Engine Coolant Temperature sensor - temperature vs resistance?

[AbsoluteZero]

Back in March of this year I installed a new thermostat (Motorad 413-192) and ECT sensor (ACD 213-963) because of low engine coolant temperature readings (scangauge data). After installing the new components a stabilized coolant temperature was approx. 200°. Recently stabilized coolant temperatures are now around 182° and will set the P0128 DTC.
Does anyone have the specs for the ECT sensor of resistance vs temperature? I'm leaning toward the sensor being faulty but thought I'd make some comparison measurements of it's resistance and also if it's being supplied the correct voltage.
Another reason I suspect the sensor is I generally observe ambient temperature, as displayed on the DIC, transmission fluid temperature as shown on the scangauge and engine coolant temperature, also scangauge data when the vehicle is first started after sitting overnight. When the vehicle has set overnight and the various fluid temperature are stabilized they generally will be within 2-3° of each other. Now the engine coolant temperature will read about 10° lower.

 

[The_Roadie]

The shop manual says:
212 degrees = 177 Ohms
194 = 241 Ohms
176 = 332 Ohms

many other entries in the table

This isn't the identical sensor, but it shows the detail you might be able to find in a search:

[PDF]http://www.roadie.org/coolant_temp-1.pdf[/PDF]

 

[gmcman]

This was copied from an Amazon review about that particular thermostat....Motorad 413-192.




I replaced both the thermostat and engine coolant temperature sensor (ECT sensor) in my 03 GMC Envoy. Replacing both often is the recommended course of action since ECT sensor is next to the thermostat. I wasn't getting a error code with the old unit but engine coolant temperature varied considerably with little change in load. Often fluctuating from the low 180°s to mid 190°s in just a few seconds.
A couple things to be aware of..... the unit I received from Amazon had the 413-192 part number stamped on it. The 192 suggests it's a 192° thermostat. Also Amazon's info shows 192/89C. If 89C is correct that's 192F however the pellet in the unit I received was stamped 87C.which is closer to 189F. Also I couldn't find an air bleed hole. The boss was on the casting where it should have been but it wasn't there. Amazon offered to have it returned but I decided to contact Motorad. A very responsive customer service group. The rep checked their stock and said the pellet showed 87, not 89 and he told me where to look under the spring for the air bleed hole.

 

[AbsoluteZero]

Thank you... I started to download mooseman's manuals thinking the info would be there but my 768 kbps DSL here at the cabin was going to take awhile so thought I'd ask.

 

[AbsoluteZero]

This was copied from an Amazon review about that particular thermostat....Motorad 413-192.




I replaced both the thermostat and engine coolant temperature sensor (ECT sensor) in my 03 GMC Envoy. Replacing both often is the recommended course of action since ECT sensor is next to the thermostat. I wasn't getting a error code with the old unit but engine coolant temperature varied considerably with little change in load. Often fluctuating from the low 180°s to mid 190°s in just a few seconds.
A couple things to be aware of..... the unit I received from Amazon had the 413-192 part number stamped on it. The 192 suggests it's a 192° thermostat. Also Amazon's info shows 192/89C. If 89C is correct that's 192F however the pellet in the unit I received was stamped 87C.which is closer to 189F. Also I couldn't find an air bleed hole. The boss was on the casting where it should have been but it wasn't there. Amazon offered to have it returned but I decided to contact Motorad. A very responsive customer service group. The rep checked their stock and said the pellet showed 87, not 89 and he told me where to look under the spring for the air bleed hole.

Yep! I wrote that review. Our Amazon acct. is in the wife's name. The 87C on the pellet is/was a mystery but as said in my post the temperature consistently ran around 200 until recently. I didn't do any trouble shooting when I replaced both in March. The ECT sensor was the original sensor and the t-stat was the second replacement. The first was a Stant that ran too cool and set P0128 so I replaced it with an AC Delco but not the ECT sensor. The ACD was fine for a couple years then I started getting the temperature fluctuation so I replaced both in March with the Motorad and ACD sensor.

 

[gmcman]

My gut says to go with an AC stat, or Stant. You could "T" a fitting in the outlet hose to the heater core if poss and monitor temps there.

 

[CaptainXL]

The Stant thermostat is USA made and IMHO a superior design. ACDelco is Made in Mexico and of cheaper construction. The ACDelco's also have the o-ring coming off and sticking it open problem. They never did fix that. Motorad's have a huge oblong restriction in the tube and do not incorporate the check ball.

 

[meerschm]

Non-Contact Infrared Thermometer with Laser Targeting

sounds like you want to check sensor accuracy.

My service manual says to use a special crayon that melts at a calibrated temperature on the outside of the case, but an IR thermometer could do the trick.

you could also pull it and check by other methods, using the info Roadie posted, or other you can find. you still need some kind of reference for the temperature. (boiling tap water should work, assuming you correct for altitude, if you are at any elevation.)


As you suggested, it would seem to me that after a long night, all the temps should agree via the PCM/OBD.

