Originally Posted By: BituminousCoal
I did the same thing w/ the 203º's and got rid of them. Made for rough idles on my trucks, higher temps, less precise temp control, and no better mileage. Went back to OEM motorcraft/Wahler 89ºC stat. Some who tow are using 180º, but I think that's a bit low.
However, 200º - 235ºF oil temp is normal for 7.3. My trucks have always seemed to run about 15-25º above the coolant temp - even the one w/ new oil cooler.
Man, I could not agree more. I changed the thermostat in December because so many were saying it was the factory temp, made for better mileage, blah, blah, blah. I noticed nothing other than a hotter coolant temp. My coolant temps now stay at the "N" or the "O". On the long pulls, after the swap, It would get to the "R", but not above. With the 203*, it would get to the "L"!!!! I was like "yeah, no thanks". I know the cooling system for the 7.3 is very efficient and my system is in great shape, so I ditched the 203*. I also live in a warm climate, so there is really no need for it. Thanks for the info! Nice to hear from a fellow 7.3 owner!
Originally Posted By: roadrunner1
I read your first thread on this topic and now this one, I had several of those 7.3's and I don't think I had ever observed oil temp.
The temps you described are perfectly normal for newer diesels being pushed as you did. I was never a fan of running the 203f thermostat as many did, so you're back to stock now which should keep everything within factory specs.
As far as the parking lot oil change, the 10w-30 should have run cooler than 15w-40, not hotter.
I do still have an '89 IDI 7.3 that has been on 10w-30 for several years without issue. It gets loaded with gear and run down the highway and I have never thought about oil temps as its being used as it was designed at the time of build and speced 10w-30. Its a Super Duty, which is what Ford called the F550 at the time, and when I said loaded I meant loaded to capacity.
In my opinion you observed temps well within operating parameters of your 7.3.
Roadrunner, thanks for the info on the 7.3! It helps my decisions going forward at this point. I am not going to stress over EOTs anymore unless they just get ridiculous. The highest though was on the really hard pull, so it seems normal. As stated above, I tried that 203* thermostat because it was touted as the "factory spec". When it got to the "L" on the first hard grade and didn't come down, I was like "yeah, no thanks".