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Coolant Temp. Fluctuating


Sampson

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So its been really cold here in northwest Ohio this year and as of lately my truck is not making it up to full operating temperature. Its been in the teens and single digits for most of 2014 and even lower with the wind chill. Since its been so cold my truck hasn't been making it up to full temp but coming close. Now its starting to fluctuate, it warms up fine but once I drive a little bit them come to a stop and start again it cools down, but once I start up again it goes back to where it was. I put a piece of cardboard in front of the grill to compelety block it off and that changed nothing. So I'm guessing the thermostat is stuck open? I replaced it with a 180 degree tstat last Janurary when I did the head gaskets. The tstat is still under warranty from Napa so I might just take it back and get a new one. Whats does everyone think?
 


McCormack

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Yep, replacing the thermostat is the first thing that I'd do.
 

RonD

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Yes, it reads like the cold weather is bleeding your engine heat pretty fast.
I would also check the fan clutch, start engine and let it run for 1 minute or so, then shut it off, pop the hood and spin the fan, it should spin easily.
If the fan clutch is stuck fan won't spin.

The fan clutch is engaged by radiator heat, as rad heats up fan clutch heats up and causes fan blades to spin closer to engine speed creating more air flow, when cold there should be little air flow.
Your description of the cooling while at idle would make me think fan is spinning close to engine speed so clutch is engaged when it shouldn't be.
The fan blowing the cold air over the engine will bleed heat pretty fast.
But it could just be engine heat bleeding off since less heat is being generated by the engine at idle.


You need to run a 192 or 195deg T-stat.

People often make the mistake of thinking a cooler t-stat is better, it isn't.
A t-stats sole purpose is to get the engine temp up to 200degs ASAP and hold it there, the 200-230deg range is where the engine gets best lubrication and best MPG.
All engine oil is rated at 212deg, so 30w is only 30w at 212deg

On colder days with a 180deg t-stat you will be running 20deg below best temp so oil is thicker and you are burning gas money out of your pocket, for no good reason.

And a cooler t-stat does not help prevent overheating, a t-stat sets MINIMUM operating temp, once it is open a 180 or 195 t-stat have the same size hole, so have nothing to do with maximum temp.
 

McCormack

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My power and MPG went up slightly when I swapped in a 180* T-stat for the stock 197* in my '00 Ranger, and my engine, belts, hoses, and sensors should last longer because they're running cooler.

The 3.0 engine is an old design that wasn't originally meant to run at such a high temperature, and I strongly suspect that the high temperatures are at least somewhat responsible for the spate of head cracking that we hear about on the boards, and also for the cam sync problems (the heat thins out the oil which lessons it's lubrication properties in an area that is already marginal).

Ford no doubt increased the 3.0's engine operating temperature in later model Rangers in response to tightening emissions standards, but my Ranger has had no problem passing emissions with a 180* 'stat, so there's really no reason to run anything hotter.
 

RonD

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My power and MPG went up slightly when I swapped in a 180* T-stat for the stock 197* in my '00 Ranger, and my engine, belts, hoses, and sensors should last longer because they're running cooler.

The 3.0 engine is an old design that wasn't originally meant to run at such a high temperature, and I strongly suspect that the high temperatures are at least somewhat responsible for the spate of head cracking that we hear about on the boards, and also for the cam sync problems (the heat thins out the oil which lessons it's lubrication properties in an area that is already marginal).

Ford no doubt increased the 3.0's engine operating temperature in later model Rangers in response to tightening emissions standards, but my Ranger has had no problem passing emissions with a 180* 'stat, so there's really no reason to run anything hotter.
Power will go up but MPG will go down, they are on opposite sides of the same coin.
Lower operating temp causes a richer fuel mix, that's an old CAI(cold air intake) sellers trick.
CAI really doesn't do anything but the lower temp t-stat, they recommend, does, lol.
This is why an engine seems to have more power in the winter, colder air, but also why MPG is lower in the winter, colder air.

