10W30 would be correct.  The 5W20 didn't start to be used until the modular engines came out.  They do have very tight tolerances, and most importantly for the thin oil, a crank driven oil pump with absurdly tight tolerances.  Now engines are even running 0W20.  The stuff pours like water.  It can be done with really good oil control and full synthetic oils, but only newer engines are designed to use oil that thin. 

This what my Haynes manual shows.

My initial thought was to call BS on that.  My 6.0 has roller lifters and the factory oil weight is 15W40, with 10W40 recommended in extremely cold environments.  But as I got to thinking about it there were some reported cases of lifter failure in the 6.0, Ford also changed their recommendation to 5W40 synthetic (Shell Rotella T6).  The belief was that this change was in the interest of improving injector life by reducing or eliminating stiction caused by oil deposits in the spool valves.  I'm now thinking that this also coincided with a reduction in the number of reports of lifter failures.  Its likely just a coincidence, Ford probably just had a run of bad lifters, and once those were sorted out after failure the problems disappeared.  Thinking about it the trucks that seemed to have this issue were all '04.5-'05, right after they changed the HPO system design, so it supports that logic.  But it can't really be completely ruled out either with the data I currently have.

My thoughts on oil weight?  Run the lightest stuff that will protect the engine.  I run 5W30 in my 289 and will run it in the 331 I'm dropping in my '89.

Last edited by TKOPerformance (11/05/2020 6:00 AM)

I found 1996 F150 owners manual. Page 320

https://manual-hub.com/manuals/ford-f-150-1996-01-pdf-manual/

Last edited by Nos681 (11/06/2020 6:25 AM)

I couldn’t figure iut how to add a PDF.  If someone wanted the entire manual for future reference.

When we were up in the Yukon and AK a few years ago. We couldn't fine 10W30 on the store shelf. A lot of 0W10 or 20. Next time we need to take some oil along. 

And that couldn't possibly have anything to do with planned obsolescence.  I think its unlikely that 5W20 would cause an outright engine failure.  All 5W20 is pure synthetic oil.  The issue you have is what putting synthetic oil in an engine that old would do, namely cause massive oil leaks.  People don't want to have the leak fixed, don't want to be embarrassed by leaving oil everywhere, so they sell the old one and buy a new one.  Unless there was a known issue which could be attributed to oil weight I would pay as much attention to that TSB as I would a tabloid headline. 

Kristang wrote:

I'm going to preface my response to this thread by saying that I have been in the oil business for 25 years, PCMO's (Passenger Car Motor Oils) is my gig.  I have worked for an oil company in St. Paul for 22 of those years and have also been an Amsoil distributor before then.  I have represented many brands so before you go thinking I'm just another Amsoil dealer looking to sell the snake oil, you're wrong.  It's not for everyone and every application.  I do wholeheartedly believe it is on of the best products in the industry.  Their quality control and R&D is second to none.  In regards to the 5w20 that Ford "recommends" in some of their engines.  This product has been manufactured for FoMoCo by Conoco-Phillips.  I rep'd them for almost 10 years and while I don't think it is the best choice, the product is good.  TKO stated all 5w20 is pure synthetic oil.  No offense but that is not true at all.  If it is API licensed, then it is at a minimum 5w20 synthetic blend and can be a full or pure synthetic if you seek it out.  My recommendation with the lighter weights is to utilize a 0w product.  0 weights are much more sheer stable than 5w or 10w motor oils, meaning that the it will keep the metal surfaces from making contact with each other.  0w's do a great job of that task.  I personally use full synthetic 10w30 in my 393w but my Dad uses 5w20 full synthetic in his 500 hp 347.  Why?  Our motors were built with different tolerances.  He decided to build his tighter than I built mine.  Nothing wrong with that, you just have to use the right motor oil weight to protect it.  Also, synthetic motor oils do NOT cause leaks, they only expose them.  They do a fantastic job of cleaning, therefor, if you have deposits sitting on cracks in seals and gaskets, the oil will clean them off and expose  the leak.  Enough for now.  I could go on forever. 

Good stuff, I run Amsoil trans fluid in my fully built E40D. Love it other than the price
 

I would not do that. It has been known to clean out the engine in big enough chunks to flow down stream and plug something up causing engine failure.

