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Old 02-01-2012, 10:52 AM
chrisjkruse chrisjkruse is offline
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Default overheats with ac OFF

Sorry if this has been answered before..but I couldn't find the answer to my particular situation in the archives:

The car overheats unless the AC is on. (it blew the cap off of the resovoir)

I have a laser temp guage and did several tests.

My conclusion is a bad temp sensor or temp sensor connection but I'd like to confirm this.

The 160 deg. thermostat opens at about 160 and water flows freely.
With ac off to eliminate the auxillary fan circuit..The fan does NOT COME ON EVER...then when checking the water temperature and the actuall sensor itself.. reaching over 230.. the warning light never comes on. Even when it blew the plastc cap off!

The temp light bulb is good.
The fan is good.(with ac on)
The radiator is perfect.
Stays cool with ac on.
Thank Chris
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Old 02-01-2012, 11:07 AM
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Lightbulb Re: overheats with ac OFF

There is a sensor/switch to activate the fan based on temperature in the manifold. (There is another one that tells the ECM what temperature the engine is. These are different sensors!) My guess is that the fan sensor/switch is either bad, its wire to the fan circuit if bad, or it is not connected.

The one you want to check has a single wire connector that is oval in shape and the "long" ends must be compressed to disconnect it. (i.e. turn an oval into a circle to remove) A picture is attached. The wire is green with a yellow stripe, I believe.
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Old 02-01-2012, 11:20 AM
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Lightbulb Re: overheats with ac OFF

Actually, check the fan connections and the fan relays, too. If it works on the high speed mode (i.e. 200+ F) you may be able to swap the relays as a test. I forget...

Could always wire in a fan switch via the ALDL connector. Even without cutting any OEM wires. At least as a stopgap measure...
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Old 02-01-2012, 07:41 PM
chrisjkruse chrisjkruse is offline
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Default Re: overheats with ac OFF

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ID:	2544AHHHH YES..You mean this brittle piece of gold that exploded in my hand. 60 bucks!

I live in florida..I always run the ac.. If i just add a 6 dollar relay to ground this wire when the ignition is on..will that cause a problem..(the fan operates when grounding this wire)

I would prefer to just have the fan running when the ignition is on..rather than having a sensor decide for me..
......plus Im 54 dollars shy right now. 6 bucks in rolled coins and a buncha wire and connectors in the garage..
.Whachathink?..pigtail off of the wire that activates the fuel pump relay.. to activate my new 6 dollar fan relay .. ??
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Old 02-01-2012, 08:16 PM
chrisjkruse chrisjkruse is offline
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Default Re: overheats with ac OFF

Whoa..wait..the other method, Scott,.. wth the aldl connector..can i leave the switch in the on position..and have it shut off with the ignition? I just don't want to forget to turn it on and off..
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Old 02-01-2012, 08:20 PM
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Lightbulb Re: overheats with ac OFF

Quote:
Originally Posted by chrisjkruse View Post
If i just add a 6 dollar relay to ground this wire when the ignition is on..will that cause a problem..(the fan operates when grounding this wire)
Problem? Well, when the fan runs (and it does draw a fair bit of power) it puts a draw on the alternator. That is driven by the belt, and causes additional load on the engine. A car in motion is less likely to need the fan than one sitting still. But this current draw will cause the engine to lose a bit of power. Not a lot, but it does. The draw can be measured, and that is a pretty large electric motor. One of the reasons the TRs got the largest alternator in GMs car fleet save for maybe a police package.

Thought: No one wants to spend $60 on a connector. Not sure where you looked, but have you thought of hitting junkards to look for one? Chances are some other GM 1980 and up car that is being pulled apart somewhere nearby has this very connector for the very same purpose, and it is just going to be recycled. Why not hit a yard and relieve the car of it? Chances are you won't be charged for it, and it may wander out in your pocket or toolbox with you. All you need is a knife to cut the wire, then splice it, solder it, and wrap it with tape or heatshrink tubing.

It is GM part number 12102621.

Or...
http://www.amazon.com/Radiator-Senso.../dp/B004HBTJAK
http://www.clipsandfasteners.com/GM_...r_p/a14580.htm
http://www.amazon.com/Pico-5640pt-Co.../dp/B0002JN05G
(Last one is not black and uses a white wire, but is the same.)
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Old 02-01-2012, 08:55 PM
chrisjkruse chrisjkruse is offline
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Default Re: overheats with ac OFF

Hey thanks..I'm ordering one right now from Amazon..10 bucks!!
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Old 02-01-2012, 10:05 PM
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Lightbulb Re: overheats with ac OFF

Quote:
Originally Posted by chrisjkruse View Post
wth the aldl connector..can i leave the switch in the on position..and have it shut off with the ignition?
If you were to do that, it would be running on the high-temp timer circuit and then you'd get the 7 minute (or whatever it is) fan run time after the motor is shut down. Not a big issue, but do you really need to have it on all the time?

Looks like your coins and a few more bucks and you'll be set.

Remember: These cars are 25+ years old. Hard for them to be perfect.
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Old 02-02-2012, 08:05 AM
chrisjkruse chrisjkruse is offline
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Default Re: overheats with ac OFF

BAD HORSE...GET UP!! I'M not done YET.

Obviously the parts store was charging 60 bucks for the sensor and the pigtail connector. (i walked the guy out to take a look)

REVELATION:
Apparently this switch does not control the dash warning light. So it could be possible that BLOWING the 25 year old plastic cap off the resovoir was not a..
" VERY SCIENTIFIC TEST" ..(Ken's words )..

Other than the "smell of coolant that ejaculated everywhere) the car showed no other signs of reaching a damaging temperature. No pinging..no nothin'.

QUESTIONS:
????-- When should the temp warning light (although deemed inaccurate) turn on..??
and at what temperature is a tb considered getting HOT!???
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Old 02-02-2012, 11:54 AM
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Default Re: overheats with ac OFF

Some more from me ...

Temp light is really stupid hot. Around 250+ degrees (edit: Found it on the attached diagram). Problem is, the idiot light switch is pretty high up in the cooling system (on the intake manifold) and if the radiator boils over, the switch usually loses contact with water/coolant and that can make the temp "look" cooler.

Wiring diagram attached ... you can see how many things are tied into making the fan work (high A/C pressure cutout, temp sensor, etc.) The dash light is connected to a separate switch.
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Last edited by kenmosher; 02-02-2012 at 12:01 PM.
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