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CATEGORY LISTINGS > GM DIESEL > 6.2L questions before buying [ REFRESH ]
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6.2L questions before buying


Created On Saturday August 28, 2004 04:18 Diesel Talk
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neutrino
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Posts: 1
Joined: Aug 2004

Note Saturday August 28, 2004 04:18 View thread in raw text format
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Hi all,

I've found a 1982 GMC Sierra Classic 1/2 ton 4x4 equipped with the 6.2L diesel and am considering buying it. I have just a couple questions that I'd like to get answered and I'm hoping this will be the place to do it.

First of all, the truck is in great shape in terms of body, drivetrain, chassis, suspension, steering, etc. I'm not a mechanic but know enough to tell when a truck has been taken care of. Put it this way, most of the original undercoating is in tact and there is NO RUST on the frame or any other part of the undercariage or body. The diesel is mated to the 700R4 transmission with a 205 transfer case (I think) and a GM 10 bolt rear diff. Not sure of the front diff but maybe a Dana44(any ideas)? The engine itself was replaced circa 1992 with a GM Goodwrench 6.2 liter crate engine and the transmission/t-case was rebuilt heavy duty at this time. This was done immediately prior to the current owner purchasing the truck from a friend so he doesn't have reciepts but I believe him for three reasons: 1) I spent over an hour with him going over/under every inch of the truck and he was brutally honest about every deficit the truck has (mostly cosmetic flaws), 2) the engine is obviously a Goodwrench replacement since the valve-covers are black and say GM Goodwrench, 3) the transmission shifts like its brand new (or better), I mean you can barely feel it shift and overdrive works well, no leaks, etc. The truck has ~175K miles miles with the replacement engine/trans in place for the last ~85K. The owner consistently adds a little ATF to his fuel (about 1/4 cup per 20 gal tankful) and he had complete records of service since he's owned it including: oil changes every 2500-3300 miles, transmission fluid drain/fill every ~50K miles, along with rebuilding the steering linkages (heavy duty tie rod with new ends, spindle seal kit, etc), and even records of regularly changing the diff fluid. It drove great albeit a bit of a dog.

So the problem is that I don't know much about diesels beyond a theoretical understanding of the cycle, let alone the 6.2 inparticular. Here are my questions:

1) What can you tell me about the replacement engine. Sounds like this is a significant upgrade compared to the pre-86 models from what I've read but why is this? This would explain the short life of the original 1982 engine. How do I find out which style engine this is (G, C, K, J)? Which is best and why?

2) One of the things wrong with it is that the fast idle solenoid doesn't work correctly. He corrects for this by gently touching the gas when starting the engine when cold. This seemed to work fine and the engine started easily but if this is my daily driver I'd want to fix it...could this be due to something more complex than the fast-idle switch itself. I've read about an inhibitor swich and glow plug controller. How expensive could this fix be assuming I do the work myself?

3) The owner claims 24 mpg unloaded at 60-62 mph. Is this realistic?

4) If I decided that I wanted to turbocharge it (Banks Sidewinder) would there be any detriment to durability/reliability/economy?

5) Anything else I should look for when I go back for a second look?

The best part is that it's only $1500 so I don't think I can loose, but I'm just a little scared since this would be my first diesel.

Thanks!


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Neutrino
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fozsey
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Joined: Sep 2003

Note Thursday September 09, 2004 12:54 View thread in raw text format
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neutrino

Sorry, I don't come here much...not much time. First of all let me say that this sounds like a good deal based on your description and I would jump all over it if it is what you say it is. Those vintage GM trucks retain great resale value if taken care of. To give you an idea of how well, I rebuilt an 84 Chebby Scotsdale 1/2 ton 4x4 with a new body and refurb work on the interior and turned around and sold it to someone for $6300. I didn't do anything with the engine. It had 294,000 original miles on it. I knew the owner very well and he kept all the reciepts. I painted it an Indigo Blue Metalic. It was pretty. That truck had a 6.2 in it.

I have driven diesels all my life living on a farm when growing up and going to school to repair them after graduating from highschool. Although they have unique problems, they can be very dependable if taken care of.

Now some facts about an 82...

First off, unless someone changed the transfer case on you you have an NP 208. Look at the case. If it is aluminum, it is a 208. A 205 is a very heavy cast iron gear transfer case that was mostly used for manual transmissions.

