Exhaust systems generate heat. Heat damages everything around it — fuel lines, plastic components, electrical cables, hoses. The Grenadier's exhaust routing has been engineered with specific clearance margins. If you're modifying the chassis, repositioning components, or lifting the vehicle, understand the thermal boundaries before you cut or drill.
Clearance Specifications: The Thermal Tiers
INEOS specifies three clearance scenarios, each dependent on shielding:
| Shielding Level | Minimum Clearance | Application |
|---|---|---|
| No shielding | 200 mm | Default — fuel lines, plastic lines, electrical cables |
| Sheet metal shielding | 80 mm | Metal barrier reduces radiant heat |
| Sheet metal + insulation | 40 mm | Tightest allowable margin |
Temperature context: the exhaust system generates temperatures exceeding 120°C between the catalytic converter and rear silencer near the floor pan. Fuel lines begin degrading around 60°C under sustained exposure.
The No-Modification Zone: Detailed
No modifications are permitted upstream of the main silencer. INEOS identifies this as "Area A" in the schematic — the catalytic converter, manifold, and connecting pipe. That's where your emissions compliance lives.
To be specific about what "Area A" includes and why each component is off-limits:
| Component | Status | Why |
|---|---|---|
| Exhaust manifold | No modification | Integral to emissions system design. Altering flow characteristics changes catalytic converter performance and may trigger emissions faults. |
| Catalytic converter(s) | No modification | Type-approved emissions component. Removal or modification voids emissions certification in virtually every market. |
| Connecting pipe (manifold to silencer) | No modification | Diameter, length, and routing are calibrated for back pressure targets. Changes here affect both emissions and engine tuning. |
| Flexible metal hose (decoupling element) | No modification | Absorbs vibration and thermal expansion between the engine and rigid exhaust. Altering it introduces stress cracks or exhaust leaks. |
| DPF (diesel models) | No modification | Diesel Particulate Filter is part of the emissions system. Removal is illegal in most jurisdictions and will trigger permanent fault codes. |
Exhaust Back Pressure
If you're changing exhaust routing downstream of the main silencer, you must measure exhaust back pressure before AND after the modification. If back pressure increases compared to the unmodified system, further refinement is required. Upon request from INEOS, these measurements must be verified by the body manufacturer.
Common Exhaust Modifications and Their Risks
Grenadier owners commonly consider several exhaust modifications. Here's what each involves and the thermal clearance implications:
| Modification | What It Does | Thermal Clearance Risk |
|---|---|---|
| High-tuck exhaust (axle-back) | Reroutes the tail section higher behind the rear axle to increase ground clearance for off-road use | Moderate — moves hot pipe closer to floor pan and underbody components. Must verify 200mm unshielded / 80mm shielded clearance is maintained to fuel lines, brake lines, and wiring above. |
| Cat-back performance exhaust | Replaces the entire exhaust from catalytic converter back with larger diameter, freer-flowing pipe and performance silencer | High — different routing changes all clearance relationships. Larger diameter pipe has different radiant heat footprint. Back pressure measurement mandatory before and after. |
| Exhaust tip relocation | Moves the exhaust exit point (e.g., from side exit to rear exit or tucked behind bumper) | Moderate — new exit point must not direct exhaust gas onto tyres, fuel tank, plastic body panels, or into the passenger compartment through any opening. |
| Suspension lift (indirect effect) | Lifting the body 40–65mm changes the relative position of the exhaust to all surrounding components | High — the exhaust stays in roughly the same position relative to the axle, but body-mounted components (fuel lines, brake lines, wiring looms) move upward with the body. This can REDUCE clearances that were factory-adequate. Must re-verify all three thermal tiers after any lift. |
Accessory Installations and Exhaust Awareness
Exhaust thermal clearances aren't just a concern for exhaust modifications. Any bolt-on accessory that changes the vehicle's geometry, weight distribution, or underbody layout can shift the equation. Owners building out their Grenadier for overlanding or daily utility need to think about exhaust proximity at every step.
