2003 expy 4x4 5.4 "overheating"

[wcm7823]

so of course my truck is due for a state inspection that ive put off all month and now everything is crapping the bed. i just replaced thermostat becuase the truck was overheating and going into limp mode. didnt fix it. im not sure how to "test" water pump.

symptoms: truck will run fine for 10 min then temp starts bouncing up finally high temp light comes on.
once or twice i was able to put truck in neutral, turn key off and restarted and temp gauge read halfway and ran another 5 min until it overheated.
i took off top radiator hose expecting to see water "pump" out of radiator. it didnt and brand new thermostat never opened (water still in top radiotor hose.
radiator hoses not getting hard.
cel is on but can drive to get tested.

any other trouble shooting steps i can do before i replace water pump and temp sensor "if i can find it"

 

[Bedrck47]

http://www.expeditionforum.com/f42/overheating-25045/#post204527

read this recent thread then get back to me

 

[Bedrck47]

have you had the codes read being you have the CEL on if not get them read and post them

 

[wcm7823]

thanks that thread helped immensely. almost exact issue im having going to change out sensor tonight.

 

[Bedrck47]

bet you won't change it out tonight as you need to pull the intake to get to the sensor

see about getting the codes read first

 

[Bedrck47]

the 03 has both the engine coolant sensor and the cylinder head temp sensor the CHT sensor is under the intake the ECT sensor is on the right rear of the engine see attached prints

 

[Bedrck47]

you could remove the t/stat just to get you passed inspection buy keep an eye on things

 

[wcm7823]

ok so i changed the cht (didnt have to take manifold off) but that didnt fix anything truck has been sitting for 2 hours and the needle is still pegged. pulled off top radiator hose while running, water was gushing out so water pump should be good. something i just noticed when i first turn key on temp is pegged but if i shut off and turn key on again temp sits in the middle range. took alt back off and looked at the plug it was a little green with corrosion so i scrapped it best i could but no change. should i start thinking about the rear sensor?

 

[Bedrck47]

again I ask did you get the codes read

 

[wcm7823]

only code it reads is p1299

it hasnt been started in 4 hours but through scanner coolant temp is anywhere from 225-316 degrees