After I turn off my 2004 Blazer, pull the key out, and the dome light shuts off. My temp gauge jumps up to about 240; when the engine is definitly not that hot. The gas gauge also comes on but is accurate. Why would this be happening? Im concerned its draing my battery and if I leave it at the airport for 5 days it may not start; in negative temperatures as well. Anyone have some ideas?

 

It does this when the truck is off? Does it read correctly when the truck is running?

 

Yes it does this when the truck is off, and right after the dome light turns off. It reads accurate otherwise when it's on.

 

Even when left overnight it reads around 240. When I open the door it drops back down then after I close the door it shoots up. The gas gauge does too, but is a accurate reading.

 

Not sure what to suggest for you, but you obviously have something that is staying on after you turn the key off. Have you tested the ignition switch to see if it is turning everything off properly? Do you have an aftermarket starter or alarm? It's possible one of those is leaving one of the iginition circuits engaged.

 

I have the same issue. Though both my gauges (temp and gas) shoot up to the center of their reading range. Same thing with the door too, been doing it for years and haven't put much thought into it.

If anyone knows would be cool to learn what trips it

 

The only aftermarket item is a car stereo amp for a subwoofer. Though I think the problem arose months after install. Haven't checked ignition though; good idea.
From some online research I think the problem could have been caused by attaching the negative battery lead with the key in the ignition. It caused all my gauges to jump to max, then after I reattached lead without the key in ignition things seemed normal. I'm leaning towards maybe a bad gauge...? But something is definitely keeping it from turning off.

 

Anyone have some more answers? Or have the same issue? I like to have everything absolutely perfect with my truck so this has been bothering me. I took it to a mechanic to have my oil changed and told him to look into it. He just said it's not a big deal but no answers to why?...

 

Pull the fuse's till it drops. That will tell you what circuit to start looking. If your airport trip is immanent then you can pull that fuse when you park and track it when you get home.

 

An interesting tool / meter I found at Harbor Freight is a "Current Meter with the Fuse receptacle leads permanently attached". Reads the current of each individual fuse contacts ( ea. Fuse ckt. ) one at a time.

Very inexpensive.

I want to buy one and try this tool soon ! Maybe I can report on this tool next week .