Not the most friendly graph, but you get the idea. 185f = 85c, follow graph from 100c to 85c, and you see how thick the oil was when you ran the 180, it is easily running like a 40 weight oil, maybe 50.
That's not exactly accurate because coolant temperature is measured where it exists the block in the water pump. What needs to be measured is the oil temperature, and that's displayed on the dash. These HEMIs are such old technology that the oil temperature is highly dependant on ambient. That's what you get when you pinch pennies and fail to install an oil heat exchanger, never mind an oil cooler. In this weather, truck empty, no towing, oil climbs to 200F~205F. Honestly, I need to try Mobil 1 EP 5W-20 for a change and see how temperatures are and how oil behaves. The thermostat isn't the big issue, deleting the grille shutters changed everything. Before the shutter delete, I was around 200F, so it was a 20F linear delete. The grille shutters dropped the temps even further. So, not to confuse anyone, I changed the thermostat first, and about a week after that I did the grille shutter delete. Maybe I shouldn't have. That being said, it's awesome for towing, the engine is strong and I have yet to see oil over 220F while towing 3000~4000 pounds going up a grade while doing 70~80 MPH.
It may run better with 5W-20 now that engine is cooler, who knows. The thing is, it runs perfectly fine, no issues. The engine warms up quickly. Before when I had the shutters, the computer would close them and turn the fan on when I started the truck up. It took forever to warm up. Now I quickly up to temperature. If I get off the highway a d sit in traffic, and I'm over 185F, say towing, while I wait at stop lights, bumper to bumper, and so on, it cools back down to 185F. The oil cools down as well. The oil temperature is highly influenced by ambient. This engine might be perfectly happy with a 5W-30 ILSAC oil all year long, who knows. I don't have the hydrodynamic data for 5W-20 and 0W-40 oils, however, I'm reasonably sure that the difference isn't that big because HTFS for almost any 5W-20 is around 2.0, while HTFS for Mobil 1 FS 0W-40 is exactly 2.3. It may be a bad idea to actually switch to RedLine for me because the HTFS of RL 5W-30 is around 2.85, that's in heavy duty territory. Coupled with a cool running oil, it might be too thick.
I remember that we discussed this before where I asked you guys if I should go to a thinner oil after I changed my thermostat, and you guys said no.
@Hemi395 encouraged me to stay with it, while
@HEMIMANN said that motor oxidation doubles with every 10F after 140F, so I don't have to worry about my oil running too cold or sludge for that matter.
Now, pardon my long post, but I'm somewhat curious how 5W-20 would behave in a cooler running engine and what the fuel mileage will be.
I did notice a drastic drop in MPG when towing. Before I was getting 14 to 15 MPG while towing, now I'm getting 12. I'm talking 2000~3000 pound loads. I will attribute the drop more to the oil that runs thicker now, but who knows. Before I swapped the shutter-thermostat job, towing that would heat up the coolant to 245F on the highway, and oil not far behind. Now it's hard to get even up to 220F doing the same thing, depending on ambient.
So, what do you guys think?
I have never seen 20. My dad claims he did all the time. I drive like a grandpa in it trying to keep my mpg up. Gotta love that 6 speed.
