What to Look For in Mopar Magnum Valve Cover Gaskets
TL;DR: A valve cover gasket is one of the cheapest parts on a 5.2 or 5.9 Magnum and one of the easiest to get wrong, because most repeat leaks are caused by the wrong gasket family, a distorted cover flange, or an installer treating a molded gasket like a cork one. Buy for your specific engine and cover — Magnum parts are not interchangeable with the earlier LA small block just because the displacement matches. Favour a molded gasket with a rigid carrier over a soft flat gasket when the application offers both, replace the breather and PCV grommets while the cover is off, and torque the fasteners in the factory sequence to the value in the service manual rather than to feel. Confirm current part numbers against the manufacturer catalogue before you order.
What the Gasket Actually Has to Do on a Magnum
The Magnum is Chrysler's 1992 through 2003 evolution of the small block, sold as the 5.2L and the 5.9L in trucks, vans and Jeeps. It is a pushrod V8 with a hydraulic roller valvetrain, and the area under the valve cover is a busy, oily place: rocker gear throwing oil at the cover roof, drain-back passages returning it to the pan, and crankcase vapour on its way to the PCV system.
The gasket has three jobs, and the order matters:
- Seal against oil that is splashed, not pressurised. Valve cover sealing is a low-pressure problem. What defeats it is not pressure but heat cycling, flange distortion and a gasket that has taken a permanent set.
- Hold a controlled crush. The gasket has to compress enough to conform to both surfaces and no further. Over-compression is the single most common self-inflicted cause of a leak that comes straight back.
- Stay put through thousands of heat cycles. Under-hood temperature swings work the joint constantly. A material that hardens and shrinks will eventually let go at the corners even if it sealed perfectly on day one.
Everything below follows from those three jobs. Valve cover gaskets and the rest of the sealing hardware live under Gaskets & Seals.
Know Which Engine and Which Cover You Have Before You Buy
This is where most wrong orders start. "318" and "360" name a displacement, not an engine family. The earlier LA small block and the later Magnum share those displacements but differ in head casting, valvetrain and cylinder head detail, and the valve cover interface differs with them. A gasket listed for an LA engine is not automatically correct for a Magnum, and vendor listings that lump both under one displacement heading are the reason people end up returning parts.
Before ordering, confirm three things on the engine in front of you:
- Engine family. Magnum or LA, established from the casting and the vehicle's build information rather than from displacement alone.
- Cover material and construction. Applications across this era used stamped steel and composite covers, and a replacement gasket has to suit what is actually bolted to your heads. Look at your covers rather than assuming from the model year.
- Fastener arrangement. Note whether the fasteners load the gasket through a perimeter rail or pass through the roof of the cover into the head, and whether they use sealing grommets or spacers. The two arrangements load a gasket very differently, and a gasket designed for one will not behave correctly in the other.
Everything for this engine family is grouped under Mopar LA & Magnum Small Block Parts. Confirm the current part number against the manufacturer catalogue for your year and application before you commit.
Gasket Materials Compared
| Type | How it behaves | Reusable | Best suited to |
|---|---|---|---|
| Molded rubber or silicone with a rigid carrier | Carrier controls crush so the fastener cannot over-squeeze the seal; conforms well and recovers between heat cycles | Often yes, if undamaged and not hardened | The default choice on a Magnum when the application offers it, including engines that come apart more than once |
| Molded rubber or silicone, no carrier | Seals well when new, but relies entirely on correct torque to avoid over-compression | Sometimes | Applications where no carrier version is catalogued |
| Composite or fibre | Firm, tolerant of a slightly imperfect flange, inexpensive | No | A budget repair, or a cover flange that is not perfectly flat and cannot be straightened right now |
| Cork or cork-rubber | Soft and forgiving on first fit, but shrinks and hardens with age and is easy to crush | No | Older-style applications; generally the least durable option here |
If the application offers a molded gasket with a carrier, that is the one to buy. The carrier does something a torque wrench cannot fully do for you: it puts a hard mechanical stop under every fastener so the sealing element sees the same crush at every position, including the ones you cannot reach comfortably.
Two material notes worth knowing:
- Silicone tolerates heat and heat cycling well and recovers its shape between cycles, which is why it dominates modern molded gaskets.
- A gasket that arrives stiff, shiny and already taking a set out of the packet is old stock. Rubber ages on a shelf. Check what you received before it goes on the engine.
What Belongs in the Kit — and What Does Not
A valve cover job is a good moment to replace the small rubber parts that live in and around the cover, because they age at the same rate as the gasket and you have the cover off anyway. Look for a kit that includes, or buy separately:
- PCV grommet. A hardened, cracked grommet leaks oil and unmeters crankcase flow at the same time. It is a small part with an outsized effect on both a leak complaint and an idle complaint.
- Breather grommet, where the application uses one.
- Fastener grommets, seals or spacers if your cover arrangement uses them. These are consumables. Reusing a hardened one is a common cause of a weep at a single fastener.
- A replacement cover, if the flange is distorted past straightening or the sealing surface is pitted.
What does not belong on the list: spark plug tube seals. Those are an overhead-cam feature, where the plug drops down a tube through the cam cover. The Magnum is a pushrod V8 with the plugs entering the head from the side, outside the cover entirely. If a listing offers you plug tube seals for a Magnum, the listing is wrong, and that is a fair signal to check the rest of that vendor's fitment data before trusting it.
