20w oil in older caddy?

[joeb]

96 STS. I live in MN so its cold. I am getting a bit of engine rattle during cold starts. i had the heads off last year so i cleaned off the combustion chambers/piston tops so i don't think its carbon rap. I have no problem with using 0w-30 oil but was thinking of trying 0w-20 for mileage help. less pumping loss supposedly. I have read many threads on oil theory and the point seems to be to lower the viscosity but maintain good pressure at the speed you intend to run. i never go over 3k rpm to tell the truth. i baby my car. not even a WOT. so why not try 20w? i don't have a oil pressure gauge so who knows what pressure i am really getting at highway speed? i do a lot of short trips in cold weather. i wonder what my oil temp really does see most of the time?

[Cadillac Jim]

Oil is very complex and there are a lot of very good alternatives out there, and nobody selling oil tells all their secrets. Thus there are a lot of good answers for your question, and not too many bad answers that meet the common-sense test. And, you will likely get a lot of opinions here, possibly one or two even before I complete this post.

What you are suggesting is probably OK. However, the bottom number of nW-nn oil represents the ability of the oil to flow at low temperatures while the top number indicates its ability to maintain viscosity at higher temperatures. If your rattle at startup is just a lifter clack for a few revolutions, this is normal for an engine that has sat for awhile because those lifters that are pressed by cam lobes will leak down, given enough time. I had a new car on the dealer back lot give me that when a salesman tried to bond me with a car by letting me start it. If it's more than that, then oil draining completely from the pistons and bearings while the car sits for long periods may be important, although this is rare in a Northstar.

I think that the best oil for second-generation Northstars like yours and mine is 5W-30 Mobil 1 for temperatures of 0F and higher. If you have temperatures much below 0F you might look at 0W-30. I don't think that going to 5W-20 will help your gas mileage but 0W-30 might, but not enough to offset the higher cost of 0W-30 oil.

In never getting your engine over 3,000 rpm, you are not babying it, you are abusing it. If you just don't like nailing it in first or second gear once in awhile, then be sure and get it out on the freeway for 15 minutes every weekend. It's a nice break for you and possibly your friends or family and your car will thank you for it with smooter running and less problems with carbon knock and oil burning.

[joeb]

yes i have read the many comment on WOT and such. i was coming at it from the rpm vs pressure curve that is mentioned so often. high rpm requires high oil pressure to maintain journal/bearing hydrodynamic space. operating a motor in a high load setting raises the oil temps very quickly and the oil does thin as the temp goes up. but in MN, where it might be 10F or less for many days i wonder what temp the oil really stays at? or is it an illusion? does the motor get up to operating temp and stay there even in winter? i refer to oil temp and coolant temp both?

[KHE]

does the motor get up to operating temp and stay there even in winter? i refer to oil temp and coolant temp both?

Yes - the oil temp will come up to temperature after about 10 miles of driving. I would stay with the 10W-30 and not worry about it.

[joeb]

i keep telling myself it gets cold here. its been a long time since we had -25F. but -8F for a daytime high is really annoying. ok, -5F tonight. i don't care where you live. thats cold. you never stop to think that you can always add about 20 deg from the overnight low to the daytime high. i still think 5w is preferred over 10w during the winter.

[Cadillac Jim]

I believe that my 1997 Eldorado owner's manual says that 5W-30 is best when the temperature is around 0 F.

[lothos]

Yeah, I'm in MN too and I use 10w30 in the summer and 5w30 in the winter. I'll be doing my oil with 5w30 in a couple days here, it still has 10w30 in it. Temp when I got up for work this morning was -5F.

[winterset]

last month or so, I had 20w in my car for a day or 2, and my '96 deville did not like it. the oil pressure light kept coming on (& a shut down engine message & chime). I put 10w30 back in, and I never saw it again. I use the car every day on Highway, and around town. not even a flicker. I would really suggest Marvel mystery oil in the gas to help cylinder lubrication in cold weather. Also I think I had the half case leak, as I had a few drops of oil on the garage floor. not sure if having the 20w built up pressure & sealed the leaky gasket. I don't have any leaks under the car anymore .

[Cadillac Jim]

The leak might be the oil pressure sensor. In some older cars they get leaky and give false low pressure warnings. They are on the oil filter adapter, so they are easy to change from under the car.

[joeb]

the viscosity of 20w oil at 212f is 5-9 while the 30w is 9-14. thinner oil will result in lower pressure readings and the sensor might be working fine. you also did not say how many miles your motor has. maybe the oil pump is slightly worn as are the bearings. you also did not say if the light flickered at cruising speed or just at idle.