Truck runs a little hotter after t-stat change?

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Birmingham, AL
Last week I noticed a small white coolant stain by the gasket for the t-stat housing on my truck. I changed the gasket, t-stat, and upper radiator hose. I used a Motorcraft t-stat, but it looked slightly different from the original one I took out (slightly longer spring with more coils). I filled the radiator up with G-05 and distilled water. I tried for a 50/50 mix, but there's more coolant than water. It is probably closer to 55/45 or 60/40. I did bleed the cooling system afterwards and I'm fairly certain I got all the air out. Anyway, I have noticed since the change that the truck runs a few degrees hotter than before. Typically the Scan Guage would show 191-193 *F before the change, and now it generally stays between 193-197 *F. I know it is not a big difference, and well within what an all iron engine can handle, but it does have me curious. What would cause it to run hotter? More coolant than water? The outside air temperature has gone up some too, so maybe that is adding to it? The factory gauge still stays right where it was, which isn't surprising considering how informative Ford gauges are (not very).
 
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779
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Indiana, USA
1-different coolants and mixes have different thermal efficiencies 2-t-stats aren't designed to that high of a tolerance 3-the hotter the outside air the slower the vehicle heat will move into it all these added together could easily account for the small change you are seeing EDIT: 4-most Ford gauges are less helpful than an idiot light, at least you know the idiot light isn't telling you much.
 
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01rangerxl

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 Originally Posted By: bdcardinal
What was the part number for the t-stat you purchased? should have been a F8DZ-8575-AA / RT-1137.
That's what I used.
 

01rangerxl

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 Originally Posted By: Eric Smith
How long since you changed the coolant? Took a week and a half for all the air to get out of my Ranger.
I last did a drain and fill back in October. There seemed to be a lot of air to bleed when I did it then. This time there didn't seem to be as much air coming out. I got the truck up to operating temperature, turned the heat on, and kept it running for a while after I stopped getting air bubbles out. I repeated this a couple days later and no bubbles came out of the radiator, so I don't think there's anything more I can do to bleed it.
 

01rangerxl

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I remembered the other day that one t-stat had "197" stamped on it and the other had "197F". I'm guessing that's the temp they are supposed to open at...so the new one is probably working exactly as it should. Should have noticed that before.
 
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19,479
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Chicago Area
Right. Thermostats are spec'd at their OPENING temps. But only kinda sorta. A few degrees either way is just fine, and who knows how fast they open. Be happy.
 
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1,183
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Canada
No problem here, like others said 5 degrees one way of rthe other is fine. My guess is the variation from new stat to new stat for this part is a tolerance of 5 or 6 degrees.
 
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Thermostats usually fail by opening too easily, ie: by letting the engine run *cooler* than it really ought to be. Replacing the thermostat will make the engine run hotter, which reduces fuel consumption and increases overall combustion cleanliness and efficiency.
 
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