Cooling anomaly experienced - Your thoughts.....

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Like to get some thoughts on an event that happened on my way to work today.

Vehicle: 2003 Chevy Trailblazer EXT w/ 4200 I6
Temperature outside: minus 4 F

I'm about a mile from work (a 10 mile trip from my house) going about 35 mph at the time and the "engine temp" light comes on and the driver information center (DIC) says to idle the engine. I check the temp gauge and see that it is at full scale (usually runs around half scale - did not notice it climbing).

I pull into a parking lot, stop, and pop the hood while the engine is running. Didn't notice any problems visually. No coolant leaks and level is good. Radiator fan is running. I grab the upper radiator hose and give it a slight squeeze. Not super hot. Seems about normal. Shut the hood.

Back in the car, the temp had dropped slightly (barely noticable), DIC is blank, and "engine temp" light is off. Since I am close to work, I thought I'd make a run for it.

Headed on to work watching the gauge. It started going down and reached normal operating temperature about 3 blocks later. It stayed there the rest of the ride.

[Twilight Zone music playing] Looking for possible suspects, any thoughts..........

posted by  theman352001

Well this does seem just a bit on the strange side. I talked it up today and didn't find anyone who has seen this problem on your particular vehicle. Of course we NEVER see ambient temperatures even close to that around here. I have a few ideas but they would all apply to an older, unmaintained vehicle unlike yours.

I have two thoughts that may apply, shots in the dark at best.

1. Is it possible the vehicle was parked nose into the wind/snow/sleet/freezing rain and the radiator became iced over externally? This could possibly cause a temporary overheat until the warm coolant melted the ice.


2. Some thermostats don't like making the transition from sub-zero temps to operating temps and will intermittently stick. Maybe, maybe not.

At any rate, if you get a good fix on it let me know what it took.

posted by  vwhobo

Temps have been slightly higher lately (about 8 degrees F). I have made the same trip 4 more times with no problem. Been watching the gauge more closely and have not noticed anything out of the ordinary.

FYI - the car was not parked into the wind. It was on the side of the street facing South (wind usually out of the North or West) with another car right in front of it. This street is pretty sheltered with large trees. It was not snowing.

I checked with my brother who works at a GM dealership and he also mentioned that they have not heard of anything like this either.

I'm leaning towards the sticking thermostat myself. I guess I will have to wait and see if it happens again. Maybe I will notice something else.

Thanks for the reply.

posted by  theman352001

Well it happened again. This time it came with another problem.

Again the outside temp was around 3 degrees, engine temp went above normal operating (N.O.)but I did not let it get too high before pulling the car over and letting it idle. Temp went down. Started driving again and it went back above N.O. but right before I was going to pull over, the temp starting dropping again and stayed at N.O. The other problem was that even after a 30 minute drive, we had no heat in the car.

Of course, we took it in.

Turned out to be the terminal connections on what they called a Hot Water Control Valve. They stated that this was a new technology on the I6 engine and that it was different than the control valve that closes off the heater core. I tried to do a little looking into it and didn't find any mention of this HWCV. I'll admit I didn't dig too far. As long as it's working......

Well, wanted to let you know what it was. Hopefully it will help somebody else someday.

posted by  theman352001

Good info to store in the back of my empty head. Thanks.

posted by  vwhobo

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