Second, the 700R4 transmission was problematic for GM. One might go 100,000 miles while the next one might only go 20 or 30,000. I have seen numerous broken planataries, torque converter lock up issues, and such. Not my favorite transmission. Now, having said that, there is a number of things that can make a huge difference keeping the transmission healthy. You mentioned that it shifted smooth and slid from gear to gear. This is bad. Your transmission should shift crisp and solid. If allowed to continue to have mushy shifting it will eventually ruin the clutch paks. There is a TV cable on the passenger side of the pump that can be adjusted to correct this. There is a plastic button near the firewall on the cable that can be adjusted to either lengthen or shorten the cable to adjust the shift points. Make small adjustments and then drive to see what your adjustment did. If memory serves me corrrectly, you need to shorten the cable to sharpen the shift points. One thing to remember, the shift points either all go up or all go down. You can't adjust individual gear ranges.

Third, the high idle solenoid is located on the front of the IP and looks like a small barrell with most likely a rubber cap on the end with a wire coming out of it. It is magnetic and controlled by engine temperature. The solenoid has a small rod in the center of it that when energized will be pulled forward toward the IP throttle plate lever. The only way it can do its job is to be activated by the foot pedal or manually by pulling on the pump throttle plate lever under the hood. You can see this happen in the morning by turning on the key (without starting) and taking your finger and moving the throttle plate lever on the side of the pump. The little rod will pop into postion if working correctly.

Fourth, if the crate engine is from a newer vintage, several improvements were made. When this particular 6.2 (82) was made there were some flaws in the engineering. The block was not able to be line bored due to some funny casting. The main bearings were metric and not available aftermarket in undersizes. The replacement bearings had to come from GM and aftermarket bearings weren't supposed to work. Kind of a bad deal. I did however build a guine pig engine using aftermarket bearings and it worked. I personally wouldn't reccomend it. The engines had some cylinder head issues also. The heads had a hole in the rear of the back of the head that GM didn't block. It was a open water port, but the block didn't have an open port to match. They relied on the headgasket to seal this hole. Frequentlly, this hole leaked coolant out of the block and down the back of the engine block. After 1984, this port was blocked. In addition, the injector bodies were changed in 1985 or 6 to a fine thread and are not interchangable.

Do you have any idea what caused the original engine to fail? The reason I ask, there is some controversy in using Dextron to lubricate the fuel system. ATF contains numerous additives that have lubricating properties, but are not combustable. Teflon is one example of this. Teflon isn't combustable and will therefore be left as a deposit on the inside of the cylinder heads inside the combustion chamber. Diesels have a very high compression ratio. Your particular engine is probalby in the 21:1 range. In order to get the compression ratio high enough to ignite diesel fuel effectively they have to leave virtually no combustion chamber in the head. I.E. no room for carbon other deposit buildup. Yes the detergent and the lubrication properities of the ATF have some use in cleaning and lubricating your IP and injectors, but there is some evidence to support that the ill effects of the ATF far outweigh the benefits. There are several high quality injector cleaning and lubricating additives that won't leave deposits in the combustion chamber. This info is "for what its worth" and not intended to sway your opinion regarding using ATF. It just gives another angle to think about.

There is no way to tell what GM used for a core in the "Crate" engine without seeing the paperwork and even then maybe not. Most likely, they have included all of the updates with the crate engine up to the year it was purchased.

As far as gas mileage is concerned, 24 would be about normal for tall gears and no/low power. Keep in mind though that this engine only came with 130 HP from the factory so it isn't a drag racing engine for sure.

Turbo chargers are great, but this particular year never came with one. Banks makes a great addition, but there is some problems with the mounting system. The firewall is too close to the engine and won't accomidate a crossover and down pipe without much modification.

Finally, I still have 94 6.5 Turbo currently with 200,000 miles on it and I can tell you that there is a world of difference between a NA and a turbo, but it doesn't come cheap. Sorry for being so windy, if there is any other specific questions you might have email me at fozsey2@cableone.net and I will try to answer them for you there. I don't know when I might be back here again. I will try to check back this weekend. I hope I have been of some help.

Drive happy...and enjoy your ride.

Edited: Thursday September 09, 2004 at 15:57 by fozsey
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