When the engine gets hot does the heater blow hot air?
If the engine gets hot and the heater wont blow hot air and then when the temp falls rapidly and the heater starts to blow hot air. You either have a head gausket problum or their is some pesky air trapped in the system.

Good point bobcat

yes the heater does blow hot air as of right now, i dont think it would be a headgasket issue since i had the head reserfaced with a .020 over headgasket and studs, i wondering if it is becasue there is not enough water, i will take a look at it tomarrow and throw a new t-stst in anyway

is the water temp supposed to fluctuate or is it supposed to stay at one consistant temp?

Should rise up to 200 ish then fall below 190 when the thermostat opens. 50/50 is the max concentration you need on antifreeze, it does not cool as well when you go above that number for some reason. Crankcase breather vent blowing cra* into your radiator?
Good Luck!

nope no crap in the radiator, just replaced the head gasket last week and the t-stat with less than 50/50 concentration now it pops just past the 190 and drops below about 1/3 between the 190 and 140

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heres my thought if i cant get a 160* thermosats. back in the day my dad and granpa used to take there thermostats out of there trucks and just run them open in the summer, i cant imagine it being hard on a an engine, corect me if im wrong. an other way to do it is totaly elimintate the thermostat and put a sorta electric valve in instead of the thermostat and set it up on a heat timer to pop at whatever temp i want

You don't want to run without a t-stat, especially on diesels. It will take them too long to warm up, and it will wear out the engine faster.

If the temp still fluctuates, need another new t-stat.

holy hell ive done 7 t-states since i bought this thing. i would rather run a 160* one if they make it, are the ones from cummins better quality than the napa ones

Coolant has to be mixed 50/50 because ethyl glycol alone does not have the heat shedding properties that H2O does, it is a false statement in the fact that it is "COOLANT", it is an additive to help with freezing ( I mix mine 60/40 water to anti).

I would spring for a geniune Cummins thermostat, I will see if I can find the number I bought, it doesn't seem to have a real temp. swing like some experience.

ill call cummins northwest and get one of them from them tomarrow, i know i had 3 gallons of anti freez to 1 gallon of water 75/25 mix. i lost the radiator amount threw the blown head gasket and filled it with streight water. whatever that mix is then. we pulled the head and replaced the gasket and i filled it with one gallon of antifreeze and one gallon of water. so whoever is good with math figure that one out