That is my guess as well. Happened to me several year back. T-stat stuck open and I never noticed until this time of year. My engine oil temp would barely get to 160-170 range on the freeway and then drop like a stone once I came to a stop. A new t-stat fixed my issue.

The IH trucks have a much larger radiator and much smaller IC so their recovery time is much quicker. I'd stick with the OEM t-stat, especially since you live here in Arizona.

The heat exchanger is in the lower tank where the coolant is expected to be cooler than the upper portion of the radiator. In an ideal situation, where the radiator is able to exchange 100% of the heat, then the OTW trans cooler should exposed to coolant temps that match ambient.

 

That's interesting. The otw cooler in my firebird isn't setup that way, since firebird t-stats are 160-180 the otw is actually used to heat up the transmission in the winter.

Do you think OTW cooler in the rad of a 7.3 would make a difference in warmup time?

This is a question for a different thread but i'm wondering if OTW cooler is a better solution than a 6.0 upgrade. Or do people with OTW coolers STILL need a 6.0 OTA coolers?

 

This has been discussed here before and resolved by Mark Kovalsky. He is a retired Ford engineer who worked specifically on transmissions. If you search through his threads you will find answers to all the questions you posted above.

In case you didn't already know....the OTW trans cooler in a Super Duty 7.3 began sometime during the 2000 production year. Earlier Super Duty trucks likely didn't have the OTW feature.

The 6.0 OTA cooler is a superior upgrade to just about anything else that is available. The OTW cooler in the transmission helps during slow speed maneuvers, especially when backing up a heavy load. If you have a 4x4, then using the low gear range helps keep transmission temps down when backing up.

So, the ideal situation is the stock OTW in combination with the 6.0 OTA.

 

These trucks with a properly operating cooling system will not have any condition where the trans fluid is warmed up by the engine coolant.

 

Mine is a E99 and I'm pretty sure it's a OTA trans cooler.

 

L99 zf6 here...OTW.

 

I just checked, it is OTA. E99 auto 4x4

 

That would be correct for your year. I have a 99.5 and have the same thing.....just the OTA cooler. My wife's 2000 has both so she must have a later build truck.

I am not sure what the manual trans trucks have. I think they have a cooler but not sure which one (or both)....

 

no cooler here, Shake...just OTW

 

Here is the undisputed fact on a warmer diesel engine in regard fuel ignition - the fuel burns faster and cleaner (can you say glow plugs?). Some diesels (I don't know which) even factor the fuel temperature into the tuning. While 8 degrees is a mere pittance of increased temperature, it's still an increase. Thermal breakdown in oil is a well-known fact, and it's not like a switch - so you can't say at XYZ temp it's there and at XZY temp it's not.

While one can ask "Aren't we picking nits?", shouldn't we also ask "Why did they take the time and expense to engineer, manufacture, package, and ship a thermostat only 8 degree warmer?"

Anybody who's driven through that "transition phase" on the the dash temp gauge can hear something going on in the engine for a few seconds - it sounds a bit "off". Anybody who listens closely to the engine (**** people like me) can almost tell the engine temp by sound. Thinner oil (faster injection on a HEUI)? Quicker combustion? Advanced timing because of the quickness of everything else? All/some/none of the above? We can theorize (I get carried away with that), but one thing's for sure - heat has a profound impact on on the behavior of the 7.3L. A small change of 8 degrees may very well be perceptible by ear, seat, or some other part of the body. Or not. I can say the engine data doesn't change between about 160 and 210 degrees F EOT - but I never timed a 0-80 WOT run at the different temperatures.

With all that, I still default back to warmer is better to a point, then anything over that is going the wrong direction.

 

Well... they did. Isn't the 203 thermostat the one that was ORIGINALLY made for international engines ? It is my understanding Ford changed that.

Why they did that is as good as a question as to why they didn't the put 24" wipers on it.

 

I want to know why they didn't put a bungee or something across the overhead opening. I have to fetch my sunglasses out of the back seat every time my right foot itches.

 

I have a similar problem...

 

As a matter of fact so do I.

 

Jumping a wash at 50mph sends everything flying...