Which engine-oil for 1979 Eldorado?

[T.Skytte]

Hi all,

I'm about to do an oil-change on my 1979 Eldorado (5.7L EFI), which has done about 55.000 miles and is in very good repair
I recently acquired it and oil seemed 'fresh' so believe previous owner did recent change but changing it anyway as I have no way to know what is in there.

Service manual says GM 6136-M spec. But how does that relate to modern oils?
I live on a cold-ish area (-10C in winter to 23C summer) but soon moving to southern Europe (+10C to 35C).

What oil would you put in there and why?
Thanks a bunch.

Regards,
TS

[64\/54Cadillacking]

A 5W30-10W30 is ideal, but I'd recommend a 10W40 to help with the warmer temps in the coming months.

[bcroe]

I have been using 10W40 in engines identical to yours for the better part
of a million miles, with good results.  However since they reduced the zinc
in oil, I have been adding my own (break in additive) again with good results. 

Don't forget the filter, lately I use K&N.  79 Eldo owner for decades, Bruce Roe

[T.Skytte]

Hi 64CaddieLacky and bcroe,

Thanks for your replies! I guess it's 10W40 then 

Would you use synthetic or conventional? I want to maximize the engine-life obviously. I have no idea what's been in there previously.

@bcroe: Would be great if you can let me know what zinc additive do you use? and what K&N filter? Manual says AC PF-45 but that's not made any more and am having a little difficulty in finding a compatible filter (ACDelco says PF-61, or 61E or 61F but I don't know the difference).

Best regards,
TS

[35-709]

Adding zinc (ZDDP) to your motor oil has been discussed here several times and at great length.  Be careful how much you add to what oils, too much ZDDP can be as harmful as not enough.    Some oils still contain adequate amounts of ZDDP.  I use Mobil 1 15W-50 which is for older engines and has enough ZDDP but other Mobil 1 oils do not.  There are excellent oils available on the internet and at some auto parts stores that do not require added zinc, I am happy with the Mobil 1 and stick with that. 

WIX oil filters are among the best you can buy, they make the NAPA Gold oil filters.  The correct NAPA Gold filter number for your 429 engine should be 1049 and should be in stock at your local NAPA store or certainly available overnight.

[bcroe]

@bcroe: Would be great if you can let me know what
zinc additive do you use? and what K&N filter?

There are some quality oil filters as described above; probably even more that
are not so good.  I started using K&N believing they are good, and this series
has a 1" nut for your wrench which helps me a lot on a certain import.  For the
79 Eldo I believe K33HP2006 works, the slim dia gives extra clearance.  Where
clearance isn't a problem, HP2003.  I have a K&N air fiter too. 

No expert on oil here, but I know a couple things.
1. They didn't put that zinc in the oil before for nothing; ancient engines didn't last.
2. In my life a lot of people said "it won't matter" who actually didn't know, or
      were outright liars. 
3. I got a small block Olds A1 a decade ago (70K miles); started adding zinc to my
      oil/filter every 3000 miles.  At 210K I can't detect any wear from new condition. 
Study and draw your own conclusions.  My pure guess is to add 1.5 oz of GM
EOS assembly lube per qt of oil, #88862586

A few words of advise on the 79 E cars, which I have driven for 3 decades. 
If the plastic toothed timing chain set is original, get it replaced before it
comes apart and mucks up your engine;
The EFI runs at 40 psi; every bit of rubber touching fuel should be renewed to
avoid a leak and big fire;
The 70s EFI love to burn out the ECU pin that feeds the fuel pumps, you can
avoid this failure mode by adding an external relay to protect the electronics
as shown in Dec 2010 SelfStarter or my PHOTOBUCKET user bcroe first album;
Check that aluminum intake manifold for coolant seeping;
If you notice sloppy shifting, its probably from a broken accumulator spring under
that big round cover on the trans drivers side.  Best fix is the mild shift kit that
replaces the spring and cleans up shifts without harshness. 
good luck,
Bruce Roe CLC # 14630
       

[T.Skytte]

Hi all,

Thanks so much for all the recommendations!

I have spent the last couple of weeks going down the oil-rabbit-hole 
So now am more confused than ever.
I kindof decided on Mobil1, but it seems the product-names are different here in Europe so difficult to figure out which one! (i.e. their US site shows zinc levels etc for various products, but not their EU sites). So I can't compare.

