Home » Public Forums » GMCnet » Engine oil, which viscosity is best? (Looking for best synthetic available today to meet specs)
| Engine oil, which viscosity is best? [message #212339] |
Wed, 26 June 2013 12:34  |
lw8000
Messages: 201
Registered: July 2012
Location: S.E. Michigan
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Hello,
We are getting close to changing the oil in our 77 Kingsley with the original Olds 403, around 64K original miles. I've been looking for the best synthetic oil for this engine, including winter grade (if possible) as we may end up starting it over the winter from time to time and temps can be down to 10-20 degrees Fahrenheit.
What is the ideal viscosity of synthetic oil to use in this engine? The original manual recommends:
SAE 30 @ 40 degrees F and up
20W-20 @ 10 to 80 degrees F
10W-30 @ -10 to 60 degrees F
I saw the thread from a couple years ago with a list of oil with high ZDDP content, and the viscosities ranged quite a bit. So far I'm seriously considering the 10W-30 Amsoil Z-Rod which has high ZDDP and is specifically designed for older engines:
http://www.amsoil.com/shop/by-product/motor-oil/gasoline/z-rod-10w-30-synthetic-motor-oil/?code=ZRTQT-EA
To my knowledge, 10W-30 runs as the same viscosity as SAE 30 once warm, so my thought was to stick to as close to the original recommendation as possible.
They also have the same oil as above but 20W-50:
http://www.amsoil.com/shop/by-product/motor-oil/gasoline/z-rod-20w-50-synthetic-motor-oil/?code=ZRFQT-EA
But maybe that is too thick.
Any suggestions on this? There are a lot of different viscosities and we want to make sure we use the correct one. We aren't sure which of synthetics run best in the 403.
Thank you!!
--
Chris
Chris S. -
77 Kingsley, 3.70 FD, mostly OEM -
S.E. Michigan
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| Re: Engine oil, which viscosity is best? [message #212347 is a reply to message #212339] |
Wed, 26 June 2013 13:02  |
Cadillackeeper
Messages: 464
Registered: October 2012
Location: Fort Lauderdale
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You should get a lot of replies on this one. I have been using ONLY 15-40 diesel oil
in my Cad and in the Coach. Rotella or Peak.... The correct oil is Joe Gibbs .Its the only proper one left,the only one left!It is a little pricey but its the only one left.
77 455 Elaganza II and 67 Animal, Built 500 Powered Eldo
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| Re: Engine oil, which viscosity is best? [message #212350 is a reply to message #212339] |
Wed, 26 June 2013 13:07 |
A Hamilto
Messages: 4508
Registered: April 2011
Karma: 39
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| lw8000 wrote on Wed, 26 June 2013 12:34 |
Hello,
We are getting close to changing the oil in our 77 Kingsley with the original Olds 403, around 64K original miles. I've been looking for the best synthetic oil for this engine, including winter grade (if possible) as we may end up starting it over the winter from time to time and temps can be down to 10-20 degrees Fahrenheit.
What is the ideal viscosity of synthetic oil to use in this engine? The original manual recommends:
SAE 30 @ 40 degrees F and up
20W-20 @ 10 to 80 degrees F
10W-30 @ -10 to 60 degrees F
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My MM says 10W, not 10W30. 10W30 is good from -10F to +120FFortuitous that I just answered this on a previous ("hijacked") thread.
10W30 for most of North America most of the year. 10W40 if you will be driving in the desert Southwest all Summer. 20W50 if you will be in temps higher than 120F all the time. 5W30 if you will be below -10F all the time.
The part in the Maintenance Manual about straight weight oils being preferred is no longer true.
In my MM, Figure 11 illustrates that 10W30 will work for temps from -10F to +120F.
If ZDDP content gives you confidence in your oil, the 10W-30 Amsoil Z-Rod is perfect for you.
If you drive in temps well over 100F all the time, 10W40 is a good choice.
I would only use 20W50 if I was going to drive in Death Valley all Summer. 5W30 in Alaska in the Winter when the temp is not going to get above zero F, and never use 5W20.
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| Re: [GMCnet] Engine oil, which viscosity is best? [message #212351 is a reply to message #212339] |
Wed, 26 June 2013 13:06 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Chris
Bear in mind that the original manual is now about 35 to 40 years old depending on the model year you have.
