Introduction
Owners of the Land Rover Discovery 3 (and early Discovery 4) know the factory plastic intake manifolds are a common failure point. Cracks, warping, and vacuum leaks can cause rough idle, reduced power, and check-engine lights. Until recently, the only fix was another OEM plastic manifold — but a cast aluminium alternative is now gaining traction in the Australian owner community.
Cast Aluminium Replacement Manifolds Are Available
Several aftermarket suppliers now offer cast aluminium replacement intake manifolds for the 2.7L TDV6 and 4.0L V6 petrol engines found in Discovery 3 and early Discovery 4 models. Made from billet or cast aluminium, these manifolds promise:
- No more cracking — aluminium eliminates the plastic fatigue that plagues OEM manifolds.
- Better heat resistance — aluminium handles under-bonnet temperatures without deforming.
- Long-term reliability — install once and forget about it.
These manifolds typically ship with new gaskets and hardware. However, they are not a drop-in replacement — there are a few things you need to know before ordering.
Installation Tips from the Field
A member of the Australian Discovery 3/4 Owners group recently shared their experience installing an alloy manifold. The overall process went smoothly, but they flagged one critical clearance issue:
“The fuel injector crossover pipe fouled on one of the alloy manifold bolts. I had to clearance the manifold slightly and use a lower-profile bolt to get it to seat properly. Watch for this before you torque everything down.”
Practical tips from the group:
- Dry-fit the manifold first and check clearance around the injector crossover pipe.
- Keep a selection of lower-profile bolts on hand — you may need to swap one or two.
- Replace all intake gaskets (don’t re-use the old ones, even if they look okay).
- Label your vacuum lines before disassembly — the TDV6 has several.
- Budget 4–6 hours for a first-time DIY install; experienced mechanics can do it in 2–3 hours.
Ticking Noise After Manifold Replacement? It’s Probably Injector Seals
Several owners reported a ticking or tapping noise that appeared after the manifold was replaced. After much discussion, the consensus from the group was clear:
“A ticking noise that starts immediately after manifold replacement is almost certainly a failed injector seal — not the manifold itself.”
When you disturb the fuel injectors during manifold removal, the copper sealing washers can fail to re-seat properly. Combustion gases escape past the seal, creating a distinct ticking sound that increases with engine load.
If you hear ticking after the job:
- Do not ignore it — a leaking injector seal can carbon-up the injector bore, making future repairs much harder.
- Replace all injector seals and copper washers, not just the noisy one.
- Use genuine LR or OEM-quality seals — cheap eBay seals often don’t last.
- Torque the injector clamp bolts to spec: 10 Nm + 90 degrees (confirm for your engine variant).
The PCV / Crankcase Ventilation Question
An interesting question was raised by a group member who noticed that both the old OEM manifold and the new alloy manifold had blanked-off PCV (positive crankcase ventilation) ports. They asked whether these blanking plugs should be drilled out to restore the PCV function.
The short answer from the community: it depends on your engine variant.
- Early 2.7L TDV6: The PCV system is integrated into the rocker cover, not the intake manifold. The blanked port on the manifold is normal — leave it alone.
- Later 3.0L TDV6 / SDV6: Some variants do route PCV through the manifold. Check your specific VIN against the parts diagram.
- Petrol 4.0L V6: The PCV system uses a separate hose to the throttle body; the manifold blank is correct.
Bottom line: Don’t drill anything unless you’ve confirmed your specific vehicle uses that port. Drilling a blanked port unnecessarily will create a massive vacuum leak.
Related Part Numbers
Here are the part numbers mentioned in group discussions for a complete manifold replacement job:
| Part | Part Number | Notes |
|---|---|---|
| Alloy intake manifold (2.7 TDV6) | Aftermarket (various — check eBay/AliExpress) | Cast aluminium; verify bolt pattern before ordering |
| OEM plastic manifold (2.7 TDV6) | LR013487 | Original Land Rover part; prone to cracking |
| Intake manifold gasket set | LR004380 | Always replace with manifold |
| Injector seal kit (OEM quality) | LR009794 (kit) | Includes copper washers and O-rings |
| Injector clamp bolt | LR004382 | Single-use stretch bolt — replace |
| PCV valve / oil separator | LR016625 | Replace while manifold is off |
| EGR valve gaskets (pair) | LR004322 | Optional but recommended |
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