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Discussion Starter #1
GM is really wearing me down........................



Well GM wont put it into writing but they tell me it might be the synthetic oil making my pressure low.

The dealer said the same thing.

I asked if the book was wrong? No comment.
I asked what kind of oil can I run. The owners manual states what I can use they said.
They then stated syn oil was for cold weather. I stated the manual says I can run it all year round.

They drained my syn. oil and wanted to run a pressure test (for the record) with regualr oil. I wont let them.

I want to put the synthetic oil back in and run the test. I told them I want the specs (factory specs of minimin low and minimum high pressure) in writing with the approved oils in writing and I will show up at the dealer with a notary republic to witness the oil pressure test.

They flat out refuse to put anything in writing and state "off the record" not to use synthetic.

My reasons for not using syn are this:
Regualr oil degrades to a low oil pressure after about 600 miles.
It starts burning oil at 2800 miles with reg and about 5k with syn.
It burns a lot of oil with reg, from 2800 on.
Syn burns less and lets me go longer between changes.
Syn lets me go into cold weather without stopping at a gas station to have my oild changed.
Syn. lets me have quicker cold starts.
Syn puts less wear and tear on the motor.

And besides I want to run it! The manual says I can use it all year round.

So what do I do now? They have no intention of allowing me to use syn to take the pressure test.

I bought 14 bottles of the mobil one diesel oil my truck will go down to about 7lbs with this oil. Their test will be waaaayyyy below factory specs.

I refuse to let them win this one. I dont want to spend endless amounts of cash buying another defective truck every 18 months.

Any ideas????
 

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are you using mobil 1? I was in a meeting with the exxon/mobil reps when I was working for a dealer here in town. Mobil 1 is the MOST used FACTORY filled syn oil in the world!! ALso has a KILLER warranty. In the entire history of Mobil 1 they have only had to buy 1 car back and that was to shut the person up. Ask them about that? SEveral Cadillac 2004 models and newer come factory filled with mobil 1, corvette, mercedes benz, lamborgini, fararri (spelling ?). Ask them about that!!!

Contact MObil 1 customer service and tell them what is going on and that GM is blaming the use of Mobil 1. See if that gets exxon/mobil involved and breathing down GM's neck. Contact everyone possible.
 

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PC, I don't know much of your story, but if your pressure is changing with miles, you must have a contamination issue. Have you sample tested it?

Synthetic DOES appear as a lower pressure very often, I have seen this myself. But low pressure does not equal poor lubrication flow, just the opposite, it likely indicates highest flow. (this assumes you also see high pressure, 70+, when cold) The oils film strength is the biggest factor, and that doesn't show up on a gauge. High pressure is a much worse problem to have (cold).

Don't get hung up on gauge calibration. If you want to see it higher, I suggest you get a temp gauge on it and go from there. These oil systems run hot, turn oil very light. The likely answer for you IMO is going to be an oil cooler.
 

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Discussion Starter #6
PC, I don't know much of your story, but if your pressure is changing with miles, you must have a contamination issue. Have you sample tested it?

Synthetic DOES appear as a lower pressure very often, I have seen this myself. But low pressure does not equal poor lubrication flow, just the opposite, it likely indicates highest flow. (this assumes you also see high pressure, 70+, when cold) The oils film strength is the biggest factor, and that doesn't show up on a gauge. High pressure is a much worse problem to have (cold).

Don't get hung up on gauge calibration. If you want to see it higher, I suggest you get a temp gauge on it and go from there. These oil systems run hot, turn oil very light. The likely answer for you IMO is going to be an oil cooler.


The only reason Im alarmed is because the truck will "oil starvation knock" when climbing into the mountains and then pulling over at a rest area etc. When you stop the vehicle to let her idle at the top it will start knocking real bad like it has run out of oil and the guage will be sitting under factory spec low pressure.

That cant be good and Im not going to get stuck with it.
 

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The only reason Im alarmed is because the truck will "oil starvation knock" when climbing into the mountains and then pulling over at a rest area etc. When you stop the vehicle to let her idle at the top it will start knocking real bad like it has run out of oil and the guage will be sitting under factory spec low pressure.

That cant be good and Im not going to get stuck with it.
Synthetic oil isn't your problem if your details are correct. You have other problems unrelated to synthetic oil. Perhaps your oil pump is bad or is losing prime somehow. Go to another dealer and get another opinion. Don't mention synthetic oil and see what direction they steer you in.
 

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I've been running Rotella Synthetic 5w-40 since 10,000 miles on my truck. I've got about 60k on it now & no issues with oil pressure. Oil is not the problem.
 

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I've been running Rotella Synthetic 5w-40 since 10,000 miles on my truck. I've got about 60k on it now & no issues with oil pressure. Oil is not the problem.
have you left Texas? Any heavy climbs?
 

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I'm still in Texas - why do you ask?
 

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What I meant was, do you get out to do steep heavy climbs? This where you can see 10-15 psi idle oil pressure.

Of course you have to be a little OCD like PC to notice it.


I do some nice steep hills towing a fifth wheel in Vermont and New Hampshire using the Rotella sync. and don't get the low psi oil pressure. Have been doing these hills 2 times a year in the summer, and this is after already being on the road for 8 straight hours stopping for fuel and food.
 

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That's total BS from GM, and don't believe any of it for a second. While you may indeed slightly lower pressure with a 5-40W synthetic, I contribute that to the 5-40W. If you live in a warm climate, I suppose I would stick with a 15-40W synthetic, but you certainly aren't harming an engine by running 5-40W in hot weather.

It seems to me that you've got a lemon engine, Problemchild. I know you've said before that your engine starts burning oil like crazy at 5,000 miles on the oil, which is a sign of mechanical problems to me. My dad and I are able to run 10,000 miles + per interval with very minimal consumption now that both engines are broken in.

FWIW...
 

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Rtquig

Not really what I was thinking. Having lived back there, the mountains out here make those climbs look silly.

The point I'm trying to make is that he is suffering heatsoak, it will affect oil temps and create some hot fuel and air charge. The percieved "oil tap" noise could be detonation. I have seen underhood temps rise over 100 degrees in one minute, upon stopping with heatsoak.

Have measured over 220 F intake air temps.
 

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Not to deffend the dealer or GM, but if the oil pressure is that low, why fight the test if they want to try it with the regular oil?

for specs...

Oil Pressure
294 KPA, 42 PSI @ 1800 RPM

Oil Pressure @ Engine Operating Temperature
98 KPA, 14 PSI @ Idle
 

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I run rotella synth and never get below 35 psi when hot.. on cold startup i usually get @75psi. Killer is right..the excellent film strength of synthetics and higher flow mean better cooling and better bearing life. Your low pressure could indicate a lot of problems but your choice of oil is not one of them!
 
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