13/06/2024 8:35 PM


If You Really

Replacing a Caterpillar 3126 – Useful Information to Help Find the Correct Replacement Diesel Engine

So you have a truck with a diesel engine in your truck and it just went bad or is about to and your looking for a replacement. This article has some useful information that can help. If you are looking for one make sure you have the serial number and horsepower off your engine.

Some engines can change out for others, but it is important to note how many pins are on the computer. The older computers will have 40 pins while the newer engines will have 70 pins. They will interchange, but you will need an adapter wiring harness to make it work. Below is a list of serial numbers that will let you know how many pins are on the computer.

Number of pins on your computer:

  • 40 pin will be an older engine
  • 70 pin will be a newer engine

Serial Numbers:

  • 9SZxxxx 8YLxxxxx 7ASxxxxx = 70 PIN computer
  • 1WM = 40 PIN computer. Twin air induction on right side of engine
  • HEP = 70 PIN computer. Air inlet on left side of engine, one tube faces forward
  • 7AS – Can be used in place of a HEP – 70 PIN computer
  • 6RW = 70 PIN computer

If you are having trouble finding a good used 3126 with low miles you can use a Caterpillar C7. It will have 70 pins so make sure your computer has 70 pins also or you will need to buy an adapter wiring harness.

You can put the same model engine with a different amount of pins with the addition of the following harnesses.

40 pin computer to 70 pin harness = Mawk Industries Harness, Phone number 602-909-1961

70 pin computer to 40 pin harness = Caterpillar part number 133-8109

Your best value will be to find a used diesel engine, just make sure the place you are buying it from knows the miles off the computer. You are able to find out how many miles are on the engine by hooking up a pro link. All quality heavy truck salvage yards will have one of these.