1994 Trooper cooling issues

I bought my 1994 Trooper S wtih the 3.2L sohc a year ago knowing that i would have some work to do on it( water pump, fan clutch, timing belt, valve cover gaskets, tube seals, intake manifold (upper only), upper and lower radiator hoses and ofcourse to top the cake a new thermostat. However today at 70 degrees it overheated.:banghead:
Its not vapor locked, i pressure tested and it held, there is no coolant in the oil, and it does not leak a drop of coolant.
At this point in time i am thinking a faulty senor because it drove 60 miles highway with no problems but once i hit the city and reduced my speed it start to read hotter then normal.
The only thing i did not replace was the lower intake manifold because its dry as a bone, could be leaking from the inside???
I know that to replace the coolant temp sensor i have to pull the lower intake but im not 100% thats the problem.

I am open to any suggetions at this point in the game.
Thanks for takin the time to read!

You've covered a lot of the possibilities there.

Just some suggestions to consider:

* stuck thermostat (even though you have replaced it)

* blocked radiator fins (external)

* blocked radiator tubes (internal)

* thermatic fan clutch

Should i pull the thermostat next time it gets warmer and see how she does? mor just buy a new one all together? i checked the radiator, no blockage i can see externaly and i have done a flush a week ago.

A thermostat can only be tested by taking it out (cold) and placing it in water and heating them both while observing readings on a thermometer.

A crude test can be done without a thermometer by just heating the water/thermostat and seeing if the thermostat actually opens.

Tip: you could *temporarily* test the vehicle without the thermostat in place - does it still overheat?

Flushing the radiator does not by itself guarantee that it is not partially blocked. Only a flow test by a rad specialist will really tell.

Overheating will also occur if your cooling system does not hold pressure due to leaks or a faulty cap (though you did say that you are not loosing any coolant).

hmm....i guess i should have a flow test done. the cap is brand new i bought that when i got the truck (its the cool saftey caps that i can manually releive the pressure fromt eh cooling system). i will have the radiator looked at and reply when i get the results.
thanks man!

No worries mate - I didn't think that you guys would be awake at the moment - it's 1:30PM on Tuesday afternoon here! :lol:

oh jeeze! its only 10:30 here in Minnesota!
you just seemed to have caught me at my online time :P

ok after further reveiw of my motor i determined that the brand new fan clutch was defective and working the opposite of how it should be (clutching when its cold but not when hot ) i replaced the clutch and now it seems to work!

Good one! :)

Also, make sure you have an OEM Isuzu thermostat ONLY in that engine, aftermarket therm's do NOT keep that engine cool enough.