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I have never sent out a post before so if I am doing something wrong please let me know.

My 2000 deville 4.6 N* run hot when I turn on the A/C, without the A/C on I can do the WOT but as soon as I turn it on it starts to run hot, What is causing this problem?, I need help PLEASE??????????

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Here is a list of things to check:

1) Is the engine in fact overheating?, or are you freaking out from the digital dash or analog gage, know the norms!

1a) check coolant level

1b) check coolant concentration, must be at least 50/50, can go up to 70/30 for higher boiling and lower freezing temps

2) check water pump belt and tensioner

3) pull purge line and check for coolant flow, before replacing hose check tank surge nipple for clog

4) check cooling fan operation, AC off, fans on at 228 off at 217 (plus or minus)

5) check cooling fan operation, AC ON, cooling fans on full time

6) check thermostat, if it has not been replaced, replace

7) check cap, if it has not been replaced, replace

8) pressure test system look for leaks at hose clamps, heater pipes, radiator tanks, surge tank, water pump

9) check for debris blocking radiator, check for proper air deflector location

10) if all of above items check out, have coolant checked for combustion by products (Napa sells a kit or some radiator shops do the test)

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It sounds like a cooling fan fuse, relay, connector, or motor to me. A quick check is to start the engine cold and turn the A/C on. Both fans should run at low speed. If not, there is a problem with them. If they both are on, run the OBD codes and post them here. here's how:

You can do this as a first step in the checklist process recommended by Ed Hall, which is excellent. Stay with us as you work this problem.

-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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I just put a new radiator in last week, it had cracked and ran hot, cat convertor was clogged, changed water pump, belt and tensioner, new radiator cap and Thermostat......I will pull the codes and post them....I am not a mechanic so when you say the surge tank is that the same as the reservoir tank???

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On the Northstar, it is a surge tank, not a reservoir. It is actually a pressurized tank that is part of the cooling system. See #3 in Ed's post. The purge line is the 3/8" line on the side of the surge tank near the top. Pull it with the engine idling (cold). There should be coolant flow. Is there? If so, quickly plug it back on. If not, locate and clear the blockage. This line, as its name implies, purges air from the sytem and if clogged will cause an overheat situation.

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  • 9 months later...

Hey I just wanted to thank all you guys again for the help with my car......The problem was a line (hose) between the engine and the firewall it was leaking just enough to make it run hot....You can't see it because it is way in the back, it will leak but will burn off on the engine....A mechanic says that a lot of people junk their cars for this $20 piece.

The CADDY is back on the road and doing well....Thanks GUYS!!!!

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