Chrysler built the 5.9 Magnum, a naturally aspirated 5.9L V8 engine, from 1992 to 2003. The engine’s displacement is 360 cubic inches, so it’s also known as the 360 Magnum. The 5.9 Magnum was phased out in favor of the 5.7L Hemi in 2003. During the same time period, the 5.2 Magnum, a naturally aspirated V8, was used as a base engine option for Dodge Grand Cherokees and Jeep Grand Cherokees, has a little brother named the 5.9 Magnum.
A pushrod overhead valve small block gasoline engine family is used in the Magnum’s construction. The LA 360 V8 was in production from 1971 until 1993, when the 5.9 Magnum completely replaced it. Even though the Magnum is a more powerful version of the LA-series engine, the name “Magnum” was just a marketing ploy.
The 5.9 Magnum’s engine, despite being significantly larger, has been criticized for its lack of power when compared to Ford’s 5.4 Triton and Chevy’s 5.3 Vortec competitors, putting out 245-250hp and 335-350lb-ft. of torque. The lower gas mileage that comes with a big engine is a drawback. The engine has come in for more criticism because of its bad reputation as a gas guzzler.
Despite having a bad reputation compared to Ford and Chevy engines of the same era, the 5.9 Magnum is still a reliable engine. Ford’s Triton engines, on the other hand, had a reputation for being unreliable compared to the 5.3 Vortec.
5.9 Magnum Vehicle Applications
- 1998-2003 Dodge Dakota
- 1992-2002 Dodge Ram
- 1992-2003 Dodge Ram Van & Wagon
- 1998-2003 Dodge Durango
- 1992-2001 Dodge Ramcharger
- 1998 Jeep Grand Cherokee 5.9 Limited
Dodge 5.9 Magnum Common Problems
- Plenum Gasket Leak
- Cracked Cylinder Heads
- Timing Chain Failure
- Weak Front End
The 5.9 Magnum’s two biggest problems are leaking plenum gaskets and flimsy cylinder heads. Aside from these two flaws, the 5.9 is a solid performer. Depending on who you ask, people either love or hate their 5.9 software. People with no problems, on the other hand, appear to outnumber those with numerous problems.
1. 5.9 Magnum Plenum Gasket Leak
The 5.9 Magnum’s intake manifold, also known as the plenum, is made up of two parts. The cast aluminum manifold at the top of the plenum connects to a stamped steel plate at the bottom. The top and bottom sections are joined using a plenum gasket.
With time, gaskets on any engine are known to degrade or fail. The plenum gasket on the Dodge 5.9 Magnum frequently fails. There will be an air leak if the gasket fails, and the engine will lose vacuum pressure, which will cause a variety of problems.
Despite the fact that there are a number of ways to identify a bad plenum gasket, most people don’t find out the gasket is bad until their catalytic converter becomes obstructed. If the cat becomes clogged, you will experience a significant drop in power. When the catalytic converter is clogged, the engine’s pressure rises because air cannot efficiently leave the engine, which increases the risk of the cylinder heads cracking.
5.9 Magnum Plenum Gasket Leak Symptoms
- Engine pinging noise while accelerating
- Excess oil consumption
- Fouled spark plugs
- Rough idling
- Cylinder misfires (commonly cyl #8)
- Poor overall performance & lack of power
- Bad gas mileage
- Fouled O2 sensors
Diagnosing a Leaking Plenum Gasket
There’s no foolproof way to tell if your plenum gasket is bad, unfortunately. The fact that you’re experiencing some of the above signs and symptoms is a good sign. While there are some diagnostic techniques that can help you determine whether or not the gasket is bad, none of them are 100% accurate.
Using a flashlight, peer into the exhaust manifold through the open throttle body. The interior of the manifold should be free of any accumulated oil or sludge. If there is a buildup of oil or any other substance, the gasket is probably faulty.
A second option is to remove the valve cover and check the air pressure inside the PCV valve. There should be air coming from the valve cover; if there is a vacuum, then the gasket is leaking.
Plenum Gasket Replacement Options
Because this is such a common issue, there are numerous repair kits available on the market to address it. It’s a bad idea to use an OEM gasket replacement because the old one will most likely leak again. Instead of using a rubber gasket, Dodge used a metal gasket, which is also known to be a temporary fix.
A thicker metal plate with heavy-duty fasteners and brand-new intake bolts are used instead in aftermarket repair kits such as the Hughes Engine Plenum Repair Kit. An experienced shop can complete the replacement in 4-6 hours, but most do-it-yourselfers can do it in less than a day regardless of previous experience.
As a final option, upgrading the intake manifold with an aftermarket option that eliminates the two-piece design will be discussed later in this article. After getting rid of the two-piece design, the plenum gasket no longer exists. Increasing the engine’s power is also possible by upgrading the manifold and intake system.
2. Cracked Cylinder Heads – Dodge 5.9
The cylinder heads of the 5.9 Magnum are particularly flimsy. In comparison to the LA 360 engine, the new heads feature increased air flow, larger valve sizes, and an improved combustion chamber configuration. Despite these improvements, the new heads have a reputation for being unreliable due to their age.
