'08 DTS overheating issue: troubleshooting

Old 08-07-2018, 09:33 AM
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Join Date: Aug 2018
Posts: 1
Default '08 DTS overheating issue: troubleshooting

Hi folks, I'm still reading the forums here looking for an overheat FAQ I saw in someone's 2009 post, but time is getting short so I needed to post:

I'm driving yesterday and noticed that the temp was high. Being near my destination I just put the heater on in the hopes of pulling heat out of the compartment and continued. It neared the red zone but didn't get into it. I got the AC OFF message on the status display when it first happened but it came back on after I torched myself in Houston with the heater on.

I checked around the car: no steam, no noise, no leaks.

After about :45 I got back to the car. Started fine, temp was around the middle mark. After a few minutes I notice it climbing again--when I slowed nearing the few traffic lights I had to pass to get back to the highway. I remembered I had my ultra gauge in the glove box so I plugged it in. My temp was around 225-230 with small fluctuations up to 240 then back down.

At one point the engine warning beeped and the needle stepped to the red, so I pulled over to stop, but then almost as quickly as I did that, the needle dropped back to the mid point. It dropped pretty quickly too.

It crept back up and stayed 'high' but within limits to my house--260 was the max on the gauge when slowing for the neighborhood. 226-240 was the average by my guess.

At my driveway I could hear the gurgle and noticed a little (very little) steam emission from the coolant surge box. I let it cool for a few hours before checking last night. I could see a level of fluid in the box but it was late and dark and I didn't see if it was to the cold line, there were no leaks on the ground.

1. 2008 DTS, about 60,000 miles on it
2. Ambient temperature was about 90F (Houston), high humidity.
3. Level terrain, 65-70 mph
4. no engine error codes
5. didn't get any coolant level message
6. didn't get into engine protection mode
7. no leaks of any kind on the ground
8. no oil lights or messages

Some questions:

Is there a good primer for troubleshooting this? I've never done a cooling troubleshoot before.
What's a good order to start?
How to check the thermostat?

thanks for the patience.

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