I think fast idle or a bit more will keep the coolant in the bottle. But I also think that the sniffer will pick up combustion gases with the engine off. The mechanic will know for sure.

alistair

On 2011-09-20, at 10:55 PM, Travis Newhouse wrote:

> Alistair:  I have seen mention of testing for exhaust gas in the
> coolant.  Can you describe the procedure?  Can I let the engine idle
> with the expansion cap off (without making a mess)?  Or, can the
> sniffer be placed in the overflow tank?