[slowmover]

The Cummins-brand thermostat is the one to have by what I have read. It opens partially at around 190F on mine, and comes fully open at 207F (which I have recently confirmed on mine; see miles in sig). Your year and model may be different slightly.

One must remember that a diesel is a highly stressed engine (cylinder pressure) and that, once the truck is doing the work for which it is designed, that the oversize cooling system becomes "adequate". Those who add gizmos, tuners, etc always run the risk that the extra fuel and engine timing will exceed this capacity (first noted on EGT; exhaust gas temperatures which exceed design parameters). Indeed, for towing, one is better off without them. There is no free lunch in the production of power without a trade-off. And, as cooling systems are the vehicle system most likely to be neglected (by all owners of all vehicles), it takes it in the neck.

This long preamble is my way of saying that I am aware that others have searched for alternate temp stats and found only -- to my knowledge -- slightly lower temp ones. I would say that, to raise coolant temp as measured currently would have only a minor benefit, but both using the oem block heater daily, and installing a grille block (partial; upper is what I'll try) one may be able to raise coolant temp faster, thus raising oil temps faster; or, on a marginally cool day with a long drive, raise combustion efficiency/lower internal friction to make the "risk" worthwhile.

We all of us -- race boys and hyper-milers -- tend to forget that the truck as a solo vehicle is almost outside of it's operating envelope. We always take a risk with component, system and vehicle reliability & longevity when we look to alter parameters to "improve" but one of many for which the truck is designed.

I do not ever wish to compromise the ability of the truck to do work. If that means slightly lower mpg -- the stock configuration -- so be it. There is plenty I can do to lower my overall cost of ownership of a particular vehicle and still have it do the same work as before. The expense of keeping one of these in like new condition takes more money than most will spend. They'll just "wear it out" in the expectation that there is always a new one around the corner . . never considering that what they drive now may be the very last vehicle they ever own.

Seen from this light, one has to plan -- to budget -- to replace things before they wear out. Failure affects other systems, not just the other components of the same system. Correctly done, one replaces entire systems before they fail, not a component here and there. To sum up: the cooling system works in a prescribed manner with some delicate components dependent on particular temperatures and chemistries. To alter the balance in order to force one outcome over others is to put reliability into question and to shorten longevity. These are highly expensive engines, so need I say what I think of those who like to hot rod these trucks?

You'll notice that those who get 1-million miles from a CTD are those who leave well enough alone and follow (or shorten) factory service intervals; in a good relationship with vehicle service facilities. Were I you, and asking this question, that is where I would spend this energy: a complete set of factory Field Service Manuals, and time taken to determine the best techs and mechanics in my area.

It's your truck and you'll do as you will, but, having asked my opinion and seen how I've learned (partly the hard way; that's where the above comes from) that some guiding principles must be in place, first, before ever operating one of these. Principle One: Leave well enough alone. Most of us are okay with maintenance schedules and the costs therein. But, emotionally, our society encourages immaturity in the costs of repairs. Just get a new one . . . .

Gasser engines are easier. And dirt cheap by comparison, practically disposable. "Mistakes" are easier to live with, too. A medium duty diesel deserves much more respect.

This has been my long way of saying that there are no easy magic gizmos or parts substitutions that will, in all ways, lower my cost of ownership. The opposite is not only more likely, it is more likely true. Be careful with your choices: the day you need to work it hard, will you want to change the thermostat?

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