31Coolant Temperature Sensor

[VR6Killer]

Hello All,

I daily drive a 2000 Malibu with a 3100 SFI motor. It gets highway driving exclusively, i've noticed for a while now that the car will never reach operating temperature on the highway. The needle only gets to about the 1/4 mark on the gauge. The car will eventually get up to normal temperatures while city driving, but it will take a while. This issue also occurs in the summer time. On another note the car never overheats.
The only thing bugging me about the issue is that the car's fuel mileage is pretty dismal for highway driving.

1. Could this be the coolant temperature sensor?
2. Where is the sensor located and how hard is it to change? I've done it before on my other car (VW) and it was super easy, i'm hoping for the same thing here.

Thanks in advance.

[bszopi]

1/4 mark on the gauge is about normal for these engines, even in city driving. When you talk about bad gas mileage, what kind of numbers are you currently getting, and how is it being driven (ie, granny or WOT on ramps, etc)?

[VR6Killer]

right now i'll maybe get 450km to a tank of gas. When i first got the car the needle was pegged at the 1/2 mark of the gauge. I'm in canada so maybe my gauge is different?

[89Hatchback]

If there is a problem, I'd look at a thermostat stuck open before I'd check the coolant sensor.

[VR6Killer]

alright i'll check the thermostat first, now that i think about it logically that does make sense.

Quick question, how would i go about checking the thermostat, and seeing if it is stuck open?

[89Hatchback]

The only thing I can think of is to monitor the radiator hose. It should remain cool until operating temperature is reached then then it should get hot fairly quick. A good excuse to go buy that infrared temperature gun. (Or if you're cheap, use your hand.)

Of course just replacing the 'stat would be cheaper. Assuming it's original, it's probably a good idea to change it anyway.

[VR6Killer]

i'll try this tonight, i am using the original thermostat and the car is getting older. So i'll probably just replace it and go from there.

Thanks.

[VR6Killer]

Okay so i checked the radiator hoses and the hose does get warm. I also checked the coolant resevoir and the coolant was warm.
How do i go about replacing the thermostat? does anyone have a guide or a link to another site that has some instructions.

[89Hatchback]

On my 2.8L the thermostat is in that little housing that the upper radiator hose connects to. Pop two bolts, yank the old one out of there, replace with new and new gasket, tighten to specs, refill.

3100 may be similar.

It would probably be worth looking for a manual for your car. Maybe not the OEM manual ($$$) but the one you can find in the parts store.

[manicmechanix]

Okay so i checked the radiator hoses and the hose does get warm. I also checked the coolant resevoir and the coolant was warm.
How do i go about replacing the thermostat? does anyone have a guide or a link to another site that has some instructions.

I think your gas mileage is good now, but if it's running as cold as you say then it would get less mileage. It should run in the center, so it sounds like your thermostat is stuck open. The manual says to just take the air filter bellows off the throttle body, unhook the radiator hose at the thermostat housing and unhook the bleed line at housing and then unbolten the thrmostat housing.

The problem is it's damn near impossible to get to the one bolt and to manuever the housing out from under the throttle body and the exhaust crossover and get it back in. I've done it once before that way and it wasn't easy. The bolt hole towards the firewall direction doesn't need to come all the way out as there's a slot on the housing. Some people take either the exhaust crossover or the throttle body off to get to it. That might be easier.