Form a 'USA shop' (specialising in stuff for US vehicles) here I am able to get 'Mobil1 Full Synthetic' (that's all it says) 10w30 and 15w50.  Does anybody know these specific ones?
As I am going to be living and driving in southern Europe would 15W50 be recommended? Anybody know the Zinc levels for that one?


It also seems Castrol is way more easy to get hold of,  would anybody know any (Europe specific!) Castrol fully synthetic 10w40 with high Zinc levels?
I think they one named Edge Syntec 5w50 specifically for flat-tappet applciations but am not able to find it (did the product name change)?


Extremely frustrating that they market under different names and seem to keep changing them... urghhh.


Best regards
TS

[35-709]

As I mentioned, I use 15W-50 Mobil 1 exclusively in my older flat-tappet engines, 1300 PPM Zinc.  10W-30 has 900 PPM, a little low for my personal taste.

You might find this Mobil 1 site useful, updated March 2017 ---
https://mobiloil.com/~/media/amer/us/pvl/files/pdfs/mobil-1-oil-product-specs-guide.pdf

[T.Skytte]

Hi 35-709,

Oh right I see, sorry somehow I missed that. I guess I will go for that then.
Thanks!

Incidently, I did see that mobil specs guide before.  The frustrating bit is that most of those products can't really be found in Europe or they're called something else here. But anyway the 15w-50 I am able to get from a US specialist that imports himself so will get that one.

Best regards,
TS

[35-709]

You're welcome and best of luck!

[Carl Fielding]

HI Tobias ! If you would like to know which oil to use and why , please look up :   selection of the Right Motor Oil- draft 17   It is a 33 page document written to give the tech minded non-petroleum engineer enthusiast better knowledge than the other 999 out of a thousand people who have not read it. It will give you more knowledge than trying to read API and SAE tech journals. Unless , of course , you are a petroleum engineer who really can understand tech journals. The author , Richard Widman can , and does so , and writes to the benefit of all of the rest of us. I have had to read it 2 times. I have had long held misconceptions corrected. You will also. For example , there are different degrees of syntheticity, Castrol is at the bottom , Mobil 1 about the middle. Perhaps you would like to use an oil right around the top of the syntheticity list. They make a very modern product with just the right amount of zinc and phosphorus for flat tappet engines. There is also an explanation of the temperature/viscosity envelope. In it you will infer that a 20W/50 oil seems to be close to ideal for hard fast driving in temperatures of around 135 degrees f. with a very high sun angle beating down on hot black pavement. I thusly played it safety first on a Summer drive through Death Valley in a big 3/4 ton brand X van with a 100,000 mile plus 460 cu. in. engine. No problems. Temperatures didn't get much above 120 that day.

Having lived in Denmark, and having spent delightful time on the French Riviera, I fully realize the climatic differences. However , until global warming turns Europe into Death Valley , I will add my viscosity recommendations to those of CaddieLacky , and bcroe. I don't know if they have read "Widman" yet, but I expect that after you do , you will join us. Oh : do you have Amsoil available ? Niether Widman nor I represent Amsoil in any way whatsoever. It turns out that Amsoil sits right around the top of the syntheticity list. I am very curious about the new Pensoil product made from Natural gas. Perhaps we should email Richard Widman.  I wish you a wonderful life on the Riv'. I sure had one there ! But of course my girlfriend Grethe was Danish !  - Carl

[Carl Fielding]

Oh , also , I have called Mobil one to ask them their recommendations for the specific application I needed. They said follow the manufacturers instructions. Seems to be good advice ! Who would know more ?  And of course with the best modern synthetic oil , your engine will have virtually no wear on any lubricated part. Will you be going South into the hotter parts of Africa ?  - Carl

[35-709]

I would venture to say that even at "about the middle" Mobil 1 is several magnitudes of quality above what was generally used in the '70s.  Even though Mobil 1 was introduced in the '70s as an early 5W-20 synthetic oil it caused a stir but was not particularly popular.  If Amsoil is easy(er) for Tobias to get than Mobil 1 and it has ZDDP in the same approximate range, then by all means buy it.  However, whichever is used it will be far superior, in my view, than what that engine was getting back in the day.

