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2002 GMC Envoy 4.2L I6
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Discussion Starter · #1 ·
Hello, I'm the new guy. My 2002 Envoy has an inline 6 cylinder and when it gets to temp the oil pressure goes to zero. I mean zero. I hooked a manual gauge to the port on the front of the engine to get this reading. It reads pressure when cold, I can't remember the exact number what I would say normal, but as the engine warms the pressure drops. I've changed the oil, the oil filter, and oil pressure sensor before I manually checked the pressure.

I am on the verge of junking this vehicle but thought I would give it one more shot here to see if there is a reasonable resolution to the problem. I can't believe a vehicle with 160,000 miles would do this. Look forward to any and all replies. T
 

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2004 chevy trailblazer_lt
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Welcome to the Forum!

OK, now this is going to sound strange/weird/whatever, but the actual oil pressure is not critical in the Vortec 4.2 L engine. Oil flow/volume is what is most important. The engine was designed with the flow of oil in mind and not oil pressure. But, some oil pressure will be generated as the oil flows through the engine

Also, the oil gauge on the instrument panel registers a dummy oil pressure reading that is specified by the PCM and is essentially meaningless, so I am glad to hear that you used a mechanical gauge to actually measure the oil pressure. I am assuming that an oil pressure of some value was registered when the engine was hot.

Now, remember that cold oil is more viscous than hot oil and hence a "cold" engine with ambient temperature oil will have a higher oil pressure than a "hot" engine with hot oil because the viscosity of the oil has dropped.

Now, for the all important question. Is your engine making noise as if there is no oil present?

One last point. If the oil pump does not push enough oil throughout the engine then there is a problem that needs to be looked into.

Please report back with an answer to my engine noise question.
 

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2002 chevy trailblazer_lt
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Just to add some information.... The factory oil pressure switch activates at approximately 3 or 4 psi. So clearly they believed that was enough. The manual states the desired pressure at 1200 rpm is just 12 psi. They make no mention of idle speed pressure. My 2002 with 287 thousand miles holds about 10 psi at idle with engine OIL temp about 195 °F. (The 2002 engines had an oil temp sensor) The fake dashboard gauge of course reads 40 to 50.

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2004 chevy trailblazer_lt
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Thanks for the additional information!
 

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2002 GMC Envoy 4.2L I6
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Discussion Starter · #5 ·
Welcome to the Forum!

OK, now this is going to sound strange/weird/whatever, but the actual oil pressure is not critical in the Vortec 4.2 L engine. Oil flow/volume is what is most important. The engine was designed with the flow of oil in mind and not oil pressure. But, some oil pressure will be generated as the oil flows through the engine

Also, the oil gauge on the instrument panel registers a dummy oil pressure reading that is specified by the PCM and is essentially meaningless, so I am glad to hear that you used a mechanical gauge to actually measure the oil pressure. I am assuming that an oil pressure of some value was registered when the engine was hot.

Now, remember that cold oil is more viscous than hot oil and hence a "cold" engine with ambient temperature oil will have a higher oil pressure than a "hot" engine with hot oil because the viscosity of the oil has dropped.

Now, for the all important question. Is your engine making noise as if there is no oil present?

One last point. If the oil pump does not push enough oil throughout the engine then there is a problem that needs to be looked into.

Please report back with an answer to my engine noise question.
Thanks for the quick response. I really do appreciate your insight and knowledge. To answer your first question, once the engine is hot the mechanical gauge goes to zero psi. Maybe it will bounce around at 2 or 4 psi if i rev the engine a little bit. But yeah man, zero. For your second question, does the engine makes noise like no oil is present, it does seem to make some noise which sounds like it may be valve noise. It sounds to me like it is in the upper part of the engine. I'm no professional mechanic obviously but as far as serious knocking I would say no. However, I've always been too afraid to let the motor run for an extended period of time once the pressure drops.

I read other posts regarding similar problems to mine but none have quite been exactly the same as mine. I've heard the oil pickup tube maybe clogged or the pick up tube o-ring maybe blown out. I've also heard that there is some sort of screen near the cam shaft sensor (?) that could be clogged. I understand what you are saying regarding viscosity when cold versus hot and these solutions I've read about don't appear to work. At least for my problem. I love my Envoy and wish I could fix this problem.
 

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2002 GMC Envoy 4.2L I6
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Discussion Starter · #6 ·
Just to add some information.... The factory oil pressure switch activates at approximately 3 or 4 psi. So clearly they believed that was enough. The manual states the desired pressure at 1200 rpm is just 12 psi. They make no mention of idle speed pressure. My 2002 with 287 thousand miles holds about 10 psi at idle with engine OIL temp about 195 °F. (The 2002 engines had an oil temp sensor) The fake dashboard gauge of course reads 40 to 50.

