I was testing the new water, thermostat, and fan plug. I let it idle under supervision until the thermostat opened and I discovered a leak in the rad. (Curious- the electric fan didn't come on) When I turned it off (or tried to) it ran on slowly util I gave it some gas. I have experince run on before, but only when the engine was really over heating, but the temp gauge was not critical at all. Is it a fact of life or is some thing wrong? Is this strictly a carb problem?

------------------
Colin Finkle
87 Sport Coupe Camaro, 5.0 L V8

 

Run-on or dieseling happens for one and only one reason: the combustion chamber is too hot. Acts like a diesel engine "glow plug" and the mixture self-ignites at the top of compressions stroke.

Why is the real question. Here's a few common reasons:

1. Idle too high. Shut that puppy down from 1300 RPMs and you're more likely to get run-on.

2. Lean mixture. Vacuum leak is the most common reason but not the only one. A vacuum leak will often cause a high idle, making the problem even worse.

3. Over-advanced ignition timing.

4. Heavy carbon buildup in the compustion chamber (can "glow" red hot even after the engine is switched off).

Any of the 4, or a combination of each will cause the problem. Carbureted engines can not just shut off the fuel supply as soon as you turn off the key, like an FI engine can.


[This message has been edited by Damon (edited September 03, 2001).]