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GM Tech (Cam)
GM Tech (Cam), GMC Mechanic
Category: GM
Satisfied Customers: 29427
Experience:  GM Grand Master Technician 2007. 14 years experience.
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2004 gmc sierra 5.3, Z71. Oil pressure gauge was pegging out

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2004 gmc sierra 5.3, Z71. Oil pressure gauge was pegging out and thermostat sticking closed. I had A mechanic say the oil sending unit needed replaced and new thermostat. I had him do the recomended repairs and a day and a half later the pressure gauge pegs out and my engine has a loud knock and oil on the dipstick does not look normal. Its not milky but more like a brounish red color. I dont know if this was just bad luck or a botched repair job. Any ideas on what might be wrong, how to fix it or opinions on what caused it. PLEASE HELP!
Welcome. Did the engine overheat then?
Customer: replied 6 years ago.

It got up to about 230 degrees.

 

Ok, the first thing to do is see if the oil pressure is actually that high with a master pressure gauge. If it is, then you know that you have a pump/pressure relief valve issues.

As for the look of the oil, that could indicate the starting of a head gasket issue.

Customer: replied 6 years ago.

I did not do well when describing the oil at first. The oil feels very thin or lacking. I do not see signs of any white smoke when starting. Could you explain where pressure relief valve is located?

THe pressure relief valve is part of the oil pump assembly which is on the front of the engine behind the front cover. IF the oil is thin, it could be leaking coolant directly into the crank case, and just because it does not smoke white does not mean there is a head gasket issue, it only means the coolant is not flowing into the cylinders.
Customer: replied 6 years ago.

If the coolant is leakig directly into the crank case what all repairs am I looking at?

That would be a head gasket(s), or less likely the cylinder heads themselves.
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