Amsoil pressure drop after 3,500 miles

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Sep 19, 2021
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Hey folks!

Bought a used Chevrolet Tahoe (2014). Changed all the fluids when I got it, all with Amsoil. Amsoil Signature 10W-30 in the engine, Amsoil filter.

After about 3,500 miles (including a 1,200 mile towing trip) my oil pressure has dropped pretty significantly. From around 28psi at idle and 42psi under acceleration, to 19psi at idle and 35 under acceleration.

While that's still within spec for the engine; I'm curious the cause.

As an experiment I used a vacuum pump to remove a quart of oil and then added a fresh quart of Amsoil. The oil pressure returned to exactly where it was before. However within just a couple hundred miles, it was back to the 19 at idle / 35 under acceleration (28-30ish cruising) from before.

Is this a fuel dilution issue? I'm running E85 almost exclusively, I'm not sure if that has an impact. It's mostly two-lane 55mph road driving (I live in a rural area), and I rarely drive for less than 30 minutes. Just yesterday I drove 90 minutes each way. Wouldn't that get the oil warm enough to cause any fuel in the oil to evaporate? It is the max trailering model so it does have an oil cooler.

Other thoughts? Is this acceptable/normal behavior? Should I change now?

Thanks!

-John
 

OVERKILL

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What's the mileage on the vehicle? Do you know the maintenance history? If you are using an EaO filter, they are very efficient and, if the engine is shedding a lot of filth from previous neglect, it's possible the filter has loaded up and is bypassing, though that doesn't explain the pressure returning when you added the fresh quart.

If you are concerned about fuel, send it off to a lab to be analyzed.
 

Circuit Rider

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What's the mileage on the vehicle? Do you know the maintenance history? If you are using an EaO filter, they are very efficient and, if the engine is shedding a lot of filth from previous neglect, it's possible the filter has loaded up and is bypassing, though that doesn't explain the pressure returning when you added the fresh quart.

If you are concerned about fuel, send it off to a lab to be analyzed.
120k.

I don't have maintenance records. Is there a way to tell if a filter is bypassing once removed? I probably will send some off to get analyzed, just to answer that question. I don't THINK fuel dilution is an issue because especially with E85, it ought to be evaporating out of the oil, right? But I'm not sure what else it might be.
 

OVERKILL

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120k.

I don't have maintenance records. Is there a way to tell if a filter is bypassing once removed? I probably will send some off to get analyzed, just to answer that question. I don't THINK fuel dilution is an issue because especially with E85, it ought to be evaporating out of the oil, right? But I'm not sure what else it might be.
It will run a bit richer on E85, so it's technically possible. The oil needs to get pretty hot to flash off fuel.

On the filter, try swapping the filter. If the pressure comes back, cut open the old one and see if it is full of particulate.
 
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120k.

I don't have maintenance records. Is there a way to tell if a filter is bypassing once removed? I probably will send some off to get analyzed, just to answer that question. I don't THINK fuel dilution is an issue because especially with E85, it ought to be evaporating out of the oil, right? But I'm not sure what else it might be.
What would the oil filter have to with the pressure drop?
 

OVERKILL

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What would the oil filter have to with the pressure drop?

If the pressure is measured after the filter (which it usually is), if the pressure drop across the media is significant, you will see it on the gauge. Remember, it is differential pressure that opens the filter media bypass, and that pressure varies depending on application. If it's 12psi, the feed side of the filter could be at 42psi and the engine side at 30psi before the bypass opens.
 
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Hey folks!

Bought a used Chevrolet Tahoe (2014). Changed all the fluids when I got it, all with Amsoil. Amsoil Signature 10W-30 in the engine, Amsoil filter.

After about 3,500 miles (including a 1,200 mile towing trip) my oil pressure has dropped pretty significantly. From around 28psi at idle and 42psi under acceleration, to 19psi at idle and 35 under acceleration.

While that's still within spec for the engine; I'm curious the cause.

As an experiment I used a vacuum pump to remove a quart of oil and then added a fresh quart of Amsoil. The oil pressure returned to exactly where it was before. However within just a couple hundred miles, it was back to the 19 at idle / 35 under acceleration (28-30ish cruising) from before.

Is this a fuel dilution issue? I'm running E85 almost exclusively, I'm not sure if that has an impact. It's mostly two-lane 55mph road driving (I live in a rural area), and I rarely drive for less than 30 minutes. Just yesterday I drove 90 minutes each way. Wouldn't that get the oil warm enough to cause any fuel in the oil to evaporate? It is the max trailering model so it does have an oil cooler.

Other thoughts? Is this acceptable/normal behavior? Should I change now?

Thanks!

-John
It's most likely some permanent shearing of the VM/VII additives. As they get chopped up, especially under high load, they're less effective at slowing the decrease in viscosity with increasing temps. Lower viscosity with give lower oil pressure.
 

Circuit Rider

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It's most likely some permanent shearing of the VM/VII additives. As they get chopped up, especially under high load, they're less effective at slowing the decrease in viscosity with increasing temps.
So in that scenario, would that mean it's time for an oil change? Or does it still have life left?
 
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Amsoil EA15K50
I thought Amsoil is not recommending that filter any longer?

 

Circuit Rider

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how much weight was the 1200 mile tow? Is this a 5.3?
5.3, towing approximately 1,200 pounds.
I thought Amsoil is not recommending that filter any longer?

Oh interesting. That's what they recommended on the website.

Aha! If I list 2013 instead of 2014, it does not recommend that filter.

In 2014, the 5.3 was updated in the Silverado models. But the Tahoe remained on the older GMT900 platform that year and moved on to the new platform in 2015. I've noticed that parts databases and accessory databases sometimes incorrectly list 2014 Tahoe's as 4th gen instead of 3rd gen. Because they, I suppose, assume that because the Pickups were new in 2014, that the SUV's must have been too.

Even their bulletin lists 2007-2013; but a 2014 is still a part of that same generation.

I think we've figured it out!
 
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