Oil pressure dropped after switching to 20-50?? - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 05-25-2006, 05:33 PM   #1
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Default Oil pressure dropped after switching to 20-50??

When I did the oil change following LIM gasket replacement, I switched to 20W-50 for the summer. Since then, my oil pressure usually hangs right around 30-40 psi, hot or cold. I was closer to 50-75 psi before the switch, when I was running 5W-30. What the heck gives? Why would thicker oil REDUCE my oil pressure?
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Old 05-26-2006, 09:04 AM   #2
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OK, I don't have your answer. Maybe you can find something at bobtheoilguy.com.

My question is, why do you do such an extreme change in oil just for the summer? This isn't an old V8 that'* burning oil.

I've use the same oil, per spec, all year long every year, winter or summer, Michigan or Florida and have never had any issues. I also change it very regularly.
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Old 05-26-2006, 09:20 AM   #3
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Yeah I would just leave 5w-30w I run my old 92 on it never seems to have any issue with the pressue running at idle 35-40 up to speed 75-80. In the winter will run higher
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Old 05-26-2006, 10:00 AM   #4
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Is this the first oil change after the LIM'*?

On possibility :
When pulling an oil pan, it'* noticed that there is about a 1/4" to 1/2" of oil that is BELOW the level of the oil plug. Water is heavier than oil and sinks to the bottom of the pan. Could there have been water or some cleaners etc in the bottom of the pan?

Another possibility:
Could enough gasket material etc be in the pan and causing the pickup tube to be clogged and not allowing much oil up the tube?

Ugly possibility:
Could your bearings have gotten affected by the LIM going bad (if it did) and be wearing, first sign is low oil pressure, then ticking, then knocking.
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Old 05-26-2006, 01:47 PM   #5
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i run thicker oil in the summer because of my driving habits. stoplight races are not uncommon for me, and i personally like the idea of having some 50 weight oil on my bearings versus 30 weight. i've always seen my oil pressure go down a lot in the summer when the motor gets hot and i'm running 30 weight. in the past, when i've switched to 50 weight, my oil pressure is raised by 10-20 psi.

i was very careful when i removed the intake and cleaned the mating surfaces; i don't believe the pickup is clogged. a definite possibility, but i don't believe this is the true cause.

it'* not bearing damage. if it were, i'd be knocking by now.

this isn't a HUGE problem, as my oil pressure is still very acceptable. it was a noticed change and i was curious as to the cause before something worse possibly happens. i'll switch to 5w-30 at my next oil change and see what my oil pressure does then.

thanks guys!
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Old 05-26-2006, 02:57 PM   #6
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CS... consider picking up a couple gallons of cheap oil to put in, run for a few min and drain out. If my theory about the water/whatever at the bottom of the pan is true, that may get most of it out.
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Old 05-26-2006, 06:18 PM   #7
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When I did my LIM gasket, I drained the oil out while the the lower intake was off. After it was done draining, I put the drain plug back in, dumped one quart into the crankcase, and drained it out. Repeated that once more, and then reassembled. Do you think this wasn't enough to flush all the coolant and other crap out?

I'm not trying to argue with you, I'm debating
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Old 05-26-2006, 06:39 PM   #8
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Change back to the oil you are supposed to use 20w-50 is too thick. The bearing clearances are too small to use syrup.

Jeff
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