My 02 CR-V doesn't get to temperature, also has HORRIBLE gas mileage. Like 10 mpg. I hear it may be the thermostat, as they fail open.

 

how is it running, otherwise? any check engine light?
do you have any idea how old the thermostat is?
when's the last time the coolant was changed? what was used?

 

I have no idea what the coolant state is, it's not running all go well. The CEL comes on and off.

 

do you mean it's not running well or not running at all?
have you had it scanned for any codes?
do you know much if anything about working on vehicles?

 

I meant not running too well. Haven't scanned for codes, know enough about cars for this.

 

a bad thermostat is certainly plausible and easy enough to replace. do that, fresh coolant, then clear the codes and see if they come back. if they do, have it scanned. you may have more than one thing going on...ie. a bad coolant temp sensor (not the gauge sensor). not saying there is, so don't be alarmed. just saying it's possible given how it's running and the poor mileage. hard to diagnose over the internet, eh

 

10 mpg sounds like real trouble. Could have a bad thermostat, but that would not put you in the 10 mpg range. Sounds like it needs some real TLC. Maybe start with a compression check. Look at the plugs while you have them out. But there are a myriad of things might be wrong with your car. The stored codes may give a clue.

 

check the oil for coolant. make sure you haven't blown the head gasket