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Correct thermostat for 258 ?
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Mr. Ed View Drop Down
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Points: 4916 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Mr. Ed Quote  Post ReplyReply Direct Link To This Post Posted: Oct/02/2014 at 8:53am
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TH_Gremlin View Drop Down
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Points: 318 		Post Options Post Options   Thanks (0) Thanks(0)   Quote TH_Gremlin Quote  Post ReplyReply Direct Link To This Post Posted: Oct/03/2014 at 12:45pm
Gonna be a few days before I can do a road test.  I was removing the accelerator pedal (different venture, not involving the thermostat), and broke that little piece of plastic (that holds the accelerator cable) that snaps into the top of the gas-pedal lever.  Ordered an accelerator cable, but it won't be here until Monday.  Road test coming, hopefully, on Monday or Tuesday :)

I did change the temperature sending unit when I first got the car.  At the time, I thought the sending unit wasn't working properly.  I could ground the wire out, and it would peg the temp gauge.  After replacing the sending unit, I concluded that the car just ran at a pretty low temperature, because it still just barely registered in the middle of the gauge.  I did not know that the thermostat was completely gone at that time.


Edited by TH_Gremlin - Oct/03/2014 at 12:48pm
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Points: 318 		Post Options Post Options   Thanks (0) Thanks(0)   Quote TH_Gremlin Quote  Post ReplyReply Direct Link To This Post Posted: Oct/21/2014 at 12:08pm
Haha, well I had a little issue with the 192 degree thermostat.  Apparently it wasn't opening, because the car was overheating in about 5 minutes.  I could grab the top radiator (return) hose, and it's cold to the touch.  Same with the radiator.  So I returned that thermostat, and got a new one (a 195 degree, with some weird brass wobble valve looking thing in it, where you would ordinarily drill the hole in the thermostat).  Installed it with the permatex #2, let it cure, and whatta ya know, it works !  The temp gauge stays right in the middle, where it needs to be.

Between that, the rebuilt carburetor, and a score of other fixes, the car runs a heck of a lot better !  The car runs best with the timing advanced at about 25 degrees (I'm guessing, it's waaaay off of the meter), so I'm thinking maybe the rubber in the harmonic balancer might be losing its rubber, and has slipped a bit.  Not sure, and that's a story for another time.

Thanks for all of your help !

TH_Gremlin
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Originally posted by FSJunkie FSJunkie wrote:

They probably had the 205* thermostat for the early part of emissions regulations to get the engines to barely skip under the wire for passing. Running the engine hotter is a great way to reduce HC and CO.

My 1972 TSM says 205*, but my 1977 TSM says 195*.

1977 should be 195*.

And actually, contrary to popular belief, running the cooling system at higher temperature actually increases it's heat transfer characteristics. Higher heat means a greater temperature differential between the water in the radiator and the air flowing through it, resulting in a greater temperature drop.

170* stat,

Radiator inlet: 170*
Radiator outlet: 150*
Net temperature drop: 20*

205* stat,

Radiator inlet: 205*
Radiator outlet: 175*
Net temperature drop: 30*

A 195* thermostat is fully open at 218*, but ever notice how some engines that are running hot at say, 225* don't always keep rising? The thermostat is fully open, so you might think the cooling system is at max capacity, but as temperature rises, it's temperature drop increases, keeping the temperature in check.

The cooler the water is, the harder it is to cool. It seems backwards, but it's true.

So running a cooler thermostat thinking you are staving off overheating is a false comfort zone, as is running without a thermostat. You'll run cooler so long as your cooling system has the capacity to support the lower temperature. Once it can't, however, the temperature will rise and pretty soon you're in with the rest of the crowd. Drive a car without a 170* stat then change to a 205* stat. Both run just as hot after a few minutes.

Most of what you said is correct. However, if a cooling system has the capacity to keep the engine at 190 degrees under certain conditions and a 205 thermostat is installed, it will run at 205 or higher. If a 170 thermostat is installed, it will run at 190, the capacity of the cooling system.
Temperature differential is a factor in cooling capacity. A hotter radiator will shed more heat. However, a 230 degree radiator might shed 30 degrees resulting in a running temperature of 200 degrees whereas the same radiator on the same day running at 200 degrees might only shed 20 degrees, but the resulting temperature is 180 degrees. The cooler thermostat can result in cooler operating temps as long as the cooling system is capable of doing more work. That might be what you said, but it didn't sink in when I read it.
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Points: 9057 		Post Options Post Options   Thanks (0) Thanks(0)   Quote pacerman Quote  Post ReplyReply Direct Link To This Post Posted: Oct/21/2014 at 1:48pm
A 205 degree thermostat begins to open at 205 degrees.  I 190 degree coolant temp operating with such a thermostat will not open the thermostat.   Joe
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