I’m thinking about getting a 6.9L diesel as my first diesel truck, but I’m curious why these seem so much cheaper than the newer Powerstroke trucks. What’s good about them? What should I watch out for?
I like the 7.3 and 6.9 IDI engines. They’re definitely underpowered compared to today’s diesels.
Some 6.9s had block casting problems, and they seem to have more head gasket issues than the 7.3 IDI. You might want to look that up.
If you want a diesel that’s easy to work on without fancy tools or super expensive parts, the 6.9 could be a good choice. But if you’re planning to tow something massive, you might want to consider something else.
@Teal
I used to have a tow truck with a 6.9 and a Banks turbo on it. It could pull just about anything. Tons of power. But, that didn’t stop the cab from rotting off the truck.
Dallas said:
@Teal
I used to have a tow truck with a 6.9 and a Banks turbo on it. It could pull just about anything. Tons of power. But, that didn’t stop the cab from rotting off the truck.
That’s a fair point. I was mostly talking about the non-turbo engines.
I have an '85 F250 with the 6.9 IDI. It’s a solid motor for its time, but it doesn’t have the power of modern diesels like the Powerstroke. The 6.9 is slow but has decent torque.
There are some known issues, like the glow plug controller sometimes leaving the plugs on too long, which can melt them. A lot of people install a manual glow plug switch to avoid that. Another issue is that some of these engines have a block seam near the heater core that can crack if you use the block heater too much. I avoid using mine. Some folks install aftermarket coolant heaters instead.
Avoid late '80s and early '90s 7.3 IDIs. They’re basically bored-out 6.9s and are more prone to cavitation damage over time.
The 6.9 engines are super reliable because they’re so simple. No computers to mess with, just basic mechanics. They’re cheap because they don’t have the performance or popularity of Cummins or Powerstrokes, which are great for tuning. You can’t really tune a 6.9 much, and if you do, you might lose the reliability that makes it a good engine.
@Caelan
Ever tried adding a turbo to one of these? Is it worth it or does it just wreck the engine?
Haru said:
@Caelan
Ever tried adding a turbo to one of these? Is it worth it or does it just wreck the engine?
You can’t push much boost with these engines because they have such high compression—like 22:1. Anything above 7-9 psi and you’re asking for blown head gaskets or worse, like burnt pistons from high exhaust gas temps.
Haru said:
@Caelan
Ever tried adding a turbo to one of these? Is it worth it or does it just wreck the engine?
I’ve got a Banks turbo on mine, but it’s not giving me much PSI. I think I’ve got an exhaust leak right behind the turbo that I really need to fix.
There are people who’ve gotten decent power out of turbos on these engines, though. Check out some videos, like this one: link.
The 6.9 IDI is seriously underpowered, but it’s tough as nails. If you’re towing, though, you might want to go with a 7.3. Either way, both engines are reliable if you know what you’re getting into with the lack of power.
It’ll get you where you need to go… eventually. I had one in an ’87 F250. It started every day and could haul a full load in the bed, no problem. But loaded up, its 0-60 time felt closer to a minute than 30 seconds.
Mine had about 155k miles when I got it, and all I ever did was change the oil and coolant. I sold it with nearly 250k miles for the same price I paid four years earlier. It wasn’t fast, but it was dependable. I think I averaged around 12 mpg overall.
These engines are loud, slow, and smelly, but they’ll do the job.
If you’re looking for a weekend trail rig or something for basic driving, the 6.9 will handle it all day. But if you’re hauling 15k pounds, be ready for a much longer trip compared to newer engines.
I’ve got an ’86 6.9 and I’m building one to hit 330 HP for a project truck. These are great engines—super simple to work on. The aftermarket parts are getting better, too.
I’d take my 6.9 over the 2014 Cummins we have at work. That thing’s been nothing but trouble, and it only has 34k miles! My 6.9 is my daily driver with a 5-speed and 3.55s, and it cruises at 20 mpg.
Super reliable but definitely a slowpoke.