[dadscad]

I have been using Amsoil lubricants and filters in everything I own since 2002. I will agree that their products are top notch and will do the job. I use their HDD 5-30 oil along with a wix filter in my 63, plenty of zinc and phosphorus to protect the engine. They offer other weights with plenty of zinc and phosphorus that will give you a choice of viscosity if you don't want to use a 5-30 oil. Their ATF in the hydra-matic made a world of difference in the transmission performance,  the severe gear 75-90 in the differential works great, too. It is easy to order direct from Amsoil and have it shipped to your door. My orders are usually delivered in a couple of days, depending on where you live yours may vary. You don't have to make a trip somewhere and fight traffic and check out lines, just open the door when the UPS man rings. Really convenient for me.

[Carl Fielding]

35-709 is 100% correct. I have used a lot of Mobil 1. A very fine product , which in the old days was the only game in town. Some towns did not even play at all. I forget where I have posted what , but did I mention here about the Montana farmers ? I needed Mobil 1 a long time ago in Billings , MT. Only place to get it was the feed store. My purchase there stimulated a synthetic lubricants discussion.The gents said that when they started using synthetic grease in their heavy agricultural machinery, wear ceased to be a maintenance factor ! I believe the military has been using synthetics since WW2 . Just read "Widman" , and take your pick.  - Carl

[bcroe]

I have been using synthetic in differentials.  But is was so expensive I couldn't use
it in engines.  The supplier proposed very long intervals between changes to make
it affordable, because it doesn't wear out.  But oil gets dirty, I don't want that buildup
in my engines.  They proposed using a bypass filter to get 1 micron particles, in
addition to full flow filters getting 10 micron.  But that is a lot of trouble, and a
filter will not remove any acids, etc.  So I have stayed with 3000 mile oil and filter
changes; my engines easily outlast the body after 200,000 + miles. 

Good to know the synthetic oils have maintained the zinc level.  How is that discerned?
It would be great of those of us of the 999 could hear a half page what-to-do
condensation of the 33 page document. 
Bruce Roe

[dadscad]

I went out on Amsoil's web site and quickly found this technical bulletin on flat tappet and camshafts. This bulletin lists their oils suitable for this application with a brief discussion on the issue. If a person signs up as a preferred customer member, they purchase at wholesale pricing.

Link to pdf bulletin.

http://www.amsoil.com/techservicesbulletin/MotorOil/TSB%20MO-2007-08-08%20Flat%20Tappet.pdf       

Link for other technical bulletins you might find interesting.

http://www.amsoil.com/technical_service_bulletins.aspx     

[Carl Fielding]

Hi Bruce ! Yes , Widman does have a simple flow chart , a block diagram kind of presentation, for those who like to just get to the bottom line. But I don't think that is exactly what you are getting at. You seem to me to be at the top 1 in 1000 analytical car guys. I would think that you would digest the material more quickly than most. As I mentioned , I had to read it twice. I should go back over some of it again. I have difficulty concentrating these days. That is why old dogs have trouble learning new tricks.

I have also wondered about acidity in stop and go , and repeated warm-up cool down cycles. We have all heard something about the publicity test Mobil 1 ran , around the world in 41,000 miles with 2 oil changes. But ? Lesser known was the test Hot Rod magazine ran perhaps a little over 30 years ago. Dismantled a Chev 350 and measured and mic'd everything. Reassembled , ran 1/4 million miles on 10 synthetic oil changes. Tore down and measured zero wear whatsoever on any lubricated surface. Recommended not to change to synthetic on a new engine until 5000 miles. Synthetic oil would prevent the polishing of cylinder walls. Some huge engines using oceans of synthetic oil never change. Periodic oil analysis determines condition. Both full flow and bypass filtration is used. Automotive full flow filtration is in the 20 - 25 micron range. Bypass can filter down to 1 micron , but is often coarser. Although carbon is quite hard , 1 micron is so fine that it passes the bearing clearance on a film of oil.

