Please help !
I have a 91 Ford F150 with a 4.9 6cly 2wd Auto.

I live in Nor-Cal and want to use the A/C.

So this is what happened I turned the A/C on and my truck over heated all the fuild in my rad. blew out thru the over flow tank. I let the truck cool down and filled it back up and I am afraid to turn the A/C again but I really want too. I did try one time and it started running hot so I turned it off.
I replaced therm. stat, all fuilds, and both rad. hoses. Checked the cluch fan and seems OK.

What do I do?
Thanks for your time

 

Someone in the past may have replaced the radiator with a non-AC radiator. AC equipt engines need a 3 or 4 core to stay cool consistantly. What temp stat did you install? Did you change the cap? Check that you have the correct pressure cap and the water pump is working correctly (remove the fan belt and see if you can wiggle the fan shaft in the water pump). For a quick test remove the t-stat and do a test run. If it still overheats you have a blockage in the cooling system and/or the wrong or bad parts.

 

How do I find out if it is a 3 or 4 coe rad.?
yes 195 temp. stat
yes new cap
I will check the water pump
and do the quick test
I will let you know what happens

thanks

 

My girlfriend has a 95 Taurus. The same thing happened to her car down in Florida. It overheated and everything boiled over. I flushed the cooling system and ran the car, it was fine. When I turned on the A/C it over heated again. Found the fan did not turn on when the A/C was on. Replaced the big relay/harness connector under the hood (im not sure what its really called) I dont know how these trucks are set up with A/C but just some advice.

 

no elec fan on these trucks unless aftermarket.

 

195 is awful high for summer driving down in N CA I would think. I run 195's up here in the winter. If running it without the t-stat fixes the over heating problem go back to a 140 t-stat and that should keep it cool in the summer and enough for heat in the winter down there, no more than a 180 degree. You don't want to run an engine without the t-stat for long periods (months or years) and/or use straight water. Electrolosis will eat up you fitting in the cooling system. Always run coolant in the system. The core is the vains in your radiator, tanks are were the cap and hoses connect. A single core (1 core) is usually about and inch thick core therefore a three core will be about 3" thick from the front, grill side, to the fan side of the radiator.

 

195 is the correct thermostat to use.

 

The temp of the thermostat should have nothing to do with overheating as long as it is working correctly. If your engine is running at 210° or 250° your 195° thermostat will be wide open, giving you maximum flow. Same for a 140° thermostat, although I hope that such a thing doesn't exist.

The lowest I would go would be 180°, and if you fealt like you had to, 160° would be the absolute minimum I would ever go. But I ran a 195° thermostat all sumer long with the AC cranking in my truck and never an issue. I really doubt that this is the problem.

 

Exactly!!!!!!

As I understand it the computer won't change from open to closed loop with a 160° stat.. Or that may be closed to open loop, my brain isn't working as it should right now,, NEEDS SLEEP!!!!!!!

Anyway, the point I am trying to make is: The system is designed to work at 195°, and anything else is just gonna screw with the system....

 

I apologize, 140 is a typo, I was thinking old days, it should have been 160.
1991 Ford F150 4.9L 300CID inline six thermostat:
195 degree standard OE
160, 180, 205 degree optional thermostat
Skyfox10,
I don't know what the boiling temp of water is in your area but every place else in the world it is 212 degrees at sea level. Even under pressure (Boyles Law) and with coolant anything above 240 for a sustained time and your going to start cooking the engine.

White 97 xlt:
The computer doesn't control the coolant flow (thermostat, water pump function). It controls the fuel, idle, and emmisions using the temp reading it is getting from the engine temp sensors as the control.

 

Another likely possibility: the fan clutch is failing, thus the fan is not turning fast enough to do its job with the A/C on. I've read that they need to be replaced every 5-6 years of normal driving. I wouldn't be surprised if your truck still has its original one as I don't think most people replace them until overheating occurs.

 

Is the overheating occurring on the highway at speed or when idling in traffic? Is the AC cooling in the cab better when on the highway or in the city-or does it matter?? If the overheating only occurs when idling-I would think that the fan would be the source of the trouble. If the overheating also occurs on the highway-the fan clutch can't be the problem.

 

Sorry for the confusion, I only meant that as an illustration. All I was getting at, was that if your vehicle is overheating because of the radiator, fan, or water pump cannot keep up, then as long as your thermostat is in working condition, it wont make a difference what thermostat you put in.

Also, remember that while water boils at 212°, a 50/50 mix boils at a higher temp than water. also remember, coolant systems are supposed to be pressurized, which raises their boiling point further.

Prestone Antifreeze is rated at 265° when mixed 50/50, and it boild at 276° when mixed 70/30.

 

I will replace the clutch fan today because that is a pretty cheap part, and then see what happens.
I do not do a lot of freeway driving mostly city driving.

 

I refered to this, as in Boyle's Law! Pressurization raises the boiling point but doesn't change the temperature of the coolant. And that is what your temp gauge in reading, the coolant temp. The engine components are much hotter and you can boil oil without boiling the coolant.