[stufr67]

I have a standard cooler setup for all grain brewing.  I was thinking of adding a pump.  As an incremental step I was thinking of using my brew pot as the RIMS direct fire heating.  I would use the pump to circulate through the mash cooler and back into the brew pot.  I would start with the full amount of water and just slowly step through temperatures that way and eventually just not push back into the mash, collecting the full boil in the pot.  Other than diluting the enzymes more since its effectively a very thin mash, is there another reason not to do this?

[klickitat jim]

Before the reasons not to, what is the reason to do it? What are you hoping to accomplish?

If I had a kettle with a false bottom (which I do) I would just mash in it and recirculate with the pump to keep the wort moving away from the hot bottom and to keep it flowing through the grain bed. You'll find it takes a very low flame to hold mash temps with this method. If it's hot out maybe no flame at times. I CAN do steps with it, but I'm not finding a real need to.

If I had a cooler mash tun, which I have never had, I would just use it normal style and vorlauf with a pitcher.

[mabrungard]

While the need to step through temperatures is generally unnecessary in modern brewing, the ability to target, hit, and maintain a certain mash temp is a very useful effect of the approach you mention. In addition, it has been proven that creating a truly homogeneous condition in a mash tun via mixing is VERY difficult...if not impossible. It turns out that it is far easier to move and mix the liquid than it is to move and mix the solid media. So moving to a pumped system will provide that benefit.

Then one thing I would caution is that the system needs to include good measures that avoid heat loss. The system needs to be capable of maintaining that target temperature without resorting to overheating the wort in the kettle. Remember that the enzymes that are working on the wort are in the liquid, not the solids. If you overheat the wort in the kettle, you will damage or alter the enzymatic activity. 

Finally, with the system you suggest above, it should be fairly easy to perform a mash-out temperature step  that can add a couple of Brix to the wort strength and that can improve your overall efficiency. Mashing-out is a PITA for most homebrewers, but your system could make it much easier and advisable. 

[stufr67]

Temperature control, mash density (enzyme density) and a good mash out are my primary concern.  I think I will use it to step temps, if the recipe or my mood calls for it.  Most importantly, I will start to recirculate to get to mash out.  Then I don't have to worry about thinning out the enzymes and I can loosen up all the sugars.

[ynotbrusum]

I have done direct heat step mashes (with a mash out) with success, but I have just constantly stirred and recirculated using a gallon pitcher at a slow drawoff rate.  It works but its work.  A pump sounds like a good way to go.  Why did I do the step mash?  A pro told me that the flavor of a Helles is improved going that route (protein rest included).  I am waiting on the results...still in primary for another week.