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Former Hoadpiler
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Discussion Starter #1
My old 86 Bronco II runs on the cool side like it doesn't have a thermastat. I'm wondering if I should check to make sure it does so I can stay warm this winter. It barely gets off the cold mark even when its hot outside. I wonder if it would improve my gas mileage if it ran a little hotter?
 

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Too cold is not good at all. Your oil will start to sludge up and yes a cold engine will burn more gas.
 

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Definitely, on both counts. I read this, & instantly started wishing I had my 87 Eddie Bauer back.:( That little sucker went ANYWHERE !! :D I loved that truck !!!
 

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Former Hoadpiler
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Discussion Starter #4
Thanks guys. I think I'll check it on Monday and replace it or put one in if it doesn't have one. After three winters of freezing in it when I drove to the mountains skiing its time.
 

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Another item you might check is the fan clutch. If it is seized, then it will pull more air thru the radiator fins, than if it was free wheeling cold,then hooking up when the viscous damper got warm. Your Bronco is carb, not fuel injected, is that true? Mileage won't be affected if it is carbed, cause the choke is electrically heated, and will open up. If it is injected, yes mileage will suffer because it won't get to operating temp, and the coolant temp sensor reads it is still cold and keeps the injector pulse rich. Kinda like a choke. Won't go into "closed loop" Put a stat in it, and check the fan clutch operation, if it has one. Or, put a chunk of cardboard in front of the rad.
 

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The thermostat in my 98 Ford Ranger (no longer have) went back (stuck open). I noticed that on really cold mornings on my way to work it would never put out much heat from the heater. That truck had a temp gauge and when it was bad the gauge would slowly climb, but never get very high. After replacing the 'stat the gauge would stay low for awhile and then all of a sudden start a fast climb - lots of heat out of the heater then.
 

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Make sure to put a 195 degree thermostat in it. On older cars you could get away with running a cooler thermostat or a hotter one if you needed to. Thermostats do more than control the water temp for the heater these days. All the sensors on the vehicle are designed to work around 195 degrees. Running a cooler t-stat can cause the sensors to tell the computer to run rich. When that happens gas mileage hits the crapper, O2 sensors begin to set codes, catalytic convertors begin to plug. Just a whole host of issues begin to happen.
 

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Former Hoadpiler
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Discussion Starter #8
Another item you might check is the fan clutch. If it is seized, then it will pull more air thru the radiator fins, than if it was free wheeling cold,then hooking up when the viscous damper got warm. Your Bronco is carb, not fuel injected, is that true? Mileage won't be affected if it is carbed, cause the choke is electrically heated, and will open up. If it is injected, yes mileage will suffer because it won't get to operating temp, and the coolant temp sensor reads it is still cold and keeps the injector pulse rich. Kinda like a choke. Won't go into "closed loop" Put a stat in it, and check the fan clutch operation, if it has one. Or, put a chunk of cardboard in front of the rad.
Clutch fan is okay. Best thing is to replace the t-stat. If I'm wrong its not a big expense.
 

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Your on the right track. Most likely a thermostat stuck in the open position. Constant flow of coolant through the system will prevent it from reaching its temperature operating zone. Conversely one stuck in the closed position will prevent flow and lead to overheating. If its never been changed then this is suspect #1. Since your system will be partially drained anyway its a good time to change out coolant and hoses if need be. Look for splits, swelling, and/or sludgy build up inside the hoses. Good luck man.
 

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as others have stated, just replace the thermostat (not too expensive)....more than likely that will fix the problem....
 

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I thought all those older Fords ran on the cool side.
 

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+1 - Your car needs a thermostat for all of the above reasons..

The parts house will have documentation on which temp thermostat your car/truck was designed for.

Running your engine colder than design temp is just about as bad for it as it gets.
 

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Agree with all of the other post here especially about checking the Fan Clutch. For what its worth...as cheap as Thermostats are, I change them every year or everytime I have to do something with the cooling system other than top it off with coolant. Its cheap insurance that I wont likely have a cooling problem caused by a malfunctioning Thermostate
 

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Former Hoadpiler
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Discussion Starter #16
Have you ever used Stop Leak. This can cause the thermo to stick open and clog the heater core.
I haven't but I bought it useds. Its an 86 and I've only owned it a few years. Your thought actually came to mind. When I change the thereostat I'm thinking of doing a flush also.
 

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Discussion Starter #17
I changed the thermostat today. It took all of ten minutes and seems to be working fine. Now that I know there are no leaks I'll flush the system tomorrow and put in fresh anti-freeze.
 
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