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Cool Coolant

bigalpha

Moderator
Location
Tucson, AZ
I know there are two coolant temp sensors. Can't seem to find them both. One is in the t-stat housing and in the block, right?
 
'96 should have 2 units, the one you have found in the thermostat housing and one in the back of the head drivers side. It is a one wire unit that operates the dash guage.
 
The sensor in the t-stat housing is the 'important' one that the computer uses, right? Does the e-fan take the readings from this, too?

Does the other sensor leak if you replace it w/o draining coolant?

Coolant is staying below 180* (verified w/ infrared thermometer). Think that's why I get bad gas mileage.
 
The sensor does not control the coolant temperature, only the temp gage reading. Your thermostat is what controls the coolant temp via an internal temperature sensing pellet built into the tstat. Change the tstat first. You need a 195 degree tstat. Bad gas mileage, carbon build up in engine, oil contamination.
 
I just replaced the t-stat. i'm thinking that if my coolant temp sensor (in the t-stat housing) is wonky, that it may be affecting the e-fan operation. It is coming on way too soon sometimes.
 
That still shouldn't make it run too cool. System should come up to temp even at zero degrees outside. Unplug the efan if you are worried about that, to test it. You did replace with a 195 tstat, right? Both your dash gage and the infrared read under 180?
 
Yeah, was replaced with 195* t-stat.

That infrared will read 160*-180*. The temp will fluctuate some while I'm taking a reading. On the dash, the needle will sit between the first line and the 210 line. Every once in a while, it will creep up to 210 but then drop back down.

No noticable coolant leak. Recent coolant change with t-stat and OEM style water pump.
 
What are you infraredding (if that's a word). On mine, the dash temp gage reads 210. I fooled around with the infrared and got 150 on the rad hose, 190 on the heater hose, 160? on the tstat housing, 230 on the brass temp sending unit. The back of the head where the second sensor goes on older motors read about 160 (IIRC). What place are you reading? Once it warms up, what does you dash gage range. Not sure what your "first line" represents.
 
I infra-redded all the hoses, rad, t-stat housing. The housing read a lot hotter than the hoses. I (stupidly?) assumed that the hoses would be around the temperature of the coolant. Where's the correct place to infra-red the system to get a correct reading?

On the dash gauge, it's split into 4 parts by three lines. 210 being the middle (second) line. The needle will hang out between the left (first) and middle lines.
 
I don't know if there is a "correct" place. I would logicaly think that the best thing to read would be the sensor itself, or the housing around the sensor. Another place would be the head. One thing about those infrared things is that the color and surface condition make a difference. They say to paint flat black if you want the most accurate reading. The hoses and radiator should be considerably cooler than the engine because the thermostat tends to contain the heat in the engine as it was designed to do. Some reports of new sticking thermostats have occurred that have freed up and help the gage steadier after more use. Possibly consider a premium Stant thermostat. They are only $5 at Rock auto and may run smoother. About the efan -- many years turn the efan on whenever the AC (including defrost) are on. You may be blaming this on your temp sensor.
 
I figured that the outlet hose would be the same temperature as the sensor, housing or head as long as the rig was at operating temperature since it would be letting out that hot coolant.

I'll test that sensor and see if it falls within specs. Heck, for <$20 maybe I'll just replace it and the t-stat again.

I'm not running the A/C or defrost. I know it kicks the fan on, as I tried it the other day. Meh. First too hot, now too cool.
 
My outlet hose was 150. The heater hose surprised me at 190. I think that bypasses the thermostat - might be the best place to check. I don't really think you have a problem. It would be a good idea to test the sensor before and after you replace it so you can tell us what happened.
 
Good idea. I'll test the sensor before I replace it then replace it with new and retest and see if it gives the same reading.

Then the temp. sender for the gauge must be fubar, then, if it's not reading proper temp. Can I replace that w/o draining the coolant?
 
Rubber, plastics, wood,... non-metalic material is a bad conductor of temperature. Any and all hoses will not yield an accurate temperature reading.

It sounds to me that you may have a bad thermostat or a poor quality unit that opens early then closes then opens,... that will be my first place to look.
 
Rubber, plastics, wood,... non-metalic material is a bad conductor of temperature. Any and all hoses will not yield an accurate temperature reading.

It sounds to me that you may have a bad thermostat or a poor quality unit that opens early then closes then opens,... that will be my first place to look.

What about taking the measurement off of the t-stat housing? More reliable?
 
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