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In my 2004 Tahoe both my coolant in my oil are disappearing. I have no trace of liquid underneath the vehicle when parked. However, every month or so we will get an engine coolant hot message and I will almost have to fill the coolant with an entire bottle. Same with the oil. But now it's every few weeks it will say the oil pressure is low and I can put in a lot of oil like 2 quarts.

About 150,000 miles on engine. Also have codes p0171 and p0174.

  • The oil doesn't surprise me as the LM7 engine will use some (known issue). The coolant makes me wonder if you have a bad head gasket. – Pᴀᴜʟsᴛᴇʀ2 May 16 '17 at 17:00
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There could be a number of things going on.

Without external evidence, high oil usage can be from worn piston rings allowing oil to be sucked into the cylinders and burned. This is called "blow-by".

In your case, with excessive oil and coolant use, there is a good chance you have a bad head gasket, or gaskets. This can allow coolant and/or oil to pass into the cylinders, or to transverse into cross system contamination (oil in coolant and visa versa).

A compression test can help diagnose the condition of the cylinders/rings. Testing the coolant for oil and other contaminates will give more information about what is going on.

You have not given us much detail about the engine (mileage, condition, etc.). Regardless, the oil and coolant consumption is quite excessive and needs to be addressed as soon as possible to avoid permanent damage, if it hasn't occurred already.

  • About 150,000 miles on engine. Also have codes p0171 and p0174. – CRAIG May 16 '17 at 16:05
  • Those are good things to know when asking the question. Both are lean codes (bank 1 & 2). – CharlieRB May 16 '17 at 16:11
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As far as I know, this chevy needs a very big amount of oil, because it burns oil to labricate the piston. The point is your Chevy needs a full can per week, check the temperature of your engine. If your engine is too hot, it needs a very big amount of oil and cooling liquid. Check your radiator, maybe it's broken! A friend of mine had the same codes as you, the point is the cover from his air filter was not closed, so his air sensor output the same codes as your car. So check the air filter cover (check it for dust) and search for some loose cables.

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Check the gasket between cylinder head and cylinder block becoz bad gasket can cause leakge of oil as well as coolent also and both can come in cylinder bore ..... is there your vehicle produced high smoke?if vehicle produces high smoke then there will will be definately something wrong in gasket

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