Bought a dead 1980 GMC 7000 at an auction

SDE · Oct 11, 2014

This truck has been parked for a long time. We got the brakes unlocked and I would like to try and pull start it tomorrow. I will change the oil and I think I should drain the old gas out of the tank. Is there a drain on the bottom of the tank? Can someone tell me what wrenches I may need to use to drain it? I would like to take the right tools with me.
Thank you
SDE

mite-help · Oct 11, 2014

Diesel tanks often have a drain. wrench size unknown--prob. the least of your problems if been 'sitting a long time'' Detroit engine? don't try to pull start it if ''been sitting a long time' most likely will start 100% w/o gov. control. give more info.

SDE · Oct 11, 2014

This is a gas engine truck. Auctioneer said it was a 350, but it appears that the 366 was the common engine in these trucks. I am going to put my car battery into it and spray gas into the throttle body while someone turns the key. It even has a hand choke on it. As old as the gas is, I do not expect it to stay running very long if at all. I hope that the distributor cap is ok as well
Thank you
SDE

504 · Oct 11, 2014

The 366 will have valve covers that are about 8 inches wide, the 350 will be a lot narrower. It will have a HEI distributor, pretty bullet proof,one hot wire in, juice out.

Steve@Advance · Oct 11, 2014

I'm thinking '76 was the last year for 366, could be wrong, and anything's possible with a truck that age. If it is a 350, good bet the poor thing has been worked really hard.

The drain plug size is anyone's guess. I would take a big crescent wrench, and a 1/2, and 3/8 ratchet or breakover. Wouldn't do a lot of twisting though, easy to tear the whole fitting out if the tank is rusty!

SDE · Oct 11, 2014

thank you for the suggestions.
Steve

2x4 · Oct 12, 2014

for that truck I believe the engine size that it was originally equipped with is stated on the spec sheet inside the glove box.

Owen Aaland · Oct 12, 2014

The 366 (6.0L) and 427 (7.0L) were available at least through 1999. Starting in 2000 the ones I worked on had either the 7.4L or 8.1L.

CenTex Farmall · Oct 12, 2014

I had half of a GMC 7000 that came with a 366 and currently still have a Chevy 70 with 427, basically the same truck. The 70 has dual saddles and does have a drain on the tank bottom. Bring a pipe wrench as backup in case someone has already rounded off the flats.

A better plan is if you can scrounge up a gallon or so nurse tank and hook to the mechanical fuel pump.

They both had an electric boost pump and a canister type fuel filter so all of that may be full of water and trash too.

Dr. Walt · Oct 12, 2014

Steve:

"I'm thinking '76 was the last year for 366,"

Nope. Couple of weeks ago I looked at an 89 GMC
7000, with a 16 ft flatbed. Had the 366 gas eng.
with a 5 sp tranny & 2 speed rear axle. 131K
miles, asking $2200. - Used & Abused, Rode Hard &
Put Away Wet!

:>)

Texasmark1 · Oct 12, 2014

I always liked to shoot some light oil in the cylinders and roll over with the plugs out first time. This also allows the oil pump to get lube up to all the moving parts before you put them under load. Since you are going to pull it off anyway, won't be that much more trouble to do this and surely your engine will love you for it.

Mark

Geo-TH,In · Oct 12, 2014

I bought an old GMC that sat for a while. I had to replace the electric fuel pump. I think the old gas was the reason it cost me an expensive fuel pump.

I think I would first pull the tank and drain it before I did anything.

RGMartin · Oct 12, 2014

(quoted from post at 00:06:51 10/12/14) I'm thinking '76 was the last year for 366, could be wrong, and anything's possible with a truck that age.

I have a 366 in a 92 C70...

notjustair · Oct 12, 2014

I wouldn't worry about the ignition. I would worry about filling the carb jets full of junk. Pull the fuse for the booster pump, strap a nurse tank to the front bumper, and go from there.

mite-help · Oct 12, 2014

Hello-understand now, gas engine. in the past I have strapped a five gal aux fuel can on back of truck to run/load ,get home, as you are prob. looking at pulling/cleaning tanks. I also have a small electric fuel pump & lines to bypass original fuel system. good luck-

37chief · Oct 12, 2014

Good idea. Check the pressure right away. I started a ford 6 flat head years ago. It sat so long the oil pump was dry, and would not pick up oil. stan

hd6gtom · Oct 12, 2014

I bought several new in the late 1970's with the 366. Great Truck and great motor. If you have no spark, check the rotor. I had the electronic ig burn holes thru them, then you are dead where you sit.

John in Ct · Oct 12, 2014

I have a 1979 Chevy C-70 Dump that we bought new that has 20,500 miles on it. It has a gas 366. Mine sat for years in a garage. My gas tank needs to be cleaned too so I am running it off a 1 gallon jug of gas. My fuel pump is mechanical (one hose to the tank). The original tank drain plug I believe is 7/16" Allen ( inside hex).

cannonball · Oct 13, 2014

easy to see 366 large block

Texasmark1 · Oct 13, 2014

That is what you look at when rolling over. Usually start seeing some pressure after about 30 sec. I bought an old non running Ford 4000 once. Did what I said and no oil pressure. Figured the gauge was bad. Turned out the rear main and seal were shot, plus the rest of the bottom end. Glad I didn't give much for it.

Mark

Bought a dead 1980 GMC 7000 at an auction

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