Measuring coolant temps on engine using thermometer?

TonyT

Original poster
Member
May 6, 2012
108
So I'm still trying to figure out where the, possible, overheating is happening from. Rad has been hosed down and rad cap replaced but I haven't done a highway run yet so not sure what'll happen after a half hour or more.

In town driving at about 55 or 60 F for 2 or 4 miles brings the sensor temp up to about 210 F. (Using a Bluetooth ODB2 reader and Torgue on my Android tablet.) I also purchased one of those $20 infrared/laser thermometers. When I stop and measure the temps on the metal hose junction from the engine to the upper rad hose the temps are 219. When he and I drove it last week that metal temp was at about 212 F according to his IR reader and mine but it was also about 40 F outside then.

Mechanic is saying that's normal but I don't quite think so.

Now is that a good place to use the IR remote thermometer? Is there a better place? That seems like on obvious spot to me but I ain't no mechanic.
 

RayVoy

Member
Nov 20, 2011
939
The needle on the dash gauge should be in the straight up (12 o'clock) position when the engine is at normal operating temps. At this position, the needle is reading 212 degrees.

From your description, I am currently agreeing with your mechanic,

Why do you think you have an overheating problem?
 

TangoBravo

Member
Dec 5, 2011
208
Guess it would depend, are you trying to see a high number or a lower number? If you want to see how hot your motor is getting the fluid then measure where the fluid returns from the engine back to the radiator. If you want to see if your radiator is working well you can check the line that returns cooled coolant to the engine. Be sure to run the engine long enough for everything to be well heat saturated.
 

TangoBravo

Member
Dec 5, 2011
208
TonyT said:
So I'm still trying to figure out where the, possible, overheating is happening from. Rad has been hosed down and rad cap replaced but I haven't done a highway run yet so not sure what'll happen after a half hour or more.

In town driving at about 55 or 60 F for 2 or 4 miles brings the sensor temp up to about 210 F. (Using a Bluetooth ODB2 reader and Torgue on my Android tablet.) I also purchased one of those $20 infrared/laser thermometers. When I stop and measure the temps on the metal hose junction from the engine to the upper rad hose the temps are 219. When he and I drove it last week that metal temp was at about 212 F according to his IR reader and mine but it was also about 40 F outside then.

Mechanic is saying that's normal but I don't quite think so.

Now is that a good place to use the IR remote thermometer? Is there a better place? That seems like on obvious spot to me but I ain't no mechanic.

You do realize that at -35° out your engine will still read 212°. It's called a thermastate and if works correctly no matter the outside temps under normal operation your vehicle will be at it's normal temp which for these is default 212° actual is usually about 194°-205°
 

TonyT

Original poster
Member
May 6, 2012
108
RayVoy said:
The needle on the dash gauge should be in the straight up (12 o'clock) position when the engine is at normal operating temps. At this position, the needle is reading 212 degrees.

From your description, I am currently agreeing with your mechanic,

Why do you think you have an overheating problem?
I don't trust the needle or any needle really. Other postings have indicated the needle should, in normal use, be a tick to the left of center. And now your stating it should be vertical. So I'm getting confused. :smile: I'm getting the temps from the sensor via the OBD2 interface.

On highway drives on gentle grades the needle moves to a tick left of 3/4s of the way and the temps rise to 230 F on the sensor.

See the history at http://gmtnation.com/f25/engine-temp-after-replacing-thermostat-sensor-106-c-highway-5224/

But I'm asking for what is reasonable when driving around town that other folks are seeing so I can understand if what I'm seeing is reasonable before I take it on a highway drive. And, like the subject stated, I'm trying to ensure that before I take it on a highway drive that I've found a good spot to verify the temperature.
 

TonyT

Original poster
Member
May 6, 2012
108
TangoBravo said:
Guess it would depend, are you trying to see a high number or a lower number? If you want to see how hot your motor is getting the fluid then measure where the fluid returns from the engine back to the radiator. If you want to see if your radiator is working well you can check the line that returns cooled coolant to the engine. Be sure to run the engine long enough for everything to be well heat saturated.

I'm trying to see what reasonable folks out there, which means you folks :smile:, are doing to ensure accruate measuring of temps. I found the one site and now I'm asking if that's a reasonable site to use. What have other folks whose cooling systems function as expected used to measure things.
 

TonyT

Original poster
Member
May 6, 2012
108
TangoBravo said:
You do realize that at -35° out your engine will still read 212°. It's called a thermastate and if works correctly no matter the outside temps under normal operation your vehicle will be at it's normal temp which for these is default 212° actual is usually about 194°-205°
Fair enough but, possibly, the ambient temperature might make a slight difference as to how fast the metal on the engine cools down when you open the hood. Not much I suspect but I don't know.

So even though the thermostat is a 185 F or 190 F thermostat the coolant entering the rad will be at 210 or so? That is part of what I find confusing.
 

