2003 Cadillac CTS overheating

Tiny
KOSTATRIAN
  • MEMBER
  • 2003 CADILLAC CTS
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 86,000 MILES
My Caddy CTS with 3.2 engine just recently over heated. I am the original owner and have had very good luck with the car. When it overheated the antifreeze turned into this brown sludge like liquid. I feared that maybe the head gasket blew. I drained the engine oil and founf no antifreeze in the oil. There are no leaks that I can see from above or below. Is this an issue with the thermostat failing or is there a more serious problem?
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Tuesday, April 21st, 2009 AT 10:55 AM

4 Replies

Tiny
FACTORYJACK
  • EXPERT
Was it low on coolant, or overfull. The sludge like fluid is a concern, you need to check the trans fluid, the cooler in the radiator could be leaking, and if the trans fluid is worn, it could be brown. Also, the engine oil cooler is in the valley of the 3.2l, it could be leaking as well. You should not have anything oily in the surge tank, unless it was added by accident. The fact that there is no coolant in the oil, can be two things, the oil pressure is greater in both the trans cooler, and oil cooler, or the amount of coolant that leaks the other direction is small enough that it is boiled out and released as steam. Is there any sign of moisture on the oil filler cap(milky substance)?
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Tuesday, April 21st, 2009 AT 10:53 PM
Tiny
TMJENKINS
  • MEMBER
It's the intake manifold gasket
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Sunday, December 17th, 2017 AT 3:17 AM
Tiny
TMJENKINS
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If it was a blown head gasket there would be coolant in the oil. I had oil in the radiator but no coolant in the oil.
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Sunday, December 17th, 2017 AT 3:20 AM
Tiny
CARADIODOC
  • EXPERT
"If it was a blown head gasket there would be coolant in the oil."

That is not correct. When a head gasket leaks, coolant in the engine oil is by far the least likely outcome. More than 99 percent of the time coolant will be dawn into a cylinder, burned, and will show up as white smoke from the tail pipe. You'll be adding coolant on a regular basis, but it won't change color.

No transmission fluid, and to my knowledge, no engine oil flows through the intake manifold. If oil does, it is only related to drain back passages where that oil is not under pressure. Oil under no pressure won't sneak into coolant under 15 pounds of pressure.

My vote is for Factoryjack's comment about the transmission cooler in the radiator, especially since this is a GM vehicle. GM uses the red Dex-Cool antifreeze and they advertised it as "lifetime" coolant to make their cost of maintenance appear to be lower than that of their competitors, then they put a sticker under the hood saying to replace it every three years. Even the Dex-Cool company doesn't recommend waiting three years. Water pump lubricant, corrosion inhibitors, and other additives wear out in about two years, then the coolant becomes acidic and attacks metal parts. That's why we need to replace it. GM owners are all too familiar with leaking heater cores and radiators due to this Dex-Cool. A lot of mechanics won't put it back in their customers cars. There are alternatives that meet the same requirements for these engines. You can't mix in other brands of antifreeze either as it turns to what we call, "Dex-Mud". That is what happens too when transmission fluid mixes in. You will likely find the transmission fluid has turned pink or light brown.

To test to see if the coolant has turned acidic, use a digital voltmeter set to the 20-volt scale. Put the negative probe on the battery's negative post or a paint-free point on the engine. If you have a radiator cap, remove it, then stick the positive probe into the coolant, but not far enough to touch anything metal. The engineers forgot to put radiator caps on most of their radiators, so you'll have to go to the reservoir. Any reading over 2.0 volts is excessive. It's not uncommon to find 4.0 to 6.0 volts. By the time it gets that high, it won't be long before the heater core is leaking. Often that leak is blocked by residual casting sand from the engine settling in the heater core. When the cooling system is flushed, that sand is washed out, then the leak becomes apparent and the mechanic gets the undeserved blame for causing the leak.
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Sunday, December 17th, 2017 AT 6:34 PM

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