Oil for 70's big block Cadillac?

[60cyclehum]

Just picked up a '79 Cadillac, low miles, 425 ci flat tappet cam engine. I've owned many of these, consider them bullet proof motors, but it's been 10 years, and oil sure has changed.
Been doing lots of reading, and haven't come up with a definite yet, so thought I'd post here.
Bit worried about the lowered ZDDP levels and the flat tappet. Low revving, high torque motor though- will never see over 5Krpm. Motor runs great, very strong, no smoke just a puff on start up, looks like it uses very little to no oil. Bit of sludge in there, got a bottle of auto-rx in right now, to begin cleaning it.
What oil do you guys think I should run in her? Or just add ZDDP with "any" oil?

 

[Drew99GT]

Any mixed fleet heavy duty engine oil, such as Rotella or Delo would work. 10w30 if you can find it, or 15w40. Thats guaranteed to not have low zinc. Or, Valvoline VR-1 10w30. Loaded with zinc.

 

[60cyclehum]

I was thinking along the same lines, but have heard even the HDEO's have lowered the zddp. Never tried the Valvoline, I assume it's fine for everyday use, as far as a robust additive package?
Haven't ruled out synthetics, but really not sure as the engine does not have nearly the tight tolerances of modern engines......

 

[72customdeluxe]

Rotella still has around 1200 ppm zinc. It's great stuff, use it with confidence. Also, stock engines with mild cams and stock spring pressures don't have cam failure nearly as often as with aftermarket cams and springs or a factory performance cam.

 

[ramblar]

Pics of car?

 

[60cyclehum]

1200 sounds safe. I saw the mobil 15w40 has about the same amount. Does the Rotella 5-40 syn have the 1200 also? 15w40 would be OK for summer, but I'm in KY and it gets fairly cold in the winter (hits zero here and there). Need a good 5-30 or 10-30 for the winter.
No pics yet. Just got it two weeks ago, had the worst oxidized paint I had ever seen ,but straight and clean, no rust, perfect interior. Spent three days wetsanding/buffing and the original dark cedar metallic looks great. 64,000 miles.

 

[JT1]

Rotella syn 5-40 has more zinc than its conventional brother on average.

Not nesscessary for a stock cam with weak springs.

 

[BuickGN]

Stock valvetrains will still experience failure with low ZDDP, just not as often as an aftermarket cam and springs. Why take a chance?

If you wanted a good cheap synthetic, Amsoil ACD is nearly bulletproof with lots of ZDDP. Or if you have the money, Redline is loaded with ZDDP and moly.

 

[60cyclehum]

I wondered that, but better safe than sorry. These old Caddy motors can go 400K with proper maintenance.

 

[JT1]

Mobil 1 High Mileage 10w30 or 10w40 would also be a good choice. Great add pack, lots of zddp, calcium, moly, and seal conditioners.

 

[60cyclehum]

So you guys think syn would be good for this old motor? I really like the syn's I've been using but am still on the fence for using it in the Caddy. If I used it, I would have an extended OCI- at least 6-8 months, would seem a waste of money +oil not to. But what about the fuel contaminents from an older carbed engine?

 

[JT1]

Originally Posted By: 60cyclehum
But what about the fuel contaminents from an older carbed engine?


All the more reason to use a synthetic.

 

[60cyclehum]

Better to leave them in longer with a synthetic, that can, supposedly , handle it better. Or to change it out every 3 months with Dino?

 

[BuickGN]

Originally Posted By: 60cyclehum
Better to leave them in longer with a synthetic, that can, supposedly , handle it better. Or to change it out every 3 months with Dino?


That's a good question and if it were mine, I would go with changing it more often though I doubt either way would hurt anything.

 

[addyguy]

Member on here has exact same car as you, and uses RTS 5W-40 in his.

 

[Steve S]

Run a HDEO of proper viscosity. Run the oil of your choice then run a uoa to see if there is a problem with feul dilution. I would bet there will not be a problem unless the carb is messed up.

 

[KW]

I'd run Rotella T 10W30 or 15W40 in the 425 BBC (Big Block Cadillac).

 

[mechtech2]

Diesel 15-40 oil is perfect for that old engine.
Synthetic oil has no magic properties that help with gas dilution, so depending on how it is driven, change the oil as needed [more often].
Valvetrain? It is already broken in . Use can use any oil now, if you wish.

 

[Jaymus]

I wouldn't feel comfortable using a 15w40 in the winter.



http://www.youtube.com/watch?v=_qRXG2mf9is



I know that's not 'scientific', but it's something you can see with your own eyes. 15w40 vs 5W-40.