The most important aspect in maintaining the quality of your pressure washer is ensuring that the pump is compatible with your pressure washer. If you plan to use your pressure washer a lot or use it for your business, consider getting a Triplex pump. It is quite expensive but it also lasts longer with consistent performance through every use.

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When buying a pump for your pressure washer, many people will recommend CAT and AAA manufactured pumps. So, what’s the difference between these two? To better understand what pump is suitable for your needs, let’s examine their differences based on various factors.

Differences Between CAT and AAA Pumps

AAA and CAT pumps have different configurations. Let’s compare their best-selling products to better understand the difference between the AAA and CAT pumps. Here are the differences between a CAT pressure washer pump model 66DX40GG1 (4000 psi) and AAA Pump 90039 Horizontal Triplex Pressure Washer Pump (4000 psi).

Product description

Because of its outstanding performance, the CAT Pump 66DX40GG1 is the leading pressure washer pump on the market, with a flow rate of 4.0 GPM and a pressure of up to 4,000 psi. CAT Pumps allows a quick changeover under any field conditions. It is ore-tested to fit engine covers with four bolts. This pump is compatible with most gas-powered pressure washers and provides powerful cleaning output for any application.

Although the CAT Pump 66DX40GG1 is pricy, it is one of the best pressure washers pumps available due to its improved triplex plunger which is built to deliver substantial power while maintaining a high flow rate. A built-in chemical injector makes it simple to operate, and each plunger is made of ceramic material for long-lasting performance.

This industrial pressure pump might be expensive but it’s designed to last for years. This pump is capable of continuous operation at is not prone to leakage. It has a 2.5 GPM flow rate, an improved oil seal, and a crankcase made out of cast aluminum.

The AAA Professional Triplex Pump model 90039, is very effective and can reduce engine stress while providing high output performance. This pump can also generate up to 4000 psi.


Both pumps are easy to install but some extra steps are needed to install the CAT pump to fit it perfectly without damaging the motor over time. The AAA pump is easier and faster to set up. It also features a sight glass and sealed oil mechanism, which eliminates the need for a dipstick. To help you install the pump as fast as possible, each package contains a siphon tube with a filter, fasteners, and shaft keys.

Thermal Relief Valves

The CAT Pump 66DX40GG1 does not have a thermal relief valve, although it can withstand water temperatures up to 140°F. 

The AAA pump 90039, on the other hand, includes thermal relief protection with its thermal relief valve to eliminate the risk of overheating. A pressure-adjustable unloader system makes it simple to determine the appropriate hydrostatic pressure needed based on your application.


The CAT pump 66DX40GG1 is a universal model that works best with horizontal shaft engines. This pump is great for ripping decals and cleaning concrete or corroded metal.

The AAA pump is ideal for gas-powered pressure washers with horizontal engines which may be used to clean walls, railings, pavements, automobiles, and more. Dual larger ball bearings are used in the 90039 model for improved durability, friction resistance, and long-term performance in the toughest cleaning environments.

Pump Replacement Compatibility

The major problem of pressure washer owners is finding a pump that is suitable for their equipment. To save you some time and money, here are some examples of pumps that you can replace with AAA or CAT pumps.

CAT Pump

  • 13 hp Honda 1 cylinder engine. A CAT Pump 66DX40GG1 is the ideal replacement for this engine to expand the lifespan of your equipment up to 1500 hours of operation instead of 650 hours with the 13 hp Honda cylinder engine. It can also increase the output pressure every use.

AAA Pump

  • Honda GX390 Engine 3500 psi pump with the 1-inch shaft. Replace this engine with a 90039 AAA Triplex pump to speed up your work. Make sure to fit this pump on the pressure washer’s bolt-up pattern and apply an anti-seize solution to the shaft and key. It will only take 10 minutes to replace your old pump with the new AAA pump.
  • Honda engine in a Dewalt washer. AAA pump 90039 will fit and operate well inside your Dewalt washer. Note that you also need to apply a small tube of anti-seize on the shaft.
  • Robin/Subaru 9.0 hp overhead cam engine in a Karcher 3100HD pressure washer. AAA Triplex pump is recommended for this type of engine configuration to solve the problem of a malfunctioning wobble pump and increase the start-up of the motor.


Both pumps can expand the operating hours of your equipment but more customers are investing in CAT pumps because they can last up to 25 years with proper maintenance.

Common Problems

You might face the following problems if you bought a CAT pump 66DX40GG1. Note that these situations happen rarely.

  • The oil cap is prone to breakage when too much external force is applied.
  • The pump won’t push water out because of water accumulation inside the crankcase.

AAA Triplex pump 90039 is concerned with the following rare issues:

  • Lasted for only a year because the pump won’t exert the required pressure.
  • The unloader failed during the test run, causing the engine to release the wand trigger.
  • Damage on the siphon barb fitting when improperly used for the first time.

Cost and Warranty

Both manufacturers offer a 5-year warranty period under terms and conditions. The AAA Triplex Pump 900039 costs around $450 and the CAT Pump 66DX40GG1 costs around $680.

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Overall, Which One is Better?

In general, CAT pump last longer than AAA pump based on many users. The better pump between these two is based on your application and usage. If pressure washing isn’t a daily task for you, either brand of pump replacement will work fine.

The CAT pump is suitable for most gas-powered engines but there is no thermal relief valve installed. Choose this pump if you want a strong flow rate of about 4 GPM. On the other hand, choose the AAA pump if you want a pump with an advanced oil seal and thermal relief valve.

Both pumps might be expensive but the investment for it will be worth it because they are designed to last longer.

This ends the comparison between the best-selling pumps of AAA and CAT manufacturers. Use this guide to know if any of these pumps is a suitable replacement for your old pump to avoid wasting time and money.

Editorial Contributors
avatar for Matt Greenfield

Matt Greenfield

Matt Greenfield is an experienced writer specializing in home improvement topics. He has a passion for educating and empowering homeowners to make informed decisions about their properties. Matt's writing focuses on a range of topics, including windows, flooring, HVAC, and construction materials. With a background in construction and home renovation, Matt is well-versed in the latest trends and techniques in the industry. His articles offer practical advice and expert insights that help readers tackle their home improvement projects with confidence. Whether you're a DIY enthusiast or a seasoned professional, Matt's writing is sure to provide valuable guidance and inspiration.

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