I have a 2004 extended TB with 30,000km. What would be a good oil synthetic or conventional? I just picked up the TB a few days ago and it more than likely was using conventional oil. Please specify the brand and viscosity.

Thank you

i was wondering the same thing for my 02 non-EXT LT. The research I have conducted over the past few days has narrowed down top either AMSOIL oils or Royal Purple. Both are synthetic and have great reviews, but I can't decide which one to go with. Sorry for not the direct answer you wanted, but maybe someone can help us both out. :) Erik

Sorry, the viscosity would be 5W30, that's the manufacture's specification. It is better that 10W30 because of the cold weather protection it offers. Erik

Synthetic oils are superior to conventional oil. I use Mobile 1, primarily because it's available everywhere. AMSOIL is a good product (but nothing near what it is hyped). Never heard of Royal Purple, but its website claims seem rather... optimistic. There is a very large jump in quality from conventional oil to synthetic; I don't believe there is as large a difference between the different brands of synthetic. Whatever you use, do not add any additives (Slick-50, in particular, is snake oil).

Research chemist Ed Hacket's Oil FAQ, first posted to rec.motorcycles some 15 years ago, is still a good reference, particularly for those who choose to run conventional oil:

http://www.micapeak.com/info/oiled.html

You can safely extend the oil change interval with synthetic, which some people do to offset its higher cost. You should change the filter on schedule, though, and top off with fresh oil. I wouldn't recommend extending the interval past 2x, although there are some people who make the case that you can safely use synthetic oil far longer:

http://neptune.spacebears.com/cars/stories/oil-life.html

It's an interesting read. IMHO, their claims that changing oil frequently increases wear are pure BS, and unsupported by their data.

I have decided to change my oil by the computer. So far it averages around 9-10k between changes. Because of this I decided to use Mobil 1 5w-30. Using a Wix filter. I just rolled up 60,000. I was hesitant at first since I am a 3-5k guy but I figured if GM says it is ok I would give it a try. Not saving a lot of money but a fair amount of time not changing so often. Anyone besides me trying this?

I was thinking if the computer states 8 - 9000km I would use synthetic oil and follow the computer schedule as well. I also have a 2002 Mazda that has 30,000km and I get the oil changed every 4 months it usually has 1,500 - 2,000 km per oil change, I bought this car 3 years ago with 13,000km on it. The warranty on this car requires oil changes every 8,000km or 4 months which ever is first so I follow the 4 month rule. I will not use synthetic oil in this car because it is not driven very much and $30 for a regular oil change every 4 months considering the low mileage every time it is changed will keep this cars engine in great shape. The TB is the primary vehicle so I will be putting about 20,000km's per year.

Mobil one seams to be pretty easy to get and I think this is the oil I am going to use. Does GM have a synthetic oil?

Did anyone hear that the front transaxle (I think that is what it caled ) uses synthetic fluid. The dealership had told me this and that is why changing the fluid in the front trans axle is more money thant the rear.

Do you require a different filter with synthetic oil changes?

Is there a problem switching back to conventional oil after using synthetic? I've heard this a is a problem.

I called a GM dealer tonight and they had mention that an engine purge should be done before changing over to synthetic and that you should not switch back to conventional oil once you have made the transition. Many questions on this subject. The GM dealership also offers synthetic oil changes.

There is no problem switching between conventional and synthetic oil, or vice versa. At worst, you may not have "pure" one or the other, as the replacement oil will mix with residue of the former oil in the engine. If this is a concern, drive a few dozen miles and change it again. Many people with older engines change from synthetic to conventional oil to prevent/reduce oil leaks.

Both types of oil use the same filter.

I called a GM dealer tonight and they had mention that an engine purge should be done before changing over to synthetic and that you should not switch back to conventional oil once you have made the transition. Many questions on this subject. The GM dealership also offers synthetic oil changes.

I also called the GM dealership that I bought the TB from and the service advisor had told me not to have the engine purged. I purged the engine on my 93 Maxima when it was four years old and ended up with seal problems. I think that I am going to change the oil to synthetic and not have the engine purged but change the oil at 4,000km to get the remainder or most of the remaining conventional oil out. The two GM dealerships I called use Mobil 1 synthetic oil. I also found out the TB I have is also equipped with a transmission cooler so I suggest you call the dealership and ask them to check with GM using your VIN code to find out if your TB has a Transmission cooler.

Read the back of Quaker State and other synt. oils. You can always go back and forth from syn. to conv. oils. I've done it for years and never have had seal problems.

WAAAYYY too much BS and old wives tales making it to this thread....

