After browsing the forum for the past hour or so searching for just about everything I've come up with a few questions. Hopefully JK23112 won't mind that I got a few ideas for these questions from his introduction post.lol.(brace yourself this may take a while to read.Its my first <nobr style="font-weight: normal; font-size: 100%; color: darkgreen;" id="itxt_nobr_4_0">truck</nobr> and I don't want to screw it up cause I got a really good deal according to KBB.com.If any of them are repetitive I apologize for my lack of searching for said topic.)

I use mobile one synthetic oil most of the time what viscosity and weight should I use at the next oil change? probably going to be soon considering the security center says change oil soon.

As far as engine Coolant goes, Whats the best one to go with.I haven't checked which kind is in it or what color it is I will do that when Its not raining.

For the differential in the rear what kind of gear oil should I use and how often should I have it replaced?

What kind of transmission Coolant should I have put in and how often should I replace it? (is that the Dexcool stuff I've been Reading about or is Dexcool the radiator coolant?)

Can I use the four pronged iridium spark plugs with this truck? How easy or hard is it to change the spark plugs in the truck? (I do most of the work on my vehicles myself with the exception of the <nobr style="font-weight: normal; font-size: 100%; color: darkgreen;" id="itxt_nobr_9_0">mazda3</nobr> which is still under warranty.)

Does a hard bed cover give better highway mileage than a soft bed cover or does a bed cover not make a difference?

Without putting the truck on a lift and manually turning the drive-shaft and watching the rotation of both the tires and the drive-shaft to calculate the gear ratio how else can I tell what gears it has in the rear and weather or not it has an LSD?

More info on the truck:
Silverado Long bed, tow package (the little button thing on the end of the gear shift lever), Upgraded bumper (seller told me the type and that it cost $600 some odd dollars made out of steel), Its a base model truck that was used by a delivery service company (thus the High mileage for a newer year truck).

Oh yeah the hood lever broke so he used a pair of pliers to pull the wire to pop the hood any idea where I could replace the wire and about how much I could expect to pay?

The seller told me he replaced the 'information console' with one from a junkyard truck and the back lights don't turn on.Any reason for this other than fuses which I'll check when It stops raining.

Hmm...Well that's all I can think up right now. Thanks for reading and any help you can give me is greatly appreciated.

 

Hi Polk540,

Welcome to the Chevy Forums.

The recommended viscosity from GM is 5W30. Some Synthetics list "0W30" which is also fine. Unless the engine is burning or throwing a lot of oil, I'd stay away from thicker blends. The OLM will tell you to change your oil at a set mileage interval which is a logarithmic calculation, not a sensor being tripped. So at a set mileage, the OLM will tell you to change your oil,regardless of whether you're using synthetic, or not. If you're using Synthetic, you can reset the Oil Life Monitor by pushing the gas pedal to the floor with the ignition in the on position before you start the car three times quickly. If you keep oil in your engine over 5K, regular filter changes are still recommended.

More than likely, you're running Dexcool. It's orange, and absolutely can't be mixed with green antifreeze. As long as it's bright and clear, IMO let sleeping dogs lie. Many here really hate Dexcool though, so it's purely a personal decision.

As to gear oil, unless you're going to use synthetic, standard 75W90 would probably be best. Change intervals for differential fluids are arguable, and many times largely ignored. I change mine every 2 years(in my '04 2500HD) and let it go at that. Yours hasn't been changed in a long time, if ever, so I'd consider doing it soon. Don't forget to change the transmission fluid in the transfer case, also.(Dexron III).

Use Delco Iridium plugs. Nothing fancy. Don't worry, they'll cost you enough. Change them every 50K. That "100,000 miles" thing is bull.

There is no "transmission coolant". There's Dexron III transmission fluid, and there is a transmission cooler in the radiator to which the DexronIII is circulated.

A bed cover makes a major difference(@3MPG for me). Hard is probably marginally better than soft. Depending on what you carry most, you may want to consider an aerodynamic fiberglass cap. You can order them in your vehicle's specific color.

You have a 6.0L Vortec engine, and probably a 4L80 transmission, with 410 gears. To be certain, look at your glove box RPO codes.
GU5=323 ratio,GU6=342 ratio, GT4=373 ratio, GT5=410ratio. "G80" is the posi generally reserved for Z71s. Z85 is a good thing, it means "Chassis Package-High Payload-Firm Ride. " also look for "HVY"-Identification 2 inch body raise, HD model.

You'll probably find that hood release cable and handle are a dealer item. Avoid opening your hood in extreme cold weather, if you can.

See if the side of the truck is marked "2500HD" on the side. The HD version is one mackin' truck. RPO code QIZ is E-rated highway radials. 80 PSI, 10 ply tires designed like tractor trailer tires. Or just look at the side of the tires for inflation specs.

 

Any idea where I can get a Factory service manual? (the one that comes with it new.The truck doesn't have one and it might explain where everything is.)

As far as the 2500HD goes Its a base model truck (manual window manual locks etc.) I doubt it'd be an HD or have any other factory upgrades.The codes for finding out what gear ratio will be very helpful though.I don't believe the hype about spark plugs lasting 100,000 miles or more.50,000 miles they get changed regardless.lol.

Would the gear oil not being changed give worse fuel economy?

Thanks for telling me the specs on the Oil I may go with Mobile one synthetic since I don't know what was previously in it and don't really like running the cheaper stuff unless I have to.

Well I guess thats all for now.Thanks for your help man.

 

Changing the transmission filter could have an effect on gas economy. Bad or low gear oil will probably just destroy your gears.

We have a couple great mechanics on this site. Use your thread search feature here at CF, and most your questions will probably be answered.

If you don't have an owner's manual, you can probably make out best at this point by just getting a Chilton's or Hayne's manual for 15$ at a parts store.

Also check out ShawnVW's "Check my VIN' thread here at CF. He'll give you a code by code rundown of your specific VIN. You might be surprised at what goodies you may find on your "base model truck".

 

Cool.I'll head over to that thread when I have the vin on me.
How much does a transmission filter cost, or are there different kinds?

 

You're supposed to re-use the gasket, it's about 80$ and it's real thick.

The filter will cost you @30-35$ at a parts store, but I got my last one online for 16$ plus shipping.(try to get enough stuff to qualify for the free shipping, if you can.

Install a drain-pan bolt for about 10$, it'll save you a lot of grief later. It takes @8qts of Dexron3 to refill the pan when you're done.

That shifter cable bracketz a b!tch, the torx bolts face upward, and catch dirt which displaces the torx bit enough to strip the bolt head. Use a q-tip and vaseline to clean out all the dirt in the torx hole. Replace the bolts with six point metric bolts from your local hardware store.