To buy or not to buy a 6.9l?

[JLep]

Hey all, I've been looking for a diesel for some time now. I had a 97 psd and should have never sold it. Needed something more fuel efficient for a long drive to my new job. Question is, I have an opportunity to buy an '86 6.9l drw 2wd, I need some help with this truck, I know nothing about them. I am a ford man, but was thinking of an old 12v just because of the reputation they have. Any input would be great.

 

[dakotajeep]

As far as the engine goes, they are super reliable. I have a 7.3 and wish I had the 6.9....I wouldnt buy a 2wd, but thats just me...

 

[argve]

The 6.9 is a reliable engine - they run for a decent amount of mileage and are pretty simple to repair when they do fail. they are not power houses so you aren't going to win any races with them but they will get the job done. Probably the most common complains we see are glow plug issues (cold starting) because they need a good glow plug system to start and air in the fuel system (return line system) both can be brought up to spec fairly cheap (under $100).

Cavitation is not much of an issue with the 6.9 because of the thicker cylinder walls.

On some of the early models the use of the block heater can crack the block because in later versions they increased the casting around the freeze plug hole used.

 

[JLep]

Thanks for the input. Couple questions, I'm not well versed on diesels, so what is cavitation exactly. And why is it that the block heater would crack the block?

Are ther some basic mods that can be done to improve mpg. I'm not looking for speed, but may someday put a turb on it. How do you pick a turbo?

I've just got so many questions. Hopefully ya'll don't mind answering them.

 

[FordGuy100]

Thanks for the input. Couple questions, I'm not well versed on diesels, so what is cavitation exactly. And why is it that the block heater would crack the block?

Are ther some basic mods that can be done to improve mpg. I'm not looking for speed, but may someday put a turb on it. How do you pick a turbo?

I've just got so many questions. Hopefully ya'll don't mind answering them.

Cavitiation is basically when holes develop in the cylinder walls, or at least thats what I think. The 6.9's didnt really have that problem, but when they came out with the 7.3 idi, which is just a 6.9 bored out to 7.3 liters, the cylinder walls became thinner which was easier for cavitation to occur.

I would say that a DRW truck isnt going to be the best bet if your looking for best fuel economy. What kind of tranny does it have? The C6 brings down the fuel economy a bit compared to a T-19 4-speed. And lastely what kind of gears does it have? If it has 4.10's, then you will want to switch them out to at least 3.55's.

To gain fuel economy you can fab up a better intake, a free flowing exhaust, and an up to date fuel system (ie injectors and IP). Then try to get tall, skinny tires, that will reduce the rolling resistance. You can swap out to 3.07 or 3.08 gears, which ever one it is, that would help out a ton. And lastely you can add a ZF-5 speed, which has an overdrive which would help a ton. Thats all I can think of right now.

And there are, or was, 3 companies that offer turbo kits. ATS, Banks (there going to stop production in December), and hypermax. You can buy them new to have the peace of mind that you have a brand new turbo system, or you can buy them used on ebay, or on your local craigslist or what not. If you want to fab up a turbo kit yourself, then you are going to be opening up a can of worms. You can fab it up, it will be alot of work, and others have done it, but its alot of work. Theres a bunch of guys on here that can calculate what kind of turbo you want, but I dont have any idea how to do that.

 

[Mr_Roboto]

Powerwise, the PSD's build tons more power than an NA IDI engine. The PSD drives like a gasser, while the NA IDI drives like an old lumbering diesel. So if you are looking for anywhere near the performance of your old truck, you won't find it.

 

[JLep]

Not looking for the power of the old truck, just the benefits of a diesel. And well, just a diesel. I would like to do a turbo later on at some point. Fordguy, thanks a bunch for the information. I really appreciate it. I went and saw the truck tonight, looks really good for the money. Only 2k, minimal rust, I'll probably put on a flat bed, standard tranny, not sure of the gears. Under two hundred k. I think it's a good buy.

 

[adrianspeeder]

I usually buy first and ask questions later, but that might not work in your situation.

Four speed will most def help over a C6 auto for getting some mileage numbers. Swap in a five speed ZF from an 88+ truck and your golden.

Get the axle code from the door jam sticker.

Adrianspeeder

 

[Diesel JD]

Buy it if you can get it for the right price. You might have to change the head gaskets, especially if they've never been done, especially adding a turbo. The C6 is not good on fuel mileage, but is pretty tough and tolerant. If you don't need it for commuting, just for pulling I wouldn't worry about it too much. Manual glow plugs or a solid state conversion and you can forget about the GP problems. Good luck

 

[JLep]

I have a commuter, I need a general work truck. I may drive it to work every once in awhile, but not often. Also, I work at a Tech. School so I can get all the work done I need to on cars with no labor costs and a 30% discount on parts. The truck is out of inspection right now, so I'm gonna trailer it down to the school and get some work done, right away. By the way, the truck is 2 grand.

 

[JLep]

Checking to see if the signature comes up. New to the site.

 

[Michael Fowler]

If I remember correctly ( and that is always an issue)...
Cavitation is present in varying amounts on all internal combustion engines. It is somehow related the compression ration. That is whay it is not much of a problem in gassers. I used to own Peugeots, and they were all wet-liner engines, ( Cyliders are not cast into the block, but are individually installed, and the coolant circulates around them--that is why they are called wet liners) Anyway, I rebuilt several gas engines, and saw cavitation present on the exterior surface of all the liners in varying amounts. It looked liked small drilled holes which were 1/8 to 1/4 inch diameter and very shallow, dish-like.

I believe the vibration of combustion casues gas bubbles to form on the coolant side of the cylinder wall. Either the gas bubbles themselves have a corrosive action or there is erosion of th wall as the gas bubble collapses.

In most engines it is not a significant problem. Diesels have mopre of a problem than gassers, and the thicker walls of the 6.9 make it less susceptible than the 7.3 ( as noted above).
Chemicals added to the coolant solve the problem.