I live in Chicago IL, USA and we've had quite a cold blast the last week. Temperatures are well below zero and wind chills of -35F Degrees. This morning I drove my (Gasoline) 3.5L Montero XLS to work (44 miles 1 hour), and it sounded like the engine fan was tapping something. The sound was like teeth chattering. When I arrived at work I opened the hood with the engine running, and put my hand on the engine wires and manifold and it was still cold. The engine was making this noise. I've owned it 7 years and always keep oil in it, as its leaked in previous years. All oil leaks have been corrected for now. The previous owner put stop leak sticks in the radiator before I purchased it with 80K miles on it - and the temp gauge is never correct. Is it time for a thermostat? No check engine lights or any lights on the dash. I don't smell anything burning, no leaking of fluids. I will verify coolant levels when I get it home. Its never been a fan of cold weather, and its always garaged. Its now 16 years old with 208K miles on the odometer. Thoughts?

 

By any chance, did you feel the upper radiator hose? Was it hot or cold? If the hose stays cold after running for this long, you may have thermostat stuck open.

With the temps as low as you have them, it might be helpful to put in a piece of cardboard in front of the radiator to reduce amount of air flowing through trying to cool the system.

 

I didn't check the hose, ugh! I will check it tonight once I arrive home. Thank you for your help! I assumed the thermostat could be the issue.

 

Update: Checked both radiator hoses neither are cold. The terrible chattering could have been lifters. I added some Lucas to a full tank of fuel and they quieted down. Now the only noise I hear is the heat shield on the cat that's directly below the driver seat. Next week it goes in for rear suspension and I will have them clamp it or tear it off!

 

I'd plan on replacing a thermostat in the near future. It sounds to me like it may have been stuck open when you had that super cold event. No guarantee that it will not do it again. If you suspect lifter noise, first thing to check is the engine oil level. Make sure you are not low. Adding additives to the fuel tank will not do anything for the lifters. It might helps somewhat cleaning fuel injectors but it does not get to the lifters - they are on the oil side of the system.