When you're working on a marine engine propulsion system, two very different parts can end up on your workbench: a set of inboard engine motor mounts or a flexible water pump impeller. One keeps the engine securely positioned and aligned; the other keeps coolant moving through the pump. The right purchase depends entirely on what your engine is doing wrong.
Quick verdict: If your engine is vibrating, shifting, or sitting at the wrong angle, the DF100 motor mounts are the structural fix you need. If the engine is overheating or the cooling pump isn't circulating water, the CAT 3412 impeller is the wearable part to replace.
| Product | Price | Role | Key Specs |
|---|---|---|---|
| DF100 Inboard Engine Motor Mounts | $119.95 | Pair of engine motor mounts | Cast aluminum base, elastomer element |
| CAT 3412 Water Pump Impeller | $83.24 | Cooling water pump impeller | Spline drive, brass insert |
Where each product wins:
- DF100 motor mounts are the pick when you need to support an inboard engine in a 4-point mounting setup up to 850 pounds. The low-profile design and corrosion-resistant steel parts are useful in a marine bilge, and the set includes both mounts for the job.
- CAT 3412 impeller is the pick when you're servicing the cooling water pump. It comes in at $83.24, which is $36.71 less than the motor mounts, and it's a replacement for CAT 3412 and C32 pumps with OEM part number references 1539123 and 1566892.
DF100 Inboard Engine Motor Mounts
This purchase includes a pair of DF100 motor mounts, each with a heavy-duty cast aluminum alloy base and an elastomer element that resists oil and fuel. The low-profile design requires only 1-7/8 inches of clearance from the casting base to the top of the leveling nut, which helps in tight engine compartments. Measured dimensions include a 4-inch overall height, a 4-inch center on bolts, a 5-inch length, and a 2-3/4-inch width, with a 5/8-18 stud. Steel parts are zinc dichromate plated for corrosion resistance, and the manufacturer recommends the mount for 4-point mountings up to 850 pounds. Choose it when engine alignment or sagging mounts are your main concern. The trade-off is the higher price relative to the impeller, and it's a structural part that must match your engine's bolt pattern and height requirements.
CAT 3412 Water Pump Impeller
This flexible impeller kit is a replacement for Caterpillar CAT 3412 and C32 marine engine cooling water pumps, referencing OEM part numbers 1539123 and 1566892 and used on CAT pump models 147-7850 and 212-7264. It uses a spline drive and a brass insert, and the kit is covered by a 1-year warranty. It's the lower-priced part in this comparison, so if you're refreshing a cooling pump, this gets the job done without the higher ticket of the motor mounts. Double-checking the outboard model, serial number, year, and horsepower before purchase is advised, since the impeller needs to match your pump's spline drive and reference numbers.
Final choice by use case:
If you're fixing a loose or misaligned engine, go with the DF100 motor mounts. If you're chasing an overheating engine and the cooling pump needs a new impeller, go with the CAT 3412 replacement. These parts serve different jobs, so the right choice depends entirely on what your boat needs right now.
