Written By, Mike McGlothlin
The largest V-8 to ever grace the American Class 8 truck market, the CAT 3408 engine is a 1,099 cubic inch, 18.0L beast of an engine that is widely respected both for its durability and its cool factor. Unlike its smaller, medium-duty sibling, the CAT 3208 engine, the 3408 boasted replaceable wet liners, along with all front-drive accessories being gear-driven. Like the 3406 (which it shares the same bore with), it was a true heavy-duty power plant intended for huge workloads, hence its use in trucks, marine vessels, power generation, and construction equipment. In many circles, CAT’s 3408 is known as a million-mile/20,000-hour engine—and legend has it that some can go twice that distance in between overhauls… Still, these V-8 behemoths do have their weak links, and from blown head gaskets to oil leaks to dropped valves, we’re covering its 10 most common ailments below.
HIGHLIGHTS
Most Common Problems:
*Fuel Consumption
*Sourcing Parts
*Blown Head Gasket(s)
*BrakeSaver Seals
*Oil Cooler Failure
Most Expensive Problem:
*Dropped Valves
*Blown Head Gasket(s)
Less-Frequent Headaches:
*Turbo Failure
*Injection Pump & Fuel System Issues
Problem #1: Fuel Hog
1981 Peterbilt Extended Hood 359 Model Caterpillar 3408 Diesel Engine V8
When it comes to fuel consumption, few heavy-duty diesel engines are as thirsty as the CAT 3408. Aside from the KTA Cummins (a 19.0L inline-six), the 3408 is one of the largest engines ever offered in on-highway applications, and it is the biggest power plant Caterpillar ever produced for on-highway use. CAT’s 3408 is a 65-degree, iron block and head V-8 displacing 1,099 cubic inches (18.0L). And, in addition to being huge, its cast-iron construction makes it extremely heavy. In fact, its dry weight checks in at 3,300 pounds.
What Happens
Class 8 Tractor Trailer Semitruck 3408 Cat Diesel V8 Engine
When you combine its large displacement and overall heft with the fact that it has eight cylinders to feed diesel to, you begin to see why CAT’s 3408 is infamous for its fuel consumption. In Class 8 tractor trailer applications, it’s common for owner operators to see 4.5 MPG. Out in the Rocky Mountains or for drivers that can’t stay out of the throttle, that number drops even lower. The 3408’s lack of fuel efficiency is part of the reason CAT axed them from their over-the-road lineup in the mid 1980s. The other reason was that the 3406, which competed in virtually all the same markets, made similar power.
Solution(s)
Diesel Truck Tachometer Rpm Hour Meter Cat 3408 Power
There is no replacement for displacement—or the thirst a big cubic inch power plant has for fuel. Because of this, there is no real solution for the CAT 3408’s lack of fuel efficiency. Our best advice would be to refrain from hot-rodding the 1,100 ci V-8, keeping rpm low, and cruising at or near the speed limit. Remember, mpg at 65 mph is going to be better than what it is at 70 mph, or 75 mph… The only other option is an engine conversion—namely to a 3406 or some other inline-six variant.
Problem #2: Expensive, Hard To Find/Source Parts
Cat 3408 Diesel Engine Parts Block Cylinder Head Camshaft
The CAT 3408 is ultra reliable. But, when it does have problems, it is serviceable, rebuildable, and much simpler to wrench on than the newfangled, electronically controlled (and emissions equipment-laced) power plants of today. However, in many ways the 3408’s biggest nemesis is time, as they’ve been removed from the factory production line for more than four decades. This means that not only can it be hard to locate cores, but most replacement parts are remanufactured or aftermarket at this point. And when you do find a good condition core, it often has a steep price tag attached to it.