Excessive heat is the leading cause of cracked cylinder heads. Increased engine temperatures can be caused by a variety of problems, including a lack of coolant, faulty water pumps, or a broken serpentine belt. Cast iron heads expand and crack as the temperature of the engine rises. Due to the valve seats being induction hardened into the heads rather than pressed in, the cracks appear most frequently between them.
Despite estimates that as many as 50% of 5.9 heads are cracked, the vast majority of these cracks are minute. There have been cases where people have driven for years with cracked heads and had no major issues, but this is something we don’t recommend.
Cracked Cylinder Head Symptoms – 360 Magnum
- Engine overheating
- Water in the oil (thick white stuff)
- Coolant or oil leaking from cylinder head
- Spark plugs are coated in gas
- Engine misfires
When looking for a cracked head, you should run a compression test or cylinder leakdown test.
Cylinder Head Replacement Options
It’s a risky game to play even with a small cylinder head crack because you can keep driving. When the heads of an engine crack, it can cause serious internal damage and necessitate the purchase of a completely new engine. As a result, we advise replacing cracked heads with aftermarket, stronger replacements.
Due to the high frequency of this issue, the Dodge 5.9 Magnum aftermarket head market is flooded with low-cost options. The cracking issue is eliminated in aftermarket heads thanks to the thicker metal in the combustion chambers and on the decks.
3. Timing Chain Failure
In order for the engine to open and close the valves, timing chains link the camshaft and the crankshaft together. The engine’s intake valves open to let gas and air in, while the exhaust valve stays closed to prevent back pressure.
The exhaust valve opens when the intake valve closes, allowing the engine’s exhaust gases to exit. The timing chain regulates the operation of the cylinders and valves through this process.
The timing chain stretches over time on the 5.9 Magnum, as it does on most timing chain engines. The 5.9 Magnum’s timing chain stretches around 100,000 miles, and this can be accelerated by not performing frequent oil changes.
While it isn’t strictly necessary to replace the chain every 150,000 miles, if it hasn’t shown any signs of wear or stretching before then, I’d recommend doing so.
It’s possible that a stretched chain will jump a few teeth and have serious consequences if it does. When the timing chain wears out, the timing of when the valves open and close is thrown off, resulting in poor performance.
Engine internals can bang against each other if the chain is severely stretched or the chain falls off its guides. This necessitates a complete engine rebuild.
Symptoms of Timing Chain Failure – 5.9 Magnum
- Frequent cylinder misfires (most common)
- Lack of power
- Rough idling/rattling while idling
- Overall poor performance
- Engine no start
The only way to fix a stretched timing chain is to replace it. We recommend using a double roller chain when it’s time to replace the old one. Using a double roller timing chain improves both strength and reliability while costing only a few dollars more.
4. 5.9 Magnum Weak Front End
The Magnum 360’s 5.9-liter displacement makes it a substantial engine with respect to weight. Unfortunately, the truck’s front ends, particularly on the 5.9-powered Dodge Rams, are a weak point.
Despite the fact that these issues aren’t necessarily engine-related, I felt the need to mention that these trucks may require additional maintenance. Parts must be replaced, as is the case with anything this old.
This means that as soon as the truck hits a certain amount of mileage, the front end components on the Dodge Ram will need to be replaced. These repairs aren’t out of the ordinary for trucks with a lot of miles on them, but you should be aware that problems with these parts may arise earlier than usual.
- U-Joints / ball-joints
- Axle seals and bearings
- Wheel bearings and joints
- Shocks / struts
- Tie rods
- Wheel hubs
5. 5.9 Magnum Transmission Problems
Despite the fact that this isn’t another problem with the engine, the transmission’s dependability is something to take note of. The 5.9’s 46RH and 46RE transmissions are, at best, shaky.
Beyond bad gearing ratios, transmission components like torque converters and cooling lines can fail. 44 transmissions frequently have problems with the reverse and overdrive assemblies as well. Tow drivers, especially those who use overdrive frequently, will run into problems much more quickly than those who do not tow and drive cautiously.
These engines are incredibly reliable when properly rebuilt with newer internal components. Because these are over 20-year-old trucks, even seemingly innocuous components like seals have degraded and worn out considerably since they were brand new. In general, if your transmission has more than 150,000 miles on it, it’s probably time for a rebuild.
Dodge 5.9 Magnum Reliability
Maintenance and proper care go a long way in making the 5.9 Magnum reliable. Many users have reported no problems with the product’s reliability, but the reviews are generally mixed. Those who do report problems tend to do so in great numbers. The fact that these trucks are over two decades old is probably a contributing factor.
Cracked cylinder heads are less common, but they are still a concern, and the cracks tend to be less severe, compared to the plenum gasket problem, which is virtually guaranteed. The 5.9 Magnum’s cruxes are limited to these two problems.
In contrast to other engines, the plenum gasket can be repaired for less than $200 with an aftermarket kit, and cylinder head replacements are inexpensive. If the truck has been driven in any way, the front-end components will almost certainly need to be replaced. As for the transmission, that depends on how it has been driven.
Up to 350,000 miles can be expected from these engines with proper maintenance. However, it’s important to note that the 5.9 will only last this long if all of the typical maintenance items are repaired. Water pumps, oil pumps, gaskets, seals, belts, and chains, among other things, will likely fail once or twice over the course of a journey of that length.