My'89 IROC-Z has close to 200,000 miles on it. It may be burning a little bit of oil. When I change my oil this weekend, should I go with Castrol GTX High Mile. 10w-40, Mobil 10w-40, or Castrol GTX Synth. Blend 10w-40. I heard that the Syth. Blend will slowly clean out the deposits in my engine (don't want to use a harsh "flush") so would that be the best? Also, I take a lot of short trips, so would it be better to go with the synth. blend or just change my regular oil more frequently? Thanks. -89IRO

 

from what i've read, mobil makes the best oil, their dyno oil is almost as good as some synthetics but at a fifth of the price. i would use 10-40 weight. i know that if you have a small oil leak and switch to synthetic it's gonna turn into a big oil leak because the molecules are smaller or something like that but i dont know if that applies to burning oil as well.

 

If mobil is so much better than other regular oils and sythetics, for that matter, why is the regular 10w-40 mobil the same price if not less, that say castrol gtx? Not arguing here, just wondering. Even the synth. blend can cause a big leak? I don't have any leaking problems right now though. I'm thinking about using the blend cause I heard it will clean my motor out over time. So then maybe I'll use the mobil synth. blend. -89IRO

 

Sure you're not lookin at the reg. Mobil? and not Mobil 1?

either way Mobil 1 is great, but AMSOIL is supposed to be the best, but hard to find.

Also, go with AC Delco filters...

 

What is the difference? I am not sure which I was looking at. Can you guys just tell me what the best 10w-40 is out there in a non-synthetic? Keep in my mind I have 200,000 miles on my IROC-Z. I've been useing Castrol GTX High. Mil., but I keep hearing people talk about Mobil (or mobil 1?) but I think that "High Mil." is just a marketing thing. Suggestions???? -89IRO

 

O.K., got it, mobil is conventional oil, while mobil 1 is full synthetic. I just want conventional oil so what is the best out there?- That's my question. I'm sure most are pretty much the same, but any personal opionions? What brand did Tony Stewart run? -89IRO

 

Well I used Castrol 10W-30 in my camaro with a 305 in it for 167,000 miles. I changed the oil every 3000 miles and I never had an oil leak and it didn't burn oil. However, when I bought a 350 and put it in I switched to Valvoline 10W-30. I am not sure that was wise considering that the ole phrase "if it ain't broke don't fix it" may come into play here. I truly believe the whole oil competition thing is just that,... competition. I also believe that synthetic is a very good thing if you can afford it and keep it up through the life of the motor after it has been broken in. That's just my opinion though.

 

Good point- my engine has never seen synthetic, so if I put it in, I'm wasting my money as well as hurting my engine. My dad just told me tonight they put synthetic oil in a machine at his work, which had always ran with "regular" oil, and the bearings took a crap and now it's dust. Maybe if I were to completely rebuild my engine and have it thoroughtly cleaned out by hand, then I may start fresh with synthetic, but not here. I'll probably just go with GTX high mil. or mobil. I know I'm beating the oil subject in the ground and it shouldn't be that big of a deal but I want only the best for my girl. -89IRO

 

Putting in syn on a dyno oil engine is not a waste, I don't see how switching would do damage like what your dad said.

 

I don't know- he's asleep right now- I'll have to ask him. Don't synth. oils have completely different chemical properties as conventional oils? Besides, I'm not strapping my engine to a dyno, it's in my car- maybe I'm not so clear on what you meant by that Mark. These engines weren't designed to run with synthetic oil anyways. Well that's all I can think of for now. -89IRO

 

read the second to last sentence iroczrockz wrote. -89IRO

 

There is a myth about synthetics causing leaks in older engines. Part of it is true, as the synthetic will wash away wax deposits from the conventional oil causing more of a weeping than actual leaks. It usually takes 3-4 changes before the swell agents in the syn oil condition the seals and most of the seepage goes away. On an engine with that many miles the seals are probably hard to the point where it may not be a good idea to change. Castrol is an excellent oil as are most of the popular brands which carry the API logo. I would recommend a 10-30wt as opposed to the 10-40. 10-30 uses less viscosity improvers which can cause ring sticking and unwanted deposits. An excellent oil is Shell Rotella 15-40. I use Mobil1 in all our cars but the cycles get changed so often it's not worth it to run syn. The Shell oil has proved to be an excellent oil for my sportbikes and would be my choice if I were not using syn in my cars. The Rotella uses less vis improvers(polymers) because it is a heavier base stock and also may help reduce your oil consumption on a high mileage engine. Check out www.micapeak.com , Ed Hackett has a good article about oils that you don't have to be a chemistry major to comprehend. He also compares various brands. It's worth looking at.

 

Danno- thanks for the help. Where on the website do I go? When I click on your link it just takes me to the homepage- then where do I go? I live in So Cal where right now the temps are real mild so I will run 10w-30, but in the hot summer, don't you think I should run something thicker like 10w-40? Even in the cooler weather when the engine is up to temp and I'm sitting in traffic my 10w-30 (what I have right now) thins out and my oil pressure drops way down (I heard running a fram filter may have something to do with that too though). -89IRO

 

On the homepage go to "what's here", then scroll down and you'll see it.

 

Danno- thanks, that really cleared some stuff up. Now I have a good idea of what oil to get. Too bad they don't have all the info in the oil brand chart. I would have like to seen pennzoil though. Thanks. -89IRO