Raymond_B wrote:

Kristang wrote:

I'm going to preface my response to this thread by saying that I have been in the oil business for 25 years, PCMO's (Passenger Car Motor Oils) is my gig.  I have worked for an oil company in St. Paul for 22 of those years and have also been an Amsoil distributor before then.  I have represented many brands so before you go thinking I'm just another Amsoil dealer looking to sell the snake oil, you're wrong.  It's not for everyone and every application.  I do wholeheartedly believe it is on of the best products in the industry.  Their quality control and R&D is second to none.  In regards to the 5w20 that Ford "recommends" in some of their engines.  This product has been manufactured for FoMoCo by Conoco-Phillips.  I rep'd them for almost 10 years and while I don't think it is the best choice, the product is good.  TKO stated all 5w20 is pure synthetic oil.  No offense but that is not true at all.  If it is API licensed, then it is at a minimum 5w20 synthetic blend and can be a full or pure synthetic if you seek it out.  My recommendation with the lighter weights is to utilize a 0w product.  0 weights are much more sheer stable than 5w or 10w motor oils, meaning that the it will keep the metal surfaces from making contact with each other.  0w's do a great job of that task.  I personally use full synthetic 10w30 in my 393w but my Dad uses 5w20 full synthetic in his 500 hp 347.  Why?  Our motors were built with different tolerances.  He decided to build his tighter than I built mine.  Nothing wrong with that, you just have to use the right motor oil weight to protect it.  Also, synthetic motor oils do NOT cause leaks, they only expose them.  They do a fantastic job of cleaning, therefor, if you have deposits sitting on cracks in seals and gaskets, the oil will clean them off and expose  the leak.  Enough for now.  I could go on forever. 

Good stuff, I run Amsoil trans fluid in my fully built E40D. Love it other than the price
 

If you want excellence, you have to pay for excellence!
 

Kristang wrote:

I'm going to preface my response to this thread by saying that I have been in the oil business for 25 years, PCMO's (Passenger Car Motor Oils) is my gig.  I have worked for an oil company in St. Paul for 22 of those years and have also been an Amsoil distributor before then.  I have represented many brands so before you go thinking I'm just another Amsoil dealer looking to sell the snake oil, you're wrong.  It's not for everyone and every application.  I do wholeheartedly believe it is on of the best products in the industry.  Their quality control and R&D is second to none.  In regards to the 5w20 that Ford "recommends" in some of their engines.  This product has been manufactured for FoMoCo by Conoco-Phillips.  I rep'd them for almost 10 years and while I don't think it is the best choice, the product is good.  TKO stated all 5w20 is pure synthetic oil.  No offense but that is not true at all.  If it is API licensed, then it is at a minimum 5w20 synthetic blend and can be a full or pure synthetic if you seek it out.  My recommendation with the lighter weights is to utilize a 0w product.  0 weights are much more sheer stable than 5w or 10w motor oils, meaning that the it will keep the metal surfaces from making contact with each other.  0w's do a great job of that task.  I personally use full synthetic 10w30 in my 393w but my Dad uses 5w20 full synthetic in his 500 hp 347.  Why?  Our motors were built with different tolerances.  He decided to build his tighter than I built mine.  Nothing wrong with that, you just have to use the right motor oil weight to protect it.  Also, synthetic motor oils do NOT cause leaks, they only expose them.  They do a fantastic job of cleaning, therefor, if you have deposits sitting on cracks in seals and gaskets, the oil will clean them off and expose  the leak.  Enough for now.  I could go on forever. 

I truly appreciate the information.  My belief that all 5W20 was full synthetic stems from the fact that when we first needed to buy it for my brother's Explorer we were told by the local NAPA that it was only available in full synthetic.  Now what that may have meant was that they only carried it in full synthetic.

Regarding synthetic oil causing leaks, its a bit of potato/potahto.  If you didn't notice the leak before because it was so minor and it was "exposed" by the synthetic; the synthetic in essence created a leak that wasn't there before.  I've had considerable experience with this, particularly with first generation synthetics, specifically Mobil 1.  Scuttlebutt at the time was that the oil did not have the right additive packing in it to keep seals plump.  I swapped an older engine over to Mobil 1 and it started leaking, I switched it back and the leaks went away.  There was also talk that part of this was a lack of parafins in the oil.  This was a problem with the initial ULS Diesel fuel that was later corrected, and caused problems with older engines that needed the lubricity the parafins provided.  Removing the sulphur also removed the parafins, and older engines could be damaged without running a lubricity additive.  Eventually this was corrected with a different additive package, and is no longer an issue despite widespread belief that it is.  This may well be the case with synthetics, but you can understand why my past experience would make me gun shy. 

With a new engine, at what point is it "safe" to switch to synthetic?