diesel guru's
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Cross-Country
Joined: Dec 2003
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From: Que. Canada
diesel guru's
i am looking at buying an 84 F350 but the 6.9 diesel in it 170k it will run for 20 min then run like crap and just quit and it is almost like it gets hydro locked. it will not turn over for a long while then when it dose won't start. if you leave it for a couple of days it will run fine for a bit and it starts all over .any ideas what this is
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Cross-Country
Joined: Dec 2003
Posts: 68
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From: Que. Canada
havent really worked on this truck at all i'm only going by what the owner has told me.it dosent leak any fluids at all as for turning it manually i will need to talk to the owner more.is there a chance the injectors could be causing this problem
what are the reliability of these engines as i have never owned or even played around with a 6.9 befor i was always a 460 guy.
what are the reliability of these engines as i have never owned or even played around with a 6.9 befor i was always a 460 guy.
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Joined: Jan 2001
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From: Virginia
Well known to go to 300,000 miles if you take care of it. Overbuilt, thick block castings, roller lifters, 4 bolt mains, etc. Diesels are naturally built well to take the high compression they run on. Though that engine doesn't have a lot of power, it's built to run wide open all day long.
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From: Virginia
I like my 7.3, but some people do not like diesels, no matter how good they run. If that engine was overheated, or too much ether was used too many times, it could have serious problems. Even a good engine can be ruined by some people.
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Cross-Country
Joined: Dec 2003
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From: Que. Canada
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Postmaster
Joined: Nov 2009
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From: Broken Arrow , OK
I dont think they are head gasket prone to fail motors. This motor is built off of the same block configuration as the 7.3 Di and 7.3 IDI. They are way over built on the head bolt department. The 6.0's are extrememly head gasket failure prone. They only use 10 head bolts per side where the 7.3's used 18 per side. The 6.9's are bad about cavitation problems. You have to keep an eye on the DCA level in the coolant or it will eat the block and heads up. This may very well be whats going on with that motor. There could be holes in the water jackets causing it to flood the cylinders out and hydroloack. If its hydrolocked it wont turn over at all and if it does you will wish it didnt. They will fold up a connecting rod in a second or push the top of the rod through the piston. I would test the coolant with a PH strip and see if it is within spec. If it isnt then I would stay the hell away from it b/c that means whoever owned it before didnt know to do this and it has probably either got holes in the cylinders or about to have holes in the cylinders.
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From: Virginia
6.9's do have smaller head bolts, but they cause no problems until you add a turbo and start turning up the boost. If that's the way you want to go, then ARP has a head stud kit that while expensive, cures that problem. But like I said, you won't have a problem if you do not run a turbo, and if you do, keep the boost reasonable.
The 6.9's DO NOT have cavitation problems. In fact most people who are going to build one of these old engines up, like to start with a 6.9 because it has thicker cylinder walls. They buy the stud kit for the head bolts, and use these engines to play with. They prefer not use the little bit later 7.3 idi like I have, because it's the same block that has been bored out to give the cubic inch increase, and this makes the cylinder walls a little thinner. This makes them flex more, which causes more cavitation, and since they are thinner, they are more prone to pit through from the water jacket to the cylinder. Most rebuilt 7.3's are sleeved to avoid this problem.
The 6.9's DO NOT have cavitation problems. In fact most people who are going to build one of these old engines up, like to start with a 6.9 because it has thicker cylinder walls. They buy the stud kit for the head bolts, and use these engines to play with. They prefer not use the little bit later 7.3 idi like I have, because it's the same block that has been bored out to give the cubic inch increase, and this makes the cylinder walls a little thinner. This makes them flex more, which causes more cavitation, and since they are thinner, they are more prone to pit through from the water jacket to the cylinder. Most rebuilt 7.3's are sleeved to avoid this problem.
Hotshot
Joined: Feb 2004
Posts: 11,697
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From: Marengo, Iowa
The only failure of head gaskets other than adding a turbo and overboosting it without the stud upgrade is not taking care of the CDR valve and it allows oil to be burned by the back two cylinders. That causes them to run hotter, stretching the rear bolts, and then causing the head gasket to fail. The CDR valve does the basic same thing a PCV valve does, but it needs to be cleaned to allow it to operate properly. When it is not taken care of, it can allow engine oil to enter the intake, giving the problem described.
Fleet Owner
Joined: May 2009
Posts: 21,437
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From: Gilbert, PA
I dont think they are head gasket prone to fail motors. This motor is built off of the same block configuration as the 7.3 Di and 7.3 IDI. They are way over built on the head bolt department. The 6.0's are extrememly head gasket failure prone. They only use 10 head bolts per side where the 7.3's used 18 per side. The 6.9's are bad about cavitation problems. You have to keep an eye on the DCA level in the coolant or it will eat the block and heads up. This may very well be whats going on with that motor. There could be holes in the water jackets causing it to flood the cylinders out and hydroloack. If its hydrolocked it wont turn over at all and if it does you will wish it didnt. They will fold up a connecting rod in a second or push the top of the rod through the piston. I would test the coolant with a PH strip and see if it is within spec. If it isnt then I would stay the hell away from it b/c that means whoever owned it before didnt know to do this and it has probably either got holes in the cylinders or about to have holes in the cylinders.
You have your facts mixed up. the 6.9 does NOT have the cavitaion problem the 87-94 7.3s DO
Last edited by ctubutis; Dec 10, 2011 at 12:27 PM. Reason: Fixed spelling of facts
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Pre-Power Stroke Diesel (7.3L IDI & 6.9L)
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