View attachment 57836
Yes, thank you for this information. This whole problem started with the stop engine warning. I installed a test gauge at the port on the front of the engine which is just above and to the side of where the oil filter is.
 

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Yes, thank you for this information. This whole problem started with the stop engine warning. I installed a test gauge at the port on the front of the engine which is just above and to the side of where the oil filter is.
I have a permanently installed mechanical oil pressure gauge connected at that same port.

Since the pressures we are dealing with at hot idle are so low it is helpful to use a gauge that is accurate at these levels at or below 10 psi. I verified my gauge against another gauge and checked that gauge with a water column which leaves no possibility of error unless one cannot read a ruler!
 

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2002 gmc envoy_slt
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What brand oil filter are you using? I battled this issue for a couple of years when using a local oil change shop and found out their OEM filters were rebranded FRAM filters and these engines do NOT like FRAM oil filters (no car should). I started using only Wix filters and the oil pressure issues went away after the first filter change.

My symptoms where similar. Once engine reached temp, oil pressure would drop very low at idle and return under increased RPMs. This would almost always occur during warmer months and seem to be less of an issue in cooler months.

It's certainly a cheap option to try if nothing else.
 

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2003 gmc envoy_sle
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I was thinking oil pickup blockage too. Alternately a poor oil filter doing the same thing. Had a car once that the previous owner didn't maintain well. Pulled the oil pan, sandy, gritty dirt was in the pan getting sucked up into the pickup. Which was half clogged. When I shut off the engine, the dirt settled back down, and I would get oil pressure when "cold". Figuring the dirt was coming from somewhere, I pulled the valve cover, and sure enough. Gunk! I cleaned as much as I could, rinsed it down with mineral spirits. Put it back together, new oil and filter. 100 miles. Changed oil and filter again. 100 more, oil change. 500 miles, oil change. Regular 3000 mile changes after that, ran for years. Eventually rust took it out, not the engine.
 

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2002 GMC Envoy 4.2L I6
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Discussion Starter · #10 ·
What brand oil filter are you using? I battled this issue for a couple of years when using a local oil change shop and found out their OEM filters were rebranded FRAM filters and these engines do NOT like FRAM oil filters (no car should). I started using only Wix filters and the oil pressure issues went away after the first filter change.

My symptoms where similar. Once engine reached temp, oil pressure would drop very low at idle and return under increased RPMs. This would almost always occur during warmer months and seem to be less of an issue in cooler months.

It's certainly a cheap option to try if nothing else.
I've always used AC Delco fillers. Maybe Wix once or twice.
 

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2002 GMC Envoy 4.2L I6
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Discussion Starter · #12 ·
I was thinking oil pickup blockage too. Alternately a poor oil filter doing the same thing. Had a car once that the previous owner didn't maintain well. Pulled the oil pan, sandy, gritty dirt was in the pan getting sucked up into the pickup. Which was half clogged. When I shut off the engine, the dirt settled back down, and I would get oil pressure when "cold". Figuring the dirt was coming from somewhere, I pulled the valve cover, and sure enough. Gunk! I cleaned as much as I could, rinsed it down with mineral spirits. Put it back together, new oil and filter. 100 miles. Changed oil and filter again. 100 more, oil change. 500 miles, oil change. Regular 3000 mile changes after that, ran for years. Eventually rust took it out, not the engine.
Interesting. I've thought of pulling the oil pan but really do not want to do it. I know it's a kind of a pain. Great food for thought though. Thanks for your insight.
 

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2004 chevy trailblazer_lt
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If you have a 4X4, removing the oil pan has been described as being more difficult than disarming a nuclear bomb.
 

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2002 GMC Envoy 4.2L I6
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Discussion Starter · #14 ·
If you have a 4X4, removing the oil pan has been described as being more difficult than disarming a nuclear bomb.
Yes it is a four wheel drive and I've always maintained it well. Always changing the oil sooner than needed.

I once heard a comment by a certified GM mechanic who said he had never changed an oil pump in a 4.2 inline 6 before. Wish I could get my hands on one of those J42907 adapters to try though. Sounds like you can isolate the oil pump. That would eliminate that at least.
 

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True.
 

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If you have a 4X4, removing the oil pan has been described as being more difficult than disarming a nuclear bomb.
Didn't say it would be easy. The old Ford Tempo's oil pan had nothing in the way of the pan. Lucky for me . . .
 
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