MrClean

So I just got an 99 300, and I was told that the oil was changed not to long ago with high mileage Mobile1, when checking the dipstick the other day it was kinda low so I filled her back up. Now my question is when doing my next oil change can I switch the car back to a synthetic oil of my choice without messing anything up, I was told once you go High Mileage you can't switch back and if you do the results will not be good.

oldManTan

Changing from any oil to any oil doesn't matter.

MrClean

I was thinking the same on the other hand i wasn't sure with High Mileage Oil having different stuff within it compared to synthetic oils.

PseudoK

high mileage oil is just a gimmick they use.

Biddles

iTrader: (2)

Royal Purple is the best if you don't mind spending a little extra. I feel it's worth it if you plan to have the car for long. If you don't want to spend extra just get regular oil/filter changes at a shop for $25, and do it every 3,000 miles.

Seefo

What you are talking about is usually referring to coolant. Some High mileage coolants use a different compound which may not be compatible with other coolants.

You are fine on oil.

Ali SC3

iTrader: (10)

actually they do say this about oils its because certain ones sometimes have this rubber/seal conditioner stuff in it and then when you use another kind it can cause some issues with oil seals or something. I have never had the problem though I have switched lots of time from a high mileage blend to a full synthetic. you may increase your chances of springing a tiny oil leak somewhere but likely it was going to happen at some point then anyways like valve cover gaskets etc..

Seefo

Yes please, post this on bitog and you might learn a thing or two.

There are seal swellers/conditioners in some oils, but your second claim just isn't substantiated. the "issues with oil seals or something" is directly related to the seal conditioner, not mixing two types or brands of oil.

Seal conditioners may use a swelling agent in an attempt to make up for lost material over the life of a seal. This usually works out ok, but sometimes the seal will tear and leak. Once again, has nothing to do with the two oils.

If you are seriously concerned about this, you are welcome to read tons of direct experience from people switching from MaxLife to conventional/synthetic on bitog (not speculation or what you heard from the guy at advance auto). Or ARX or whatever other high mileage stuff you may consider.

Ali SC3

iTrader: (10)

it is related to using the 2 different types cause one is high mileage oil where they use the conditioners and the other one being a full synthetic probably doesn't have it to near that same level.
Bob knows stuff about oil I got it.. hes the oil guy lmao

Mobil 1 high mileage is what the OP said in post 1, see the seal conditioners they use on the high mileage?
http://www.mobiloil.com/USA-English/...age_5W-30.aspx

now see the non-high mileage full synthetic one, notice how there is no seal conditioner.
http://www.mobiloil.com/USA-English/...l_1_5W-30.aspx

So in the 2 types of oil he asked about, mobil 1 high mileage and a full synthetic, the main difference besides synthetic oil content % is the seal conditioner, which is the 1 thing I said.

Seefo

You don't make sense. You made a claim and just keep repeating it.

the leak is ONLY due to the seal conditioner and deteriorated state of your oil seal. it has nothing to do with synthetic oil. That's what I am saying.

Ali SC3

iTrader: (10)

when you switch to synthetic you loose the conditioner, and if that was the only thing helping the seal you get a leak, its not rocket science.

Twojaybee

The guy I bought my sc3 from told me he used gtx hm since 130k. I bought the sc at 173k. I didn't even think about it when I got the vehicle and changed the oil almost immedietly to mobile 1 full synthetic. I am now at 220k and have a couple different issues with my sc but none mechanically engine related. My NA runs smoother and quieter than most newer vehicles today. Dunno if I got lucky or if it really doesn't matter but that is my experience. I do have a possible bhg which I believe is unrelated to the type of oil I use. Nonetheless, she runs smooooth!

Ali SC3

iTrader: (10)

that is good, just keep an eye on the valve cover gaskets and the rear main seal if you have drips under your transmission area in the future. most SC's will get a rear main seal leak over time anyways, but sometimes these things can speed up the process. for the most part it should be fine though synthetic is a good thing.