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Oil mixed with coolant in reservoir

Tiny
PACKERS27
  • MEMBER
  • 2000 GMC SIERRA
  • 5.3L
  • V8
  • 2WD
  • AUTOMATIC
  • 238,000 MILES
No water mixed with oil though. No milky oil caps or dipstick. No drivability issues whatsoever. The truck runs like a top. I do have low oil pressure. I crank the truck up and the pressure sits at 8. It doesn't drop or rise. I'd like to know why oil is in my coolant? I seen a video of someone replacing the oil cooler? What would that have to do with it? Thank y'all.
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Wednesday, February 5th, 2020 AT 10:19 AM

6 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Just so I am clear, you only have oil in the coolant and no coolant in the oil?

As for the pressure, your spec is attached but if you have 8 PSI at idle then that is actually oayk. I am a little surprised as it does seem low but according to the spec it is okay.

https://www.2carpros.com/articles/coolantantifreeze-in-the-engine-oil
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Wednesday, February 5th, 2020 AT 4:17 PM
Tiny
PACKERS27
  • MEMBER
  • 187 POSTS
You are correct. There is no coolant inside the oil cap or on the stick. When I changed the oil, there was none in there either. 6 psi may be normal at idle but like I said, the reading does not change, no matter what the rpm's are. It's fixed on 8. I highly doubt it's normal.
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Wednesday, February 5th, 2020 AT 5:05 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Sorry I missed that. I thought it was just at idle. If you have low oil pressure, it is one of three things. First, faulty sensor, wiring or gauge. We need to hook a mechanical gauge to the engine and confirm the reading is correct.

If it is then it is either a faulty pump or excessive clearance in the bearings. The pump creates pressure by the resistance it has to overcome when forcing the oil in the oil galleys and between the bearings.

As for the oil in the cooling system, how much oil was in the bottle? This is normally a sign the head gasket is starting to go. When it begins to fail, oil can get pushed out of the combustion chamber and into the coolant passages. You can confirm it by testing for hydrocarbons in the cooling system.

https://www.2carpros.com/articles/head-gasket-blown-test
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Wednesday, February 5th, 2020 AT 6:56 PM
Tiny
PACKERS27
  • MEMBER
  • 187 POSTS
There's a lot of oil in the coolant. You also smell it every time you get out of the truck. It smells burnt. You don't see any possibility of a leaking oil cooler in the radiator?
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Wednesday, February 5th, 2020 AT 7:20 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good evening,

Just to add one thought. Are you sure it is oil and not transmission fluid? You have a cooler in the radiator for the transmission.

Check your transmission fluid stick for any coolant.

Roy
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Thursday, February 6th, 2020 AT 6:12 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
I just saw that this engine has an oil cooler.

The engine oil cooler is located in the left side of the radiator. Engine oil flows through the cooler and reduces the temperature of the engine oil. The cooled engine oil then returns to the engine.

Good chance you need a radiator.

Roy
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Thursday, February 6th, 2020 AT 6:18 PM

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