: 79 deville: 10-40 or 10-30 and air filter questions

03-24-05, 06:12 PM
'79 7-liter 4bbl engine with 160k miles. should i use 10w-30 or 10w40? now, they both run about the same, but i would like to know which one would be better for the long term. my mechanic has always said 30, because thats mostly what they had back than. friends with other big old cars say 40, because its..big and old. another question is my ghetto air filter set up. its suppoused to have a J or something shaped fitting to put the air fliter on. mine doesnt, its just a straight peice of screw that, when the air filter cover was flipped upside down when i got it, exposes alot of the filter. some people like it like this (supposedly more power, deeper growl), but im wondering what it would be like to have it the normal way. would it actually be better? any response would be great.

ps: getting windows tinted: 20% up front, 5% back windows, leaving rear blank. would this look dumb? or how about 20%, 5%, than 20%?

03-24-05, 07:25 PM
I had a 79 Olds 403 Shaker scoop UNDER the hood of my 76 Delta 88!!

So how is that for the ghetto scoop?

It was better on power because the opening on the scoop opened up to the cowl under the hood. Man did that 350 Olds sound awesome under WOT!!

My thougts are this on oil (yes, feel free to disagree with me all!!)

10W40 was shy'd away from because of the higher additives that were rumored to cause ring deposits (sticky rings), so 10W30 became the norm, then with fuel economy being more an issue, 5W30. The 30 is the hot viscosity weight, so that is really all that matters to the engine for clearances. In theory, at hot temp, there should be no viscosity differences to the engine.

So personally, due to additives, of the 2 choices, I would run the 10W30. But, because the engine is older and higher miles, the 10W40 would benefit oil pressure if it is getting low due to wear and tear. Your call. If oil pressure is LOW LOW, then consider 20W50 for warmer months, that is mainly for a worn engine. A good comprimise that is "Bbob approved" is 15W40 Delvac/RotellaT oils. It is likely what I would run in an older engine if it was my choice. Or if you have lots of $$ to spend, RotellaT or Delvac (forget which) has a 5W40 Synthetic. But likely the benefits aren't worth the cost. ($4-$5/qt)


Night Wolf
03-25-05, 01:26 AM
I remember hearing that 10W-40 in these aren't good... causes the lifters to starve of oil? also some of the oil passages are kinda tight, and the 10W-30 flows better.....

I have use Mobil 1 synthetic 10W-30 in my 425 since I bought it... I put 4k miles on it so far and it dosn't leak, burn or even use any oil..... I would stick with 10W-30....

03-25-05, 01:52 AM
The only caution I would have on using synthetic on a older engine tat never had it is the ester and diester base stocks of synthetics are much more "detergent" if you will, they clean the engine better (or so I am told, and after seeing the inside of my 4.9L valve cover, I believe it), and synthetic oils tend to clean a lot of the old sludge dino oil built up in the seals and gaskets, forming leaks. Compatibility isn't an issue, just the potential for leaks.

I am doubtful the 10W40 would have any issues getting in the oil passages, the passages aren't that tight. Most engines I have torn down (GM) send oil to the lifters from the main crankshaft oil feed. In high oil pressure modified engines and engines that have poor oil return from the heads, it is common practice to add oil restrictors. This is two fold, keeps too much oil from getting to the heads and getting it trapped there (in poor return engines like Olds V8's and AMC V8's) and to keep more oil on the mains and rod bearings. Again, modified high rpm engines that see 6000 rpm and above for sustained driving....

In summary, the passages are huge in comparisson to the oil.


03-25-05, 07:01 AM
Anything but 10w-40.

03-25-05, 09:33 AM
I've used synthetic in the 425's and 500's, and it usually resulted in leaking gaskets! Unless you want to change out gaskets, stick with regular oil.