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Lower temp thermostat

randypmartin

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Need to replace the thermostat on my 1990 2.9L 6 cylinder Bronco II.

Is it advisable? And what are the pros/cons?

Thanks for your thoughts guys!
 


alwaysFlOoReD

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No, put in the same. Your motor is engineered for that.
 

Bronco ii Man

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Biggest enemy of the 2.9L is heat! But as floored mentioned, it was engineered to run at a certain temperature. I think it being a 90 model you should have the upgraded head design. Changed the design, basically all they done with it is made the water ports bigger to help it flow coolant better! Ford seen the problems with the 2.9 and heat! Just sucks they took around 3 years to decide to fix the problem!
 

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Not to get off the subject of the bronco. Chevy had a problem with there trucks in the 90’s! Coolant temperature sensors would get a bad ground or short in the wiring causing the computer to read that the engine was not to normal operating temperature! Therefore causing them to run rich, and wouldn’t idle properly! I’m sure almost everyone remembers seeing a 90’s model Chevy and GMC with a v-8 in it loping across a parking lot sounding and running like it’s cammed up! But if you know anything about engine’s, you can tell the difference! Remember in high school a lot of guys driving there pop’s truck and thought they had a race truck because it wasn’t running correctly! And god knows you couldn’t tell them any different!
 

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Thermostat is minimum operating temp. If coolant system isn't designed well or maintained, you can overheat.
 

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Do your research dude! I have a 85 bronco ii with the 2.8 and I run a 160 in it! It’s not an everyday driver, could be if needed but I don’t! No a/c sucks in 95* degree weather. Lol
 

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Got an 89 I pulled the transmission from with a blown head gasket! The guy I got it from drove it about another year with it blown! Which wasn’t the smartest thing to do! Kept water with him all the time and kept a check on it. I’m not mad he parked it. He gave me the whole bronco with a new clutch kit to boot, just to get it out of his yard! So I lucked up on it! Not saying the 2.9 is junk, just had some issue’s mainly from lack of maintenance!
 

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I'd be tempted to run a lower temp thermostat if I lived further south where it gets hotter. They are not a fix for overheating, they simply open sooner, which is nice because you have air flowing through a hotter radiator more often...so it can help to proactivcely keep the engine closer to operating temp. I have a 180 degree stat in my 302 swapped truck and it has absolutely helped on really hot days - it will stay around 200 degrees for longer periods of time instead of slowly creeping up way past that.

I would never run one in really cold climates and it will hurt your heater output in the winter, possibly have a negative effect on fuel mileage as well.
 

randypmartin

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I'd be tempted to run a lower temp thermostat if I lived further south where it gets hotter. They are not a fix for overheating, they simply open sooner, which is nice because you have air flowing through a hotter radiator more often...so it can help to proactivcely keep the engine closer to operating temp. I have a 180 degree stat in my 302 swapped truck and it has absolutely helped on really hot days - it will stay around 200 degrees for longer periods of time instead of slowly creeping up way past that.

I would never run one in really cold climates and it will hurt your heater output in the winter, possibly have a negative effect on fuel mileage as well.
I've never had an issue with mine getting even a little bit warm. Always operates at a very low temp even on a 95 degree day with a/c on. So I would assume stick with the OEM thermostat then?
 

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I've never had an issue with mine getting even a little bit warm. Always operates at a very low temp even on a 95 degree day with a/c on. So I would assume stick with the OEM thermostat then?
That's what I would do. Motorcraft thermostat is preferable if you can find one. Will be a good time to flush out your radiator and heater core, sludge and debris are the #1 killer of the cooling systems in our trucks. Often people blame "junk head designs" which is partially true but 35+ years of no coolant changes and no maintenance is worse.
 

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I tried a bunch of different temps and brands during my cooling issue. Ended up keeping the Motorcraft of stock temp. Haven't had cooling issues since. I live in a hotter climate.
 

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I've pulled apart a few rbv radiators. Most have been about a third full of sediment collected at the bottom of the rad. Easy way to check is get the truck to operating temp then shut off engine. Feel along the rad for temp differences. Or better use a heat sensing gun.
 

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The biggest problem with at least some of the 2.9s was improper cleaning out of the casting material out of the heads.

If the cooling system is sediment free, you’re probably ok.

As far as the thermostat, I would stick with the OEM temperature for the thermostat unless you are doing something special that requires differently bit that normally doesn’t apply to most people.
 

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So… here’s my input…

@sgtsandman is correct, improper cleaning out of casting sand was a big problem. @PetroleumJunkie412 noted that and also noted that the European market didn’t have the overheating and head issues that we have with the 2.9, so I’m going to say there was poor quality control here that caused a lot of problems. Throw in poor maintenance and general abuse and it’s no wonder there were so many problems and a bad rep.

Sediment in the cooling system from lack of or improper maintenance is another problem. My first Bronco II, I wanted to flush the radiator and when I opened the drain plug. Well, nothing came out. Unscrewed it completely and still nothing. Poked around in the holes and hit it with the hose a few times and finally got the tiniest drip. Ended up pulling the upper and lower hose and going to town spraying water in everywhere. After generous water useage, water would come out the drain hole. Hosed out the heater core and block as best I could, filled it with coolant flush, ran it, drained, sprayed, filled with water, ran, drained, sprayed, more flush, ran, drained, sprayed, water fill, ran, drained, sprayed, water fill, ran, drained, sprayed and finally wasn’t getting any more junk out. Then the motor ate a valve.

My choptop had been overheated by the previous owner when I got it and cracked a head. I chased the overheating problem for awhile and broke a couple more heads. Turns out a substantial part of my woes was a result of a leaky heater core and someone sealing the heater core box with RTV. Looking back, I’m also suspecting an issue with the block being choked up with casting sand. It might be buried in my shed still. The 2.9 that went in the last time I broke heads never gave a bit of trouble. I flushed it and ran a new water pump with a 180* thermostat and a 4.0 radiator. With a manual transmission, 4.10 gears and 33’s, it ran great and was a solid 18/19 mph around town and low to mid 20’s highway, so I have my doubts that there was any negative effects to my cooling alterations. It didn’t like 35’s though, so it got replaced with a 4.0. Well, a few of them. Haven’t had much luck with those motors either in that.

One thing to note, factory spec for thermostats for the 2.9 was 192*, however most “stock” replacements for it are 195*. I don’t know if there is a 185* or 190* thermostat available for these, but I would definitely be a little more comfortable running slightly colder than slightly hotter.

Overkill on the cooling system is possible. My F-150 is a prime example. Even with a new radiator, water pump, and a flushed cooling system in the winter, it wanted to overheat with the plow on. 180* thermostat, super-wetter and a 50/50 or 40/60 mix of antifreeze/water and tilting the radiator slightly back at the top solved that problem. But without the plow on it runs cold. Even in the summer working it hard.
 

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Just to be clear...
A lower temp thermostat will NOT cure an over heating problem. All it does is slightly delay a overheating problem. One of the main reasons for the higher thermostat temp is to help the oil burn off moisture that condenses inside during cool down.
 

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