6.9 "Wellness Check"

[Mad Maxine]

Howdy.

Wondering if there's a way to check the overall health of my old '86 6.9 IDI.

Necessity dictates that I sell one of my vehicles, and I'd rather keep my truck. However, I'll have to depend on it getting me around as my main mode of transport. Of course there will be the general fixes that an old truck requires, and I'm not averse to spinning a wrench. Should the engine go south though, I'd be in a bad spot considering what even a good used 6.9 seems to cost.

She runs good, and hasn't let me down thus far, though I only drive her maybe once or twice a week. Doesn't leak oil or coolant, 230,000 miles on the truck and engine. I bought the truck from the original owner, and he maintained her well. Obviously, there's no crystal ball, but if anyone has some advice I'd appreciate it. I suppose the first indicator would be a compression check, but other than that, is there anything should I look for? How many miles are these engines typically good for?

Thanks much

 

[shawn deere]

Ive read about 300k is the intended lifespan. Good maintenance would be key tho. A compession check would be a very good place to start. Checking blow by would be a fair indicator, but these high compression beasts have blow by.

 

[Hydro-idi]

Do a compression test if you want to know how your engine is holding up. I don't have the acceptable baseline numbers on hand, but I'm sure someone on here has that information for ya.

 

[OLDBULL8]

Unless your sure about the 230,000 miles, I wouldn't think a compression check is necessary, but it's up to you.

These engine with the proper oil changes and maintenance will last for a Million miles. The cylinders are well oiled.

Any engine can break down at any time for various reasons. It's up to you to know your engine.

 

[Hydro-idi]

Unless your sure about the 230,000 miles, I wouldn't think a compression check is necessary, but it's up to you.

These engine with the proper oil changes and maintenance will last for a Million miles. The cylinders are well oiled.

Any engine can break down at any time for various reasons. It's up to you to know your engine.

Haven't heard of anyone going 1 million miles on an idi before rebuilding. Semi trucks most definitely, but not a 6.9/7.3 idi engine. Chances are it'll need to be rebuilt long before that amount of miles are reached, but anythings possible I guess. I have heard of multiple Cummins engines reaching that # before an overhaul was in order.
Just like a stethoscope is checked for human health, compression tests are used in the same manner to check overall health of an engine. Good idea to do it if your curious.
Just my .02.

 

[pelky350]

I would say if you drive like a normal road going citizen, not wot throttle everywhere and not hauling anything extreme, I'd say 500k isn't out of line for how long it will last, you never now though. It also depends on if those are mostly highway miles or town miles. I wouldn't see why you couldn't go a million miles on the highway with a idi, it's the in town stop and go that Wears and tears on motors in general, hauling heavy and racing around may also play a factor. Change the oil and fluids on time, drive "normal" and keep it clean it should have a good long life!

 

[IDIBRONCO]

When I worked in a shop that remanned these engines, the average 6.9/7.3 life was 200,000 to 300,000. Several went more. Some went less, but that's the range that most of the trucks seemed to have on them. Several had 400,000+. A small handful claimed to have over 600,000 on them. We had no way to verify with a 5 place speedometer. The Cummins vs IDI is just like the old I6 vs a V8 gas engine. The inline engines always last longer due to design. The pistons put practically no side load on the cylinder walls to accelerate cylinder wear. I wouldn't be scared one bit of a 6.9 with 230,000 miles if it always had proper maintenance.

 

[Macrobb]

It pretty much comes down to how it's running /now/, not how many miles it's had. 300,000 highway miles is going to be a lot less rough on the engine than, say 50,000 miles and a couple thousand hours of idling.

Also, it's pretty hard to /kill/ an IDI. When your compression gets /really/ low, it won't start well... but you can have a lot of broken rings before that happens, provided your glow plugs are in good shape.
You'll also probably be using a ton of oil at that point, just from it not getting pulled off the walls by the rings.


I've had a number of unknown-mileage, "worn out" 7.3 motors come back to life just fine with some maintaince type stuff - glow plugs and controller(or atleast checking these), IP(tuned for good timing or replaced), injectors(need to be replaced/fully rebuilt with new nozzles) etc.

With a turbo on an IDI, you'll find that a 'worn' 7.3 will feel a bit weak off idle, but will have just as much pep once you get the turbo spooled as a newly rebuilt motor. At least, that's what I found.


As far as other things to check - water pump(look for side play and leaks. If so, replace), radiator cap(go with a lever lock), Lift pump(cheap and easy replacement, if it hasn't been done in a few years, you might as well), and the tank pickups(tend to disintegrate after this many years; easy replacement but you need to remove the bed or drop the tanks)

 

[OLDBULL8]

Should the engine go south though, I'd be in a bad spot considering what even a good used 6.9 seems to cost.

If your paranoid about that, I'd suggest you get another 6.9 or 7.3 and rebuild it so it's ready to throw in just in case.

 

[Thewespaul]

Maintained a tow truck in a friends fleet that had over 1mil on it. I had resealed the entire engine once and by the time they sold the truck it was drinking a gallon a week. Still brought home the loads though.

 

[Mad Maxine]

If your paranoid about that, I'd suggest you get another 6.9 or 7.3 and rebuild it so it's ready to throw in just in case.

Yep, I'd like to do just that. Seems it's hard to find a good 6.9 rebuild candidate at a decent price (or what I consider to be a decent price for a builder). All the ones I've seen, they want a grand or close to it for an engine that's sitting in a mud puddle.