Spark plug heat range

Thought I'd get some thoughts on heat ranges of spark plugs for older engines.

1] Ex. 100K, not burning oil, but plugs looking a bit fouled after around 15k on them. Engine running okay, but was better.

2] Ex. 60k, all is showing not so good, very brown deposits, engine stumbling but running

3] Ex. 120k, seems to be burning oil, black deposits on the plugs, but nada to do a $$$$ fix, just want to keep the ride going.

Approach this from a heat-range of the spark plugs, there is a certain method to my madness here, from all I have read so far of the prob.'s some members have faced.

TY for responding!!!!!!!!!!!!!

Well Tam, I'm not really sure what you want - and you're measuring in Kelvin (I think??) so that throws me off even more. But I thought I'd throw in this chart I had - maybe it'll help.

http://img92.echo.cx/img92/9408/charttempfiringend7ck.gif

Thanks, Lee, yeah that helps with my research. The Ex. means example, and 'course the 60k etc. are miles on the engine. My thinking is using a differring heat range on the plugs themselves to help remedy [short term] some engine problems members have, when they may not have the $$$ to do the more expensive fix.

The thing is to have some idea of how "hot" or "cold" to go for some hypothetical situations [as my three examples] without getting into making things worse than they already are. Such as detonation, sludging, such as that from over "cold" or over "hot" plugs.