1984 suburban oil help.

[Gokhan]

Make sure the first-time you change the oil, especially with a synthetic or high-mileage oil, use a large-size, lower-efficiency oil filter such as Purolator Classic. Avoid fancy higher-efficiency filters such as Purolator Pure One, Mobil 1, K&N etc., as a lot of dirt will come up thanks to the good oil and clog them, opening the bypass valve. Change the oil after 5k, especially after the first-time use.

My ultimate recommendation is Mobil 1 0W-40 SN but Mobil 1 High Mileage 10w40 or in fact any brand-name conventional or synthetic oil will be just fine with this engine. The far more important thing is the oil level in the engine and frequent oil changes (every 5k).

By the way, for some reason people are forgetting the GM / AC Delco dexos1 5w30 full synthetic, which is recommended for every GM car with a gas engine and what GM probably would recommend for this engine if you gave them a call.

 

[mechtech2]

Lot's of good advice above.

Use the highest ZDDP oil from day one until now, and that engine will show cam and lifter wear anyways!

An additive at a weak dose may help.

 

[3311]

Originally Posted By: KD0AXS
I'd think QS Defy would be a good choice, it's got a good amount of ZDDP. Otherwise, a 10w30 HDEO would work well too.

+1!!!!!

 

[jdawg89]

Thanks to everyone for the great advice so far! That viscosity chart is really helpful....and yeah...there's gonna be some dirt/sludge...I looked down the filler hole...YUCK! That's all I got to say. Yuck yuck. And I'm going to stick with castrol,considering I use it in everything else. And would the lowest-grade fram be a good option?

 

[jdawg89]

And since that viscosity chart is a little old,is 10w40 now an ok option for below zero?

 

[uart]

Originally Posted By: jdawg89
And since that viscosity chart is a little old,is 10w40 now an ok option for below zero?


How many miles are you going to be putting on it per year and are you going to be using the same oil year round?

If you've already decided that you're sticking with Castrol then you may as well use GTX high mileage. If you're going to do 6 month (or shorter) changes then I'd use 10W40 in summer and 5W30 in winter.

 

[jdawg89]

Its going to most likely be used as a daily driver...but daily driver is about 12-15 mi a day and 2-3 trips into town a week,so it migt get changed every 3 months

 

[Gokhan]

10W-xx (even modern ones) shouldn't normally be used below 0 F (-18 C). Chances are that it won't damage the engine but it would still be too thick to be recommended for such low temperatures. Note that this is the API recommendation but my owner's manual recommends that it could be used down to -10 F (-23 C). Nevertheless, for such cold months, 0W-xx and 5W-xx suit better, and if you're worried about oil becoming too thin due to permanent shear of VIIs, go with a fully synthetic 0W-xx or 5W-xx.

If you're worried about deposits and sludge, use a cleaning synthetic like Mobil 1, Purolator Classic filter or similar (which has large size and is not super-efficient [so, it doesn't fill up with dirt quickly]), and do 5k OCIs a couple of times. I would recommend Mobil 1 0W-40 SN -- thicker oil doesn't get any better and it will do all the cleaning you need while providing the ultimate protection. There is no need to be afraid of synthetics -- changing from conventional to synthetic is not much different than changing between different brands of conventional oil.