427435 wrote:Wes Tausend wrote:427435 wrote:
A 5w-20 oil is no thinner at, say 0 degrees, than a 5w-40 oil. They both meet the viscosity requirements for a 5w oil at cold temps. And a 5w-40 oil is far thinner at operating temp than either 5w-20 or 5w-40 is at start up temps.
The person that said the 5w-20 oils are for improved mpg is spot on.
True about the 5w's being about the same cold, cold pouring no different. Not so with 10w30 etc.
But one must rethink about the so called 20 wt mpg factor. Since the 5w20 oil is thinner than the 5w40 at high temps, it flows(leaks away) faster. The pre-set pump torsional load force remains about the same (30-40# oil bypass) and more hot 20 weight is ultimately pumped through bearings in volume, than hot 40 weight. Basically the comparable hp parasitic drag of pumping either oil ends up about the same when hot, so the "claimed marketing" mpg gain of 20 becomes basically moot.
The Ford Triton engines pressurize the RH cam tensioner only after the oil has traveled from the front pump all the way to the rear of the engine, up to the RH head and forward all the way to the RH tensioner piston. The revised 20 weight oil better maintains more even pressure over this long passage than heavier oil. Oil pressure over lengthy passageways drops just like long, small garden hoses drop sprinkler pressure furthest from the supply. Ford has had some minor issues with the RH cam and RH tensioner over this long oiling path and 5w20 helps solve it. (The V-10 is longest of all.) Of course they are not going to advertise this.
I haven't seen it done, but I imagine installing a custom direct oil line, pump-to-the-front of the RH cam, would be a good performance durability mod. The LH head already oils this way. With no distributor shaft cam drive, the Triton oil pump is totally forward, keyed on the crank snout right in front of the 1st main bulkhead, not set back (centered-like) nearer the 2nd main web like older Ford engine designs, or 3rd web like early GM.
Wes
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Yes, 10w-30 will be thicker than a 5w-30 at cold temps.
As for pressure drop to the tensioners, that's only true if there is significant flow. There isn't as the tensioners don't require much flow.
In any event, those tensioners have to work with oil much, much thicker during cold starts. The chart below is informative when you look at how little difference between different weight oils at 200 degrees despite lots of difference at cold temps.
That's a great chart, Mark. It amply demonstrates that there is very little viscosity difference in hot oils. The oil pump works very nearly as hard and causes nearly the same drag between 10W30, 5w20 no matter.
I don't regard the idea that 5W20 makes much of an improvement in mpg for that very reason.
My suspicion is that, at least in Fords case, the thinner oil supplies better lubrication for their cam problem. But admitting this would be bad marketing. Thus the marketing claim that the sole reason for switching to 5W20 was for helping meet EPA, if you can follow my reasoning.
You are correct, the front right(FR) cam tensioner does not require much flow at all. But the oil passageway to that FR tensioner is a long, narrow one. On the way to the tensioner, several bearings leak pressure away, each causing a slight drop in pressure, especially as the engine ages. The effect is identical to a series of lawn sprinklers on a long, thin garden hose. The last sprinkler barely sprinkles because there is very little pressure left.
The loss of pressure can be minimised by using large diameter hose, or water with less friction, such as the slippery water wetters that are often used with fire fighting tank equipment. Water wetters serve the same increased flow rate function as thinner oil, especially since it is too much trouble to increase the oil passage diameter or shorten the oil feed-path in existing Ford OHC engines.
Another more simple way to look at this is to fill a bucket up with a short hose and time it. Now fill the same bucket up, from the same faucet, with a long hose and time it. The flow will simply be greatest (quickest) with the short hose because of lower pressure loss.
I did have a longer, more elaborate, write-up on the V10, here on rv.net I think, but I believe a successful "search" of the thread is trapped (lost) by a gap between recent posts and those "over a year old".
On a different note, you are absolutely correct about the tolerances being tighter, not the clearances themselves. Not everyone here is able to follow this insightful concept. Perhaps it will help with their understanding that the reason that clearances don't get tighter is that hot crankshafts still expand a certain amount, so historical clearances must remain large enough to avoid seizing under hot conditions.
I once even ran into a misunderstanding by my local machinist who ground down my crankshaft too far for my taste. He ground the crank looser than official GM service limits "to be on the safe side". When confronted, he pointed out that all the local circle track guys ran these loose clearances to prevent bearing seizure under race conditions. He was right about race conditions, but I just desired long service life under moderate conditions.
I tightened up the clearances back to factory recommendations with tapered shim stock and the engine was fine. The next ground crank was correct. I always double check actual clearances with Plastigauge on assembly, but many did not back then. Plastigauge is more reliable than a micrometer even.
Wes
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