Low temp thermostat

[Geoff Richards]

<snip>
Grumpy wrote
>IMHO it's a cheap + dirty way to "feel" faster.  In some back to back 
>testing when optimized for AFR, I found no difference, and since I care 
>about the engine I went to 190.
>  
>For every day use, I use a 190..
>I still haven't seen a good reason for a 160/140 thermostat, period.
>Other than it feels faster, or someone who did this without trying to 
>optimize the AFR first.  
</snip>
Whats the best way to check the AFR without the expensive wide
range sensors, is the 10 led sensor or multimeter OK ?
BTW I am not building anything just checking on standard vehicles
to get a better idea of the workings
where I work we do not have any emission test equipment :(
Geoff