Why Parts Are Expensive
3408 Cat Offset Crankshaft 65 Degree V8 Diesel Engine Hard Parts
In short, core components and parts are expensive because they are scarce. Mechanical injection versions of the 3408 were last produced more than 40 years ago, and thanks to some of the more unique pieces this engine employed some components are very pricey. For example, a crankshaft alone can run you $15,000. Highly unique for this engine segment, the 3408’s offset crankshaft was designed to cut down on NVH, but its rather exotic design makes it a high-dollar item. As for complete engines, a core 3408 that turns over (never mind run) can bring an asking price of $40,000 or more.
Solution
Used Caterpillar 3408 Diesel V8 Engine Class 8 Marine Construction
If you’re on the hunt for a CAT 3408, the salvage yard is likely your best bet for finding a “deal” on a core engine (or core parts, for that matter). If you’re already in possession of a running 3408, keeping it in good working order is the best way to avoid the need for replacement parts. A sound, routine maintenance regimen is ideal, with regular oil analyses, and filter and fluid changes being performed. And when you do have to make any repairs, source genuine Cat parts whenever possible or, at the very least, OEM-equivalent aftermarket components.
Problem #3: BrakeSaver (if equipped)
Cat Brake Saver 3408 Diesel Engine Jake Brake Hydraulic Retarder
Fun fact: the CAT 3408 never came with Jake brakes. However, it was commonly used (and often revered) for pulling huge loads up and over the immense grades out West. So, how was this possible? CAT did it through the use of the BrakeSaver. Technically a hydraulic retarder, the BrakeSaver is positioned between the crankshaft and flywheel. Pressurized engine oil effectively floods the BrakeSaver housing, where a larger impeller present in its housing reacts against the fluid, ultimately creating drag. While not as effective as a traditional, compression release style Jake brake, it got the job done.
What Happens
Brake Saver Engine Braking Retarder Cat 3408 Diesel Engine
While effective, the BrakeSaver did have its share of problems, and its issues were more frequently experienced than on engines equipped with conventional Jake brakes. First and foremost, the hydraulic retarder doesn’t activate as quickly as a Jake brake. Its activation isn’t immediately felt, making the timing of its engagement paramount for the operator. Its biggest issue? The BrakeSaver generates a boatload of heat when in operation. The engine oil present within the BrakeSaver housing was known to superheat, pressurize, and blow out its seals, causing leaks. Another common failure point was the unit’s diaphragm, which also often meets its end after exposure to excessive pressure.
Solution(s)
BrakeSaver Lever Class 8 Tractor Trailer Semitruck Cat 3408 Diesel Engine
For most Class 8 truck mechanics, BrakeSaver repair isn’t a major headache, though it does obviously require transmission and flywheel removal. Caterpillar offers a genuine BrakeSaver gasket kit for any mechanic looking to completely reseal it, and OEM replacement control valve diaphragms are also readily available. As far as keeping a BrakeSaver alive? That requires an astute and alert operator who eases into its engagement and (more importantly) keeps an eye on engine oil temperature. Properly utilized, the BrakeSaver—on any CAT engine—will last a long time.
Problem #4: Blown Head Gaskets
Blown Head Gasket Block Deck Caterpillar V8 Diesel Engine 3408
Boiling coolant temps, disappearing coolant, pressurized coolant, or extreme fluctuations on the water temp gauge all point toward a blown head gasket in any internal combustion engine. As the CAT 3408 ages, its propensity to lose a head gasket increases, and lack of fluid or an abusive driver is often what sends a high-mile head gasket over the edge. Unlike the 3406, there are two head gaskets to worry about on the 3408. But similar to the 3406, a failed head gasket can often be traced back to the same place.
What Happens
Cat 3408 Diesel Engine V8 Cylinder Head Removal Blown Head Gasket
Rather than a blown head gasket being the fault of the head bolts or the gasket itself on a CAT 3408, it’s most often the result of improper liner protrusion. On the 3408, the replaceable wet liners sit on top of the cylinder block. As the years go by, the liners tend to progressively wear into the block’s deck surface. This is often referred to as a “sunk liner” or “sunken liner.” All it takes is a tiny protrusion issue (we’re talking only a few thousandths of an inch) and you’ve toasted a head gasket.
