82 Datsun 720

[Tsnider]

Just picked up my first 720. It’s an 82 diesel that is pretty clean. I’ve done a few maintenance things to it and added wheels. When I was cleaning it up, found the original owners manual and window sticker along with a few receipts of things bought for it thru the years. It’s really slow but I love this truck. 

[bilzbobaggins]

You did not find squat, till we see pics.   Welcome to the show. 🤣

[wayno]

I like the diesels, I have had a few of them but I searched around for years till I found SD25 engines for them, the SD22 just doesn't have enough power for me, fact is the SD25 doesn't have enough power either but I figured out how to turbocharge them and now I am happy.

The SD22 has about the same amount of torque as an L20b, but on the freeway an L20b will kick the diesels ass, but the SD22 diesel will kick the L20b's ass fuel mileage wise.

The 1982 720 diesel should have a pre-filter on a clip on the firewall, when you change out your filter you need to find a pre-filter made for diesel fuel, they look the same but they are not the same, I went thru this so there is no need for anyone else to, if you cannot find a pre-filter made for a diesel fuel pre-filter(strainer), I used this one in my Datsun 521KC turbodiesel in the link below.

https://www.ebay.com/itm/Diesel-Fuel-Pre-Filter-90-degree-elbow-for-Mercedes-240d-300cd-300d-e300-300sd/372281401371?hash=item56adb3601b:g:D3AAAMXQkN5RC2PX

You need a filter because there is a screen in the lower in-feed line banjo fitting on the bottom of the injection pump, it is a pain to get to and the screen is easy to break, I have found no replacement for it, so it is just easier to use a pre-filter.

I use a real diesel Delphi fuel pre-filter on my 720 diesel, it is a traditional type diesel fuel filter found on most diesel trucks, if I had the room in the 521 turbodiesel I would have one of them in there also.

https://www.ebay.com/itm/2656615-Genuine-Fuel-Filter-Assembly-P556245-BF825-FF167-Perkins-CAV-Delphi/173682392359?epid=14026888652&hash=item287046fd27:g:mdUAAOSw5qdcDENi:sc:USPSPriority!98683!US!-1

 

I brought this up because one likes to keep their diesel engine running good and using the wrong pre-filter can make your day a nightmare, it took me over a month to figure out what my issue was, but I learned how to get more power out of my engine going thru that nightmare so I am happy it happened.

 

You should get at least 25mpg in the city no matter what, if you can drive 55mph you can likely get at least 35mpg on the freeway, but if you want to go 70mph you will get maybe 27mpg, since turbocharging my SD25 engine I get almost 31mpg going 75mph on the freeway.

 

If your not in a hurry you will like these diesel trucks.

 

Does your truck shut off when you turn the key off or do you have to use a choke cable to shut your engine down?

[Tsnider]

Well, no one is getting in a hurry in it. I’m getting used to just driving at my own pace. It has a cable shutoff like some tractors. Funny you mentioned the pre-filer, going to change it out tomorrow. I’ve read some of your post on the diesels and it good to know someone has knowledge about them. I might have questions about it in the future. Thanks blitz, I’ll work on getting pics up ASAP. 👍

[wayno]

OK, the cable question was just so I know what is going on, in stock configuration they shut off with the key, but when that system quits working a lot of folks put a cable in.

Is there a button to warm up the glow plugs or does a light come on in the dash?

Do not just start replacing fuel lines because they look bad, it can be a real pain to get the engine started or keep in running when you get air in the fuel lines, especially that line going from the fuel filter to the front of the injection pump, when you change a line you need to bleed the fuel system of all the air in it before you start the engine.

 

[Tsnider]

It has a light to the left of the steering wheel on the bottom of the dash. The lines I replaced were spewing fuel everywhere under the hood. It was so bad that it was running out from under the truck. I thought the fuel shutoff looked like someone added it. How is the best way to prime the fuel system? 

[wayno]

If it is running it doesn't need primed.

To prime it(get the air out of the lines) there is a plunger on top of the injection pump, the handle is threaded to lock it into position when not in use, turn it counter clockwise to release it, with the choke cable you use to kill the engine in the run position you pump that plunger till you feel resistance, then you loosen all the banjo fittings one at a time and pump the plunger till you get fuel puking out without any air in it, you can hear and see air, don't forget the feed line/banjo fitting on the front of the injection pump, that one is the most important.

Do you have a button you push to warm up the glow plugs?

The glow plug light I am talking about is the bottom right light in the dash, when you turn the key on it is supposed to light up and when it goes off you start the engine, there are 4 lights on each side, the top lights are the blinkers, the bottom right is the glow plug light.

 

[Tsnider]

Yes, the glow plug light is on the bottom right on the dash. There isn’t a button on here.

[wayno]

So you turn on the key and let the light go out and then you start the engine, correct?

[Tsnider]

Correct 

[wayno]

All I can say is don't love your truck engine to death, don't fix what is not broken.

Carry new fuel hose in case you get a crack in one, you can tell when everything starts smelling like diesel in the cab, replace the bad hose then open the banjo fitting that that hose leads to and bleed the system(get the air out of that hose), then start the engine, do not start it with air in the line, if air gets to the injection pump the engine will die and it will be a pain to get it started again and keep it running.

