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Oil weight question

gfh77665

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#1
I have a 2017 Fiesta with the 1.6, 40,000 miles. I love my car, its been excellent. I have let my dealer do all my oil changes so far. My factory warranty will expire in one year. I live in a very hot climate, in south Texas. 90-100 degree temps 9 months out of the year, and our "winters" are very warm, usually 45-75 degrees.

My question is, I just got 100 quarts of Quaker State oil free. Can I use this 10w-30 in the 1.6 engine in a hot climate without issue? I tend to think that a 10w-30 in hot temps is pretty much equivalent to using the recommended 5w-20 in the cold north. Of course I will not use it until the powertrain warranty is up. Has anyone tried a heavier weight in the 1.6? Any experiences with this?
 

scotman

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#2
Welcome to the forum gfh. The big issue with using that oil will be that it is going to effect the fuel economy. Thicker oil is harder to pump through the engine. You also don't mention the API rating on the free oil. Which is an indicator of how long ago it was refined.
Today, the oil industry is at the GF6 level. With quite a bit of GF5 product still being sold.
Additives and stabilizers have improved tremendously since the mid 1980's introduction of 5W30.
Not knowing how long ago that stuff was created is concerning. Would i put it in my 1992 Ranger pickup truck that call for that exact grade? Maybe. Or maybe only one quart of that free oil per change. Engines are very expensive to replace or rebuild. The most expensive oil we can buy is LESS costly than the FIRST HOUR OF LABOR on removing a destroyed engine.
So, it's very important to have a good understanding of the true cost- value relationship in this particular area of car maintenance.
In forty years of car ownership i have never destroyed an engine. But, i have purchased over a dozen cars (very cheaply)in that time with blown or seized engines!
 
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gfh77665

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Thread Starter #4
You also don't mention the API rating on the free oil. Which is an indicator of how long ago it was refined.
Today, the oil industry is at the GF6 level. With quite a bit of GF5 product still being sold.
Thanks for your informative answer. Its an SN rated, GF5 oil. I noticed that GF5 was superseded by GF6 just recently on May 1, 2021, so of course that was well after my 2017 year model Fiesta was made.

Specifically, do you think that a 10w-30 in hot south Texas would behave much like a 5w-20 would in a cold climate? Thanks.
 

LionsTooth

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#5
Thanks for your informative answer. Its an SN rated, GF5 oil. I noticed that GF5 was superseded by GF6 just recently on May 1, 2021, so of course that was well after my 2017 year model Fiesta was made. Specifically, do you think that a 10w-30 in hot south Texas would behave much like a 5w-20 would in a cold climate? Thanks.
I would have no issue running 10-30 in Texas in the summer. I used to run 10-50 in the Colorado summer and never had an issue. But I always went down to 10-30 for the winter or it wouldn't start when it was cold....oil was too thick at 15 degrees or less to allow the starter to turn the motor. Seems to me, one step thicker is not an issue.
 

scotman

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#6
Thanks for your informative answer. Its an SN rated, GF5 oil. I noticed that GF5 was superseded by GF6 just recently on May 1, 2021, so of course that was well after my 2017 year model Fiesta was made.

Specifically, do you think that a 10w-30 in hot south Texas would behave much like a 5w-20 would in a cold climate? Thanks.
I would not use the 10W30 GF5 oil in a Fiesta. It's range of viscosity is too far out of spec for my comfort zone. I run a full synthetic 5w30 in my 2016 Fiesta ST. It immediately lost 1 mpg on average when I made the switch from semi synthetic 5w20.
My reason for the change was to have less oil vapor migration into the pcv system and valve cokeing.
So far, i am satisfied with the tradeoff.
In my 2011 Fiesta, i use full synthetic 5w20. Either Castrol Syntec or Mobil 1. On both cars i always replace the oil filter at every change. And always use Motorcraft filters.
10w30 would probably do the job. But, we would like to hear back from you in a couple of months regarding how the fuel economy is affected. With price per gallon rising, it is a point of interest here on the forum.
 
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scotman

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#8
I will guess that the basic fiesta will lose a bit more than 2 mpg on 10w30 semi synthetic. If its just dino 10w30, i have no clue.
Will the cam phasers function the same or maybe slower?
Drivability and acceleration?
 

Handy Andy

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#9
Specifically, do you think that a 10w-30 in hot south Texas would behave much like a 5w-20 would in a cold climate? Thanks.
You ask a good question because of the Blend of viscosity you want to use.

Remember too, your Fiesta runs a 180~185 degree (F) thermostat - so really - the 10W number is where I would worry.

That is your start up - with properties of a 30W. May be ok for 100 degree Summer days, but not so much for 40F mornings in the Fall.

Most other vehicles run a 190~195 degree (F) - warm up is pretty quick but run in a rather narrow range of heat capacity - sure it's 195(F) but the engine doesn't have much more "rise" after that because of the Latency of the fluids both oil and coolant - that keep the engine stable and in a range for the emissions to be more predictable. So those thermostats make the engine hotter to help with emissions, power and the fuel economy - but pay a price in having to have larger reservoir to exchange heat.

The Fiesta has an ability to operate a wider range of heat - but remember too, has a smaller cooling "jacket" that affects how this heat is passed thru and taken away from the system. The Oil has to do the rest of the job in pulling heat out and away. You want it thinner to help it pull the heat out of the motor - the Coolant can only do so much - the oil has to bear it's burden too. You have two coolers on the engine one for the Coolant and one for the oil. (At Least on mine) This let's them use smaller capacities - cooling on two fronts.

Another aspect to look at is the Fluid capacity of both the Radiator and your Oil by volume - compare this to other vehicles you've owned. You will find many of the 190(F) hotter running cars had greater larger capacities than your Ford, not by much in some cases - but what is in the Jacket of the engine that counts.

You asked about the viscosity - the lower number is your base, 10 - but properties of 30 - so the oil will take longer to pump thru - but pressures will also be different in areas that affect engine timing The fluid will take time to build pressure, and will also need more time to empty from the valve cam..

So the thicker fluid will also take more time to get thru the oil ports - remember you're dealing with a 180 degree F thermostat car, that it's emissions and timing are based upon a given power curve at the temperature - trying to raise up the heat may destroy the ability for the vehicle to take advantage of valve timing to develop that power. Oil starvation can occur because the oil pump is pulsing thicker fluid at a given volume versus the thinner fluid at that same volume.
 
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Thread Starter #10
Great replies, all. Thanks. What would you all think of me blending the 10w-30 with a similar 0-20 with a 50/50 ratio? It would be something like a “5w-25” (yes I know that’s not a real weight).
 

Handy Andy

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#11
I think it would work if you just used 1 - 0W-20 just to thin it out per oil change. Holds easily 4 quarts but this would make it more of a 3:1 ratio versus straight 10W-30.

Is it a Synthetic blend you're getting?
 


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