Temp gauge takes a long while to react.

[mikesbaron]

2003. I noticed that if I idle my car for 5 mins th temp guage needled doesn't move at all. This despite the fact that I can turn the heater on and it's blowing hot air.
Once I start driving for a few minutes the gauge will then move to warmed up position.

Why is it so slow to react and how can I fix this?

 

[Muadeeb]

The dash gauge uses a different sensor than the engine. If you follow the top radiator hose, you'll get to a metal tube with two sensors in it. The one closer to the front of the truck should have a single wire coming off it, check that the metal tab on the sensor is well attached.

Also check your coolant levels. You may also have a thermostat that's stuck open, but it's not enough for the ECU to complain about it.

 

[TJTJ]

Yup.

You can do an OBD port reading on the temp, and see if its showing the heat. If the dash gauge is off, typically it reads hot, but, assume the port reading is right if there's a difference, especially when the evidence indicates it...such as heat blowing when the dash says it should not be, etc.

 

[mikesbaron]

Could it be the thermostat itself not opening to the sensor correctly but still allowing the heater core to get warm water? IDK, not sure how it works exactly. I'm just throwing ideas out there.
I can let my car idle for ten minutes and the guage won't move until I start driving it, despite it being able to blow warm air after five mins of idling with guage not moving.

 

[Muadeeb]

Just FYI: the fluid circuit for the heater core is on the engine side of the thermostat, so it could be running heat before the temperature gauge responds. The radiator side of the thermostat is just that and the temperature senders, so that side is stagnant until the thermostat opens.

 

[mikesbaron]

The dash gauge uses a different sensor than the engine. If you follow the top radiator hose, you'll get to a metal tube with two sensors in it. The one closer to the front of the truck should have a single wire coming off it, check that the metal tab on the sensor is well attached.

Also check your coolant levels. You may also have a thermostat that's stuck open, but it's not enough for the ECU to complain about it.

So There are the two brass temp sensors. One is large, one is smaller and both appear to be attached properly to their tabs/connectors. I figure one has to be bad. Which one do I replace? Or which is responsible for sending the signal to the temp guage, the small single wire one is what it sounds like you are describing to me.

 

[Muadeeb]

I've got a pic, Just need to figure out how to get it off Flickr. Basically, the one with the single wire is the one for the dash gauge. I'm not saying the sensor is the problem, not without looking at what the ECU is seeing. That one can be read with a scan tool.