What brand, weight and type motor oil are you using?

When was it changed last?

I've seen brand new DINO juice cause this problem by having just the minumum amount of VI additives, thus the oil doesn't increase in viscocity as the internal engine temp increases. Theviscocity needs to increase to maintain the proper lubricating film. A lower VI at higher temperatures will cause low oil preasure and a lack of protection. If the oil doesn't maintain it's viscocity properly, then it looses it ability to maintain its high temperature film strength. It would also loose its High Temperature/High Shear Viscosity causing the oil to break down and you should know that outcome.

So at higher engine speeds, instead of the oil being pumped thru therequired lubricated surfacesat a given rate, the oil is being slung out and the pump can't keep up with the loss of internal oil pressure.

Hope this makes some sense

 

The problem is not at High RPMs it is after traveling over 1 and half hours at highway speed IE 2500 - 3500 rpm (mostly 2600) and coming to a stop that it occurs. The oil has been changed every 3k. Now I have tend to notice it after 1000 miles but that may also be that the 1st 1k was not at speed long enough IE local running, under the 1.5 hour mark. Until the most recent oil change (1st signs were prior to a brand switch) Synthetic blend 5-20 motorcraft. Also note that a shut down of less than 5 minutes (more like under 2 but more than key off key on) stops the flicker............oil is still way to hot. Is it possible it just over sensitive due to age....94K and it is a 2002. PS yes the syncro has been replaced.

 

Due to age/wear, I would probably go to a 5W-30 or 10W-30 motor oil (It won't hurt the engine in any way).

I use nothing less than a 10W-30 motor oil in my vehicles I just changed the oil on my Freestar. I use AMSOIL's regular 10W-30 and have 57,750 miles on the van. I change it once a year and it's had AMSOIL's 10W-30 in it sincebuying it new in April 2004. I ran AMSOIL's 20W-50 in my 1988 Ranger S/C 4x4 with the 2.9 since buying it new in May 1988. Sold it in 2000 with about 203,000 miles on it. It lived it's whole life in the snow-belt and the engine was nevertouched and ran like the day I bought it.

Ford first started using a 5W-20 to reduce the amount of hydrocarbonsto meet the "GREEN" requirements and to increase fuel mileage to meet the CAFE requirements. The lighter oil can remove heat at a faster rate, but the differencebetween the 5W-20 and a 5W-30 or 10W-30 for heat removal is minimal. The lower viscocity oil also has a higher evaporation rate.

Then again, you could have a bad oil sending unit as the guageis not real guage. Ford uses a "It's ON or OFF" guage.

Oil pressure is higher when the engine is cold due to the increased viscosity of the oil, and also increases with engine speed. Oil pressure is lowest under hot idling or low RPM drivingconditions. Too low of an oil pressure will cause excessive bearing wear due to the loss of the hydrodynamic film between the surfaces.

I personally would try a 5W or 10W-30 motor oil.

 

I will try a 5-30 at the next change. The on off characteristic of the pressure guage would answer a lot of questions, as that is the exact type of activity on the needle, small quick drop past threshhold at high temp and then return. It tends to follow what I call the little giggle in most of these newer engines at idle. I have not had an engine idle dead smooth in 15 years or more, be it new, mid life or 196K as was my 92 Grandam.

PS: I guess I should not be concerned about the use of 10-30 and the like, as it my understanding that the block design, and internals are basiclly the same for 3.0 Vulcan engine since the early 90's, and thats why we have a "Syncronizer", Ford needed something to run the oil pump when they switched it to direct ignition.