The oils listed in it were available 40 years ago and the modern oils available today were not being made back then.
So, you should be looking at other oils than the 10w30 listed in your manual.
I use Mobil 1 15w50 which is a synthetic and I have been using it for over 10 years now with no problems in my 455 engine.You will get other suggestions from other GMCers and there are a lot of oils out there that will work. I do suggest that you consider synthetic oils through and they have a lot of advantages.
Emery Stora
77 Kingsley
Frederick, CO
On Jun 26, 2013, at 11:34 AM, LW wrote:
>
>
> Hello,
>
> We are getting close to changing the oil in our 77 Kingsley with the original Olds 403, around 64K original miles. I've been looking for the best synthetic oil for this engine, including winter grade (if possible) as we may end up starting it over the winter from time to time and temps can be down to 10-20 degrees Fahrenheit.
>
> What is the ideal viscosity of synthetic oil to use in this engine? The original manual recommends:
>
> SAE 30 @ 40 degrees F and up
> 20W-20 @ 10 to 80 degrees F
> 10W-30 @ -10 to 60 degrees F
>
> I saw the thread from a couple years ago with a list of oil with high ZDDP content, and the viscosities ranged quite a bit. So far I'm seriously considering the 10W-30 Amsoil Z-Rod which has high ZDDP and is specifically designed for older engines:
>
> http://www.amsoil.com/shop/by-product/motor-oil/gasoline/z-rod-10w-30-synthetic-motor-oil/?code=ZRTQT-EA
>
> To my knowledge, 10W-30 runs as the same viscosity as SAE 30 once warm, so my thought was to stick to as close to the original recommendation as possible.
>
> They also have the same oil as above but 20W-50:
>
> http://www.amsoil.com/shop/by-product/motor-oil/gasoline/z-rod-20w-50-synthetic-motor-oil/?code=ZRFQT-EA
>
> But maybe that is too thick.
>
> Any suggestions on this? There are a lot of different viscosities and we want to make sure we use the correct one. We aren't sure which of synthetics run best in the 403.
>
> Thank you!!
>
> --
> Chris
> _______________________________________________
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| Re: Engine oil, which viscosity is best? [message #212354 is a reply to message #212339] |
Wed, 26 June 2013 13:21 |
jknezek
Messages: 1057
Registered: December 2007
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You will get as many opinions on this topic as we have members. However, since collectively we use many different oils, and few of us suffer catastrophic failures, it's probably safe to assume that the advantages and disadvantages that we all like to harp on are probably negligable.
Personally, I use Mobil1 10W40 Synthetic High Mileage. Mainly because I use it in my own car and it's just easier to keep one oil around. Before I started using the synthetic high mileage I used 10W30 Dino and 10W40 Dino and didn't see much difference. Now that I'm using synthetic I stick to it. Costs more, but I like it in my daily driver.
I also add a ZDDP additive. Does it matter? Probably not. I didn't add it for the first four years I owned the coach and had no problems. I started adding it 2 years ago just for piece of mind. It costs more, but I feel more responsible. Personally, I doubt it makes much of a difference in my non-rebuilt, 85K 455.
Pick an oil you like and use it. So long as it's reputable and correctly formulated, there is a very low probability that whatever you pick will have an outsize contribution to a failure. There are lots of other more likely culprits than a properly changed and filled oil pan on a 35 year old engine...
Thanks,
Jeremy Knezek
1976 Glenbrook
Birmingham, AL
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| Re: [GMCnet] Engine oil, which viscosity is best? [message #212379 is a reply to message #212368] |
Wed, 26 June 2013 15:44 |
sgltrac
Messages: 2797
Registered: April 2011
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Michael,
I think I read the same paper and it was posted here. I believe at the end of his whole "lesson" he stated that he ran 5w 30 mineral oil in his daily driver ;/
Todd Sullivan
Sully
77 royale
Seattle
On Jun 26, 2013, at 12:41 PM, Michael <lilmyk@gmail.com> wrote:
>
>
> I read an extensive article written by a doctor about oils and his collection of Ferrari's. I am not sure where I found the link.
>
> But in a nutshell, he recommended with today's oils the lowest possible first number 0W-XX, 5W-xx and so on. This represents how thick the oil is at start up and directly corresponds to how quickly everything gets lubricated. The lower the number, the quicker the lubrication. As for the second weight, he recommended the lowest possible number required to achieve the required volume of oil being pumped. He used expensive equipment to measure this and not oil pressure. Oil pressure will inherently increase as oil density increases which is not always a good thing.