Outside of overheating, sensor life/operation wouldn't be hurt or helped by the 15 deg difference, same with the oil viscosity.
The cracked heads are from repeated heating and cooling cycles and a weak point in the original casting, a high temp overheat expands the metal even more so the weak point will often crack at that time regardless of age.

I think it was Ford that pioneered the high temp t-stat, around 1965 was when some ford engines were first equipped with 192deg t-stats.
The reasoning was from long term tests they and SAE had been doing, it seems that with a 200deg minimum operating temp the fuel and water in the oil will be dissipated faster, their testing indicated about a 30% increase in engine life with the higher minimum operating temp.
I think the 30% is a bit optimistic, SAE tests do show much higher engine wear when operating temp is below 140deg, above this the decrease in wear gets less and and less, so 192-197deg t-stat would produce less wear on oil lubed parts than a 160 or 180deg, I don't think it would be 30% better.
Ford also started recommending 6,000 mile oil change schedule around this time, for engines equipped with 190+ t-stats, because oil would stay cleaner longer.

Anyway that's the reason for the 190+deg t-stats they use now, less engine wear, and added benefit was better fuel economy.
As far as emission, I don't think it would matter too much, but burning less fuel per mile on it's face would seem to lower emissions, but never looked at that specifically.

But you will get more power with a 160 or 180 t-stat, for sure, ask any racer.
 
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Sampson

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I tried what you described in your first post Ron D and I was able to spin it after I shut it off. But the fan kicked on 15 seconds after I started the truck and stayed on, I turned it off and was able to spin it, then turned it back on and the fan started spinning right away. I went for a 15 minute drive and was able to spin it after I reached my destination. So is my fan still good or is it my tstat?

I also have less of a grill opening with my custom bumper, so the only way air can pass through the radiator is through the grill, that was one of my resons for going with the 180.

 
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RonD

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Fan clutch reads like it is fine.
It would not get hard to spin until rad temp heats up, and in cold weather that may take awhile if it gets warm at all.

I would switch back to a 192 t-stat next time you change coolant or do work that requires coolant to be drained.

T-stat doesn't do anything about max temp, only min temp, so the brush guard shouldn't be an issue as far as the correct t-stat.

If brush guard was preventing air flow enough to effect engine temp then starting at 180deg or 190deg doesn't matter, both would be open all the way if temp was running at 230deg(above 1/2 on gauge), so the 180 doesn't "cool" any better, that's not what a t-stat does.

Driving thru Death Valley in 120deg temps, engine would run at exactly the same temp with a 160, 180 or 190 t-stat, they are all open all the way, so coolant is flowing thru engine and rad exactly the same.

What a t-stat does do, and the reason engines even have one, is to set a minimum operating temp, this is done, as said above, to get better lubrication and MPG, and also better heater function, bonus :).
So use a 190+ t-stat
In cold weather you will be glad you did(min temp), and in hot weather it will make no difference(max temp).
 
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Tractor Dan

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I would second the thermostat if you haven't done it. I was having similar issues and i'm a bit south of you floating between the lima and dayton areas of ohio. So i know how the temps have been. I started chasing my hoses down with a temp gun. I found out at the thermostat i was running 160 degrees. Apparently even though the engine had a 197 degree thermostat in it, it wasn't functioning correctly. Dropped a new one in and problem solved.
 

Sampson

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I replaced the test at about a year ago with a Napa one just as preventative maintiance. What brand would you guys recommend? I was thinking of just getting one from Ford.
 

Rearanger

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I prefer Stant. I also like their new "Superstat" which they say maintains a more even temp without the fluctuations of older ones that open and close. They are also more robust in the build.

I would caution those who run lower temp stats hoping for more power - you may want to get a used oil analysis to see if fuel is contaminating the oil, which could lead to higher bearing wear. Running rich after engine warm up is inviting trouble.
 

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