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Discussion Starter #1
Apparently thermostat temp ratings are a touchy subject on other forums so let's see if yous guys are better mannered! I'm wondering if there is a scientific reason to with one temperature thermostat versus another; an example being 165* vs 195*. I have looked at (and posted on) some other forums and this question really turned into a s##t storm with no real answer. I need to replace my thermostat but every parts store lists a different one for my truck and everyone I talk to about it has a different opinion on which one is the right choice. Also, I live in the colder end of Michigan and I don't know how or if climate should effect my thermostat choice.

The truck in question is my 1985 F150 with a carbureted 300ci straight 6. The truck is used for commuting durring the week and towing 5,000 pounds of either tractor or sled dogs on the weekends.

Thank goodness my Deere runs of a thermo-siphon system and doesn't have one!
 

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Well, this won't be the scientific reason but I'll throw in my $.02.

From what I see off hand, the original equipment specs for your truck are for a 195 degree thermostat. But you can use alternate models for 160, 180, etc... degrees.

Now, I'm not all the familiar with the Ford 300 cu. in. but I know that on many of the 70s/80s AMCs and Chrysler products, if you used the lower temp thermostats in the winter time (below freezing temps) the engine would knock and then diesel when you shut it down if you only drove short distances. The higher temp thermostat allowed the engine to heat up more so it didn't knock or diesel as often. On the flip side of that, the lower temp thermostats allowed it to open up earlier and cool the engines better in hotter weather.

On the completely-unrelated-to-performance side, the higher temp thermostat also got more heat into the passenger compartment sooner which is nice in the winter.
 

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What temp does (or did) your truck run at? If it ran goodat that temp and didn't give you any problems that is the thermostat temp you need.
 

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A lower temp thermostat allows for a cooler, denser intake charge, (although slight) and provides a very minimal power increase. The power increase from this alone on a street car is negligible at best. It does help engines with a pre-detonation or knocking issue. Older engines that are tired and weak could benefit from the lower temp thermostats. A lot of race car engine builders go this route.

A warmer temp thermostat allows for more engine efficiency as there is less heat needed to expand the incoming fresh fuel and air charge. It also makes for better heat exchange on the radiator to the ambient air. It also gives the cab air heater more "power" as there is more heat energy in the coolant to give off to the cab. You'll find all of the "mileage maximizing" cars these days run the higher temps for the efficiency.


Personally I'd find out what the factory thermostat was rated for. I believe your truck will operate the best at design temp. The biggest factor being emissions. If the truck is running outside of it's design window, how can temp related components like fuel controls and exhaust after-treatments work correctly.
 

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Apparently thermostat temp ratings are a touchy subject on other forums so let's see if yous guys are better mannered! I'm wondering if there is a scientific reason to with one temperature thermostat versus another; an example being 165* vs 195*. I have looked at (and posted on) some other forums and this question really turned into a s##t storm with no real answer. I need to replace my thermostat but every parts store lists a different one for my truck and everyone I talk to about it has a different opinion on which one is the right choice. Also, I live in the colder end of Michigan and I don't know how or if climate should effect my thermostat choice.

The truck in question is my 1985 F150 with a carbureted 300ci straight 6. The truck is used for commuting durring the week and towing 5,000 pounds of either tractor or sled dogs on the weekends.

Thank goodness my Deere runs of a thermo-siphon system and doesn't have one!

Go down to your local Ford dealer and tell them that you need a thermostat for your particular model pickup. When they hand it to you, look at it and you will find it is likely a 192 degree thermostat. That is really all you need to know. I just sold a 1993 F150 and had replaced the thermostat in it fairly recently. By the way, the same thermostat at O'Reillys is $4, while it is $24 at the dealer. I went with the one from the dealer as I did not want to have to replace it again next year. Anything with a lower temp rating will not keep you warm in the winter. The only reason to consider a lower temp thermostat is if your pickup is overheating.

Dave
 

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Discussion Starter #7
Thanks for the prompt response! The big issue is that "stock" doesn't mean much to this truck... The block and moving bits are from 1985 but the rest of it has been frankenstined from other years and even other model trucks.
I have been running the same thermostat for 12 years and 250000 miles. Truthfully I have no idea what thermostat is in there. What I do know is that the temp gauge has been showing some strange fluxuations over the last couple of weeks.
 

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If the old thermostat is not holding a fairly consistent temperature, then it is time to replace it. In your case, you probably should take the old one to the dealer and tell them you want another one just like it. 250,000 miles on one thermostat deserves another one just like it.

Dave
 
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Dave's correct, I think a 192 degree 'stat is what is available for the 300-6 now.

I had a '78 F150 with carb'd 300-6, and an '87 F150 w/300-6 EFI.
Watch your automatic choke on your carb. In cold temps it will not kick off and you'll run rich and get really poor mpg. A manual choke conversion would be one way to fix. The Carter YF or YF 1A carb was a really crude device, about as good at metering gas as a soup can with a hole in the bottom. In winter my '78 would always flood if I started it cold and only let it run five to ten minutes. Try to restart it before it completely cooled off again and it would flood. The EFI was so much better!

You could also have water pump and/or radiator issues. They probably haven't had much service the last few years, or 20 or 30 years. But the 'stat is cheaper and easier to swap to start. My '78 got a cheap rebuilt replacement water pump about every two years the 7 yes I had it. Also got a replacement radiator just before I traded it too.
 

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You could always try to place the old thermostat in a pot is water and turn up the heat. Take the temp of the water when the thermostat opens. This is only good for reference purposes as you said you think yours may be failing.