 

[AbsoluteZero]

Non-Contact Infrared Thermometer with Laser Targeting
Actually have one. With my aging hands I can't get close enough to the thermostat housing to get an good measurement. But on the housing on the pass. side by the power steering pump I measured 190° when the scan gauge was showing 182
sounds like you want to check sensor accuracy.
Basically yes
My service manual says to use a special crayon that melts at a calibrated temperature on the outside of the case, but an IR thermometer could do the trick.

you could also pull it and check by other methods, using the info Roadie posted, or other you can find. you still need some kind of reference for the temperature. (boiling tap water should work, assuming you correct for altitude, if you are at any elevation.)
Amazon is delivering a new ECT sensor tomorrow. I'll check it's characteristics vs. the one that's in there now. Presently don't plan on changing the t-stat.
As you suggested, it would seem to me that after a long night, all the temps should agree via the PCM/OBD.

This morning the Envoy's ambient displayed 54° and when first started the ECT sensor was 49°. The garage was 55.

 

[AbsoluteZero]

I started taking things apart to install the new sensor when it comes tomorrow. As soon as I started to back out the old sensor it broke leaving the threaded part in the block. My Easy Outs are 130 mi. south but I found a T40 Torx head gently tapped in the hole of the threaded part was able to back it out. I ran a M12-1.75 tap in the hold to clean it out.
I think what happen was recently the ECT sensor was seeping coolant. I took it out, put some more Teflon tape on the threads and retightened it. Probably over tighten. Not too fond of the sealant that's on the threads

 

[meerschm]

Thanks for the update.

would be interesting to see a comparison of the pass side inlet temp compared to the pcm temp indication after you put the new sensor in.

 

[meerschm]

Hooked up the computer and drove to work today in the TB

7:20 am temps (before starting, parked outside for days)
HVAC indicated exterior temp 74
Intake Temp 73.4
Coolant 77
IR measured coolant inlet (to radiator from block) 75
IR measured driveway cement 74


after driving to work, I compared the coolant temp to the IR coolant inlet temp, with the engine still running and it rose ten degrees while I was fiddling around. (from just over 200 to 212) I suspect reduced flow while idling and heat sink from exhaust manifold. not sure if just running at idle would result in closer match between coolant inlet surface and measured temp indication (which is located on the other side of the block)

 

[AbsoluteZero]

Your observations mimic what I've found by casually looking at the various temps before starting. That's why I suspected the ECT sensor rather than the t-stat. I had ordered a replacement thru Amazon late last week. Per UPS it's out for delivery this morning. Our deliveries are out of Flagstaff and tend to be in the afternoon..... it's a matter of installing and put all the pieces and parts back on!
I wish I had the gumption to tackle tightening the intake manifold bolts. I can see some with a mirror but the bracket under the ECM has more things attached to it than I cared to remove. Another day! So far no symptoms suggesting a lean condition.
The actual thermistor is about 1/4" from the end of the cavity is surrounded will a thermal grease.... looks like the stuff used on the heat sink to CPU interface. With the unit cracked I'd assume the heat transfer to the actual thermistor would be reduced thus the lower reading.
Thanks for the feedback....

A note to CaptainXL..... I don't see any necked down portion on the Motorad stat... maybe they changed design. I can post a pix if of interest. The AC Delco that I had replaced has Behr marking on it. I had bought it thru Amazon as an ACD stat. It does have some crinkles in the bend but doubt a flow restriction. As I said it's a puzzle why the pellet is marked 87C but it's spec'd as 192°.

 

[bobdec]

This is my opinion only..they say 192 but 87*C = 186.6* F, the Gates and Stant T-Stats say 190* (that's 88*C). My guess it it's just stamped 87C/192 that way to satisfy buyer requirements. Were looking at 3-5* difference at low end, not important, since the T-Stat low end temp controlling engine temp is only applicable when moving over 30 MPH in cool air. A T-Stat typically fully opens at 10*F above rating. So you may never, or rarely, see the low 186.6 or 192 end as the T-Stat is just partially opened at that temp. You will only see close to low ends temps when moving on a cool day w/AC off (no fan). When slowed or stopped, T-stat starts to open fully, radiator coolant starts to get hotter, the engine temp starts to rise and the PCM will start the fan (7%) when engine hits 210*F. Fan cools the radiator, at that time T-Stat is wide open and cooler coolant holds the engine at 210 +/- a couple of degrees. So you have then switch from T-Stat control of engine temp to PCM control. The PCM then regulates fan to required speed to hold 210 So you usually see gauge hovering near 210 at that operating scenario. Key is the T-Stat controls the low operating temperatures of the engine, but the PCM controls the operating and high temp end (that assumes no defective components). Very rarely do we see the engine running temp at the T-Stat spec, therefore it's rated temp is not as critical. More important is how fast and how far it opens at specific temperatures. I left out AC on scenario, the PCM will start running the fan (6%) when AC pressure hits 105 PSI, so that will cool the radiator even if engine is not at 210*F, At that time you may see the temp below 210 even when stopped.