>
> My last oil change I put in 5W-30 and my pressure according to the possible accurate gauge was above 40psi, it did drop slightly at idle after driving for over an hour, but was 40-50 when under throttle.
>
> I will continue to run this until I notice a substantial pressure loss.
> --
> 1973 GMC 26' Glacier - Unknown Mileage - Has a new switch pitch transmission with Powerdrive :)
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Sully
77 Royale basket case.
Future motorhome land speed record holder(bucket list)
Seattle, Wa.
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| Re: Engine oil, which viscosity is best? [message #212383 is a reply to message #212339] |
Wed, 26 June 2013 16:20 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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For what it's worth, as a personal preference, I generally use heavier weight oil in older engines. I use 10W-40 in my 199,000 mile Cherokee instead of the recommended 10W-30, and 20W-50 in my '53 Willys Jeep CJ-3B, and the GMC.
My uncle used to work at a British Leylend dealer back in the 70s and their oil of choice for all performance applications seemed to be Castrol GTX 20W-50. He changed the oil in my Jeep one time (yes, the same one I have now) and mistakenly put in Gulf 30W. I noticed, on the drive home, the oil pressure was substantially lower than normal. When I called him and asked about it, he realized that he had previously used the 20W-50 in it and asked me to bring it back. He changed it to the Castrol 20W-50 and the oil pressure went back up to what it normally ran at. I have been using either that oil or Valvoline VR-1, 20W-50 in it ever since, for over 40 years and two different engines.
I use Valvloine VR-1 20W-50 in the coach, and have ever since I took it over from the previous owner. That is the high ZDDP content oil that Jim Bounds recommends and uses as well. I will continue to use this oil as long as it is still available at which point I will probably switch to 15W-40 Rotella. Hopefully, if and when that switch takes place, I won't have an oil pressure drop like I did in the Jeep.
I seem to remember hearing Dick Patterson say that the heavier oil is not necessary and puts extra strain on the oil pump and some other oiling system components, but I have always had good luck with it.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| Re: Engine oil, which viscosity is best? [message #212387 is a reply to message #212339] |
Wed, 26 June 2013 16:32 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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I'm particular to Shell Rotella T6 Full Syn 5w-40. The price point is a little less than Mobil 1 products and reviews from Shell (of course) and others are excellent. Since most wear occurs at startup after long disuse, I like the 5w for fast flow. I think 40 is plenty heavy on the hot side and don't want the parasitic drag of a 50 wieght.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Engine oil, which viscosity is best? [message #212390 is a reply to message #212353] |
Wed, 26 June 2013 16:42 |
emerystora
Messages: 4442
Registered: January 2004
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Urban legend. All oils have detergents that keep the passages clean. Regular oil and synthethic oil. Draining regular oil and filling with synthetic oil WILL NOT loosen any crud -- unless , of course, you were using some very, very cheap regular oil that didn't have the right detergent additives.
Emery Stora
On Jun 26, 2013, at 12:16 PM, A. wrote:
>
>
> emerystora wrote on Wed, 26 June 2013 13:06
>> ...I do suggest that you consider synthetic oils through and they have a lot of advantages. ...
> Wasn't there some discussion here how changing to synthetic after close to 100k miles on dino oil can clean out the "protective" layer of crud on stuff like the seals, and then the seals start to leak? It is an expensive proposition to replace the seals.
>
> Urban legend?
> --
> '73 23' Sequoia For Camping
> '73 23' CanyonLands For Sale
> UA (Upper Alabama)
> "Time is money. If you use YOUR time, you get to keep YOUR money."
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| Re: [GMCnet] Engine oil, which viscosity is best? [message #212394 is a reply to message #212368] |
Wed, 26 June 2013 16:54 |
emerystora
Messages: 4442
Registered: January 2004
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That is almost like saying your auto mechanic is giving you advise on your heart and blood pressure.
I doubt that the doctor is driving a 12,000 pound vehicle which gets very hot in the engine compartment.
At the risk of getting a whole bunch of negative comments back to me all I will say is that I would ignore the good doctor's recommendations when it comes to the GMC motorhome. I also doubt that he is taking his Ferraris on 2000 or 4000 miles trips.
