What is the name of the part of the oil additive package that swells, causing the oil to maintain its viscosity as it heats up?

the viscosity is what will maintain oil pressure so check that the new oil was the same viscosity rating as the oil you replaced
have the oil pressure checked with a mechanical gauge to make sure that it is not a problem in the engine

synthetic oils maintain a fairly constant viscosity through out the operation heat range , where as mineral oils change viscosity as the engine gets hotter ( synthetic oils 20 w and minerals 15w-40 )
It could be a manufacturer requirement to maintain warranty but it is generally accepted that mineral oils and synthetic oils have small differences in the life of an engine
Talk with an oil manufacturer such as castrol, shell etc and with your service dealer to get a better understanding of the requirement

May be due to oil pump wear, filter blocked by dirt, oil filter is exposed out of the oil surface, the oil level is low, the oil mixed with air and the pressure gauge is caused by the failure of the. In addition, the oil viscosity is low, the oil seal and poor lubrication, lubricating oil viscosity is too large, too cold oil sludge deposition too much also can cause the oil pressure indicator display abnormal.
source: obd2 tool car diagnostic

Motor oil thickens when cold- on very cold days, some grades of motor oil can be nearly the consistency of honey. It takes time for the oil to make its way from the oil pan to the top of your engine.

The ticking you hear is usually caused by the valve lifters running nearly "dry" - meaning that they are getting very little oil. As your Cruiser warms up, the oil thins and makes it "up top" much easier, so the noise decreases.

Make sure that you are following your manufacturers recommendation for the grade and viscosity of oil (example: SG SAE 10W30) for the temperatures you are operating your car in. In extreme cold weather environments, such as Chicago or Milwaukee, you may want to use an even "lighter" oil (example: 10W20 instead of 10W30) - you just have to be certain that when spring arrives, you go with the higher viscosity oil- your manufacturer normally covers this info. The grade (example: SG) is very important because it refers to the detergent content of your oil.

No vehicle manufacturer that I am aware of recommends a "straight grade" viscosity oil (example: SAE 30) in cold weather. Multi-grades, which act "lighter" in cold weather are called for.

The "W" in the oil viscosity designation means "winter" - it is the viscosity of that particular oil at 0 degrees F..... For example, "10W30" oil is as thick as an oil with a viscosity of 10 at 0 degrees F, and is as thick as an oil with a viscosity of 30 at 70 degrees F.

Pretty Cool, Huh?

It is not a good idea to use any oil thickening additive (STP, motor honey, etc...) in cold weather because they tend to add even more viscosity.

"The Court is out" regarding teflon additives such as "Slick 50" to your oil- the principle sounds good to me, and I have used them myself. Personally, a similar product has seemed to help tone down the "startup ticking" I myself have experienced.

Bearing wear is measured in thousandths and if somewhat worn they can become noisy till the crank heats and swells a bit. Naturally if the crank is very cold it will take longer to swell. Only way to check is by using an oil pressure gauge (mechanical) and see if oil pressure is below normal. Absolute best way to check though is by removing the pan and using plastigage to measure for wear. If you are referring to an oil filter with an anti-drainback valve, if you have the recommended filter or the proper cross-over number installed that should be fine unless it's defective. Oil pump will never do that.
If you need to use it, often an additive such as lucas engine treatment which is a viscosity improver may help to stop the noise but remember...it will not fix a worn part.

A low reading of 20psi is not dangerous. As an engine wears, clearances increase and allow some oil to escape out the sides of the bearings. Even at 15 psi you would still be OK.
There are several other causes for a low reading. Make sure the oil is not contaminated with fuel (smell the oil on the dipstick). If the oil has been in service too long, pressure can also drop...Oil has a VI rating (viscosity index). Especially in inexpensive oils this index is maintained by additive packages added to the oil base. Those additives break down from heat and shearing forces inside the engine.
If you are using any 5w oil (except synthetic) discontinue using it. Even in colder climates, most engines don't need anything that thin. Most synthetic oils are thinner than conventional lubricants and will give low readings...in that case, it's not a problem because they are so far superior that there is no sacrifice in protection.
As far as the difference between at idle pressure and at speed pressure, that is normal. Your oil pump is driven off the camshaft. As the engine rpm's increase the pump spins faster, giving you higher pressure as needed. When I build any engine, I always use a high pressure high volume pump. Even with those, idle pressure is lower than driving pressure and pressure always becomes slightly lower as the oil heats up.
So, the pressures you see are good, providing you hear no noises. Use a good quality oil 10w or 20w (better) as a first # and no less than 30 as the second number. If you want to add your own additive package, Use Lucas oil stabilizer or a small amount of marvel oil. Lucas will increase the VI number and marvel is a good cleaner as well as the fact that it seeks out hot spots where other oils run from them. Change your oil at 3,000 to 4,000 miles (depends on how hard you drive), Always use a good quality oil filter and you should not have a problem

Fist things first if it is a differential there are 2 grades if you are in cold weather you nead a lighter oil (85-120W) if you are in a hotter climate (98- 168W) this is like this cause of the weight of the oil when in use under climate change a tropical area needs a thicker oil do to the heat so it can maintain viscosity under heat .

Recommended GM DEXRON® VI, Low viscosity transmission fluid.
Note: make sure you don't over fill transmission and the Montana's transmission are know for failures due to high fluid retention caused by high viscosity transmission fluid from additives or dirty transmission oil and filter.
Thank you for using Fixya and good luck.

1989? When was the last time the Transmission was drained and new Transmission Fluid (oil) put in?
This Fluid (oil) loses viscosity and get particles in it causing additional loss in viscosity. I would go to even having the transmission drained and FLUSHED (cleaned) and new Fluid (oil) put in. Recheck the operation.
Boyles and Charles Laws are applicable here: (P*V)/T. Heat causes the Fluid to Heat and Expand (in molecules) but because of the limited sealed volume (transmission case) this increases Pressure allowing the smoother shifting and placement into gears.
Change the Transmission Fluid (oil) and have the Transmission Flushed (cleaning the insides) and your problem should go away.
Let me know if this helped, or if you have any additional information or questions. Feel free to contact me at FixYa.com!

try running a higher viscosity oil.
Instead of 5w30 (W stands for winter or cold viscosity) try a 10W30 or maybe more like a 20W50 the higher number is when the oil heats up.
You may try and add a can of No-Smoke or STP oil additive since you recently changed oil.