Ask the Mechanic

Mystery Button

(Steve Thompson)

READER: I read with interest your previous column regarding the Simms injector pump on a 3000 Ford tractor. I have one, too, and have always wondered what the purpose of that little rubber coated button on the side of the pump is. It does not look like it is any kind of transfer pump. Can you tell me the purpose of this little button?

STEVE: Yes, sir. That little button (see photo accompanying this article) is there to be used for cold-weather starting. Many times, owners think the button changes pump timing for cold-weather starting, but it's there to allow the pump to inject a much greater amount of fuel into the injector for cold-weather-starting purposes. Any internal combustion engine requires excessive fuel for starting (like a choke on a gas engine), and a diesel engine is no different. That is why an older diesel puts out a black puff when it starts. The newer engine with engine controllers monitors ambient temperature and allows for cold-weather starting, as needed, without excessive smoke. If you live in Florida, you will probably never use the button; however, if you live in Michigan, you need to push it in for cold starting. When the engine reaches a moderate rpm, the button releases, and the pump works as usual.


-- Write Steve Thompson at Ask The Mechanic, 2204 Lakeshore Dr., Suite 415, Birmingham, AL 35209, or email, and be sure to include your phone number.


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