Tech Letter of the month:
Is High-mileage oil worth it?
Question:
I'm confused about what oil to use in my '94 Suburban with 101,000 miles on it. It has a 454 and an auto tranny. Should I use regular oil, which is on sale at around $0.79 per quart, or a more expensive high-mileage oil which is touted for vehicles that have more than 75,000 miles on them? I have used the cheaper varieties for years on vehicles from new to well over 100,000 miles. Is the more expensive stuff worth it?
Ray Foster
via 4wheeloffroad.com
Answer: This is such a good question that it deserves the Tech Question of the Month prize: a new Currie tire deflator for airing down your tires when headed off-road.
Unfortunately, we don't have access to the type of testing facility required to scientifically determine the value of high-mileage oils versus regular oil, so we can't give you an answer that you can take to court and argue. However, here is the reasoning we use when buying oil. First, do cars seem to run any longer now compared to back before these special oils were available? Not really. In fact, if you drive reasonably, don't abuse your vehicle, use the recommended weight oil, and change said oil and filter every 3,000 to 7,000 miles, you should be able to drive any vehicle well over 100,000 miles. The technology of engines have made them less dependent on maintenance and more resilient to wear, but even so the special oils are but a small part of that longevity.
On the other hand, here are just a few of the things these oils claim to do:
Restore engine performance and power
Prevent engine leaks and oil consumption
Protect worn engine parts
Reduce oil consumption through evaporation and leaking engine seals
Increase cylinder compression
Resist oil-related spark-plug fouling
Resist intake valve deposits
Protect engine parts found in high-mileage engines from wear and harmful deposits
It's seems to us that if an oil could do all these things you would want to start putting it in the vehicle from the first day you bring it home from the dealer.
Imagine how much better it would be! In fact, you would think that it would actually increase the power and performance of your ride. Does it indeed do these things? We haven't tested it, so you are going to have to decide. Do you run the oil that is working just fine for you, or do you spend the extra money for oil that is at least as good as what you run now and could be better? Do you go with the security and financial reward of running the cheap stuff that has worked for years, or do you invest a bit more to get an oil that may indeed help clean and refresh the seals in your engine, but might also be a sales pitch for rebottled regular old oil.
Changing Gears
Question:
My project vehicle is a '78 fullsize Bronco. I plan to build it around a race/trail vehicle with the ability to still have some street use. I have a 460/C6 combo that I am going to install in it and am planning to install an NP208 transfer case. My planned tire size is 38.5-11-15 Boggers. I am looking at putting 3.73 in the front but no one makes a 3.73 for the 9-inch rear. Since I am planning to run the same tire size on the front and rear, how much of a different front/rear gear ratio is safe to run so I am not scattering drivetrain parts every time I drive?
Sean
via 4wheeloffroad.com
Answer: We understand your logic of running a 3.73 gear since the 460 should have plenty of grunt for getting the truck moving. Since the C6 has no overdrive, the higher gears will keep it from revving to the redline on the highway. As a rule of thumb, don't go more than .03 points in gear ratio difference unless you always run different tires to protect against binding. We found 3.75 Ford 9-inch gears and they should be just fine for your truck.
Three-Speed/OD?
Question:
I have an '87 GMC 1/2-ton 4x4 with a TBI 305, manual transmission, and a NP208. The transmission is not the desirable SM465 but rather another four-speed with a high First gear ratio and an Overdrive. I pride myself on knowing every engine, transmission, transfer case, and differential out there, but this particular one eludes me. I remember a tech question many years ago in some 4x4 rag about an overdrive tranny like mine that may have been put in some GM diesels. They tagged it an NP833. Could this be it? Also, the reverse in my tranny is up and to the far left. This thing must be rare so I will probably yank it for a milder project down the road that may see some road time before I break it.
Justin Baker
via 4wheeloffroad.com
Answer: The crew at All-Trans transmission parts verified that you do most likely have an NP833, also known by GM as an MY6. The case is usually aluminum, but was available in cast iron. First gear is 3.09:1 followed by 1.67:1, 1:1, and .74:1 overdrive. These cases were found in light-duty GM trucks and vans between 1982 and 1987 as well as some Chrysler vans and trucks between 1976 and 1985, but never behind a big-block or a Cummins diesel. The major issues with this transmission involve failure where the counter gearshaft goes through the case, but if your case is not leaking from the front of the case it is probably fine. To make it last, do not put the truck under excessive loads while in overdrive.
Big-Butt Trucks
Question:
My wife has a '94 Dodge Ram 3500 four-wheel-drive dualie. We would like to put larger tires on it because the stock ones are too small and look silly. Is there a safe way of doing this so the rear tires don't rub, overheat, and blow?
Matt Nagy
via 4wheeloffroad.com
Answer: I'm also a fan of the big-butt look, and I'm not talking about your wife, who I'm sure is gorgeous, but rather a dualie with big ol' muddy tires. The best way to make big tires fit under a dualie is to have custom wheels made. One source to have that done is Taylor Made Wheels (323.567.3998), but if that is out of your price range, contact Off Road Unlimited (818.563.1208) about its dualie wheel spacers. ORU offers a kit made of billet steel for strength. When installed between your inner wheel and outer wheel the spacers keep the tire sidewalls from rubbing and getting hot. Even still we would recommend a set of tall skinny tires for this type of truck.