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how to change the thermostat


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hello folks this is my first post,i have a 97 deville 4.6 northstar and I just replaced thermostat.is there any way that air can be purged from system.the running temp seems to have went up about 10 degrees. Ive read about air being a problem but nothing about how to remove it...

I wouldn't worry about 10 drgrees.

The system has a pirge line to automatically purge the air from the system. It is connected to the surge tank at the top. Disconnect the line and hold it over the surge tank neck and start the engine. Coolant should flow out of the hose. If not, it is clogged - trace it back to the water pump crossover, remove the nipple tht is threaded into the water pump crossover and clean it out.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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thanks for that..also ive been reading a lot about fan operation ....my fans never run on low ..when I turn on a/c fans run on high never low speed is the middle relay responsible for low speed operation if not which relay should I be looking at...please and thank u

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From a schematic of the fans and relays circuit in the 1997 FSM page 6-176:

All three fans are involved with the fans speeds. There are TWO fuses, one shared with the A/C clutch relay (10 Amp AC COMP fuse) that powers the relays and the 50 Amp COOL FANS Maxifuse that powers the fan motors.

For low speed, relay #1 closes and the other two are open.

For high speed, relays #1, #2 and #3 close.

In low speed, the circuit is from the Maxifuse through relay #1, then to the LH fan and through the "open" contacts of relay #2 (which is SPDT) and then to the RH fan.

In high speed, the circuit is from the Maxifuse through relay #1 to the LH fan, then through the "closed" contacts of relay #2 to ground. Also, power from the Maxifuse goes through relay #3 to the RH fan.

If your fans turn on and off, relay #1 is working OK.

If the RH fan goes on HIGH and the LH fan stops at high temperatures, relay #2 isn't working right.

If the LH fan goes on HIGH and the RH fan stops at high temperatures, relay #3 isn't working right.

If they won't go on high speed even when the ECT reads over 234 F, both relay #2 and relay #3 aren't working right.

Relay problems can be due to a bad or loose connector on the fans or the PCM connector, or a broken wire in the wiring harness.

A short in the wiring harness that grounds both the DK GRN wire from relay #1 and the DK BLU wire from relays #2 and #3 can cause the fans to run on HIGH whenever the AC CLUTCH fuse is inserted. If the fans go on and off when you turn the A/C on and off, the DK GRN and DK BLU wires aren't shorted.

The fans pull a pretty good air flow on LOW. Are you sure that they are running on HIGH?

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