15w40 oil?

[rcool217]

I had a flickering oil pressure light only at idle, so I put in some Rotella 15w40 motor oil on my next oil change. After a few days the light stopped coming on and all was well. Will this hurt my engine to continue to run such a thich oil viscosity?

[epricedright]

I use it in mine, but I have a 4.9 with the main bearing thump and it helps that. Not sure about the n*.

[JimD]

I had a flickering oil pressure light only at idle, so I put in some Rotella 15w40 motor oil on my next oil change. After a few days the light stopped coming on and all was well. Will this hurt my engine to continue to run such a thich oil viscosity?

There is little to no risk using Rotella or other non-starburst symbol oils in a pre-2000 engine. In fact, there are some benefits that involve higher levels of ZDP in non-starburst oils compared to starburst oils.

If your cold weather starting is not greatly affected, use it. Too bad it is not commonly available in 10W-30.

I have been using up a supply of starburst "SL" 10W-30 in my '98 engine. Advance Auto has Castrol Tection 15W-40 on sale right now for $21.00 for three gallons. That compares to the house brand of starburst 10W-30 at $18.96. I plan to buy a supply of 15W-40.

On the other hand, maybe your oil pressure switch is failing??

[rcool217]

I thought the switch was failing also but it was like a miracle cure once I put in the 15w40. I have read a few other posts here with the same results as mine all with 96 model cars. Maybe its a 96 model year problem or something.

[BodybyFisher]

I heard that using *W40 anything in a NS was not advisable. When I first read your complaint, I thought, you might have a bad pressure switch or connection, as JimD did...I would check your pressure switch

However if JimD states that there is little or no risk using it, I would go with that...

Its possible that your oil had become diluted and thinned out and an oil change using 10W30 would have solved the problem.

[JimD]

Here is a part of a much longer seminar on the subject of API oil grades and starburst oils vs. diesel spec'd. oils. Some will recognize the writing style.

"....

More modern, current production engines are designed to

run with the minimum ZDP oils and friction modified

oils. Clearances are changed, designs are changed to add

roller followers everywhere that are not ZDP dependent

for preventing wear, wear surfaces are hardened where

necessary, etc.....

Older engines designed for the SF and SG oils that had

more ZDP in them are not as well protected against ZDP

depleted oils.

So...technically the older engines should be OK with the

new SM oils since the SM oils "technically" supercede

the older oils and are backwards compatible. But the

newer oils probably are " barely" adequate in terms of

anti-wear additives such as ZDP. If the engine is

perfect inside it will likely be fine. But if the engine

is marginal for wear the ZDP depleted oil MIGHT cause a

problem and accelerate wear. Certainly you would not

want to use the newer ZDP reduced oils for long change

intervals in the older engines.

An older 93 Northstar, for instance, has 32 rubbing

element tappets (flat tappets) that require much more

ZDP for protection against wear than the 2000 and later

Northstars with roller tappets.

If you want to be sure your engine has the best wear

protection you can do two things. One, use one of the

non-"gasoline engine" oils such as the diesel Rotella or

Delvac or Delo oils. Those oils have much more anti-wear

protection since they are also certified for diesel use.

The other thing you can do is to spike the oil you are

using with extra ZDP by adding a pint or quart of GM EOS

(General Motors Engine Oil Supplement). The EOS is

available at any GM parts counter and is sold as an

assembly lube. It is basically plain motor oil with a

high concentration of ZDP that will fortify any

crankcase fill with the extra ZDP desired for more

anti-wear protection. It is the only oil "additive" I

would ever recommend as it is specifically designed for

this purpose.

...."

[BodybyFisher]

Thanks Jim

[MAC]

What happens if the oil pan is leaking so bad you add fresh oil every 400 miles? I guess this means the system always has a fresh batch of ZDP. So much for Rotella.

[JasonA]

I thought the switch was failing also but it was like a miracle cure once I put in the 15w40. I have read a few other posts here with the same results as mine all with 96 model cars. Maybe its a 96 model year problem or something.

These switches are set to close at a relatively low, and very specific, oil pressure. Like 4 or 5 psi at idle. Any slight variation in this can cause the light to come in even if your oil pressure is good. And it probably still is -- the Northstar engines have a very robust oiling system. I would personally use the correct weight oil and replace the switch. It will likely fix your problem.

[JohnnyG]

My thinking is more in line with Jason's.

First of all, there are many "diesel" rated 15W-40 oils which are actually dual rated. You'll see it on the label as SL/CI or something to that effect. Since they are dual rated, they cannot be considered strictly diesel oils (non- "gasoline engine")regardless of the starburst presence, so that makes me wonder about Jim's quote.

I do agree with Jim's quote regarding the "fortifying additives" but would like to add Valvoline Synpower Oil Treatment to the list ( http://www.valvoline.com/pages/products/pr...asp?product=21) this oil additive is extremely high in ZDP and will fortify SM rated oils with extra protection when using as little as one TABLESPOONFUL.

Further, I know dual rated oils are known for their exceptional cleaning ability and thier ability to keep the by-products of diesel combustion (black soot) in suspension. Now, I don't know the EXACT mechanism for the operation of the oil pressure switch on a N*, but it may be possible that it needed a little cleaning and is now working properly.

I would run the oil you have for a while, being assured that it will not hurt anything more than fuel economy, but go back to a good 10W-30 at the next oil change to see if the problem returns.

[KHE]

The 15W-40 oil won't hurt anything but the correct grade oil is 10W30. Rotella has a 10W-30 grade - I have been running it in my '97 STS due to the increased amount of antiwear additive. I buy it at Menards of all places....Once the oil life monitor indicates that it is time for an oil change, I will use regular 10W-30.

My '93 Fleetwood Brougham gets Rotella 10W-30 due to the distributor gear, etc.