Thread: Temperature Problems

I just replaced manifolds (2) and everything was fine except for coolant sensor code. Replaced coolant sensor, purged system of air pockets. Now gauge reads hot, but also varies. Never had the problem before! I'm perplexed.

!0 years as a mechanic 1984-94 ...Feb 2000 se with gt 3.8
Parts that have been replaced:
Coolant sensor
upper (delphi updated) and lower manifolds, felpro gasket sets
2 thermostats
lower rad clamp
Map sensor
pcv valve from kit
radiator cap 16psi
Dexcool replaced and comprehensive flush prior (system seems brown sludge free)
No visible leaks.

I replace the the thermostat since the last post, I noticed that the thermostat that came in the upper intake kit was not allowing the motor to heat up at times. now it is overheating. Seems there is an air pocket in the system as well.
The way I purged the coolant system is as follows:
At a cold state, I remove the rad cap and top off coolant. brake open the bleeder on the thermostat housing... then close bleeder.
Start the motor, turn heater on high. wait until coolant begins to cycle (thermostat opens) crack the the bleeder again for sign of coolant ...then close.
Rev and hold motor at 2200 rpms and top off radiator with coolant.
Replace cap at this time, with rpms at 2200.
at idle I crack the bleeder once again with only coolant coming out.
heater on high is pumping out plenty of heat.
Drive the car 350 miles in 2 days.. gauge consistently on the high side.
Today after 15 mins apon startup on the freeway... climbs to almost over heat. Turn the motor off allow to cool enough to check fluid in rad. level is fine, over flow tank fine. Start the motor up, head back down the freeway... now no heat for 10 mins. air pocket????? am I doing it wrong or is there a secret here.

I am new here and never have posted on forums before.
The car I bought for my daughter 20 miles outside of town. she needs the car for college (first year). She drives it 90 miles a day just to school.
Please help.. thanx in advance, neither one of us is wealthy..

OK update...... tried again to purge air from system, using an old technic that I used to get the air out of the system..... well no air pocket. also put infrared gun on various locations on the motor. The readings were within 210 fh. BUT... changed the CTS/sending unit again.. after testing ohms impedance. sure the new sensor I replaced 2 weeks ago failed. Yep the guage was not accurate.... that did not explain the vary in temp but the large vacuum leak does (right above the bleeder for the TS housing) when cold no vacuum noise.. engine hot with hood closed.. noticeable. I'm sure it running a bit lean and messing with the PCM and fans had soething to do with this bizar experience. leave it to me to come up with this. Thanx for the data presented to me folks. Poor shame not one reply with everyone on board here,