Is 10W40 going to harm my engine?
Thread Starter
Burning Brakes
Joined: Jun 2009
Posts: 787
Likes: 11
From: Santa Rosa California
Is 10W40 going to harm my engine?
So I just had some work done to my car and I told the mechanic to swap out the old oil with 5W30 like I have for years. I went to pick up the car and he told me he put 10W40 because he likes it better for these cars with higher miles (im at 155k).
I wasn't very happy with him making that call when I specifically asked for 5-30. Just wondering if I should drain the 10-40 or if it should be OK for a few thousand miles.
I live in Southern California so the weather is pretty mild if that matters for the viscosity.
I wasn't very happy with him making that call when I specifically asked for 5-30. Just wondering if I should drain the 10-40 or if it should be OK for a few thousand miles.
I live in Southern California so the weather is pretty mild if that matters for the viscosity.
Last edited by mikex7; Jan 5, 2016 at 04:54 PM.
Le Mans Master
Joined: Sep 2003
Posts: 8,812
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From: eastern NC
So I just had some work done to my car and I told the mechanic to swap out the old oil with 5W30 like I have for years. I went to pick up the car and he told me he put 10W40 because he likes it better for these cars with higher miles (im at 155k).
I wasn't very happy with him making that call when I specifically asked for 5-30. Just wondering if I should drain the 10-40 or if it should be OK for a few thousand miles.
I live in Southern California so the weather is pretty mild if that matters for the viscosity.
I wasn't very happy with him making that call when I specifically asked for 5-30. Just wondering if I should drain the 10-40 or if it should be OK for a few thousand miles.
I live in Southern California so the weather is pretty mild if that matters for the viscosity.
Good luck... GUSTO
Thread Starter
Burning Brakes
Joined: Jun 2009
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From: Santa Rosa California
Thanks. It's Castrol Edge Synthetic. I've used Mobile 1 5-30 synthetic for the 9 years I've had the car.
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If it is full synthetic oil, you'll be fine, but if you really like that shop, I would make it clear to him that in the future he is not to change your directions unless he clears it with you first. It's not his final decision on what happens to your car, it is yours. He should only make recommendations and await your approval.
Le Mans Master
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From: OK
If it is full synthetic oil, you'll be fine, but if you really like that shop, I would make it clear to him that in the future he is not to change your directions unless he clears it with you first. It's not his final decision on what happens to your car, it is yours. He should only make recommendations and await your approval.
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Le Mans Master
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I agree I would question any shop that would suggest an oil viscosity other than stock recommended--especially without your permission---This is wintertime so I would want thinner oil in my engine --especially if you live in a cold snowy area----
I would leave it in for awhile but change back to the factory recc viscosity-- as soon as 2000 miles
On some of these new cars with AFM it is imperative to use the recc oil----as the AFM system is highly dependent on oil viscosity and pressure--
Thicker oil creating more oil pressure and flow is an old school wive's tale and not relevant on today's modern engines
I would leave it in for awhile but change back to the factory recc viscosity-- as soon as 2000 miles
On some of these new cars with AFM it is imperative to use the recc oil----as the AFM system is highly dependent on oil viscosity and pressure--
Thicker oil creating more oil pressure and flow is an old school wive's tale and not relevant on today's modern engines
Team Owner
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You'll be fine.
HOWEVER, I would make it clear that your next oil change is on them. If they don't like it, find someone who WILL follow your directive.
HOWEVER, I would make it clear that your next oil change is on them. If they don't like it, find someone who WILL follow your directive.
Melting Slicks
Joined: Jun 2013
Posts: 3,473
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From: West Virginia
I would take it back and tell them to put in what you asked for.
(a) the manual says 5-30, and (b) that's what you asked for.
They should have asked you first before they went against your instructions.
Many people like the Mobil 1 5-30 high mileage, as the additive package is pretty much the same as the M1 spec was when the factory selected it.
Going to 10-40 won't break anything, but to me it would be a matter of principle.
(a) the manual says 5-30, and (b) that's what you asked for.
They should have asked you first before they went against your instructions.
Many people like the Mobil 1 5-30 high mileage, as the additive package is pretty much the same as the M1 spec was when the factory selected it.
Going to 10-40 won't break anything, but to me it would be a matter of principle.
Last edited by jackthelad; Jan 6, 2016 at 10:44 AM.
Tech Contributor
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LOL! Don't lose any sleep or get grey hair over the issue.
Like was previously stated, If you were in an area where the temps were in the 10-20 deg range, I MIGHT be a little more concerned.
When its time to change the oil, just go back to the 5-30..
Like was previously stated, If you were in an area where the temps were in the 10-20 deg range, I MIGHT be a little more concerned.
When its time to change the oil, just go back to the 5-30..
Team Owner
Joined: Mar 2002
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I do live in Central FL, but even in colder climates, the difference between 5 and 10 weight will hardly make a difference.As has been mentioned, what matters most is the fact that it's synthetic. C5s really need the synthetic as they tend to run hotter than other LS engine'd vehicles. I've noticed my car consumes about 2x the amount of conventional oil as synthetic.
Last edited by wcsinx; Jan 6, 2016 at 03:13 PM.
