillar 3304 Diesel Engine Cooling System Parts
The best part about the 3304 water pump is that, thanks to its location on the engine, it can be accessed and rebuilt without disturbing any coolant lines, or any other gear-driven accessories for that matter. Better yet, a reputable aftermarket rebuild kit can be had for less than $100. Even for a novice mechanic, it’s a 3-hour job in most applications, with many experienced CAT techs able to bang it out in two hours or less. For complete water pump replacement, you’re looking at $250 to $300 or more for a new unit.
Problem #7: Fluctuating RPM
Tachometer Gauge Cat 3304 Diesel Engine High Speed Rpm
On some high operating hour CAT 3304’s, a surge in engine speed will develop over time. Not only can these fluctuations in rpm effect its performance, but they can lead the operator to attempt to diagnose the problem—many times incorrectly. At the first sign of unstable rpm, a lot of folks start with a fuel filter change. That’s not it (and rarely ever is). However, this problem is almost always fuel system related. More specifically, it’s often an issue with the injection pump. On the 3304, an inline, 100-percent mechanical (scroll type) injection pump is employed. While it’s highly reliable, its components still wear with age and long-term usage.
What Are The Causes?
Cat 3304 Diesel Engine Fuel Scroll Pump Governor Assembly Filter
While a fuel filter change won’t solve the problem, it does pay to inspect all fuel lines and fittings for cracks and leaks. It’s important to remember here that small air leaks don’t typically leak fuel, but they do allow air to enter the fuel system. As for surging rpm as it relates to the injection pump, a broken torsion spring on the pump’s sleeve control shaft is sometimes the culprit. In other scenarios, the pump’s governor linkage is found to be in a bind and unable to move freely. The final common cause is also governor spring related, with the springs not fully seating against the spring seat.
Solution(s)
Diesel Engine Injection Pump Cat 3304 Fuel System Parts
Once all fuel lines and fittings have been ruled out, the injection pump governor assembly should be thoroughly inspected. Start by checking the cable linkage where it connects to the pump lever. Also make sure to check the pump lever for play (side-to-side, up and down) to make sure the shaft bearing hasn’t failed. Finding play in the pump lever is the direct cause of any rpm fluctuation. Luckily, it’s a problem that can be fixed with the injection pump still bolted to the engine, although some 3304 owners opt to pull the pump and governor for a refresh at this point.
Problem #8: Oil Pump Failure & Oil Leaks
Oil Pump Bolts Gear Cat 3304 Diesel Engine Failure
While fuel serves as a diesel engine’s lifeblood, the oil that lubricates its internal components is arguably more important. Maintaining sufficient oil pressure is vital to long-term engine life, and oil leaks—be they major or minor—should never go unaddressed. As you already know, oil-related issues range from life-threatening (no oil pressure) to inconvenient (leaks), but we’re covering them both here. After all, with 50 years on some CAT 3304 engines at this point (along with a few overhauls likely), mating surfaces, seals, O-rings, and gaskets all become points of concern, with an oil pump failure being the biggest worry.
What Happens
Cat 3304 Oil Pan Pump Bolts Diesel Engine Parts
Thousands of operating hours, and especially prolonged high rpm, can take its toll on the CAT 3304 oil pump’s mounting bolts. Rather than the oil pump outright failing, it’s these fasteners that typically give up first—in the form of backing out while the engine is running at full steam ahead. Almost immediately, all oil pressure is lost and, many times, toasts the engine’s main and rod bearings while also bluing the crankshaft and connecting rods. As for the most common locations to spot an oil leak on a 3304, you’ll typically find those at the valve cover and/or the front timing gear seals.
Solution(s)
Oil Pump Mounting Bolts Pan Gasket Cat 3304 Diesel Engine Repair
Obviously, a loss of oil pressure can mean you’re out an engine, but if an alert operator can get things shut down quickly enough there is a chance of only minimal damage being incurred. Still, in most cases, and at a bare minimum, a 3304 that loses oil pressure is going to need fresh bearings, as well as a fresh oil pump and (especially) mounting bolts. On the oil leak front, solving a leak at the front cover will call for a bit of labor, hence why many owners put off addressing it until significant oil loss becomes impossible to ignore.
Problem #9: Valve Seats
Corroded Valve Seat Cat 3304 Cylinder Head Failure
In virtually every internal combustion engine that utilizes overhead valves, valve seat failure can occur—and this type of problem always carries with it the risk of catastrophic engine damage. Age is a common factor in valve seat and dropped valve failures with the CAT 3304, but abuse at the hands of an aggressive operator can’t be overlooked either. Combine old age with maintenance neglect and aggressive, high heat (and high rpm) operation and you’re literally begging for trouble with one of these timeworn power plants.
What Happens
Cat 3304 Cylinder Head Valve Seat Damage Diesel Engine Failure
Most valve seat problems within the 3304’s cast-iron, 2-valve cylinder head begin with miniscule hairline cracks. In other instances, corrosion takes place in the valve seat region. Either issue can contribute to a valve seat becoming dislodged and falling in-cylinder. Key ingredients associated with valve seat failure are: exposure to extreme exhaust gas temperature (EGT), exposure to boiling coolant temps such as in the case of an overheat, and natural causes (i.e. age) leading to the development of cracks within the head.
Solution(s)
Cat Pre Combustion Chamber 3304 Recondition Cylinder Head Diesel Engine
Unfortunately, valve seat issues often go unnoticed until it’s either too late, or they’re discovered during a different, in-depth repair such as a blown head gasket or engine overhaul. When the former discovery unfolds, you’re out a new or reconditioned cylinder head at the very least. But if piston-to-valve contact occurs (and is allowed to occur for any length of time) you could be looking at bottom end damage and possibly even a windowed block. In some cases, a reconditioned head (if the original is repairable) is all that’s required, but some circumstances require a brand-new replacement head.
Problem #10: Catastrophic Engine Failure
Used Heavy Duty Diesel Engine Cat 3304
Not to keep harping on it, but CAT’s 3304 is a very old platform at this point. And though highly reliable, these near-ancient engines have all kinds of hours and time on them now. Simply put, every day a well-used 3304 is once again put through its paces, it could be one step closer to a very destructive type of engine failure. Whether it happens out of the blue or there were ample warning signs, a 3304 with 15,000 hours or more on the meter is going to have a problem eventually.
What Can Happen
Cat 3304 Catastrophic Engine Failure Damaged Piston Rings Sleeves
The types of 3304 failures we see on a regular basis here at Big Bear Engine Company run the gamut. From spun crankshaft bearings and cracked cylinder heads to full-on crankshaft failure and dropped valves, we take in engines with a wide range of issues. Other common killers are lack of oil pressure (or no oil pressure), extreme blowby, connecting rod failure, camshaft failure, and even lifter failure. Scored liners and damaged pistons are common discoveries once inside the crankcase of these old-school workhorses. None of these failures are surprising given how hard these engines work, be it in construction, forestry, power generation, or marine equipment.
Solution(s)
Gen Set Power Generation Cat 3304 Diesel Engine Stationary
You can’t always avoid what’s coming when dealing with a tired 3304, but you can plan ahead in an effort to minimize your downtime if or when something does happen. Some operators, many of which perform their own repairs, keep spare parts on hand (and some even compile the parts they’ll need to rebuild it when the time comes). Others keep a backup engine on hand—although we would advise against trusting a second or third-hand “running” take-out engine to be 100-percent reliable. Some even have plans to swap engines when their 3304’s life expires. No matter what your backup plan is, it pays to have one when older engines and equipment are part of your fleet.
