Tech Tip #115: Cummins A/Onan L Series Water Pumps

A guide to identifying your Cummins A/Onan L series water pump

This Tech Tip focuses on the Cummins A Series engine. While we specialize in Deutz, Deere and Perkins engines, many of our customers turn to us for help with their Cummins A Series engine.  It discusses how to identify the correct replacement water pump and gives a tip on how to install the pump. It is one in series of Tech Tips that we publish to advance the knowledge base in the industrial engine field.

The Onan L Series engine has had a short but troubled history. The Onan Corporation launched this water-cooled diesel shortly before the Cummins Engine Co purchased Onan in 1986. The Onan L Series was not widely adopted by equipment manufacturers. However this engine series was widely used in airport ground support equipment (i.e. GSE) such as airline baggage trucks, conveyors, and tugs. Shortly after Cummins bought the Onan Corporation they launched their B Series engine, which was offered in the same power and size category as the Onan L Series. Because of this overlap, Cummins emphasized sales and support of their B Series and renamed the Onan L, the Cummins A Series. They then gradually withdrew parts and service support from the Cummins A Series engine.

But, if you run a Cummins A Series we can help. This Tech Tip is designed to help you identify which Cummins A Series water pump you have and to assist you in ordering the correct one.

Identifying the Cummins A Series Water Pump

1. How many cylinders does it have?
   There are a total of 5 different water pumps for the Cummins A Series 4 cylinder engine and only 1 water pump for the Cummins A Series 6 cylinder engine.
2. How many thermostats are there?
   Three of the water pumps on the 4cylinder engines have a single thermostat, and 2 have a dual thermostat. The 2 dual thermostat pumps have different casting numbers. Casting number 170-3… is for the early version of this Cummins A Series pump and casting number 170-4 is for the late version. There is only 1 dual thermostat water pump for the 6 cylinder Cummins A Series.
3. What is the casting number?

There are three casting numbers: 920-8000, 920-8001, and 970-5587.

Installation Tip

When installing the 920-8991 pump in a 6 cylinder Cummins/Onan, be sure to install the mounting spacer between the block and the water pump. This spacer is depicted as “X” in the photo. If this spacer is not installed, the accessory drive belts will not line up. Lack of this spacer will also cause coolant leaks at the O-ring, depicted as “Y” in the illustration.

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Written by Dr. Diesel

Knowledge is power. Power to build ties to engine users. To build a relationship with our customers, we share with you our 105 years of knowledge in many ways. We have this special section called “Ask Dr. Diesel™” where you can pose questions about engines, transmissions, industrial hand clutches, exhaust scrubbers, etc.