Solution(s)
3408 Cat Engine Rebuild New Pistons Cylinder Head Head Gasket Repair
Addressing a blown head gasket on a 3408 is an extensive undertaking. First, you need to consider—and actually should plan on—starting with a fresh head gasket on both banks. After all, both banks need to be inspected for proper liner protrusion anyway, so it pays to go ahead and tackle both head gaskets at the same time, especially on high-mile/high operating hour candidates. In most cases, new counter bores will need to be cut, which calls for special tooling and a trained mechanic to perform the work. Don’t DIY this repair. Leave it to an expert.
Problem #5: Injection Pump
Caterpillar 3408 Diesel Engine Mechanical Fuel Injection Pump
The original CAT 3408 engines produced between 1975 and 1985 featured 100-percent mechanical injection. No electronics were employed for any engine control. The engine’s fuel system worked by the transfer pump supplying the plunger pump in the valley (a V style pump), and the injection pump pressurizing fuel high enough to fire the pop-off style fuel injectors. But just because a fully mechanical injection pump is used on the 3408 doesn’t mean it’s without its shortcomings. Make no mistake that this pump, which has to be properly timed, has a lot of moving components—all of which need to be in good working order.
What Happens
Cat 3408 Diesel Fuel Injection Pump Overhaul Repair
It goes without saying that injection pump issues will be noticeable. But before you jump to any conclusions, it pays to check several things before venturing inside the pump. First, check the fuel shutoff linkage for any binding and that the governor shaft is intact. Follow that by confirming the pump is turning over and then verify there are no timing issues. One other common failure point is the fuel rack seizing inside the pump. With many injection pump-related issues, plenty of fuel will be making it to the injectors when you prime the hand pump, but there will be very little pressure at the injectors themselves.
Solution(s)
Injection Pump Rebuild Cat 3408 Diesel Engine Fuel Injectors
Many injection pump issues can be diagnosed, and sometimes even pinpointed, by the novice mechanic, but any time you’re pulling the injection pump, having it rebuilt, and reinstalled, it pays to have an experienced CAT 3408 mechanic do the work. While there are some simple fixes that can be performed out in the field, many problems stem from old age or corrosion and warrant an overhaul (or once-over) of the pump. When downtime hurts the bottom line in your operation, it pays to have a veteran 3408 tech fix, calibrate, test, properly time, and even reinstall the injection pump.
Problem #6: Cracked Exhaust Manifold
Cat 3408 Semitruck Diesel V8 Engine Exhaust Manifold Rust
Speaking of age and corrosion, it shows its face on more than just the 3408’s injection pump. Not unlike many other diesel power plants, its exhaust manifolds are susceptible to cracking. And because there are two exhaust manifold assemblies on the 3408, you get twice the worry. While the exhaust manifolds don’t see boost pressure, they do see drive pressure and are responsible for routing exhaust gases into the turbine side of the turbocharger (i.e. driving it). With a cracked manifold, exhaust gases escape, dropping both boost and drive pressure. This means a loss in responsiveness, power, and fuel economy.
What Happens
Cracked Exhaust Manifold Cat 3408 Turbodiesel Engine
Heat cycles, extreme heat from abuse, age, and corrosion from exposure to the elements can all contribute to a cracked exhaust manifold on a CAT 3408. Unfortunately, one of the worst side-effects of this type of failure is overheating—not to mention a mess of soot all over the engine bay. As a nightmarish bonus, exhaust manifold replacement is typically hampered by broken manifold studs. With time, the factory manifold studs become corroded and seize within the cylinder heads. They are prone to snapping off during removal. Thankfully, Caterpillar makes an exhaust manifold stud remover kit specifically for the 3408 (and 3406).