TangoBravo

Member
Dec 5, 2011
208
TonyT said:
Fair enough but, possibly, the ambient temperature might make a slight difference as to how fast the metal on the engine cools down when you open the hood. Not much I suspect but I don't know.

So even though the thermostat is a 185 F or 190 F thermostat the coolant entering the rad will be at 210 or so? That is part of what I find confusing.

Ok you have a Tstat that opens or begains to open at 185-190F now that's NOT what your engine is going to run. Really measuring temps by hand and thinking your going to get reliable readings is not accurate. The proper way if you don't want to trust the gauge on your dash is to use a scan tool and have someone else drive your TB with you in the Passenger seat recording your readings. You see when your Tstat is closed your engine may be hotter then 212 and when your Tstat is starting to open you could be showing less then 212. With a scan tool I can watch my Tstat open and close. It's actually kinda cool.
 

RayVoy

Member
Nov 20, 2011
939
TonyT said:
On highway drives on gentle grades the needle moves to a tick left of 3/4s of the way and the temps rise to 230 F on the sensor.
Temp of 230 is not good. As someone suggested-- it should be rock solid and not move around (unless you are towing heavy loads).

TonyT said:
But I'm asking for what is reasonable when driving around town that other folks are seeing
Around town and on the highway, an engine that is up to normal operating temperature should read the same. It should be straight up at, in your case, 100c.

TonyT said:
the ambient temperature might make a slight difference as to how fast the metal on the engine cools down when you open the hood. Not much I suspect but I don't know.
That's like throwing an ice cube into a bath tub of hot water, raising the hood will not change the water readings.
However, using the metal clamp on a hose is not going to give you an actuate indication of the water temperature (it will be close, but not actuate).

TonyT said:
So even though the thermostat is a 185 F or 190 F thermostat the coolant entering the rad will be at 210 or so? That is part of what I find confusing.
The temp on the thermostat is the opening temp. At this point the water pump is able to start moving the coolant (the restriction has been removed). Once open, the thermostat stops becoming a factor. The radiator and it's ability to cool takes over. On a cold winter day, the rad may cool the water too low and the thermostat will close to allow the water to heat, but the engine temp should stay at the 100c mark.

As someone suggested, you may have air in the system, or air flow restriction in the radiator.
 

TangoBravo

Member
Dec 5, 2011
208
RayVoy I have to dissagree. If you have ever done what I have suggested to do with a scan guage you will for sure see exactly what Im talking about. You can watch the ACTUAL temp raise and lower as the Tstat cycles when the coolant is hot and then cools down. The guage on the cluster really is a very unreliable way to tell what temp you're really running. In the winter I can watch my scan guage and see my Tstat open and then the engine temp dive off to 165° then come back up as it closes now thats in a really cold day going down the highway but meanwhile my dash guage never moved(yes it does work) much and certainly not down to 165°. But what Im getting at is even under light load even just at idle your Tstat is continuosly cycling to keep your engine as cool or warm but it is never going to be at a steady temp of 212° because of this chevy has basically made these guages "dummy" guages. If the guage moved half as much as your real temp does then alot of people would be taking there cars to the shop over nothing.
 

TonyT

Original poster
Member
May 6, 2012
108
TangoBravo said:
But what Im getting at is even under light load even just at idle your Tstat is continuosly cycling to keep your engine as cool or warm but it is never going to be at a steady temp of 212° because of this chevy has basically made these guages "dummy" guages. If the guage moved half as much as your real temp does then alot of people would be taking there cars to the shop over nothing.
The ODB2 software I purchased and have installed on my spare Windows laptop has some logging capability. I should investigate that a bit more and try it out on a highway run from a cold start. The Android tablet software I've been playing around with doesn't have any logging but then, hey, it's free. :smile:

And maybe I am getting concerned about not much. Now that I know it's reasonable for the coolant temps to hit 210 F around town then I'm not quite as concerned as I was.
 

TangoBravo

Member
Dec 5, 2011
208
If you are able to log the data you will see what Im talking about. You may climb up to 210-212 then you will see it drop off and if you can graph that it makes it even easier to see. Really though I think you're worried over nothing. If you want send me the graph or whatever data you log and I will go over it too(kinda what I do for a living) and make sure something isn't getting missed altho I really dont think it is.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Around town and on shallow hill climbs, sensor temps of 190-220 are normal. The gauge needle will display 210 because of the filtering/lying the PCM does to make sure the average numbnuts driver doesn't get alarmed. The gauges were designed to have straight-up as "good" numbers so the driver can scan the gauges quickly and see if one is out of position and needs more attention paid to it. When you take training for a private pilot instrument rating, in planes without autopilots, you learn how critical it is to develop a good instrument scan.

