Have we tried to bleed the cooling system yet?

On a 5th gen. Cooling fans should come on, car on, when the temp on the t-stat housing (lower hose) is 194 to 205. The cooling fan, when car is off, should come on when the housing on the upper hose is 217 to 228. Did you check temps, using the thermometer today?

 

I think the business of what comes on "when the car is off" only applies during the first 15 or 20 minutes after shutting off the car. There's a timer module that prevents the fan from running forever. So in order to test the "engine off" operation, you have to turn it on then turn it off.

 

My new guess is that its the primary cooling fan. i tested the sensor on the hose with the thermostat and it failed. there was no resistance at all. but there is also another senor in the line in the back left of the engine that looks exactly the same and i havnt tested that one yet they both have 2 wires leaving them and im not sure which one swtiches the primary fan on. I drove the car today for about 16 miles and the heat on and the car was fine but after i drove with the heat of and it did get quite hot but not to the boiling point. when i parked the small fan was spinning but the large one never turned on. I kept the heat off and drove on the highway and the temp guage dropped a bit but once i got off and started driving through town the guage quickly went back up to just under half (which is where it always stops at for some reason) I have not had a boiling radiator problem again yet tho. Im wondering if all i need to do is get the primary fan working to solve the heat issue.

 

Well i drove to autozone to get a new cooling fan switch.. i bought it at a hefty $30 compared to many cheaper brands .. oh well. Drove home parked and what do i hear? my primary fan running! I cant seem to win! so i also got my infrared thermometer and found that the thermostat housing was 209 degrees F and the lower hose was 72 degrees. im guessing this indicates something but i also left the heat blasting to aid in the cooling

 

There are two fan switches. The one on the theromstat housing turns on the fans when the engine is running. The one on the cylinder head with the green plug turns on the fans when the engine is not running if the coolant reaches a certain temperature.

It sounds like based on the difference in temperatures that you either have a stuck closed thermostat, or there is a clog in the radiator. I would get a thermostat from the dealer, because they open at the proper temperature.

 

i was being told that the temp difference was a sign that the cooling system was working. the hot coolant coming into the top and leaving through the bottom as cooled coolant. I didnt notice the fan on while running just when the car was shutoff did i notice it turn on. It must bee circulating, how else would the hot fluid from the engine make its way to the radiator. i might juat buy a thermostat anyways and replace it because there cheap enough. and are both sensors the same? i bought one and they appear to both be the same type of sensor so i could try replacing the one that controls the running engine fan.

 

The sensors are not the same. The one on the t-stat (lower hose) controls the fans while the car is running.

The one on the upper hose controls the fans when the car is off.

The bottom hose being "cool" while the upper is "hot/warm" sounds like a stuck t-stat.

 

yes, the two sensors both activate different things but are the sensors in the lines the same? the thing that threads into the coolant line with the flat base and the plug with the two small prongs inside. They appear to be identical on the outside.

 

No, those 2 sensors have different temperature setpoints.

When you said it had "no resistance", do you mean open-circuit? It's a switch. It's supposed to be open (no continuity) when cold. It's supposed to close the switch at the set temperature (different temperature for each of those 2 switches).

Cold lower hose can also be caused by a plugged radiator. The flow is almost blocked off, so the flow rate through the radiator is small. Plenty of residence time to cool the fluid, but the flow rate is way too small to cool the engine.

 

i drove the car to the boiling point today and found the top hose once again to be very hot (214-220) and the radiator boiling into the resevoir and the lower line still compartment temperature. when it doesnt boil over i can always hear it boiling inside the line near the engine on the upper hose. so the fan not turning on while driving must be because the hot fluid is not making its way to that swtich so something is causing there to be no coolant flow. im going to check the thermostat tomorrow i already purchased a new one.

I tested the upper sensor while the engine was damn near cold so that would explain why my multimeter picked up an open circuit.