: Using 20w50 oil in N* 99STS

05-31-05, 10:24 PM
I had a 92 Eldorado that I drove to 226000 miles before selling. I bought it around 162000 and used 20W50 oil the entire time. My family owns 3 other Cadillacs 91-94. My question is this: my 99STS has a northstar engine unlike the other Cadillacs I've had experience with. It has 141000 miles on it. I know it is harder in the winter time on the engine and makes fuel economy decrease. I would think using a heavier oil like 20w50 instead of 10w30 would only help lubrication. Can anyone give me a reason why I should or should not change to 20w50 my next oil change in my 99STS? Thanks.

06-01-05, 06:32 PM
The one reason I can think of is because the owner's manual says not to. It says to use 10W-30, or in colder conditions use 5W-30.

06-02-05, 11:42 AM
You could do a search, but try this one

06-03-05, 09:23 AM
Not much talk about 20w50 in that forum.

06-03-05, 10:33 AM
Not much talk about 20w50 in that forum.

You need to read in to it. Bbob is a GM engineer whose knowledge of the N* engine has proven very valuable time after time. He specifically says "The 1999 and earlier engines need the 10W30 viscosity because of the flat follower cams."
Why do you want to change from what is recommended? Viscosity is not the only measure of oil lubrication. Or, more is not always better!

06-03-05, 08:19 PM
Why do you think 20w-50 lubricates better????????????????????????????? Why do you think a heavier oil lubes better? Would you use 90w gear oil?

It isn't just one factor, there are several. You lose more in cold start lubrication than you'ld ever gain in film strength. In standard, even high performance street driving you should never have a problem with 10w-30 if you keep it full and changed reasonably often. I don't run 20-50 in anything anymore.

06-06-05, 12:07 AM
Gee, this question looks familliar... Haven't I seen it asked in another thread...

Funny, I work in Tech Support and we have customers who open cases and then when they don't like what they hear from us, they open other cases hoping that another Tech Support Engineer will give them another answer (one that the customer would like better). They don't realize that engineers talk with one another, so we laugh when they call again asking the same question and getting the same answer.


06-06-05, 12:45 AM
Hey, lets all run alchohol in our cadillacs, since top alchohol funny cars do it and they're really fast! It must be better, right? Even though the people who designed the engine say to use gasoline... ... ... :D

06-06-05, 12:12 PM
Don't, it's just that simple. 10w30 or 5w30, nothing else, or you are risking engine damage. Today's engines are designed to run on these oils even in extreme heat(I live in Las Vegas) and the oil ports are smaller in the engines and can't push around heavy oil. 10w30 will give you excellent lubrication in 40F and up. If you live where it gets really cold, then run 5w30 in the winter time.

06-07-05, 12:01 AM
not to be a smart ass, but ...

some of us live in climates where 'really cold' means 30 below or less. yes, that actually happens several times a year here in great North Dakota. so, the manual says 5-30 for cold climates, should i use 0-30 in winter as we get colder than the temp ranges given in teh manual?


06-07-05, 12:27 AM
Dkoz is in Alaska where it gets a bit colder than that even...you'll be fine with 5w-30. They're designed to run everywhere from death valley in August to Northern Canada in January...otherwise they wouldn't sell them there, warranty them there, and still put the same oil in them there.

06-07-05, 11:24 PM
Round and round we go...

Again, IIRC, the Owners Manual has a tempertaure chart which shows you what oil to use depending on the climate the car drives in.

From sub-zero to tropical - it is all in there...

Just RTFM. (Read the *Fine* Manual)


07-08-05, 12:27 PM
I found out the other day I have a bad oil pan gasket. Apparently on N* you have to move the transmiaaion out of the way to replace the gasket. My local repair guy said I'm looking at about 14 hours of labor or about $900 of labor. He said it was a fairly slow leak and I could put a lot of oil in an engine for $900. I'm thinking 10w40 might slow the leak even more and isn't really all that different from the 10w30 I put in now, not to mention the average temp now is about 80F here. I know there are additional things you can add to coolant for example to try and stop a leak in a radiator. Is there anything out there that would do something similar for an oil leak in an engine? I know it's apples and oranges, but I'm no expert, and that's why I'm asking.

07-11-05, 10:30 PM
With modern oils and engines, thick is not necessarily good and thin is not necessarily bad. I seriously doubt any thicker oil will leak less. If it's the pan gasket, try just keeping it a quart low (admittedly not difficult :D) and see if that helps.