I think your observation of 230 on the sensor on shallow hill climbs is evidence of a problem, but the IR sensor isn't going to help troubleshoot it. Just trust the ECT sensor and your Torque data, and troubleshoot a debris mat between the AC condenser and the radiator, or a clogged radiator or an old, collapsing hose first.
 

dfc739

Member
Jul 29, 2012
170
Des Moines, IA
TangoBravo said:
RayVoy I have to dissagree. If you have ever done what I have suggested to do with a scan guage you will for sure see exactly what Im talking about. You can watch the ACTUAL temp raise and lower as the Tstat cycles when the coolant is hot and then cools down. The guage on the cluster really is a very unreliable way to tell what temp you're really running. In the winter I can watch my scan guage and see my Tstat open and then the engine temp dive off to 165° then come back up as it closes now thats in a really cold day going down the highway but meanwhile my dash guage never moved(yes it does work) much and certainly not down to 165°. But what Im getting at is even under light load even just at idle your Tstat is continuosly cycling to keep your engine as cool or warm but it is never going to be at a steady temp of 212° because of this chevy has basically made these guages "dummy" guages. If the guage moved half as much as your real temp does then alot of people would be taking there cars to the shop over nothing.

That's a really big drop... Are you sure your thermostat isn't going bad? Sometimes they will stick open/closed until it gets cold/hot enough and then snap shut/open. I've monitored my temp with city and highway driving (so far only in the winter and spring) and once warmed up it doesn't vary more than +/- 3 degrees F centered around 195 F. I haven't towed anything with it yet though. I use an OBDII bluetooth interface with Torque to monitor the temp.
 

TangoBravo

Member
Dec 5, 2011
208
Yes everything functions fine. Like I said this kind of drop is in the winter time(-20°-45°) usually near highway speeds which to some doesn't sound like much but when you have -20° weather and you drive lets say 55mph you just added a wind chill factor of 55mph so as soon the tstat begains to open you can watch the temp drop with a scan tool. This is all very normal which is why the guage is made to lets say absorb a certain amount of change, so as not to freak the owner out. Now remember I live in Wyoming where we have extreame winters, not everyone will have the spread I do I just used mine as an example. However big or small the change you can still graph it out and see your tstat in action.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
TangoBravo said:
...you drive lets say 55mph you just added a wind chill factor of 55mph...
Just a clarification. Wind chill factor due to wind speed only applies to exposed human skin where the wind evaporates some moisture and removes surface heat from the skin to make it SEEM like it's equivalent to a colder temperature without wind. Zero degree air blowing on metal at 100 MPH still only acts like zero degree air. It won't have the ability to make the radiator think it's like -20 or anything.
 

TangoBravo

Member
Dec 5, 2011
208
Right that is correct. I should have said the temp outside is without windchill factor, because that factor really only applies to us not the truck.
 

RayVoy

Member
Nov 20, 2011
939
TangoBravo said:
RayVoy I have to dissagree..
Tango, I agree completely. Perhaps I was unclear in my post.

What I was trying to say, is that the t-stat controls the heating of the coolant and the rad controls the cooling of the coolant.

I was not suggesting that the t-stat only had one cycle. On a very hot day, or while towing the t-stat may not close very often, as the rad is doing all of the work; however, on a cooler day, the rad may cool the coolant to the point where the t-stat must close to allow the engine to heat the "coolant" to maintain the "normal" temp.

All dash gauges have some damping built into the gauge, if it wasn't there, the driver would see needles moving all the time (go over a bump and the gas needle would move).

The digital transmission temp display (as in my Avalanche) has some internal damping, the digital outside temp display has some internal damping.

In this case, damping is good. :biggrin:
 

TonyT

Original poster
Member
May 6, 2012
108
To close the loop.

the roadie said:
Around town and on shallow hill climbs, sensor temps of 190-220 are normal. The gauge needle will display 210 because of the filtering/lying the PCM does to make sure the average numbnuts driver doesn't get alarmed. ....

I think your observation of 230 on the sensor on shallow hill climbs is evidence of a problem, but the IR sensor isn't going to help troubleshoot it. Just trust the ECT sensor and your Torque data, and troubleshoot a debris mat between the AC condenser and the radiator, or a clogged radiator or an old, collapsing hose first.
As I said before how do I know where the problem is? Is it a sensor problem or not? By using the IR scanner I could verify that the ECT sensor was accurate.

Pressure washing the radiator fixed the problem. There was lots of dirt on the pavement. On a hot, for us at this time of year, day of 85 F, the scanner temp varied from 206 to 210 when going up slight grades on a highway drive whereas before those same grades were hitting 230 F. Also when I stopped to check the metal pipe on the engine just where it enters the upper rad hose it was showing pretty much the same temps as the computer was showing me of 206 to 210.

So last fall before I had the thermostat and sensor replaced there was a definite problem of some sort before the replacement with either of those as it was supposedly running cool. Replacing those two items showed another problem.

We also replaced the rad cap as that appear to be malfunctioning too as it was bubbling into the reservoir after a highway drive. Which it isn't doing now.
 

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