Related sealing and valvetrain hardware is grouped under Full Gasket Sets and Valves & Valvetrain.
Installation Habits That Decide Whether It Leaks Again
The gasket is rarely the reason a repeat leak happens. These are:
Flange distortion. Stamped covers deform around the fastener holes when they have been over-torqued, usually pulled up into a dimple at each hole so the rail between holes no longer touches the gasket. Lay the flange on a known-flat surface and look for light underneath. Mild distortion can often be dressed flat carefully with the cover supported; a badly dished or creased flange should be replaced.
Surface prep. Both faces must be clean, dry and free of old gasket material and old sealer. Take care around the head rail: aggressive scraping and power abrasives leave scratches that give oil a path and drop grit into the valvetrain. Cover the head openings before you clean.
Sealer discipline. A molded gasket is designed to seal without sealer, and coating one in RTV usually makes it worse — it slides on uncured sealer and squeezes out of position as you torque it down. The exception is a small bead at a step or corner junction where two sealing planes meet, if the service manual calls for it. When the manual does specify sealer, use the type specified and respect the assembly time window.
Torque and sequence. Valve cover fasteners are low-torque by design. Tighten them in the sequence and to the value the factory service manual gives for your engine, working up in stages rather than pulling each one down in a single pass. If you find yourself reasoning about how tight it feels, stop and look up the number. Over-torque is what caused the flange distortion described above.
Re-check after a heat cycle. Once the engine has been up to temperature and cooled, look at the joint again. Whether the fasteners should actually be re-checked at that point depends on the gasket type and the manufacturer's instructions, so follow those rather than a universal habit.
When the Cover Gasket Is Not the Source
Oil ends up on the side of a Magnum block from several places, and a valve cover gasket often gets replaced twice before someone finds the real one. Before you buy, clean the engine thoroughly, run it, and find the highest wet point. Oil travels down and back with airflow, so the top of the trail matters, not the puddle. Common look-alikes on this engine family include the intake manifold end seals, the distributor and its sealing surface, the front cover area, and a crankcase ventilation system that is not flowing — which pressurises the crankcase and pushes oil out at whichever joint is weakest, often the valve cover you just resealed.
Frequently Asked Questions
Are LA and Magnum valve cover gaskets interchangeable? Do not assume so. They are different engine families with different heads and different cover interfaces, and matching displacement badges do not make the parts common. Identify the engine family first, then order to that, and confirm the part number against the manufacturer catalogue for your year and application.
Can I reuse a molded valve cover gasket? Sometimes. A molded gasket with a rigid carrier that is still pliable, undamaged, correctly seated and free of hardening or tearing can often be reused, and some manufacturers say so explicitly. A gasket that is hardened, cracked, distorted, or that has taken a permanent set is finished. Given what the part costs relative to the labour of doing the job twice, replacing it is usually the better call.
Should I put RTV on a Magnum valve cover gasket? Generally no. Molded gaskets are engineered to seal dry, and sealer smeared over the whole gasket tends to let it slide out of position during torque-down. The exception is a small bead at corner or step junctions where the manual calls for it. Follow the service manual for your engine rather than a general habit.
What torque do the valve cover fasteners take? Look it up. Valve cover fasteners sit in the low range typical of light sheet metal and composite covers, and the exact figure and tightening sequence vary by cover type and year. Torque to the value and sequence in the factory service manual for your engine — this is the fastener where guessing does visible damage.
Why does my valve cover keep leaking after a new gasket? In order of likelihood: a distorted cover flange that no longer contacts the gasket between fasteners, over-torqued fasteners crushing the seal, a leak that was never the valve cover to begin with, or a crankcase ventilation fault pressurising the case. Check the flange for flatness and confirm the PCV system is actually flowing before buying another gasket.
Do Magnum valve cover gaskets include spark plug tube seals? No, and they should not. Plug tube seals belong to overhead-cam engines where the plug passes through the cam cover. The Magnum is a pushrod V8 with the plugs in the side of the head, outside the cover. A listing offering them for this engine has its fitment data wrong.
Is it worth replacing the cover instead of just the gasket? If the flange is dished at the fastener holes, creased, or pitted across the sealing face, yes. A new gasket cannot bridge a surface that is no longer flat, and a second failed attempt costs more in shop labour than the cover does.
Sources
- General Chrysler small block background: the Magnum family of 5.2L and 5.9L pushrod V8s produced from 1992 through 2003 in truck, van and Jeep applications, with a hydraulic roller valvetrain, distinct from the earlier LA small block.
- Standard sealing practice for low-pressure cover joints: material selection, carrier-controlled crush, surface preparation, sealer discipline, staged torque in sequence.
- Common repeat-leak causes drawn from general engine service practice — flange distortion, over-torque, misidentified leak source, crankcase ventilation faults.
- Torque figures, tightening sequences, sealer specifications, reuse criteria and part numbers were deliberately left qualitative. Confirm each against the factory service manual for your model year and against the current manufacturer catalogue before ordering or assembling.
Questions on fitment for a specific year, engine family or cover type? Reach the Core Powertrain Parts tech team at sales@coretransmissionparts.com. Orders over $70 ship free.