Safe Oil Temp?
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Senior User
Joined: Oct 2006
Posts: 320
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From: Salem, OR
Safe Oil Temp?
Main question is that if running a 203* vs 195* t-stat could cause premature oil brake down.
What is safe opperating temp of engine oil?
At what temp does the oil start to break down?
A quick google search yeilded these awnsers:
+Banks brand EOT gaudge show 170*-240* in the "green"
+From what i see most of our 7.3L run from 180*-220*.
+Also found someone stating that above 260* is bad. But its worse to run long time at 260, then a quick spike to 280*.
From this i gather that a 203* vs 195* T-stat is NOT going to affect the oil.
****But whats your guys thoughts on these matters?***
What is safe opperating temp of engine oil?
At what temp does the oil start to break down?
A quick google search yeilded these awnsers:
+Banks brand EOT gaudge show 170*-240* in the "green"
+From what i see most of our 7.3L run from 180*-220*.
+Also found someone stating that above 260* is bad. But its worse to run long time at 260, then a quick spike to 280*.
From this i gather that a 203* vs 195* T-stat is NOT going to affect the oil.
****But whats your guys thoughts on these matters?***
Post Fiend
Joined: Jun 2004
Posts: 9,293
Likes: 10
From: Parker, CO
For a truck that is stock or mostly stock, it shouldn't be an issue.
Oil temps will depend on RPM's and engine load. As you said, engine oil temps will range. I've datalogged PSD's in winter and saw that driving on the highway engine oil temps struggle just to reach 170 degrees. Other's I've seen driving up a mountain pass in the middle of summer have oil temps reaching 210-220.
A big thing to consider with the 7.3L PSD... engine oil temps are taken at the HPOP reservoir. A truck with a modified HPOP system (such as two pumps), and having oil dumped back into the reservoir rather than down the front cover, will have higher engine oil temp readings. Simply because there's hotter oil at the reservoir, but cooler oil elsewhere in the engine.
Engine oil temps typically hover close to coolant temps for most conditions. So for most people, a 203 degree thermostat won't have any ill effects on oil longevity.
Oil temps will depend on RPM's and engine load. As you said, engine oil temps will range. I've datalogged PSD's in winter and saw that driving on the highway engine oil temps struggle just to reach 170 degrees. Other's I've seen driving up a mountain pass in the middle of summer have oil temps reaching 210-220.
A big thing to consider with the 7.3L PSD... engine oil temps are taken at the HPOP reservoir. A truck with a modified HPOP system (such as two pumps), and having oil dumped back into the reservoir rather than down the front cover, will have higher engine oil temp readings. Simply because there's hotter oil at the reservoir, but cooler oil elsewhere in the engine.
Engine oil temps typically hover close to coolant temps for most conditions. So for most people, a 203 degree thermostat won't have any ill effects on oil longevity.
Elder User
Joined: Sep 2003
Posts: 582
Likes: 0
From: New Baden IL
When I tow in the summer my oil temps reach 230 degrees.....I have to admit this has me worried, because the oil temp was at least 15 degrees lower before I installed my 203 degree. I fully trust Bob Riley and he's said the temps are where they should be.....I'm still leery. I'm planning on swapping back to OEM this spring; no good reason other than gut feel since I've chipped the truck. The older 7.3's with a 203 were factory set. In other words, their timing was affected by a chip.
Post Fiend
Joined: Feb 2007
Posts: 14,541
Likes: 2
From: Dallas-Ft. Worth
I agree with you, Chief.... Not a big fan of EOTs getting that hot. I've never seen over 200, but I don't tow heavy either, and I have the factory 192 deg stat. I was thinking of putting a 195 back in. In "normal" driving in the summer, I will see the EOT get to 192, but no hotter, so I know the stat is pretty accurate. Towing a fairly light load (~7k) on the highway in the summer at 70mph, it got to 198.
Senior User
Joined: Oct 2001
Posts: 184
Likes: 0
From: Goleta, CA
Main question is that if running a 203* vs 195* t-stat could cause premature oil brake down.
What is safe opperating temp of engine oil?
At what temp does the oil start to break down?
A quick google search yeilded these awnsers:
+Banks brand EOT gaudge show 170*-240* in the "green"
+From what i see most of our 7.3L run from 180*-220*.
+Also found someone stating that above 260* is bad. But its worse to run long time at 260, then a quick spike to 280*.
From this i gather that a 203* vs 195* T-stat is NOT going to affect the oil.
****But whats your guys thoughts on these matters?***
What is safe opperating temp of engine oil?
At what temp does the oil start to break down?
A quick google search yeilded these awnsers:
+Banks brand EOT gaudge show 170*-240* in the "green"
+From what i see most of our 7.3L run from 180*-220*.
+Also found someone stating that above 260* is bad. But its worse to run long time at 260, then a quick spike to 280*.
From this i gather that a 203* vs 195* T-stat is NOT going to affect the oil.
****But whats your guys thoughts on these matters?***
PWRPROD
of American machinists
Joined: Oct 2004
Posts: 1,014
Likes: 0
From: NORTH IDAHO
How does putting the sender in the HPOP compare to by the oil filter? Will there be a tempurature diifference between the two locations? What is the ideal location for sampling EOT?
Senior User
Joined: Jul 2009
Posts: 211
Likes: 0
From: Trona, CA
Given that you have a turbo with oil going thru it that will reach much higher temps, and the oils used in these engines are designed for that...I don't think 220 or 260 is a big deal at all
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Senior User
Joined: Aug 2007
Posts: 412
Likes: 0
From: Fresno, CA
I wouldn't want it much over 220. The 6.0s seem to start developing high pressure leaks around 230, so I imagine it wouldn't be good for our trucks either, even if our high pressure leaks are easier to fix 
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Post Fiend
Joined: Nov 2007
Posts: 9,549
Likes: 14
From: Payson, AZ
Good question Walt. I was going to put my aftermarket EOT sender in that 1/4" plug spot at the filter housing. Do you know which way the oil flows through the oil cooler? Away from the filter or toward the filter?
of American machinists
Joined: Oct 2004
Posts: 1,014
Likes: 0
From: NORTH IDAHO
I agree with you, Chief.... Not a big fan of EOTs getting that hot. I've never seen over 200, but I don't tow heavy either, and I have the factory 192 deg stat. I was thinking of putting a 195 back in. In "normal" driving in the summer, I will see the EOT get to 192, but no hotter, so I know the stat is pretty accurate. Towing a fairly light load (~7k) on the highway in the summer at 70mph, it got to 198.
Thanks!
Post Fiend
Joined: Nov 2007
Posts: 9,549
Likes: 14
From: Payson, AZ
I would be willing to bet Joe is reading it on his Scan Guage which is the same as the PCM, at the HPOP.
Posting Guru
Joined: Jul 2008
Posts: 1,736
Likes: 0
From: Dalton,Ga
mine reads no more than 210f at the scan guage but runs reguarly 230-235f towing on my EV2 which the probe is by the oil cooler...
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