Emery Stora
On Jun 26, 2013, at 1:41 PM, Michael wrote:
>
>
> I read an extensive article written by a doctor about oils and his collection of Ferrari's. I am not sure where I found the link.
>
> But in a nutshell, he recommended with today's oils the lowest possible first number 0W-XX, 5W-xx and so on. This represents how thick the oil is at start up and directly corresponds to how quickly everything gets lubricated. The lower the number, the quicker the lubrication. As for the second weight, he recommended the lowest possible number required to achieve the required volume of oil being pumped. He used expensive equipment to measure this and not oil pressure. Oil pressure will inherently increase as oil density increases which is not always a good thing.
>
> My last oil change I put in 5W-30 and my pressure according to the possible accurate gauge was above 40psi, it did drop slightly at idle after driving for over an hour, but was 40-50 when under throttle.
>
> I will continue to run this until I notice a substantial pressure loss.
> --
> 1973 GMC 26' Glacier - Unknown Mileage - Has a new switch pitch transmission with Powerdrive :)
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
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| Re: Engine oil, which viscosity is best? [message #212395 is a reply to message #212339] |
Wed, 26 June 2013 17:33 |
Cadillackeeper
Messages: 464
Registered: October 2012
Location: Fort Lauderdale
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Deisel Oil! 15-40 Will not let you down. I think they have subtracted all they can subtract out of it now "EPA" Big Rigs and Big Blocks need proper oil.Everyone will have an opinion!
There really Is no argument. Joe Gibbs or Deisel
77 455 Elaganza II and 67 Animal, Built 500 Powered Eldo
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| Re: [GMCnet] Engine oil, which viscosity is best? [message #212398 is a reply to message #212395] |
Wed, 26 June 2013 17:44 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
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Well, I did the best part of a million miles in Jetta turbodiesels using Rotella synthetic 15-40. I have only ever seen Rotella synthetic at Wal-Mart, it is normally half the price of other synthetics. I run it 3k miles in the turbomotors, 5k in my normally aspirated, 3k in the GMC. So far, so good.
--johnny
________________________________
From: anthony ezzo <ezzo@earthlink.net>
To: gmclist@temp.gmcnet.org
Sent: Wednesday, June 26, 2013 6:33 PM
Subject: Re: [GMCnet] Engine oil, which viscosity is best?
Deisel Oil! 15-40 Will not let you down. I think they have subtracted all they can subtract out of it now "EPA" Big Rigs and Big Blocks need proper oil.Everyone will have an opinion!
There really Is no argument. Joe Gibbs or Deisel
--
77 455 Elaganza II and 67 Animal, Built 500 Powered Eldo
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Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: [GMCnet] Engine oil, which viscosity is best? [message #212427 is a reply to message #212392] |
Wed, 26 June 2013 21:50 |
lw8000
Messages: 201
Registered: July 2012
Location: S.E. Michigan
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| emerystora wrote on Wed, 26 June 2013 16:50 |
>
Amsoil is a synthetic oil and it would not have as much VI improvement additive in it (VI=fiscosity improver).
|
Understood... so is this good or bad for a GMC?
| emerystora wrote on Wed, 26 June 2013 16:50 |
>
There are also those that are concerned about the zinc levels in the GMC motorhome oils. The 10 w 30 doesn't have what most people think we need.
|
Just to confirm, you are talking about standard dino 10W-30, correct? The Amsoil claims to have high levels of ZDDP... but I'm still doing some research on just how much it has.
Chris S. -
77 Kingsley, 3.70 FD, mostly OEM -
S.E. Michigan
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| Re: Engine oil, which viscosity is best? [message #213590 is a reply to message #212339] |
Sun, 07 July 2013 10:19 |
lw8000
Messages: 201
Registered: July 2012
Location: S.E. Michigan
Karma: 1
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We've decided to give the Amsoil Z-Rod 10W-30 a try. We've received very good feedback on using this oil in the 403. Will post back any further feedback on it. Thank you very much!
--
Chris
Chris S. -
77 Kingsley, 3.70 FD, mostly OEM -
S.E. Michigan
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My understanding is the Amsoil Z-Rod 10W-30 is a direct replacement where conventional 10W-30 was recommended in older engines.