I do believe that all modern motor oil is very good. Is "very good" good enough ? There can be no doubt that the best synthetic is a superior product to everything else. Does it matter if you change oil every 3000 miles to the same less than synthetic oil ? Will there be a difference ? Any risk ? Which is better for your engine : change out your "crippled" non-synthetic mixture every 2-3000 miles , or your engineered , what's the word ? Iso-polymeric ? (Hmmmm ... Is that a word ? Anyway what I am trying to say is a "pedigree" oil , one in which every polymer chain is exactly the same as all others. A complete hard-working macro-molecule , with no broken , incomplete links. Present in non-synthetic oil , those incomplete links are floating around looking for a "hook-up". Unfortunately , no match made in Heaven , diabolical oxygen rather makes a "marriage of convenience". That oxidation reaction is a type of "burning". It then does not do much good for you. A real waste.) , superior oil every 10-12,000 miles ? How much does any of this conjecture matter ? Today , tomorrow, next year ; maybe not that much. Maybe not. But I was talking to Paul about all this while seeking shelter in the CLC tent during the Great Hershey Flood of 2013. At least the synthetic addict that I am , he points out that "all engines have hotspots". What lubricant would you want at a hotspot ? Oh , and speaking of flashpoint : what about a bad day ? Raise your hand if you have ever overheated your engine , please. Um , just a little , was it ? Or did it get considerably more hot than that ? I know I have written somewhere about the time I was driving hard and fast in my '76 Eldo. Very hot So. Cal. Summer day. It had never before worked so hard. Got VERY hot. Hot enough to crack both exhaust manifolds. Turns out there was enough radiator mung to cost me some money. But the mill itself survived well. It did have a belly full of full synthetic 20W/50 in it for hot summer travel. That is why that 500 has carried me scores of thousands of miles since then. I am a bit of a gambler. What about you ? Wanna increase your odds ? Read "Widman". And let's try to compose some CLC questions for Richard Widman who invites correspondence.  - Cadillac Carl

P.S. : Bruce , you are a vastly superior engineer to amateur me. You are also a much better tech writer. Please consider gliding your way through "Widman". For you , it should be as easy as "Tom Sawyer" , and far fewer pages. Remember , this has been GREATLY SIMPLIFIED from the ponderous imponderable tech journals which might as well have been written in Aramaic for all a mere mortal can make of them. 93% of all the car people who read it understand all of it. You are FAR from the 7%. A good read. Be assured , we are not talking about "Radiative Transfer" (Remember your post-grad Physics ?) , here. Nor even a light jaunt through "A Brief History of Time". Take notes , and CLC and all other car clubs will be grateful if you produce a condensatIon from the 33 pages for the 7% , or those who just cannot be bothered. Make sure to keep Richard in the loop !  With great admiration , CC

[7gen]

The FSM for my 76 Eldorado convertible says to change the oil every 6000 miles. On SE mineral oil, no less. I found that a startling recommendation for 1976. So why the recommendations I hear about 3000 miles on modern mineral oils in these cars? And why only 5000 miles on a modern synthetic, which must be unbelievably better than an old SE mineral oil from back in the day?

Where are these mileage recommendations coming from? Is there some research that indicated that Cadillac's oil change interval was wrong somehow? Is the 3000 mile mark just so taken for granted that no one questions it anymore? Not trying to be a nudnik, just wondering where these mileage recommendations come from that are so different from the manufacturer's.

[bcroe]

Industrial engines get the oil TESTED regularly to see if it needs changing.  A good
engine might run a very long time on the same oil.  But most owners don't test the
oil, and besides the marginal designs could burn a lot of the oil from wear or past
abuse.  So then its a guessing game, HOW OFTEN IS OFTEN ENOUGH? 

My early engines used a lot of oil, and no doubt a lot of bad stuff went past the
rings into the oil too.  There was a lot of wear.  When I started at 40,000 very hard
miles a year, I changed the oil every 2000 miles.  By the end of the 70s, apparently
from emissions requirements, engines were doing much better.  If the filter is going
to be changed at 3000, hardly any more investment to do the oil too.  So until I start
testing my oil and use bypass filter systems, I hope 3000 miles is GOOD ENOUGH.  I
have no doubt they could be driven 6000, with quarts added; I'll wager there would
be more wear than at 3000. 

Her Honda goes 7500 miles; I'll allow that because it uses practically no oil in the
interval.  And it can be replaced.  Bruce Roe