: Correct oil for sixties seventies & eighties Caddys

425 Dual Quad
09-14-10, 05:03 PM

What spec would yo say the correct oil should be for sixties seventies & nineties Caddys - 429, 472/ 425 engines and the LT1s in the '94 Broughams?

I'm asking mainly becuase of the zinc issue for upper head lubrication - an oft discussed issue 2 years or so ago.
My motor factors her is into classics and has offered to track some down for us sixties and seventies American car owners over here but I need to tell him what.

At the moment I just put 10w40 dino oil in the '73, '77 and '79 and semi synthetic 5w30 in the '93 and '94 Broughams.
However if there is a specific spec of oil he should hunt out and buy in quantity for us please let me know. He can get Gulf and Valvoline oil relatively easily.

Thanks all! regards, Nick

09-14-10, 05:59 PM
Valvoline VR1 is an excellent, ZDDP-laden oil. The 10w-30 should be easy enough to come by.

09-14-10, 06:25 PM
Easier to transport would be GM EOS or Lucas engine Break In additive. You need 1/4 bottle of Lucas with every oil change so that will go a long way.

You do not need a ZDDP additive in an engine with a roller lifter cam like the 93 (L05) or the 94 (LT1).

425 Dual Quad
09-14-10, 08:13 PM
Hi - long time! Thanks - I was thinking I was OK with the LO5 and LT1 motors but it was the old yatchts I was concerned about. Plently of seventies Eldos and 77-79's with 425s and a good few 429 and 473 powered cars. We are nto allowed to ship oil in by air. it has to be sea freighted so I'm hoping I can find the right formulation made in Europe. It seems I can - at 10 a litre for the heavier weight 20w50 racing oil. It also seems the heavier weight oil is used for racing and the high zinc content ruins the cats. I don't think the racers are overly concerned about that!

Here's an intersting link I dug up.


regards, Nick

Bicentennial Cadillac - thanks too.
What weight would you put in these older engine now given they've now done 70-90 k miles.

09-15-10, 01:28 AM
Royal Purple, is still a SL rated oil, so it has more Zinc and Phosphorous than an SM rated oil. I remember speaking to customer service from RP, and they told me that there Racing Oil has a very high ZDDP package, way higher than there standard line which equals even better protection.

So any of the better premium brands like RP, Redline, Mogul, will usually have higher levels of additives than other brands, mainly because of the base oil content and above normal levels of anti-wear agents.

09-15-10, 04:39 PM
I'm surprised Jay didn't answer with "the slippery kind." :)

09-16-10, 11:56 AM
Forget the 5W30! It's like lin-seed oil! Forget 10W30 for that matter, too. I would be running 10W40 in an LT-1 if nearing 100,000 miles or over. All of our big, pushrod, carbed Cadillac big blocks are running high-zinc 15W40 heavy duty oil normally for use in diesel motors. Nothing lighter than 10-40 though guys! Can't speak for the 4100's though...

09-16-10, 02:02 PM
All of our big, pushrod, carbed Cadillac big blocks are running high-zinc 15W40 heavy duty oil normally for use in diesel motors.

Same for me on all my classics.

09-16-10, 02:22 PM
do you guys run these thick oils in the winter also? I know you probably don't run the old caddies in the winter but isn't it bad to run thick oil in the winter? :o

Just wondering because I was told it was at one point in my life.

Also, what brand of 15w40 and where do you get it? Interested now :)

425 Dual Quad
09-16-10, 03:00 PM
so 15w40 for the sixties and seventies cars and 10w40 for the 93 and 94 Fleetwood? The '94 has just turned 100k and the 93 is on about 130k. I still use 5w30 in both and run them all year round and change the oil every 3000 miles religiously
regards, Nick

09-17-10, 11:24 PM
Curious on this - I run 10w30 in the wagon. Should I step it up to 10w40, Jay/Geezer? I'm due for an oil change next week anyway.

