Coolant Temp wrong at startup

[crash813]

Just replaced a blown 3.0 with a running 3.0. Runs great at operating temp but having a problem getting there. At cold start-up, the temp guage is indicating normal operating temp, not cold. Within a few minutes, it will finally fall and then start its slow climb back up as the engine warms. The problem is the car idles way too low and tries to die when its cold. I'm thinking it might have something to do with this issue and maybe reading that the car doesn't need the cold start injector. I don't know. When I switched over sensors, I took them out and cleaned up the brass probe. Not sure what else to look at here.

Any advice is appreciated. I'm trying to avoid removing the sensor since is a PITA to get to, but ultimately, I might have to.

thanks

 

[Reluctanse]

Just an FYI, the gauge and the ECU are on different sensors. Not sure how much that helps you, other than, maybe don't trust what the gauge is telling you. An aftermarket temp gauge might be helpful to at least see what the engine temp is actually doing, it's possible the issues. Do you have the sensors out of the old engine you could swap in?

 

[RonJR]

It's possible you may have an air bubble in the cooling system. That will throw the temperature sensors off and make for poor engine operation.

Google "burping the cooling system" and see what you come up with. There are writeups on how to do it. Generally involves pointing the vehicle as nose-high as you can get it and running it for a while with the radiator cap off, adding water as space becomes available.

 

[goatfarmer]

Not an authority, perhaps with the engine swap there's the possibility of a bubble in the cooling system? Had similar problem, 'fluctuating temp gauge' and at the advice of member burped and no longer a problem? Considering replacing thermostat, with 110K believe occasionally has a tendency to stick?

 

[crash813]

thanks guys for the response. Guess there's a few things I need to check out. Probably start with both the cold start timer and the temp sensor and go from there. The testing procedures doesn;t look that bad from the manual if I can get the room back there.

I thought it sounded like an air bubble too at first, but I fill the coolant from the back in the highest hose and usually don't have any issues with air bubbles, but might double check just to make sure.