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Discussion Starter #11
I had a dump truck and a pickup with EFI 300's but neither were as reliable as the old carb' one. Mostly gremlins in the wiring or faulty computer components. Actually, this old truck as outlived all of my other "bullet-proof" shop trucks and farm trucks including a Cummins 12 valve and a 7.3 Powerstroke! It's not like it's had an easy life because it's smaller and older than the others... it has a gooseneck plate just like the rest of them.

You guys have been very helpful! I think I'll go with a 185 or 190. I have never had over heating issues with this truck and I'd never complain about adding a little more efficiency.
 

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Ha-Ha. You must have got "Lemon" 12-valves and 7.3 PSD. My 7.3 has 50% more miles than BOTH my 300-6's had combined. But they still had more miles left in them when I got rid of them.

The carb'd truck I cringe when I think of how much work I did to it to keep it on the road. Makes me wonder almost 30 years later why I bought an '87 set-up identical to the '78. My EFI was definetly the better of the two F150's. But like you said, it also had wiring corrosion issues and electrical module problems.

My '96 PSD gets better mpg than either 300 ever did by at least 30%, pulls more weight faster than the 300's ever could. The 300's are O-K in a half ton, but the 120 HP they make is frustrating in anything bigger. They're slightly better than 302 unless you have lots of gears, but a 351 Windsor or little FE makes a much better work truck engine.
 

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Discussion Starter #13
They weren't 'lemons' at all! The 7.3 had at 300k on it when a faulty injector back-fed the wiring harness and set the engine bay on fire. The 12 valve had 370k on it when the body fell apart. My little 300 gets 19 mpg highway, passed 500k last October, and it's not showing any signs of quitting! It lacks the brute force of a modern diesel but it isn't that bad when you consider that Ford introduced the 300 almost fifty years ago. It is a simple, tough, and reliable truck. I don't like hauling any load heavier than 5000 pounds with it just because it struggles to break 65mph, but it can do way more than that. I haven't had any major issues with the carb besides the choke sticking on occasionally. Someday I'll get a fancy intake and run a 2 barrel but for now I'm not going to mess with a good thing. It has a new-ish radiator which probably helps but I have absolutely no idea how old the water pump is... It seems to work ok. A 190 thermostat seems to be what everyone is recommending so I think that's what I'll get.
 

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Dave's correct, I think a 192 degree 'stat is what is available for the 300-6 now.

I had a '78 F150 with carb'd 300-6, and an '87 F150 w/300-6 EFI.
Watch your automatic choke on your carb. In cold temps it will not kick off and you'll run rich and get really poor mpg. A manual choke conversion would be one way to fix. The Carter YF or YF 1A carb was a really crude device, about as good at metering gas as a soup can with a hole in the bottom. In winter my '78 would always flood if I started it cold and only let it run five to ten minutes. Try to restart it before it completely cooled off again and it would flood. The EFI was so much better!

You could also have water pump and/or radiator issues. They probably haven't had much service the last few years, or 20 or 30 years. But the 'stat is cheaper and easier to swap to start. My '78 got a cheap rebuilt replacement water pump about every two years the 7 yes I had it. Also got a replacement radiator just before I traded it too.
THIS!!!
EVERYTHING.

:lolol::lolol:

we have had several 300-6 Fords, and at least a couple irrigation pumps powered by the Ford I-6.

195F Theromostat or pay the price.
That carb hanging out in nowhere NEED'S the block heat to keep from icing up on cold mornings, when there is an inversion blowing in off the lakes.
Convert the Carter to a cable choke, or invest in a Holley with a manual choke.

The mid to late 80's I-6 300, was choked to death with smog crap, and they don't run happy until they get warm and stay there.

On the temp gauge freaking out..check to make sure the sending unit isn't freaking out with a bad ground, and the wires are making a good connection.
Generally, when thermostats croak, they fail closed and stay there, or fail open, and stay there, until you knock the housing a couple times, and then they jump if they aren't totally fried.

Also...check the radiator and give it a good flush if you haven't done so in a while.
Have had crud block a thermostat a time or two on old motors, that had some rusty gunk in the radiator.:lol:

One thing I learned with the 300's...keep a spare housing on a nail in the barn, and go easy with the screwdriver when forcing the return hose off.
They are a lot more fragile than they look.:cry:
 

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Discussion Starter #15
The mid to late 80's I-6 300, was choked to death with smog crap, and they don't run happy until they get warm and stay there.
Well then it's a good thing all that junk mysteriously "fell off" a few years back. Michigan has no smog testing. :lol:

I'll go with a 195 thermostat then. The gauge shows that the truck warms up to near the middle of the "normal" zone but then the needle drops down towards the "n" unless I'm really working the truck hard. Sometimes it comes up to the "n" and doesn't go any higher. I'm taking this to mean that the thermostat is stuck open but occasionally comes loose.
 

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Well then it's a good thing all that junk mysteriously "fell off" a few years back. Michigan has no smog testing. :lol:

I'll go with a 195 thermostat then. The gauge shows that the truck warms up to near the middle of the "normal" zone but then the needle drops down towards the "n" unless I'm really working the truck hard. Sometimes it comes up to the "n" and doesn't go any higher. I'm taking this to mean that the thermostat is stuck open but occasionally comes loose.
Either it's loose, or a bad ground.
I went totally nuts on an old Ranchero that did that. It blew plenty of warm air through the heater, so I knew it was open, but how open. I decided it was the thermostat, and swapped it out twice, because the first one stuck open. Shortly afterwards the gauge quit working...bad ground finally worked it's way completely loose.:crazy:

Ya know, if you need 300 I-6 smog parts, I happen to remember a bunch of them laying in a wind row..dunno how they got there either.
They are right next to a couple clogged up Cat converters, and among several Rochester carbs from the late 70's and 80's.
I just assumed they grew in wind rows like rusted through tractor rims.:lol:
 
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