[schaptacular307]

here's a little thing that's been on my to-do list....
my father's '89 L sedan (yes, legends are heridetary) has had intermitent overheating problems since around 75,000 miles. well now he's at 130,000 and with about 20,000 on a new thermostat still overheating. but here's the kicker-- it only overheats when the a/c is OFF when the a/c is on it generally brings the temp. back down.
i'm guessing fan/fan relay?
anyone else got a better guess?

 

[pnoye2]

here's a little thing that's been on my to-do list....
my father's '89 L sedan (yes, legends are heridetary) has had intermitent overheating problems since around 75,000 miles. well now he's at 130,000 and with about 20,000 on a new thermostat still overheating. but here's the kicker-- it only overheats when the a/c is OFF when the a/c is on it generally brings the temp. back down.
i'm guessing fan/fan relay?
anyone else got a better guess?

When was the last time you service the radiator... core restricted; rust and scale form in the cooling system when it has been neglected.

 

[EnterUserName]

When was the last time you service the radiator... core restricted; rust and scale form in the cooling system when it has been neglected.

This was happening to me recently,
The first thing I would check is if the fans are turning on properly. Start the car raise the hood and wait till the engine warms up. Look at the larger fan is it turning on and spinning after the car warms up?

If not replace the Thermosensor at the bottom of the radiator , check to see if the fan turns on after that if so then you have probably solved your problem.

If not make sure your fan even works , have some one turn the key while you are outside to see if the fan cycles for a second.

If it does yet still does not turn on after the car starts to get warm you probably have a bad FCU. I know because I just replaced mine.

(FCU - Fan control Unit. )

The reason it cools down when you run the airconditioner is the condensor fan kicks on.

Hope that helps I just tackeled the problem myself.

Another thing is replace your radiator cap if it is worn you are loosing pressure and your cooling system is pressurized.

Hope this helps I have just battled my heating problem mand have it finally under control..

 

[schaptacular307]

When was the last time you service the radiator... core restricted; rust and scale form in the cooling system when it has been neglected.

as for that i did a complete drain, flush, and fill about 15k ago.... not to mension replace a few quarts of coolant after it bioled over a few times....

i noticed that that fan does work, but intermittently (thus the intermittent problem), ill take a look at some of those fan sensors and maybe swap out the FCU from my '89 ls just to test some possibilties

 

[pnoye2]

i noticed that that fan does work, but intermittently

Normal operation for a cooling fan (to your right, facing the car) schaptacular307... motor is switched on and off as the engine temp. rises and falls, other fan can be switched on to cool the A/C condenser.

Oddly enough though, your symptom is out of the ordinary; overheats when A/C is off, it's usually the other way around... try EnterUserName suggestions.

Also, do a visual check on the following;
fan blades, ensure they are in good shape (not bent)
damaged or missing radiator/fan shroud
belt that drives the water pump is not loose

Other ODD causes of engine overheating are;
late ignition timing, if retarded 2 or 3 degrees from spec
exhaust blockage, partially block cat or exhaust system

Okay, you've got u'r hands full now see if these helps, good luck!