Well guys I am stumped and I need to turn to you for some help.

Working on a 1997 Sidekick sport 1.8.

I can not get the water pump to circulate any coolant.  I have had the thermostat out, the rad disconnected to try pulling coolant from a bucket (after filling the block with coolant).

Rad flows freely, I can pour coolant in the top of the engine and it comes out the bottom so I don't believe there to be any blockages.

Thermostat is new.  Pump is new.

Funny thing is I get circulation through my heater core.

I don't understand.  Any insights?

the pump is not the kind that will lift much water. sucking out of a bucket would not suck much and certainly not prime itself. i've never seen an impeller break off
it is overheating?
sounds like you have looked at the obvious.

Thanks for the reply.

Yes it overheats.  The upper rad hose builds lots of steam pressure and the lower stays stone cold.

strange- seems a little backwards from a bad thermostat, and i see you've replaced that....and run without thermostat?

perhaps pressure test the system(i have my own tester, but some parts store may lend one)

i have seen radiators loose enough of that fin stuff to not loose enough heat, but that would slowly overheat.

i don't think the pump is bad- that would be way weird.

I'm pretty sure the thermostat is operating correctly.

If I shut it down hot and disconnect the upper had hose and squeeze the lower hose fluid will come out the top.

Perhaps I should try run without it again.

Boggling.

I removed the spring from the old thermostat and using this everything works.  Runs cold of course but circulates at least.

Why on earth would these two new thermostats not operate properly?  I know it's the right part number and for reverse flow...I looked it up myself.  I tested it in my kitchen...I know it opens.  I know it's hot down there, the return from my heater which was getting scalding hot dumps right on it.

I did read a thread on another forum saying that he would only use a suzuki thermostat.  Is there really that significant a difference?

Thermostats have various temp ratings are you sure your is right for you engine...and you cant go wrong with OEM.

You could also have a blown head gasket...

Yes, positive the temperature is correct.

I sure hope it's not a head gasket...it runs beautifully otherwise and I don't see any other symptoms.

remove all the plugs and turn the engine by hand and take a look at the pistons if any look clean and shiny odds are you have a blown head gasket. Of course a compression test and leak down test are better ways to confirm...

Would running the thermostat open as I am now disguise a head gasket problem?

check the rubber on the bottom pulley, the rubber will wear out and the pump will not spin fast enough, (I know after about 275.00 for a new one) from the harmonic balancer, and yes some times the blades on the new impeller will spin on the shafts also so the blades just sit there in the pump.

i don't think it would mask it for long.
also, the low operating temp. could screw with the engine control. on mine the computer adjusts stuff until the engine is warmed up- like a choke. much more efficient when it's "hot".
you probably should try another thermostat.
if it continues to overheat as you decribed, i think you probably are looking at a head gasket.
it's only time and money.
the comp/leak test and pressure tests could confirm, and sometimes compression gas can be seen coming out the radiator fill(running, cap off). fix it before coolant starts mixing with the oil. that's hard on the bearings.

I agree, running cold is not a long term solution.  I just thought it might hide some symptoms when it is this way.

I guess I will try different brand of thermostat tomorrow and failing that do some head gasket testing.

I'm not sure what mrfuelish is referring to about rubber wearing down.  The pulley that drives the pump is just a metal pulley on this model.  Maybe on the 1.6 things are different.

Thanks again for all the guidance and help!  Will report back tomorrow.