i bought a 4.3 liter 1990 blazer the other day and it has a few issues, one thing is the car will run at 180 degrees at idle but when driving temp will reach 240-260. I replaced the radiator, hoses, thermostat (180), and tempature sending unit. I also tried running the heat while car was running. What could this problem be , water pump???

Another problem is the car will not hold idle. could this be the pcv valve, or egr valve?

motor has 200k miles but was rebuilt 150k miles ago

 

bad water pump is possible but usually if they are
turning they are pumping-when it is hot are the
radiator hoses hot and hard?is the air blowing back from
the fan warm? fan blowing right way?(in case it has
been replaced with wrong rotation)If coolant is
circulating well,timing could be wrong causing excess
heat while driving..

 

yeah the hoses do become hard and hot while running, and no the heat dosnt work in car ... will not blow hot air. but the engine fan is blowing cool air onto motor and going the right way

 

i'd say water pump. i can't remember, but do those gen blazers have air dams? i could have sworn that my dads '83 s-10 had one, but not sure if that has changed from 83-90.

 

Have you verified the sending unit and/or gauge is correct on the temp?

 

problem fixed... open the radiator when car was running and didnt see anything flowing in there... so i was guess it was the pump... replaced the pump and now the 300 $ blazer runs like a champ, also replaced a pvc valve and car stalls alot less often