Water Temperature Sender Accuracy?

jdemara

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Apr 28, 2008
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North Delta
I just purchased a prosport digital water temp. gauge.
Couldnt find the M16x1.5 adaptor to thread into the temp sender for the stock gauge, but I have a 3/8", so i threaded it into the hole where the bvsv goes to try it out (temporarely).

I will drive around and let the car reach operating temp. and the gauge will only read 165-166F. However, as soon as I turn the car off, the gauge will slowly climb and hit 213*

Then when i turn the car back on, it will decrease again!!

What is causing this!? Could the temporary location where the bvsv usually goes not be very accurate? Will i get a more accurate reading where the stock temp. sender goes for the stock gauge?

I have a new 192* thermostat in there if that helps any of you with coming up with an answer?...
 

Frank Rizzo

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Jul 25, 2007
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Go to a cheap parts store and pick up a metric adaptor kit, sunpro makes a good cheap one.

Using a factory radiator?

How much teflon tape did you use to seal the the 3/8" NPT adaptor? How much teflon tape did you use to seal the temp gauge sending unit? You might have used too much causing a disturbance in the resistance of the ground path for the sending unit.

I have my aftermarket water temp gauge installed in the exact same spot and I see 190-195 F temps while running. With a new factory radiator and 180 F thermostat.

It will be more accurate if you replace the factory temp sending unit, as it is located before the thermostat. My aftermarket temp gauge does not move until my thermostat opens.

On a very hot humid day, I can shut it off and my temp will spike close to 210 F after 10 minutes of heat soak. But will go down to 195 F as soon as I start the engine.
 
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CyFi6

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Oct 11, 2007
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Pretty normal. Mine does the same thing. If you drive it longer/harder the temp will go higher, but i have noticed for the majority of short trips and non highway use my temp doesnt really get above 175~180 until i get on the highway.
 

jdub

Official SM Expert: Motor Oil, Lubricants & Fil
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If you guys are not getting to at least 180 deg (as measured at the water neck where the ECU temps sensor is) after warm-up, something is wrong. The stock ECU "looks" for 176 deg F to come completely out of warm-up enrichment...the amount of additional warm-up fuel decreases as coolant temp increases to 176 deg F. Below that temp, the engine is going to run rich.
 

jdemara

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Apr 28, 2008
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North Delta
I think possibly too much teflon tape.. makes sense. But I will be getting a metric adaptor kit because I want the most accurate reading, before the thermostat :)
I am going to go remove some of the tape and put it back in and see what happens.

I drove around for about half an hour (highway, city and everything) and it would only hit like 166 or 167. Not even close to what it should be at.
 

jdub

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Teflon tape is fine for water/oil fittings. It's not for fuel. It should also have no effect on the temp readings since the sensor bulb is not covered.

It could be a gauge accuracy issue.

What make/brand thermostat is it?
 

figgie

Supramania Contributor
Mar 30, 2005
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jdub;1042313 said:
Teflon tape is fine for water/oil fittings. It's not for fuel. It should also have no effect on the temp readings since the sensor bulb is not covered.

It could be a gauge accuracy issue.

What make/brand thermostat is it?

actually

unless teflon is an extremly great conductor, it will affect the reading.

Remember the temprature sender has only one connection so it relies on the engine ground to be the - side of the circuit. Anything impeding that flow will cause issues with overall resistivity.
 

jdemara

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Apr 28, 2008
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Nope, this teflon tape stuff isnt true. Its a prosport gauge, and it has two wires coming off the sender: one green to go to the gauge, and a black which is ground. I have made sure there is a good ground, and taking the teflon tape off the threads didnt do a thing what so ever.

Motorad thermostat, 192 degree.
 

jdub

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I've tested the opening temps of various thermostats, including the Motorad. Stant and OEM Toyota were the best concerning opening temps. The Motorad I tested opened up 15-20 deg F early. If you want to see what yours does, just get a 250 deg thermometer and bring some water up to boiling (with the thermostat in it) on the stove...note the temp when it opens.

You should be able to do the same thing with the Prosport...you'll need to connect to a 12V source.
 

jdemara

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Apr 28, 2008
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North Delta
Alright heres the deal. Got the fitting to install the sender where the stock one goes (before the thermostat). No teflon tape.
Prosport gauge still reads about 165ish driving for more than half hour, with a peak of about 171F.

I parked my car and checked the thermostat housing with an infrared temp thing, and it was in the 190 area.

Now, I have noooo idea what to think because my car I think is running too hot (coolant slowly dripping out of overflow resevoir). I have a newer stock radiator and new rad cap.

Anybody know what my real problem is here? Could it be a bad sending unit from prosport gauges? or is my car somehow not reaching full operating temp?
 

jdemara

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Apr 28, 2008
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North Delta
the only thing that comes to mind is maybe the sender unit needs all around 360degree contact with the water? Because with the M16x1.5 fitting, its mostly just the tip that the water would hit but I beleive there is a space around so the water can in fact cover all the surface area... would that matter that much:S ??

ahhhhhhh I dont know what to thinK!!
 

johnathan1

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Aug 19, 2005
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171F isn't really running too hot...even 190 if the conditions are right. You said you parked the car and the thermometer read 190? Was the engine running when you got this number?

I would pressure test the rad cap to make sure it's holding the proper 13lbs.