Thermostat Question

No, if you read my posts in that thread carefully, you will see that the only automatic engine shutdown that is mentioned in the manual, and the only one I tested and confirmed, is that at a significantly lower temperature, 221 ℉ (105 ℃), the ECM will shut down the engine if there is a current active water pump trouble code.

When there is no current water pump trouble code, of course the temperature can rise right past 221 ℉ (105 ℃) with nothing special happening, and later at 248 ℉ (120 ℃) the warning light comes on, and the manual doesn't say anything about any automatic shutdown for that, and I've never tested for one either.

 

You may have some sort of flow restriction within the 7CO coolant pathway loop or there's corrosion, wire, or connection damage on that sensor. Those sensors are variable resistance temperature sensors; so oil or any contaminate in the connector will change it's reported value.

Hope this helps.....

 

No other that I know of, but I'm not claiming to know everything.

 

The Car Scanner app developer is routinely changing the custom "connection profiles" that decode manufacturer specific points. He had an update about three days ago and the water pump rpms don't work even though the points are there. I sent the developer an email yesterday. The problem is he configures this app for almost all cars so I don't know how he can properly test changes.

I would expect the exhaust heat recirc sensor 7CO to be slightly hotter since its source of coolant is the output of the engine. So it starts with coolant at engine temp and heats it more until a separate thermostat bypasses the exhaust. This flow is small compared to the larger engine to radiator flow and is further split between the egr cooler and the exhaust heat recirc system. I suspect the warmed up secondary flow heat increase is negated by the egr cooler. I normally find both sensors to be within a few degrees of each other when both mechanical thermostats have operated, eg at full operating temperature.

Part of the problem with visualizing these flows is Toyota does not have an official flow diagram for gen3. There are sketches from the gen4 to gen3 engine experiments but each ends up being a compromise solution for those engine swaps.

As noted earlier, the exhaust recirc thermostat could be stuck in the heat exchanger position adding unnecessary heat after warmup. This was reported at least once. The engine temp could be fine but the exhaust heat exchanger sensor could trigger the light.

Testing the thermistors is as simple as verifying their readings after an overnight cooldown. They should read within a few degrees of the car's outside ambient temp as displayed on the ac controls. The connections are unlikely as it takes 40 or more ohms resistance to change ten degrees in most temperature ranges.

Your engine sensor is well within normal but you may not be monitoring at high engine load. Outside temperatures have little impact with a normal cooling system. But reduced cooling capacity is always possible as noted in Chapman's earlier post. If it's reduced cooling capacity I would expect the engine sensor to rise significantly above 204f under high load and be slow to recover.

I don't have access to the v today, it's on its daily 90 mile round trip commute. But when I do I will warm it up and test the exhaust heat recirc sensor vs engine sensor on a high slope hill.

 

The flow is from the output of the engine, through the cabin heater, then splitting off between the EHRS and the EGR cooler. So, during heating season, it will have given up heat to the cabin and will be coming in cooler than at the engine outlet (which is desirable, to increase the rate of heat exchange into the coolant from both the EHRS and the EGR cooler). During cooling season, of course, the cabin air mix will all bypass the heater core, and the coolant should be coming out still close to the engine outlet temperature.

I'm not sure what you meant there, but the direction of heat exchange is from the exhaust gas into the coolant, in both the EHRS and the EGR cooler. In one case the purpose is to raise the coolant temperature, and in the other the purpose is to lower the EGR gas temperature, but the effect of both is that the coolant temperature goes up.