Solution(s)
Cat 3408 Diesel Engine Exhaust Manifold Stud Replacement
The only solution for a cracked exhaust manifold is a new one. But thanks to the manifold studs and their penchant for breaking off, the job can quickly go from a simple replacement to an all-day event. We would advise having the aforementioned exhaust manifold stud remover kit in your arsenal, sourcing new exhaust manifold studs and nuts, and using anti-seize on each new fastener during installation. Whenever possible, always source new exhaust manifolds. Although secondhand manifolds are available, the long-term durability of used versions is completely unpredictable.
Problem #7: Oil Leaks
Engine Removal Cat 3408 Oil Leak Repair Reseal Diesel Truck V8
Oil leaks are a part of life for most heavy-duty diesel engines. Once again, these CAT 3408’s are old. If you find one that happens to still be holding all of its fluids, consider yourself lucky. While the 3408 isn’t notorious for oil leaks like the 3406 is, like most diesel engines it too has its trouble areas. Decades of use (and abuse), thousands of operating hours, constant exposure to NVH and, to a lesser degree, the elements have a way of taking their toll on gaskets, seals, and O-rings.
Where Leaks Happen
Cat 3408 Oil Pan Gasket Failure Leak Main Caps
Every engine has its “hot spots” for developing oil leaks, and on the 3408 those locations are at the front and rear structure. To a lesser extent, oil escaping the oil pan is common. That’s followed in frequency by leaking front and rear main seals. It’s also not unheard of for a 3408 to develop oil leaks at the oil feed and return lines for the turbo. In a lot of cases, addressing an oil leak is put off until the leak can no longer be ignored. This is often because of the cost and labor hours involved.
Solution(s)
Caterpillar 3408 Diesel V8 Heavy Duty Engine Replacement
It goes without saying that solving an oil leak between the front or rear structure requires some digging. And with any 40- to 50-year-old engine, you’re bound to find other issues to address once you’re inside it. Without question, front or rear structure oil leaks are the most time consuming to address on the 3408. At the oil pan, the oil pan gasket is typically the culprit—although it’s not unheard of for an oil pan to corrode enough to develop a leak. Addressing front and/or rear main seal leaks is a straightforward process for most repair shops and, while it requires some special tooling, shouldn’t break the bank.
Problem #8: Oil Cooler
Oil Cooler Removal Cat 3408 Diesel Engine Contamination Failure
Hardworking, industrial-grade diesel engines need an oil cooler that’s up to the task of keeping engine oil temperature in check during the most demanding conditions. Just picture a Class 8 tractor-trailer operating at GCWR in 100-degree ambient conditions with the BrakeSaver fully engaged. On the CAT 3408, the oil cooler uses coolant to help maintain safe EOT. Its sizeable fluid-to-fluid heat exchanger is located on the passenger side of the engine, along the block. Though oil cooler failure isn’t as common on the 3408 as it is on the 3406, it still happens frequently enough that it made our Top 10 list.
What Happens
Plugged Oil Cooler Cat 3408 Diesel Engine Parts Failure
The oil cooler can fail to function properly in several ways, and the first is due to restriction. Passages within its internal core can plug up—often due to corrosion, casting sand, or some other contaminant—and hinder coolant flow. In other, more severe cases, the oil cooler core can crack, and even completely rupture. When the latter occurs, oil (which operates at a higher pressure than coolant) is allowed to infiltrate and contaminate the cooling circuit. The most common symptom of a failed oil cooler is finding oil in the engine coolant.
Solution(s)
Cat 3408 Replacement Oil Cooler Diesel Truck Engine Parts
The only sound solution for oil cooler failure is to start over with a new unit. However, before installing the new oil cooler it’s vital to make sure the cooling system is completely flushed clean of any engine oil. Flushing the system calls for water and a strong degreaser. Many old-timers are adamant that the powder form of Cascade dishwasher detergent works best. In addition to flushing the engine’s coolant circuit, take care that the radiator has been properly cleaned, too. Finally, start over with Cat extended life coolant (ELC).