Always carry an extra fuel pre-filter in the glove compartment, I used to use them cheapo fuel filters I bought at the auto parts stores, they were good for a year maybe before they would get plugged up, when the engine started loosing power I would stop and shut the engine down, then remove the old plugged up filter and install a new one from the glove compartment, start the engine and let it idle a few minutes and then I was good to continue on for maybe the next year.

The mentioned cheapo fuel filters.

 

Keep in mind that I have heard of the cheapo fuel filters like the top one in the photo above getting plugged and then getting sucked into the fuel line, I had mine back by the tank so I used the lower fuel filter in the photo above, but even it got sucked flat.

Like I said I use this pre-filter screen in my 521 turbodiesel.

 

And I use this Delphi fuel pre-filter in my 720 turbodiesel, the filter on the firewall.

 

I might be able to figure out what is wrong with your engine shut down issues so it will shut down when you turn the key off, but first I would need to know if you have everything needed , there is a black box on the right inner fender(pass side) right behind the main fuel filter, do you have that, there is also a device below the injection pump with an rod/arm that connects to the the  injection pump, do you see that under the injection pump?

Edited August 26, 2019 by wayno

[Tsnider]

I’ll have to look tomorrow but I know the arm under the injection pump is still there. I replaced the pre-filter today with the one that you sent me a link to. I think it’s off a 300d Benz. I had replaced the main filter a week or so ago. It runs like a top. I ran into a brake light issue today and I’ve not had time to address it yet. I’m going to have to replace the tail light as one of the sockets is completely rusted and another one the bulb is rusted into it. I have access to a parts truck so I’ll probably rob one off it.

[wayno]

They are just old trucks, rust is always going to be an issue, especially on the bottom side of the truck, having a donor truck for parts is always good.

[Tsnider]

This truck is fairly rust free. The man that had it before me had left it out of gear and it rolled into a brick wall. He had the truck painted  so it doesn’t look to bad. It has a small amount of rust in the drivers side bed and a small area in one rocker. 

[Tsnider]

https://imageshack.us/my/images. https://imageshack.us/i/pmLmHFEwjhttps://imageshack.us/i/pmXOsuFRjhttps://imageshack.us/i/pna1R9DTjhttps://imageshack.us/i/pm1eSpsAj

[Tsnider]

Here are a few pics of it. The first one was right after I got it. The other ones of how it is now. Also added a few pics of some of the original paperwork on the truck.

[wayno]

It would be interesting to me to see if the injection pump controller worked, it has a plug that plugs into the wiring harness near the battery, without the arm connected to the injection pump plug it back in, if it is already plugged in unplug it and plug it back in, then unplug the oil sender wire from the sender on the rear of the block on that side, then have someone turn the key on while you watch to see if the arm moves when they turn the key on, if it doesn't move then while leaving the key on unplug the plug and plug it back in(cycle the plug as sometimes they get dirty and don't make a good connection), you could even use electrical cleaner on both plug ends, if it doesn't move at all then it could be the black box or the IP controller that has gone bad.

 

This is the only photo I can see.

 

[Tsnider]

That’s weird, I can click on the links and see them. I’m not real good with technology, I’ll try again. I’ll try and take some pics under the hood tomorrow and post them. I think the man I got it from said that that it quit working years ago so they put the choke type setup on it. It works fine but you have to remember to get the keys out after you shut it off. Ask me how I know.

[wayno]

You likely locked your keys inside the truck.

 

My mistake, I thought that it was just one link as it is all just one long line of links, but there are 4 different links there.

#2

#3

#4

 

These are all the rest of the photos I can see, I can see no more of the truck.

Edited August 27, 2019 by wayno

[Tsnider]

That’s all I have at the moment. Yep, you guessed it. Luckily the window was down far enough to get a coat hanger in there to get it unlocked.

[wayno]

It appears to be a decent looking truck, this was my first diesel 720 I ever owned.

 

[Tsnider]

Looks very similar to mine. Do you still have this one?

[wayno]

I sold that one 10 years ago.

That silver/black 720 behind it was a diesel and the red 720 on the other side was a diesel also, the red one is the only 720 I have left.

That silver one was a good running truck, but gutless on the freeway, I was always floored or almost floored trying to do 70mph, I finally gave up on SD22 engines and found a SD25 for the red 720 and my 521KC diesel, then around April 2017 I decided to turbocharge it after dreaming about doing it for 8/9 years, best thing I have ever done to that date, what a great upgrade, both my diesels are a pleasure to drive now.

[Tsnider]

Nice, so you’ve had a few diesels. I’ve read some of your posts and from searching online about them, you’re the diesel guru. I’ll probably have questions for you in the future. I just drive mine to and from work and around town. It should serve me well in that role. I don’t plan on being on the interstate much with it. What did the sd25 come out in originally?

[wayno]

Later 1985/86 Nissan 720 diesel trucks had them but they are rare, other countries like Australia had a lot of diesels, Canada got SD25 diesels, forklifts also had them also.

I would not say I know a lot about them, but I know the common stuff that goes wrong with them as all that stuff has happened to me, I have likely made every mistake one can make, some of them mistakes I only want to make once, so I learned not to do that again.