CUB CADET 603P08720-0637 Black 42" Deck Shell RZT-SX 42 EFI Zero-Turn Lawn Mower Review

Overview

The Cub Cadet 603P08720-0637 Black 42" Deck Shell RZT-SX 42 EFI is a zero-turn lawn mower designed for homeowners with medium-to-large lawns who want commercial-grade cut quality without the commercial price tag. It’s built for efficiency, with an EFI engine that eliminates carburetor headaches, and a 42-inch fabricated deck that’s tough enough to handle uneven terrain. This mower is best for owners of 1 to 2 acres who prioritize speed, precision, and reliability over budget-basement pricing.

Who Should Buy This

• Homeowners with 1–2 acre lawns – The 42-inch deck and zero-turn maneuverability let you cut a full acre in under 45 minutes, making it ideal for properties that are too big for a push mower but don’t require a 60-inch commercial rig.
• Buyers tired of gas engine hassles – The EFI (Electronic Fuel Injection) system means no choke, no priming, no flooded starts. If you’ve ever spent 10 minutes coaxing a carbureted mower to life, this is your upgrade.
• DIY landscapers who value cut quality – The fabricated steel deck (not stamped) and adjustable cutting height (1.5 to 4 inches) give you a clean, even cut on fescue, Bermuda, or mixed lawns, with less scalping on bumps.
• Owners of sloped or obstacle-filled yards – Zero-turn steering and a low center of gravity let you trim around trees, flower beds, and retaining walls without constant forward-reverse shifting.

Key Features Breakdown

• 42-Inch Fabricated Deck Shell – This isn’t a stamped deck that dents easily. The fabricated steel shell is welded, not pressed, so it holds up to rocks, roots, and years of use. The deep-dish design improves airflow for better bagging and side discharge.
• EFI Engine (likely a 725cc or similar) – Electronic Fuel Injection adjusts the fuel-air mixture automatically based on temperature, altitude, and load. You get instant starts, consistent power on slopes, and up to 25% better fuel efficiency compared to a carbureted engine.
• Zero-Turn Steering with Lap Bars – Lap bars give you independent control of each rear wheel, letting you spin 180 degrees in place. This cuts mowing time by reducing passes around obstacles and eliminates the need to reverse constantly.
• Adjustable Cutting Height (1.5–4 inches) – A single lever adjusts all four spindles simultaneously. This is critical for seasonal lawn care: cut low in spring to prevent scalping, raise in summer for shade retention.
• Heavy-Duty Transmission – Likely a Hydro-Gear or similar sealed unit, which means no transmission fluid changes. The sealed system handles hills better than entry-level hydrostatic drives.
• Operator Presence System – The engine shuts off if you leave the seat with the blades engaged. This is a safety feature, but it also prevents accidental starts when you’re dismounting.

Pros

1. EFI eliminates carburetor problems – No stale fuel issues, no choke, no ethanol-related gumming. Start it after winter storage with zero drama.
2. Fabricated deck is built to last – Won’t warp or dent like stamped decks. Expect 10+ years of service if you keep it clean.
3. Zero-turn speed saves time – You’ll cut a 1-acre lawn in 40–50 minutes versus 60–75 minutes with a traditional tractor.
4. Quiet operation – EFI engines run smoother and quieter than carbureted equivalents. Your neighbors will notice.
5. Excellent cut quality – The deep deck and sharp spindles produce a manicured finish, even on tall or damp grass.
6. Single-lever height adjustment – Switching from low spring cuts to high summer settings takes 5 seconds, no tools needed.

Cons

1. No electric start option – You pull a rope. For a mower in this price range, a key start would be welcome, especially for those with arthritis or limited upper-body strength.
2. Deck cleaning is tedious – The fabricated deck’s welded seams trap grass clippings. You’ll need to scrape it after wet cuts or invest in a deck wash kit.
3. Not for tight suburban lawns – The 42-inch deck is too wide for narrow gates or tight spaces between houses. If your yard has 36-inch gaps, look at a 30-inch walk-behind.
4. Limited dealer network for service – Cub Cadet dealers are common in rural areas but sparse in cities. If you need warranty repairs, you may drive 30+ miles.

Bottom Line

The Cub Cadet RZT-SX 42 EFI is a smart investment for homeowners who want zero-turn speed and EFI reliability without stepping up to a $4,000 commercial mower. It’s not perfect—the manual start and deck cleaning are minor annoyances—but the fabricated deck, fuel efficiency, and near-instant starting make it a standout for 1–2 acre properties. If you value time over money and hate dealing with carburetors, this is your mower. Skip it if you have a tiny yard or need electric start.

Frequently Asked Questions

Q: Does this mower have a bagger or mulching kit included?
A: No, the base price covers the mower and deck only. You can purchase a Cub Cadet 42-inch bagger (sold separately) or a mulching plug for about $200–$350, depending on the kit. Plan for that cost if you don’t want side discharge.

Q: How does the EFI engine perform in cold weather?
A: Very well. EFI adjusts the fuel mixture automatically, so it starts in temperatures as low as 20°F without choke or throttle manipulation. It may crank a few extra seconds, but it won’t flood or stall like a carbureted engine.

Q: Can I use this mower on slopes?
A: Yes, but with caution. The low center of gravity and zero-turn design give it good stability on gentle slopes (up to 15 degrees). Avoid side-hill mowing on steep grades—zero-turns can tip if you turn aggressively. For slopes over 20 degrees, consider a tractor with a wider wheelbase.