My aeroforce Interceptor scanguage (OBD) reads lots of parameters.... BUT, what I find odd is the reading of coolant temp.

When I start the truck, it begins displaying around 200*, give or take. It slowly builds more temp, and finally reaches 237*.... then it drops to 179* and increases or decreases - usually floating around the 195-205 zone.
If it's already hot and I start the truck, it will sometimes show a reading of 180*ish and appear to be normal - then rise and fall as one would think it should.

Does this sound legit?
Why the strange initial reading? Is it do the location of the temp sensor in relation to the thermostat? Or something else? Possibly an unreliable gauge?

 

I'm no authority on the Aeroforce ScanGauge, but I believe it may be similar to my Linear Logic ScanGauge II. The ECT reads wrong up until it hits 254...as soon as it does, it drops back down to 127, and reads 15-20 degrees (lower) different from the EOT. I am guessing you have an automatic trans, which everyone says doesn't really have an ECT sensor......so the gauge does calculations (black magic, voodoo, whatever) to display the ECT... Just my $0.02.....

 

At least I'm not alone . I feel better knowing it's the truck side, and not some Pac-man software running through the gauge.

Yes, Auto. I didn't know the auto trucks calculated ECT in-directly. Interesting.

EDIT: FYI, I updated my sig to include Auto.

 

I have one of these gauges as well, and mine reads 200-ish at start-up too. Then after a while of warm-up, it will begin to show a 'normal' reading, at least one I'd expect. As with your truck, when I drive around unloaded, mine usually runs 200 -205.

When towing hard, my coolant temp will read as high as 220-ish. I think 222 is as high as its ever gotten. It is usually within a few degrees of the EOT reading when I'm running fully warmed up. After the truck is warmed up, the readings don't go back to 200-ish at first anymore, but read a 'normal' temp.

I also have an auto, and just did the coolant flush/change, with a new 192* t-stat as well.

I know a lot of guys have posted here and there that the coolant temp reading isn't accurate, but I bought an infrared heat gun/thermometer and its readings, when pointed at the t-stat housing, reads very close to the interceptor gauge. Based on that, I'm going with the opinion that it's at least semi-accurate........

 

Great Info!! Exactly what I experience!!

 

The PC/ED manual (for all years '99-'03) say the PCM reads ECT sensor data on manual transmission vehicles only. Wiring diagrams confirm this.

Vehicles fitted with the 4R100 are wired differently. On 99-01 vehicles, the ECT sensor wire runs directly to the OEM gauge in the instrument cluster. '02-'03 models feed the instrument gauge module, which is on the SCP bus so there is a possibility that ECT data could be sent to the PCM via module to module communication but it doesn't appear that's happening either. If a capable scan tool can not see the VOLTS or HZ for that sensor..then the PCM can't either.

The engine coolant temp picked up via scan tool is a calculated value by the PCM and not related to the sensor in any way shape or form. You can test this by disconnecting the ECT sensor and it will have zero effect on the reading shown in your scan tool.

It does appear that over the years the PCM calculated value appears to become more and more accurate so the software engineers must have fine tuned the lookup table over time. For example...'99 models are all over the place. Yesterday I drove home with ECT temps in the 257-289 range at 65mph. In stop and go traffic the temps read about 197-205 degrees.
At idle that same truck will rise all the way to 300 degrees and then start over again at 100 and slowly climb. Very random.

The real question is why would Ford choose to ignore the ECT sensor for automatic transmission vehicle only? Perhaps it has something to do with the cold operation look up table for shift points and line pressures. At cold temps the line pressures are reduced. According to Ford, they did this for driver comfort. Of course, the PCM will need some way to know when the transmission fluid is warm so the 4R100 has it's own temp sensor internal to the unit so there really isn't any need for ECT except for a double check to verify trans cooling temps. However, the EOT would be a much better sensor to use for a double check so I bet the engineers decided to use that value instead. Keep in mind that the transmission solenoid pack receives what's called "Injector control pressure" signal to modulate the line pressure solenoid but that signal is ICP as calculated by the PCM and not ACTUAL ICP. Again, you can prove this by disconnecting the ICP sensor yet the transmission will still receive a value at the solenoid pack on that wire. It may not be the correct value but it does the job about the same...

Be advised that values shown on a scan tool may NOT be actual look up values reported by the sensor but CALCULATED values instead. The way to cross check is to also look at sensor voltage, hz etc to make sure you are actually seeing the sensor. Never assume the temp or psi value is accurate without also checking to make sure the sensor passed the CCM test and is online with the PCM. The PCM runs the CCM test on a regular basis, even with the engine running so things can change at any time, even during a live monitoring session.

So, why calculate a value for ECT at all? Well, perhaps that could be for the double check for engine load and/or overheating. I bet the PCM looks at EOT, TFT and (calculated) ECT and possibly some other readings to determine if it's time to pull back the fuel in order to save the engine from damage. Of course I am just guessing as to the thinking (or lack of) behind the programming so if anyone has some inside info to share then I am all ears.

 

The PCM take a wild azz guess at ECT from EOT.

The scangauge ECT reading is pretty close to actual ECT after it finally drops.

 

I have the same gauge and when the temp hit 237* it drops to 179*. I though that was the temperature the thermostat would open and thats why you see the drop in temp.

 

I believe the ECT signal is derived from the EOT signal with a some math in the form of 1's and 0's mixed in. I measured and graphed them together.

 

The OEM t-stat begins to open around 193-195 degrees and is fully open by 205 degrees. The fan clutch comes on around 212-215 degrees.

If you think your Scangauge is actually reading the sensor, then unplug the sensor and see if it makes any difference on the Scangauge. It is not possible for any scanner to interface with the ECT sensor via OBDII port on a 4R100 vehicle model year '99-'01. It is technically possible on model year '02-'03 but I have been unable to confirm that ECT data is passed to the PCM via SCP. The PC/ED manual for '03 still says "Manual Transmission Vehicles Only" so I presume the ECT is not providing any data to the PCM even in those later year vehicles.

Any scanner that registers engine coolant temp is doing so from a calculation performed by the PCM. It has nothing to do with the sensor. The ECT sensor is completely offline and detached from the PCM on 4R100 vehicles.

 

So i have a manual trans and my aero force does the same thing BUT i know that after it drops it IS reading accuratly on the account that when it hits 213ish my clutch fan comes on...

 

So, all it does is sweep the needle? Tough to get accurate measures like that.
I guess we could add an aftermarket ECT gauge that has it's own sending unit. (I already have one, just no place to install it / don't want to risk the 'fighter jet' look).

 

Correct. All it does is sweep the needle.
You can easily add another sensor in the side of the water pump. I have seen two plug sizes...1/2" and 3/8" (both NPT thread). You will need an adapter to match the thread pitch for your sending unit.

 

Of course I just used that port for my coolant filter bypass...

 

Ken (woodnthings) mounted his coolant temp sender in the coolant bypass filter housing. He said the temp readings are still pretty accurate there. I have mounted mine there also, but haven't finished the wiring up yet. I will get that done this weekend.