Investing in a pre-owned diesel pusher requires thorough due diligence. Our team recently completed a detailed pre-purchase inspection on a 2021 Tiffin Phaeton M-40IH, one of the most sought-after luxury Class A motorhomes on the market.
Chassis & Powertrain Performance
Built on Tiffin’s proprietary PowerGlide XSH Raised Rail Chassis, the 40IH floorplan provides a completely flat interior floor from the cockpit to the master bath.
- Engine:Cummins L9 8.9L Turbo Diesel (450 HP / 1,250 lb-ft Torque)
- Transmission:Allison 3000 MH 6-speed automatic
- Suspension & Brakes:Independent Front Suspension (IFS), front disc brakes, and HWH hydraulic automatic leveling system
- Capacities:39,600 lb GVWR, 10,000 lb hitch rating, 100-gal fuel tank
Inspection Focus: We conducted fluid sampling for both the Cummins engine and Allison transmission, verified air brake drop rates, checked slide-out hydraulic pressures, and confirmed zero structural stress fractures along the custom-designed raised frame rails.
Essential Specifications
| Feature | Specification |
| Overall Length | 41 ft 4 in |
| Exterior Height / Width | 13 ft 3 in / 101 in |
| Interior Height | 6 ft 11 in (83 in) |
| Basement Storage | 232 cu. ft. pass-through |
| Fresh / Gray / Black Water | 100 gal / 100 gal / 55 gal |
Key Inspection Findings by System
1. Exterior & Roof Integrity
- Roof Cap: One-piece molded fiberglass roof inspected for lap sealant degradation around key penetrations.
- Awnings & Paint:Tested full-body paint condition, Girard power patio awnings with integrated LED lighting, and slide-out topper tension.
- Underbelly: Checked heated basement compartments and thermal insulation layer for seals.
2. Electrical & Auxiliary Power
- Generator:Onan Quiet Diesel 10.0 kW generator evaluated under load with thermal imaging on breaker panels.
- Electronics:Tested 2,000-watt pure sine wave inverter, 50-amp power cord reel, and Firefly Multiplex system.
3. Interior Comfort & Floorplan Layout
- Bath-and-a-Half Layout: Inspected rear master suite dual-sink vanity, 31.75″ x 40″ fiberglass shower, and mid-ship half bath.
- Living Area:Verified 4 slide-outs (including King bed slide), Ultraleather seating, lift TV mechanisms, and central vacuum system.
- Galley:Tested residential French door refrigerator, induction cooktop, and convection microwave.
- Climate & Plumbing:Checked triple 15,000 BTU A/Cs with heat pumps and the Aqua-Hot hydronic heating system.
Inspection Summary
The 2021 Tiffin Phaeton M-40IH remains a premier choice for full-timing and long-distance touring. A professional pre-purchase inspection protects buyers from hidden structural, mechanical, or electrical failures before money changes hands.