Burning Brakes
Joined: Aug 2011
Posts: 1,071
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From: Odessa TX
I agree I would question any shop that would suggest an oil viscosity other than stock recommended--especially without your permission---This is wintertime so I would want thinner oil in my engine --especially if you live in a cold snowy area----
I would leave it in for awhile but change back to the factory recc viscosity-- as soon as 2000 miles
On some of these new cars with AFM it is imperative to use the recc oil----as the AFM system is highly dependent on oil viscosity and pressure--
Thicker oil creating more oil pressure and flow is an old school wive's tale and not relevant on today's modern engines
I would leave it in for awhile but change back to the factory recc viscosity-- as soon as 2000 miles
On some of these new cars with AFM it is imperative to use the recc oil----as the AFM system is highly dependent on oil viscosity and pressure--
Thicker oil creating more oil pressure and flow is an old school wive's tale and not relevant on today's modern engines
Drifting
Joined: Sep 2009
Posts: 1,862
Likes: 594
From: Prescott, Arizona
That oil will be fine.
I have been running Red Line 10W40 since I started tracking the car five years and 25,000 miles ago.
Mobil 1, through their oil expert, made it clear some time ago when Mobil 1 recommended that Corvette owners who track their cars drain out the Mobil 1, 5W30 and replace it with Mobil 1, 15W50.
A primary reason that auto manufacturers have gone to thinner multi viscosity oils over the last 20 years is to help them achieve their required corporate average fuel economy (CAFE).
I have been running Red Line 10W40 since I started tracking the car five years and 25,000 miles ago.
Mobil 1, through their oil expert, made it clear some time ago when Mobil 1 recommended that Corvette owners who track their cars drain out the Mobil 1, 5W30 and replace it with Mobil 1, 15W50.
A primary reason that auto manufacturers have gone to thinner multi viscosity oils over the last 20 years is to help them achieve their required corporate average fuel economy (CAFE).
Le Mans Master
Joined: Aug 2005
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From: CA.
St. Jude Donor '13-'14-'15
Funny guy---" some of these new cars" Yes on Silverado's with AFM GM has had many lifter failures that will take out and destroy the whole engine----AFM is very clean oil--correct viscosity and pressure sensitive---As a matter of fact in 2016 because of so many failures GM has re-designed the entire lifter shut off process in them---as well as the AFM lubrication process----That being said even on older LS's I would never alter from the recc oil viscosity---Typically LS oil pumps are hi pressure low volume designs---Using thicker oil changes the lubrication characteristics of the oil system---
C7 Corvettes and all DI engines have changed now to a high volume and low pressure oil pump--- C7 tops out at only 40-45 PSI at WOT----Radically different than older LS1 and LS2 engines----
Engineers have spent months on lubrication and I don't think anyone other than them would have the best insight on what is correct for a particular application---
C7 Corvettes and all DI engines have changed now to a high volume and low pressure oil pump--- C7 tops out at only 40-45 PSI at WOT----Radically different than older LS1 and LS2 engines----
Engineers have spent months on lubrication and I don't think anyone other than them would have the best insight on what is correct for a particular application---
Le Mans Master
Joined: Dec 2006
Posts: 7,251
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From: Phoenix Arizona
Bill knows his stuff! You guys would have a heart attack if you knew i ran 20-50 in the winter lol Does anyone even know what the numbers mean? i have been on and seen so many oil threads, it is just hilarious how ignorant everyone is on oil LOl 
If you don't bounce it off the rev limiter every time you shift, you can damn near run anything, these motors are tough as hell! fricken amazing engines!
Fyi i have owned 5 of these puppies, raced all of them and owned over 80 vehicles been wrenching for 45 years
Drifting
Joined: Sep 2015
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That oil will be fine.
I have been running Red Line 10W40 since I started tracking the car five years and 25,000 miles ago.
Mobil 1, through their oil expert, made it clear some time ago when Mobil 1 recommended that Corvette owners who track their cars drain out the Mobil 1, 5W30 and replace it with Mobil 1, 15W50.
A primary reason that auto manufacturers have gone to thinner multi viscosity oils over the last 20 years is to help them achieve their required corporate average fuel economy (CAFE).
I have been running Red Line 10W40 since I started tracking the car five years and 25,000 miles ago.
Mobil 1, through their oil expert, made it clear some time ago when Mobil 1 recommended that Corvette owners who track their cars drain out the Mobil 1, 5W30 and replace it with Mobil 1, 15W50.
A primary reason that auto manufacturers have gone to thinner multi viscosity oils over the last 20 years is to help them achieve their required corporate average fuel economy (CAFE).
Racer
Joined: Jul 2005
Posts: 274
Likes: 0
From: oklahoma
Your oil will be fine
As a motor gets more miles bearing clearances increase as well as any other moving parts (piston to wall, the lifters internal piston, valve guide etc)
The higher the number the more viscous (thicker) the oil is. It flows out of these clearanced areas slower, possibly closer to the flow rates when the engine was new.
The suggested 5-30 is for standard driving conditions to achieve good fuel mileage when new.
What's important is the oil pressure. If the thicker oil exceeds the factory pressure it *may be an issue but this is highly unlikely.
What is more likely is the oil your mechanic installed probably brought your oil pressure closer to factory spec.
As a motor gets more miles bearing clearances increase as well as any other moving parts (piston to wall, the lifters internal piston, valve guide etc)
The higher the number the more viscous (thicker) the oil is. It flows out of these clearanced areas slower, possibly closer to the flow rates when the engine was new.
The suggested 5-30 is for standard driving conditions to achieve good fuel mileage when new.
What's important is the oil pressure. If the thicker oil exceeds the factory pressure it *may be an issue but this is highly unlikely.
What is more likely is the oil your mechanic installed probably brought your oil pressure closer to factory spec.
