Hi all, I'm looking at swapping an '86 6.9 diesel into my '87 F-250 to replace my blown 300. The truck that has the 6.9 is still in good running shape, the body is just ready to fall off of it. It has 154,000 miles on it. Just how durable is the 6.9? How many miles can I expect to get out of it with proper maintenance? Does it have any known problems or issues? At least my F-250 has 3.55's in the rear so that will slow the engine down and hopefully make it live a little longer. The donor 6.9 is coming out of a 4x4 and has a 4 speed tranny. What tranny is this? Is it an overdrive tranny? Sorry for all the questions, I just want to make sure this is a good idea before I go ahead with it

 

You are talking about a lot of work. Is your '87 worth it? Basically the 6.9 is a great engine. The only major problem is blown head gaskets. If yours was going to blow, it would have by now or it already did and has been fixed. Do you know the service history of the 6.9?
Have you already bought the 6.9?
The 4 spd. is NOT an overdrive. It is most likely a T-19 from what I have learned from this forum. It is a good trans. Some like it better than the ZF 5spd Overdrive. The t-19 is stronger according to some sources.
One thing is that you will have to get a 2wd tailshaft for the trans. since the doner is a 4x4. You will also need the 2wd driveshaft. The wiring is much easier to change from gas to diesel. Don't know all the specifics.
You have found a great source if info here on this site. Just do a search. I'm sure this swap has been done and discussed numerous times. There are other more experienced members than I, that can fill in details for you. Good luck with the project if you do it.

 

Thanks for the info. Yeah, my '87 is worth it, the body is still REALLY solid. I didn't buy the 6.9 yet, wanted to check here first. While I was at it I was going to convert my '87 to 4x4. A bunch more work, but nothing I can't handle. The tranny is most likely a T-19 since 1st gear is synchro'd. So what axle gear ratio does the '86 F-250 4x4 most likely have??? I thought it would have 4.10's. At 60mph, the diesel is turning about 2250. Is the tach way off? My 300 used to spin about 2600rpm at 60mph with 3.55's... Something doesn't quite make sense here...

 

If you look to the right side of the screen there is the TECH ARTICLES section.Click on it and go to the Ford Axle Code section. There is an axle code on the drivers door of the truck. It helps if it is the original door! You may have a tire size diffenece. Most 6.9's axle ratios I have read about are 3.55 or 4.10.
I'm not sure if the 2x4 and the 4x4 frames are the same in the front. It might be better to swap the bodies from one frame to the other. The cab and wiring would be the only booger I think. Somebody out there should know about the frame similarity. You probably have the Dana 50 TTB 4x4 front axle being a 250 chassis.
Are you near Jamestown, NY?

 

The 6.9 diesel was notorious for perforated cylinder walls. If the antifreeze in the engine wasn't monitored throughout its life for the condition the anti-cavitation additive, that engine could be eating antifreeze right now. When the additive wears out (or is not put in with fresh antifreeze ), the vibrations from the diesel combustion create cavitation in the antifreeze where it touches the cylinders in the block. This cavitation quickly eats away the cast iron.

The antifreeze loss starts off very slowly and makes the owner wonder where that little bit of antifreeze is going. It doesn't seem to leak out on the ground. The condition continues to get worse until one day the owner goes to start the truck and it hydrolocks.

The 6.9 blocks had thin cylinder walls when compared to the 7.3. Because of this, the 7.3 is more forgiving when considering cavitation. In the days of the 6.9, virtually nobody knew to check the condition of the anti-cavitation additive.

The 6.9 was also known for leaking intake manifolds. I think this leak was typically misinterpeted to be a blown headgasket. The aluminum manifolds had little tabs near the back of the heads and those tabs block off coolant passages. Over time, the manifolds would warp ever so slightly and create what appeared to be a head gasket leak. This problem was corrected in the 7.3 when International place neoprene plugs in those coolant openings before installing the intake. They never fixed the problem in the 6.9.

I don't recall "blown head gaskets" being anywhere near as bad as the problem with perforated cylinders. Unless you are absolutely positively sure that the antifreeze in that engine received "heavy duty diesel" antifreeze maintenance, you should run from that engine. Also, the naturally aspirated 6.9 had good torque for its day but it couldn't get out of its own way when accelerating. My 300 6 cylinder gas engine Ford would run circles around my Ford that had a 6.9 in it. Find a good used 7.3 if you really want a used diesel.

Search this forum and you will find plenty of data to back up what I am saying.