Let me hit a couple of them. After working on literally hundreds of cars, I can say without doubt that synthetic is FAR superior to conventional....and suggest it for any car. I did some testing a while back, from Blackstone labs, to check my oil as the mileage racked up. There wasn't measurable breakdown in the additive package and protection capabilities of the oil until over 25K miles! That was with Mobil1, but I'm sure any decent synthetic would do the same. As for flushing the engine....BS. No need. When you drain it out of regular oil, 99% is removed through the drainplug. The remaining 1% is still compatible with the synthetic...and won't hurt it. As for guys having problems with seals leaking....this is probably due to the materials used for seals in the 80's and prior. Conventional and synthetic oils have slightly different effects on swell/shrinkage of seals. On the older seals, they can shrink and leak as they are marginal anyhow. Most cars from the mid 80's to present will have no leaks due to seal shrinkage. You can always switch back and forth at will between the two, but IMO, I will always run synthetic, even whrn the oil change costs more than the car is worth :) As a point of reference, I have a 1995 Lumina that has been fed a steady diet of synth. It has 220K miles on it, and the internals look perfect. Like new compression, power, gas mileage, smoothness, etc. And no leaks either!

I have used Amsoil 0w30 since my first oil change. I change the filter when the change oil light comes on, about 10-12k miles. I change the oil after it has been in for 30k miles. I have 70k miles on the engine now and it still will not be a pint low after 10k miles. I have used Amsoil for 25 years now and have never had an oil related problem, leaks or oil consumption that was not there before the swap.

Bill

If you want a REAL synthetic, use AMSOIL or RedLine as they are pure synthetics. The rest of them are GroupIII sythetics (super refined and only about 30% synthetic). Mobil1 is great, there has been a lot of back and forth as to whether it is GroupIII or not. I use Mobil1 as it is readily available to me, unlike AMSOIL, and costs less, unlike RedLine. Either way, "A" synthetic is definately the way to go.

Thanks Chris

Mobil1 is a pure synth oil:

http://www.mobiloil.com/USA-English/MotorOil/Oils/Mobil_1_FAQs.aspx#FAQs3

A great site for oil research is:

http://www.bobistheoilguy.com

Check out some of their forums.

Every vehicle Ive ever owned, Ive changed the oil every 2000 miles. Used conventional oil. Personally I think all this synthetic crap is just to empty your wallet faster. The dumbest thing Ive seen recently is that Mobil 1 5000,7500, and 15000 mileage oil. Are people that focking lazy that they cant change oil every 3000 miles?

While we're on the subject of oil, I would just like to thank the designers at GM for designing another shitty drainplug/filter location on the Trailblazer. I changed my oil for the first time since buying the TB about 2 months ago. What a PITA to get at the filter. And why have a cover to get at the drain plug?

Why are somepeople using the TB's computer to tell them when to change the oil? Isn't that bad?! I don't see why it is so hard to get it done every 3K.

Is it really that bad to wait longer than 3 months to change it though?
It is going on 4 months & I still haven't had it changed. Not there yet with the 3K miles.....but I don't know if I should press it..............I will get it done sometime this week just to play it safe.

Sigh.....

OK, for you guys that continue to use dino oil, or insist on changing it every 2000 (!) -3000 miles...power to you. It's your car/truck.

However, it has been documented all over the net, and I personally have done oil analysis on my Z28, and have verified that the additive package in the synthetics (Mobil1 in my case) don't start to fall off until well over 12K miles. From a pure engineering and chemical basis, there is NO REASON to change your oil before then. NONE. The oil change monitor on the truck is used to calculate oil change intervals based on driving habits and conditions. The old 3000 mile rule was good for the most extreme circumstances, and still left you a margin of error. Read your manual, and you will see that even without the monitor, suggested oil changes under normal conditions is WELL over 3000....

I do have to qualify this and say this is true only for late model fuel injected motors. If you have an old school carb'd motor, then I would say test the oil, or stick to the 3K rule. With the precision fuel metering of fuel injection, there is little if any wash down or dilution of the oil...from either raw fuel, or combustion byproducts. Carbs are different.....

Bottom line:

Synthetics are MUCH superior to dino oil

As long as the chemical nature of the oil is within spec, there is no reason to change it early.

I personally ... have done oil analysis on my Z28, and have verified that the additive package in the synthetics (Mobil1 in my case) don't start to fall off until well over 12K miles. From a pure engineering and chemical basis, there is NO REASON to change your oil before then. NONE.

Perhaps... but there is a reason to change the filter before then.

I agree 2K is silly, but IMHO 12K is stretching it. 6-8K works for me (synthetic), swapping a new filter at half that. Probably more important than the oil change frequency is religiously checking the oil level, and monitoring the pressure. And avoid the gimicks, like Slick 50.

As for changing the filter more often....

The only reason to change the filter, is that it's efficiency gets reduced due to buildup of crap. Most of this crap is sludge or other carbon deposits, which are normally formed by overheated/broken down oil. As the synthetic doesn't break down like conventional, nor does it form sludge....the filters could, in all honesty, probably last the lifetime of the vehicle. The biggest breakdown factors while using synthetic is contamination due to blow by, condensation from the normal heat up, cool down cycle, and particulates passed through from bad air filters...

The only reason to change the filter, is that it's efficiency gets reduced due to buildup of crap. Most of this crap is sludge or other carbon deposits...

And wear metal from the engine (rings, bearings, etc.), which is largely independent of oil age, assuming the oil is still within its useful lubrication life. Granted, it is more of a concern at break-in than later in the engine's life. A magnetic oil plug will attract metal filings, as an indicator of their relative accumulation. Sure beats cutting open a used filter.