Side Steps and Rock Sliders
Side steps mount along the rocker panels — the same corridor where exhaust pipes route from the engine bay toward the rear. Quality side steps like those from DVA Mechanics are engineered with proper standoff distances, but owners who fabricate custom brackets or relocate factory mounting points need to verify they haven't introduced new pinch points between the step structure and the exhaust pipe. The 200mm unshielded clearance rule applies to any structural metalwork near the exhaust, and side step cross-members that bridge the gap between frame rails can easily encroach on that envelope if not designed with the exhaust routing in mind.
Rear Carriers and Departure Angle
Heavy rear carriers — spare tyre swings, jerry can holders, recovery gear mounts — add significant weight behind the rear axle. This additional load compresses the rear suspension, effectively lowering the rear of the vehicle and changing the relationship between body-mounted components and the exhaust. A DVA rear carrier loaded with a full-size spare and two jerry cans can add 60–80 kg to the rear overhang. On a stock suspension, that compression can reduce exhaust-to-body clearances by 15–25mm — enough to push a borderline clearance below the 80mm shielded threshold. If you're running a loaded rear carrier, check your clearances with the vehicle fully laden, not empty on a lift.
LED Lighting and Underbody Wiring
Auxiliary LED light kits — whether mounted on a DVA utility belt, bumper mounts, or routed underneath for work lighting — require wiring that often runs along the chassis rails. These wiring harnesses must respect the same thermal clearance tiers as factory wiring. Routing LED power cables or signal wires within 200mm of an unshielded exhaust section is asking for melted insulation and intermittent shorts. Plan wiring runs on the opposite side of the chassis from the primary exhaust routing wherever possible, and use high-temperature sleeving where crossover points are unavoidable.
Roof Loads and Suspension Compression
Even accessories mounted far from the exhaust can have indirect effects. A full roof setup — DVA crossbars loaded with a rooftop tent, solar panels, or a Starlink mount — adds weight that compresses all four corners of the suspension. The cumulative effect of roof load plus rear carrier plus passengers and gear can drop the chassis 30–40mm from its unloaded ride height. That's 30–40mm of lost clearance everywhere the exhaust passes near body-mounted components. Always verify thermal clearances at full gross vehicle weight, not with an empty vehicle on jackstands.
The Loaded Vehicle Check
After installing any combination of accessories — side steps, rear carriers, roof loads, bumper-mounted equipment — park the fully laden vehicle on level ground and inspect every point where the exhaust passes within 300mm of any component. Measure at ride height with realistic load. Factory clearances were validated at kerb weight with driver only. Your build is different.
Forum Reports: What Goes Wrong
Lessons from the Community
- Melted wiring loom after lift: An owner installed a 2" body lift without checking exhaust clearances. The body rose but the exhaust stayed put. A wiring loom that previously had 120mm clearance from the exhaust was now at 40mm — without shielding. The insulation melted within two weeks of driving. The repair required replacing the entire loom section.
- Heat-damaged fuel line: A high-tuck exhaust installation brought the rear pipe within 80mm of a fuel line section — acceptable with sheet metal shielding per the thermal tier table. The installer didn't add shielding. The fuel line's outer jacket softened and deformed, caught during a routine underbody inspection before failure occurred.
- Back pressure fault codes: An aftermarket cat-back system with wider piping and a straight-through silencer reduced back pressure below the ECU's expected range. The engine management system threw persistent fault codes and the vehicle entered a subtle detuned state. Emissions output also increased.
- Exhaust drone at highway speed: Owners who replace the factory silencer with a "performance" unit sometimes get resonance frequencies that produce a low-frequency drone at 60–80 mph. The factory exhaust is tuned to avoid this. Replacing it is an acoustic gamble unless the replacement has been specifically developed for the Grenadier's exhaust note profile.
- Side step bracket contacting exhaust: An owner who installed aftermarket side steps with custom-welded brackets found one cross-brace was resting against the mid-pipe heat shield. The bracket absorbed enough heat over a long motorway drive to discolour the paint on the step and warp the mounting plate. Repositioning the bracket 50mm outboard solved the contact issue, but the warped plate had to be replaced.
- Clearance loss under full load: A heavily equipped Grenadier — roof tent, rear carrier with spare and jerry cans, four passengers and camping gear — sagged enough on the rear suspension to bring the fuel return line within 60mm of the exhaust mid-section. The owner only discovered it during an oil change when the mechanic flagged the fuel line's discoloured sheathing. Adding a simple aluminium heat shield restored the clearance to within spec.
