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This is my first post here and I hope my last of this nature. I just bought my 2005 STS and I love it. Being a used car I anticipated a few issues from wear and tear and simply setting. I believe I might have an o2 sensor issue right now but my main concern is my coolant leak. Every day I have to fill the coolant and idk where is leaking at and even if I found it I'm not sure how to fix it. I don't have a lot of experience dealing with things like this but if someone could point me in the right direction that would be awesome. I have searched too the ends of the earth and beyond for a manual for this car and have returned with. I thing to show but bloodshot eyes for hours of looking at my phones screen and not being rewarded. But the matter at hand is the leak. So anything on a fix or even a troubleshooting guide would much appreciated

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:welcomesmiley:

You can get free PDF files for the 2005 Cadillac STS owner's manual, navigation guide (manual for the nav system), and warranty guide (service schedule) here:

https://my.cadillac.com/learn/2005/STS

You can get new and used paper copies and the soft case they come in with new cars on Amazon, Helm Inc., eBay, and other sources.

If you are looking for the service manuals, you can get new ones from Helm, Inc. or a used set from eBay.

The first thing I would think of for a 2005 model is, when is the last time you have had your coolant changed? If it's never, you should have your coolant checked for combustion by-products.

If there is no coolant on the garage floor, that means that the loss is happening when you are driving. If there are only a few drops, that means that there is a small leak that stops when the car cools off and the pressure drops. The best way to look for a leak like that is to rent or borrow a pressure tester and look while the cooling system has up to 15 psi pressure. Places to look include

  • Radiator tanks, including the sides where it's hard to look without a small mirror,
  • Radiator itself, usually at the rear where it's exposed,
  • At the hose clamps, including the bypass hose and the surge tank,
  • At the water pump (at the rear [driver's side] of the engine, driven by a belt off a camshaft on the front head), and
  • The heater core.

Other causes of coolant loss include steam pockets in the heads while running, which can cause coolant to be pushed out the overflow through the surge tank. This can be caused by a lot of things, including

  • A loose or leaking radiator cap that doesn't hold pressure,
  • A radiator cap that is for less than 15 psi (use an AC/Delco rated at 15 psi or 16 psi, no higher, no lower),
  • Other problem with the cooling system that prevents it from holding pressure when the engine is warm,
  • Less than 50% anti-freeze in the coolant,
  • Thermostat sticking,
  • Slipping water pump belt or bad water pump, and
  • Head gasket compression leakage.

You can confirm or eliminate the head gasket problem by testing the radiator for combustion by-products. Sometimes if this is happening, you can smell exhaust in the surge tank, see bubbles in the surge tank when you start the car, or smell coolant in the exhaust (particularly when you start a cold engine in the morning, then shut it off after a few seconds).

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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  • 1 month later...

When I bought my 2005 STS five years ago I had a very small leak. I had to top up a little but after many weeks. The shop checked everything very carefully but could not find anything. So I changed the coolant and added two GM coolant tablets, haven't lost a drop since :)

Your leak is significant larger so I there must be a more severe problem.

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First post was April 3, 2016, and nothing since. It's been about five weeks, but I hope she solved her problem. It does seem more like a leak, like a cracked radiator tank, than a head gasket problem. But I would like to hear back and know for sure.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Every few months, we should all inspect our radiator and surge tank for stress cracks and/or leaks. This is especially true on a car older than ~8 years as imo, this is the life of an aluminum and plastic radiator. Once a N* overheats (or any engine with an aluminum block or head), it's "anything goes" as far as reliability.

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