oil temp hit 260 degrees , whats the best synethic oil

The “best” synthetic motor oil is subjective.
However, being that you have asked the question, the correct answer is Amsoil Signature Max Duty 5W40 Diesel motor oil. I’ve used Amsoil synthetic lubricants and their filters since 1976.
Here’s a link to their Signature 5W40 Diesel oil.
Amsoil Signature Seies Max Duty Synthetic Diesel Oil 5W40

theoldwizard1 wrote:
Motorcraft Super Duty 10W-30 Diesel Engine Oil is sold at Walmart for under $20. It is API certified CK-4.

Even the old non-synthetic transmission fluid was good for over 250F.

Did you mean CJ4 ?

Motorcraft Super Duty 10W-30 Diesel Engine Oil is sold at Walmart for under $20. It is API certified CK-4.

Even the old non-synthetic transmission fluid was good for over 250F.

DIESEL MOTOR OILS MEETING FORD WSS-M2C171-F1

There are several full synthetic oils on the list that meet Ford’s specifications for your engine.

:):)

I call 260 the high end of normal and while I recommend synthetic for all motors I would not get too worked up about it. Not enough to get an oil cooler anyway.

You should know that not all oils are Ford approved and making modifications to your engine can be of concern if you engine is still under warranty. You pulled one of the hardest pulls in the country with a large load. I wouldn't get to carried away based on that one pull.
You didn't mention your engine, but the diesel is a beast, well suited for towing heavy loads.

What RPM were you pulling? If you happen to be lugging the motor it will get hot. Best thing you could have done then is change gears and let the motor rev. Turn off your AC also to help reduce load. All motor oils are made to a certain standard so brand is kind of irrelivant. Your owners manual spells out the correct oil spec for your motor. It generally also gives grade recomendations for normal and extreme conditions. When summer towing fill to the extreme specs and go.

were on flat land now. plan on getting oil changed in the next couple days. Be in one spot couple months looking into a after market oil cooler. TRAVELINGMAN I heard the fan kick in.

What you should do is call the oil manufactures and talk to their engineers.

The Nodwell track rig that appears in my tag line below has a 453 Detroit in it that gets very hot when traveling through miles of mud up to the front bumper. I have a separate oil temperature gauge on it.

I called and talked to the Mobile 1 engineers. They said the engine oil could handle 250F without any problems, BUT if it went up to 290F for more than five minutes, that it would ruin the oil and it should be changed. This was several years ago, but again, call and talk to the mfg's engineers.

Bill

Full synthetic AMZ/OIL 15-40.