 

I could be bass ackwards here, but from what I've read the 7.3 (444cid)is a bored out 6.9(425 cid), therefore leaving the 7.3 with thinner walls and more succeptability to cavitation. Cavitation is a problem with all diesels.
It pays to search these sites. There is a lot of info and fact available.
The 6.9/7.3 are not going to be rockets, that is why people put turbos and propane injection on them. An engine rebuild can vastly exeed the value of the vehicle quickly if you are not careful.

 

Umm, your confused. The 7.3 was the engine with the thin cylinder walls, and cavitation problem. Using a coolant additive controls the problem. I've never heard of an intake problem.

Basically, the 6.9 is bullet-proof. Just be prepared to change the head gaskets @ around 100K. The improved design and 10 lbs more of torque, seems to hold the gaskets for over 200K miles.

Lets put 1000lbs in your 300/6 and 1000 lbs in my 6.9 and we'll see who runs circles.
You've got some funny views, have you ever owned a 6.9l truck?

 

Yup, it looks like I was confused. It's not the 6.9 that had the cavitation problem. It's the 6.9 and the 7.3 that had the problem. In fact, any diesel has the potential to suffer from cavitation issues. I remember when the 6.9's came out and I saw a quite a few suffer from porous cylinder walls. I guess my memory has become selective because of that.

http://www.shopdiesel.com/index.cfm/...coolantfaq.htm
Cavitation%20Analysis

It is my opinion that when the 6.9's were in production, VERY FEW owners knew about cavitation issues and they did nothing about maintaining the proper additives in the engines. Maybe this made the 6.9s seem to be worse than the 7.3s?

The point to consider here is that if you are buying a diesel, be absolutely sure that the previous owner used heavy duty cooling system maintenance on the engine. If he didn't, you are asking for trouble. These are not cheap engines to rebuild.

Before buying the engine go to NAPA or some other parts store, and buy the coolant test strips used for testing Supplemental Coolant Additive (SCA). When you show up to look over the truck, pop off the radiator cap and test the antifreeze. If the coolant fails this SCA litmus test, it is probably a real good assumption that the coolant has not been properly maintained and the engine is questionable. If the coolant passes, you might have a good motor.

 

How about doing a body swap instead of engine swap. As long as the drivetrain and frame are in good shape on the 86 I think thats what I'd do.

 

The '86 is an extended cab longbox, my 87 isn't an extended cab. Everything on my '87 like brake lines and fuel lines etc are in much better shape too. For me anyway, swapping an engine is not a big job at all. It's a whole lot easier to do that than to try to pic up a cab and move it around.

 

You do know that the 6.9 prolly weighs 850 lbs more than the 300/6?

You'd be much better served keeping the 6.9 in the chassis it's in. There's a lot of beefing up on it, to handle the rigors the diesel engine puts it thru. You get a higher GVW too. Plus heavier brakes

 

I just talked to the guy with the 6.9 again. He said he doesn't know if the head gaskets have ever been done, but he knows for sure that they don't leak. It has 154,000 on it, and he said that they probably would have decided to leak by now if they were going to. He also said that it uses no coolant, so I'd assume that the cylinder walls aren't perforated.
Fonefiddy, I looked at the frames and didn't notice much of a difference between the two. What did they reinforce on one that they didn't on the other? I'd assume that just the springs would have a heavier rate, but if I put the 4x4 front axle in my truck that solves that problem. My truck already has the big brakes on it too.

I'm still so torn about what to do. I always said that when the 300 hung it up I was going to do something to cure my power problems. The 6.9 certainly would do that, but with a considerable amount of work, but nothing I haven't done before. I put a Chevy 283 in a '55 ****** Jeep . If that worked, this sure will. On the other hand, another 300 will drop right in and be a whole lot cheaper....but then I'll kick myself for another 150,000 miles for not putting the diesel in. UGH...decisions, decisions....

 

There's a lot to it. From the radiator support, all the way to the rivets used on the frame that are different. I believe the diesel trucks were the only ones rated OVER 8600 GVW. They do have different brake rotors than the ga$$ers. Take a look at the build plates on the D side door jambs. See if they're different

 

I've had F250 Gassers with 8800 and 8900 GVW's, so that shouldn't be to much of an issue. Just buy the 6.9 put it in your truck and don't look back. Simple as that. You know what needs done ,your willing to do the work, that good enough in my book. So get it done. If you take care of the 6.9 it will easily last you another 150K. It will tow more than that 300 six ever dreamed of.

 

Just DO it!
The 6.9 is the most durable of all these Ford (IH) diesels, also has the least punch, but since you only had a 300, it will be a step up, you can keep your truck forever. The wiring will be VERY simple, all the 6.9 needs is 12V at the pump, and a momentary push-button switch for the glow plugs.