Problem #9: Turbo Failure
Marine 3408 Cat Turbo Diesel V8 Engine
Despite hot-rodded Class 8 and performance marine engines being equipped with twin-turbo configurations, the CAT 3408 is predominantly a single turbo engine. The turbo is a fixed geometry unit that sits at the rear of the lifter valley in on-highway applications, opposite the position of the valley-mounted injection pump. On well-maintained engines (i.e. those that see regular oil changes and routine air filter replacements or cleanings), turbo failure is rarely a worry. But with maintenance neglect, engines that operate in dusty conditions, or for those with high miles, turbocharger health can become a big concern.
What Happens
Cat 3408 Heavy Duty Class 8 Diesel Engine Used Turbo
So, what can go wrong within a CAT 3408 turbocharger? Its journal bearings can fail, the thrust bearing assembly can die, the compressor wheel’s blades can become damaged, chip away, and become thin, the turbine wheel can overspeed, and the seals can let go. Typical symptoms associated with turbo failure are: low power, increased lag (or an engine that never spools), excessive black smoke, oil around the turbo, and squealing from the turbo (i.e. wheel to housing contact or bearing noise). In most cases, the cause is traced back to ingestion of foreign debris.
Solution(s)
Cat 3408 Diesel Gen Set Generator Turbo Engine
There are primarily two routes available when a 3408 turbo checks out. The first is to rebuild the original turbo. This is typically performed by a turbo shop using a minor component rebuild kit and ensuring the completed assembly is balanced. A second option is to source a brand-new/remanufactured turbo. New (or reconditioned) compressor and turbine housings, fresh compressor and turbine wheels, new bearings and seals, and a warranty make justifying the higher cost of this option easier to stomach. The upside to starting over with a new turbo is that it’s a direct swap replacement—meaning very little downtime for you and your engine.
Problem #10: Dropped Valves
Cat 3408 Diesel Engine Dropped Valve Failure Piston Damage
As far as valvetrain failures are concerned, it doesn’t get much worse than a dropped valve. It’s the kind of failure you can’t really prepare for, outside of overhauling the engine or pulling the heads for a related repair and discovering cracks near or in the valve seats. It’s also the type of failure that sometimes costs you an entire engine. Unfortunately, dropped valves are a common theme on high-mile engines, or those with excessive operating hours on the clock. Oftentimes, it’s a result of the owner rolling the dice on just how long his 3408 will last and then paying the price when it drops a valve.
What Happens
Valvetrain Failure Dropped Valve Carnage Caterpillar 3408 Diesel Engine
Age, countless heat cycles, and abuse can all contribute to dropped valves. And like many CAT engines, overheating can lead to the development of cracks within the 3408’s cast-iron cylinder heads. In time, these cracks can spread into the valve seat region. This can culminate in the valve seat becoming compromised, dislodged, and it falling in-cylinder. At the very least, the valves are destroyed, but many times the cylinder head itself incurs significant damage. Of course, the damage can be more extensive than that. Cracked or damaged pistons, gouged liners, and even connecting rod failure can all come about due to a dropped valve.
Solution(s)
Cylinder Head Repair Valvetrain Failure Cat 3408 Diesel Engine Machining
Bare minimum, cylinder head repair or complete replacement is in store in a failure like this. Oversized valve seats, pressed deeper into the head(s) than the OEM versions were, is a common request when buying and spec’ing a new cylinder head. As far as preventing the failure, a good maintenance regimen looks like this: routine and regularly scheduled valve adjustments, oil changes, the proper coolant in the cooling system (and maintaining the correct fill level), and putting a good operator in place. Lack of maintenance and extreme heat (be it via ECT, EGT, or even EOT) is never a path toward longevity with the CAT 3408.
