Cracked exhaust manifold

The specialist supplier who imports replacements for the 3.5-litre V6 describes cracked original manifolds as very common, and the shape of their catalogue tells the same story: they stock left and right castings, they warn that a junkyard unit has a high probability of being cracked too, and they list all three gaskets the job consumes. The symptom this entry leads with — a tick from the engine bay on a cold start that fades as the metal expands and the crack closes up — is not in that source; it is the ordinary mechanical reading of a cracked casting, and it is set down here as inference so a reader can weigh it as such. It is worth knowing because it is exactly why the noise is so often mistaken for a valvetrain problem and chased in the wrong place. This entry is scoped to the years the cited source covers; the later 3.8-litre trucks take different castings and are not claimed here. Two things to be careful about. An exhaust leak upstream of the oxygen sensor changes what the engine management sees, so a fuel-trim or sensor code here may be a symptom rather than a fault of its own. And any exhaust leak is a reason to keep the cabin ventilated until it is fixed; if you smell exhaust inside the vehicle, that is a different and more urgent problem than this one. Everything here comes from one specialist supplier's product documentation, which is why the entry is filed at the weakest tier: it is a trade opinion, not an aggregate of owners agreeing.

Gen 32001–2002Works worseAnecdotal

Drive gently — repair soonManeje con cuidado — repare pronto

Anecdotal. This entry is not backed by factory documentation — treat its values and steps as a starting point, not as if they came from the factory manual.

Anecdótico. Esta entrada no se apoya en documentación de fábrica — tome los valores y los pasos como punto de partida, no como si vinieran del manual de fábrica.

Symptoms

A sharp tick from the engine bay on a cold start
The tick fades or disappears once the engine is warm
The smell of exhaust around the engine bay with the hood up
A check engine light for an oxygen sensor or fuel trim reading

Likely causes

The manifold casting itself is cracked
The gasket between the manifold and the cylinder head has blown
The gasket at the pipe flange below the manifold has blown
A manifold stud has broken and the joint is no longer clamped

Diagnostic steps

Listen at the engine bay on a cold start, then again once it is at temperaturePoints toThe manifold casting itself is cracked · The gasket between the manifold and the cylinder head has blown
Look for black soot tracks around the manifold, its head joint and the pipe flangePoints toThe gasket between the manifold and the cylinder head has blown · The gasket at the pipe flange below the manifold has blown · A manifold stud has broken and the joint is no longer clamped
Clean the casting and inspect it along each runner and around the collectorPoints toThe manifold casting itself is crackedRules outThe gasket at the pipe flange below the manifold has blown
Check every manifold nut and stud is present and tightPoints toA manifold stud has broken and the joint is no longer clamped

Fix paths

Replace the gaskets and any broken stud

$$Difficulty 3/5

The cheap outcome, and worth confirming first before buying a casting. The head gasket, the pipe flange gasket and the third gasket the source lists are three separate parts and all three are disturbed by this job.

Partsgen3-exhaust-manifold-gasketgen3-exhaust-manifold-pipe-flange-gasket

Replace the cracked manifold

$$$Difficulty 4/5

Factory castings, aftermarket ones and used units are all on the table, and the supplier is candid that a used one is likely cracked as well. Whichever you choose, fit new gaskets — reusing them is how this job gets done twice.

Partsgen3-exhaust-manifold-leftgen3-exhaust-manifold-rightgen3-exhaust-manifold-gasket

Sources

Luso Overland — MONTERO Gen3 NM 3.5L Exhaust Manifold, Left / Driver: «if your Montero has a cracked manifold (as is very common on the original OEM ones)», with the three gaskets the job needsVendor cataloguearchived copy2026-09-02