09-20-10, 05:34 AM
I have noticed certain oil brands 5W30 oil varies in thickness. I compared Royal Purple 5W30 motor oil to a 5W30 Pennzoil Platinum, and the RP oil was a lot thinner than the PP, almost like water. The Pennzoil looked and felt much thicker when pouring it into my Cad. So thats one factor people could take into account. My guess because the RP oil was so thin, this helps with oil flow, especially in cold climate areas, and it helps relieve stress and pressure on oil pumps in older cars.

10W40 is fine, but not necessary for increased protection, I look at oil specs to determine the oils performance instead of weight alone. Flash Point, Viscosity index, and Oil Base Count is a good way to know how well that oil can hold up overtime to withstand the punishment of stop and go driving, high engine temp that can cause shearing, and overall longevity. Usually the better the specs, the better protection you'll have inside your engine.

Pennzoil Plat and Ultra always receive high praise, because of how great the oil performs on oil analysis sheets that people upload to Bobsistheoilguy.com

02-01-13, 11:07 AM
Sorry to "mine" the old threads but didn't want to start a new one just for this.

I received it today from my Hemmings Daily newsletter. Thought it may be of interest. :noidea:


02-01-13, 11:36 AM
that was a great read. :)

Thanks for sharing

02-01-13, 11:58 AM
Thanks for sharing that.

The Ape Man
02-01-13, 05:13 PM
Weighing in on only the 368 425 472 500 here. These engines are very easy on the valvetrain. They do not fall under the same umbrella as a high performance engine with heavy valve springs and high lift cams.

Another consideration is older cars that use carbonators will crap up engine oil with unburned gasoline long before their modern fuel i njected counterparts.

Better to change the oil more frequently even if it is done with less expensive oil.

Alwars used 10w-40 or 15W-40 in my Cadillacs. All the good ones were highway driven and did not need topping off between oil changes. Try that with 5W-30.

02-01-13, 06:37 PM
I always use whatever oil the car says to. 91 Brougham is 5W30. Older ones I'd be generally using 10W30.

02-02-13, 03:52 PM
I should probably change the title of this thread. The ZDDP levels are only relevant for flat tappet cams, and none of the 90s Cadillacs had them. All the Chevy motors that were used in the 90s (L03, L05,, LT1) were all roller cams.

02-03-13, 04:56 PM
So I have been using Walmart dino 10w-40. Last time, because I wanted to try it, I also put in some of that Marvel Mystery Oil. Haven't noticed any ill effects yet.

Maybe I'd be better off with some of the Lucas additive? Running your normal 307 in my 88 Brougham.

02-03-13, 05:59 PM
There's a bit of a grey area with flat tappet cars that still have cats. The elevated ZDDP levels are bad for cats. I would probably just stick with regular oil. Why are you using 10w40 instead of 30?

02-04-13, 10:23 AM
Why are you using 10w40 instead of 30?

Quite honestly? Because that's what I've always been told to use by family.

I have always figured that the thicker viscosity was perhaps better for our very hot Florida summers.

02-04-13, 08:41 PM
I mean this with zero disrespect, but have you considered the possibility that the engineers at GM might know more about what viscosity oil to run in your engine than your relatives? At the least, check your owner's manual and see what it suggests for your climate.

02-04-13, 09:04 PM
I've considered it, sure. :) I'll have a look.

02-04-13, 09:14 PM
I mean this with zero disrespect, but have you considered the possibility that the engineers at GM might know more about what viscosity oil to run in your engine than your relatives? At the least, check your owner's manual and see what it suggests for your climate.

I agree with using the oil recommended.

That said, I wouldn't be so positive that the GM engineers know more than his relatives.:hmm:
Having owned GM products almost exclusively for 37 years and selling them for 6 years I have seen some things come out of GM Engineering that would make me doubt you premise.:lol:

02-06-13, 04:33 AM
I'm not seeing anyone else mention it, so i'm going to throw out that i Use Mobil-1 high mileage 10w-40. I would say it works great, but what exactly does that mean when you say that about oil?? If the engine is still running then, uh, yeah, i guess it is working great!! However i can say that the stuff has served me well in some other vehicles which have been around for ages as well.