Pipe Geometry
Pipe bend maximum: 90°. Bending radii must exceed 1.5d (1.5 times pipe diameter). Avoid additional pipe bends beyond what the original routing requires. The free cross-section of the exhaust pipe behind the main silencer must not be reduced.
Exhaust Gas Flow Direction
Exhaust gas must not enter the passenger compartment — especially when designing access points and doors. Direct exhaust flows on tyres, aggregates, hoses, cables, and sheet metal must be avoided.
If you change the direction of exhaust gas flow, the body manufacturer is responsible for functional safety of all exposed components.
Engine Cooling: Don't Touch It
The cooling system — radiator, grille, air ducts, coolant circuit — must not be modified. Cross-sectional areas of cooling air intake must be kept free. No warning plates, badges, or decorative parts in front of the cooler.
The Flexible Metal Hose
The decoupling element between exhaust manifold and rigid exhaust pipe must not be changed. It absorbs vibration and thermal expansion.
Common Modification Risks and No-Go Zones
Exhaust modifications are among the most requested — and most dangerous — aftermarket changes on the Grenadier. The thermal clearances specified by INEOS aren't conservative estimates; they're hard limits derived from materials testing.
The No-Modification Zones
- Flexible metal hose (decoupling element): Between the exhaust manifold and rigid pipe — absolutely cannot be changed. It absorbs vibration and thermal expansion. Replacing it with rigid pipe will crack the manifold or the pipe within months.
- Catalytic converter section: Surface temperatures reach 600–800°C during regeneration cycles. No wiring, hoses, or accessories within the specified clearance envelope.
- Turbocharger heat shield zone: The area around the turbo housing requires minimum clearances for both thermal radiation and airflow cooling. Mounting accessories here guarantees heat damage.
- DPF (Diesel Particulate Filter) area: During active regeneration, the DPF reaches extreme temperatures. Any modification that restricts airflow around the DPF risks thermal runaway.
High-Tuck Exhaust Modifications
Some aftermarket exhaust systems promise additional ground clearance by "tucking" the exhaust higher under the chassis. While the concept is valid for off-road use, the execution must respect thermal clearances to brake lines, fuel lines, and wiring looms that run along the chassis rails.
"I'm thinking wheels, exhaust, and a lightbar. I'm waiting for aftermarket ones that don't require an entire roof rack too."
— Grenadier owner discussing planned modifications, The INEOS Forum, January 2023
"If future modification, although not essential, will be to free up the exhaust system, a little bit for improved fuel economy and sound."
— Owner on exhaust modification goals, Reddit r/ineosgrenadier, October 2024
"I had a Milltek exhaust on a Renault Sport RS250 Megane and it sounded the business — heaps of pop and crackle on overrun. Not sure that's the vibe you want on a Grenadier."
— Forum member on exhaust tone expectations, The INEOS Forum, August 2023
"Mate, check your clearances after fitting side steps and sliders. My exhaust was practically touching a bracket — found it by smell before I found it by sight."
— Owner warning after accessory install, The INEOS Forum, March 2024
"Loaded up for a week in Scotland — roof tent, full rear carrier, the lot. Noticed a burning smell after the A9. Turns out the fuel line sheathing was cooked where it passes the exhaust. Stock clearance is fine unloaded, not so much with 300kg of kit."
— Owner reporting load-related clearance issue, The INEOS Forum, June 2024
What Goes Wrong: Common Failures
| Modification | Thermal Risk | Typical Failure Mode |
|---|---|---|
| Removing heat shields for "cleaner look" | Critical | Melted wiring, burned brake lines, underbody panel deformation |
| Routing accessories near downpipe | Critical | Plastic connectors melt, creating intermittent electrical faults |
| Replacing flex coupling with rigid pipe | High | Manifold cracks from thermal cycling stress, exhaust leak at engine |
| Aftermarket DPF-back without clearance check | Medium | Rear diff breather hose or fuel return line heat damage |
| Underbody storage near exhaust path | High | Stored items reach ignition temperature during long highway drives |
The principle is simple: measure twice, and if you're within the specified clearance envelope, don't mount it there. The exhaust system gets hot enough to ignite fuel, melt plastic, and weaken steel. Treat those clearance numbers as the minimum, not the target.