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Discussion Starter #1
97 sts, 127k miles.

It's starting to get colder here in Michigan and I'm noticing that my coolant isn't getting that warm.

When it's 70+ degrees outside the coolant runs at about 185. If I idle it obviously goes higher.

Yesterday driving home it was 55 outside. My coolant never broke past 160.
Today driving it was 40 outside. My coolant never broke past 140. After driving for 30 minutes, I idle'd for a few minutes in a parking lot, coolant never broke past 170.

Something to be concerned about?
 

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Discussion Starter #3
I haven't check the coolant yet. I'm probably going to do a change here in the near future.
 

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1999 STS - diamond white
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5,229 Posts
If your t-stat is stuck open you should be able to feel water flowing thru the hoses when you pinch them. It shouldn't be flowing when the engine is cold.
 

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Discussion Starter #6
Alright... so I had a coolant flush done, and I was told the tstat was missing, and that's why my engine was running cool. Sounded fishy but whatever. They put one on and it seemed to be running good. Instead of being at 140-160, it was running at 201. That is until this weekend. It's back to running around 160.
Any ideas??
 

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Cadillac Technician
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It should run between about 190 and 210 usually, in cooler weather it might even hover closer to 190.
Most T-stats open at 180 or 185, if it's below that they are stuck open or missing.
A 5 minute drive down the highway should tell you if it's open or not. If it keeps dropping with good airflow on the front of the car it's bad.
In stoplight traffic it might even run at normal temps.

Glad you got it fixed.
 

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1996 STS
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Can someone tell me what would the problem be with running at a cooler temperature like he is?
 

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'98 STS (RIP @ 206,xxx miles)
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STS 310 said:
Can someone tell me what would the problem be with running at a cooler temperature like he is?
There are several reasons why the engine cooling system is designed / intended to operate at or above 200 degrees F.

But for me, the number one problem with coolant temperatures lower than 200F is reduced opportunity to vaporize fuel and condensation (from the most recent cold start) out of the crankcase. Short-trip engines in cold climates suffer the most.

Obeying the Oil Life Monitor will protect you.

Emission control is also involved in the temperature equation.
 

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Colder engine temps require a richer air/fuel mixture. Basically it would get crappy mileage and depending on the weather outside it likely wouldn't run very good (in cooler weather).
Not to mention the heater won't work very well with no heat.
 
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