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Solved Where is too hot on these temp gauges?

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FR-425

Used to be a road here.
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Phoenix, AZ.
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1994 Explorer Limited
Non-numerical temp gauge 101

To get an "eyeball" on your temp gauge, I have a trick up my sleeve.

I the morning from cold start, keep your "eyeball" on the temp gauge.

The temp will rise until it hits "thermostat" temp.

Then you will see it drop fast.

Make a mental note of that point on the gauge.

The thermostat is rated at 185 degrees. (adjust the math for different ratings i.e. 195* t-stat)

You now know the 185* mark.

210 degrees = shut down time.

So where is 210* on this gauge?

It's an educated guess.

Mine hits thermostat temp in the middle of the letter "M" that's my 185* mark.

So when/if it ever reaches the right edge of the letter "L" I'm shutting my engine off immediately.

(Educated guess) The full range of the gauge = 100%

Thermostat temp (on mine) = 75% of total sweep (which happens to be where the "M" is)

The usual range of a coolant temp gauge = 100 - 250 degrees

So if 75% of 250* = 185* (which it does) do the math.

Then 210* = 85% of total sweep.

So in my case; and probably most cases, the letter "L" is the (210*) danger zone.

These are 20 year old trucks! (results will for sure vary)

Everyone should get their "eyeball" on their temp gauge!

At 240* you are doing serious damage to the engine: Cylinder Head cracking time!
 



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Only thing is, stock should be 195*
 






Stock replacement spec is 195-198*. 180 degrees is listed as an alternate.
 












My '92 runs around mid-scale and my '94 just barely goes past the low line on the range scale. Both have the same part number thermostat. The zero (cold) point of the pointer is different on each. If either vehicle shows more than about one letter distance increase, I want to know why.
mr cribb, I have to disagree with you on this. I wanted to use an automobile temperature gauge and sender for a project a few years ago so purchased a Stewart-Warner gauge and sender. Using a calibrated electronic thermometer as a reference I found over 15 degrees error at 200 F, increasing as the temperature increased. After some searching I finally found a sender (non-SW) that gave more accurate results. This is, I agree, just one instance, and if you know the error it would work fine.
 












Never had a problem on my aem digital gauges, they are dead on.I always boil test my tstat to make sure they work and where they open/close at.i run 180* in both my trucks.my ex fully opens at 188*(+-2*) my ranger opens at 183*(+-2*) both came stock with a 195* which I tested and one open almost at 205*:( my efan kicks on at 185* and off at 175*.a 10* difference on my dash gauge is huge,@175* it appears the truck is cold (little under ""N"")
 






I've had various OE Motorcraft (190 degree), cheapo Autozone (192 degree) and Stant Superstat (195 degree) thermostats, and they all generally read in the very middle of the stock temp gauge, between the R and M in "NORMAL". The 195 Stant might read a hair farther to the right than the 190 Motorcraft.

Sometimes the needle goes over a little bit to the right, either on really hot days, or when climing a long hill at speed in the higher gears.

If the A/C is working, then of course the hot air going through the condenser makes the air going through the radiator warmer, so the coolant temperature is going to be warmer, and result in the gauge reading over to the A or maybe even the L in "NORMAL".


I would say that ANY time that the temperature gauge needle creeps up past where it usually sits is a problem, rather than relying on temperature numbers. All the times I've had a thermostat fail, I didn't need a gauge with numbers on it - the needle shot up past the middle at an incredible rate, and the buildup of pressure in the system caused the coolant reservoir to overflow.

If a thermostat is starting to fail slowly, or there are other cooling issues, and the temp gauge needle is higher than usual but not past the L, you can usually get away with turning on the heater (and opening the windows if needed) and turning off everything else to keep the coolant termperature in check while you drive back to replace the thermostat, fan, clutch, water pump, etc. If the needle climbs up really fast, you better pull over and turn off the engine immediately and let it cool, and then either replace the thermostat, or re-burp the system (or replace the thermostat again and re-burp the system if you overheated the new thermostat by not burping the system), otherwise you'll either blow a head gasket or crack/warp the heads, especially if they're stock.

Best advice is keep an eye on the temp gauge every so often to know what is normal for your particular vehicle under a variety of circumstances, and check it out when the needle reads higher. If you want to be a little more prepared than most, carry a cheap spare thermostat, a gallon of distilled water (and maybe another empty gallon jug to drain enough coolant to change a thermostat), and the tools needed, so you can change the thermostat wherever it may fail, rather than winding up stranded (or at least delayed) and having to get a ride and a tow because of a $2-5 part.
 






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