6.9 IDI vs. 7.3 IDI - Diesel Forum - TheDieselStop.com
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Old 08-22-2005, 08:52 PM   #1 (permalink)
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6.9 IDI vs. 7.3 IDI

I'm trying to sell the wife's 2000 Dodge Grand Caravan and buy a 3/4 ton diesel truck. Since funds will be low I'll probably only be able to afford a 6.9 or early 7.3 Ford. I'm somewhat familiar with the 7.3 IDI and 7.3 PSD (my father-in-law owned a 1991 F250 and a 1996 F250) but I've never been around a 6.9 IDI.

What are the pro's and con's of each engine?

Given the choice, what would be the better engine?

The truck will primarily used for commuting with some occational light hauling/towing. I also plan to use biodiesel and maybe even WVO.

Anybody have any experience using BD and/or WVO in a 6.9 IDI or 7.3 IDI?
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Old 08-22-2005, 09:27 PM   #2 (permalink)
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Re: 6.9 IDI vs. 7.3 IDI

Well the cons of both engines kind of weigh out evenly(somewhat). I mean in the 7.3 you have to watch the SCA level in the coolant-otherwise she will cavitate, and on the 6.9 you have to watch that you dont lay your foot into it so much you blow a head gasket or shoot a head through the hood. [img]/ubbthreads/images/graemlins/frown.gif[/img] [img]/ubbthreads/images/graemlins/sick.gif[/img]
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Old 08-22-2005, 11:04 PM   #3 (permalink)
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Re: 6.9 IDI vs. 7.3 IDI

I'd go with a 6.9 and treat her nicely. The 6.9 and 7.3 are NOT fragile. I have a 7.3 and at 200,000+ miles it sings along just fine.

When I was deployed a couple years ago they were running old school buses with the 6.9s in them pretty hard 24 hours a day. Early 1980s vintage schoolbuses with 6.9s still doing their job. Not bad.

If not for the cavitation issue, I'd wholeheartedly endorse the 7.3. I took the chance and have been okay so far... but you never know who's kept SCAs up and who has not.

I put a turbo on mine and it'll pull 10,000 pounds of brick-shaped gooseneck horse trailer all day long at interstate speeds, slightly less on hills depending on grade. Good enough for me, and no new truck payment.

Find a 6.9 with a good body and run it.

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Old 08-23-2005, 09:20 AM   #4 (permalink)
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Re: 6.9 IDI vs. 7.3 IDI

If I had it to do over again I would have stayed away from the psd and gone with an old 6.9. The 7.3 have thin cylinder walls because it is a bored out 6.9. The 6.9 tend to blow head gaskets if you are very hard on them. You can fix the head blowing weaknes. You cant fix thin cylinder walls.
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Old 08-23-2005, 09:47 AM   #5 (permalink)
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Re: 6.9 IDI vs. 7.3 IDI

http://img.photobucket.com/albums/v2...562_edited.jpg

In the link above ^^ is the 1986 with a 6.9 I sold last year. Best pick-up (and motor) I ever owned. Perfect-straight body and all stock expect dual exhaust. Always garaged and never off-road since I bought it new in the winter of 1985. I sold it on here (thanks TDS) a few hours after I posted it. Wish I had it back. The 6.9 is a great motor!!
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Old 08-23-2005, 04:07 PM   #6 (permalink)
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Re: 6.9 IDI vs. 7.3 IDI

if you do have head gasket problems on a 6.9, you can install ARP head studs and your problem will be solved. i would choose a 6.9 with studs over a 7.3 IDI any day. mine has 300k (see sig) and it gets run hard every day with no special maintenance aside from regular oil changes at 3500 miles. still a great truck. they dont need to be babied like some here think.

i test drove a 2002 superduty gasser and decided it was no better a truck than my '86 for what i need it for. [img]/ubbthreads/images/graemlins/cool.gif[/img]
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Old 08-23-2005, 04:17 PM   #7 (permalink)
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Re: 6.9 IDI vs. 7.3 IDI

I'd go with the 6.9.
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Old 08-23-2005, 10:10 PM   #8 (permalink)
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Re: 6.9 IDI vs. 7.3 IDI

Well, actually, you CAN have the cylinders sleeved... common practice among folks who rebuild 7.3 IDI engines...

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Old 08-23-2005, 10:13 PM   #9 (permalink)
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Re: 6.9 IDI vs. 7.3 IDI

These old motors just feel different... I like driving them a whole lot.

The new engines are nice for pickup, but there's something to be said for driving the uncivilized IDI trucks... :-) I've had several folks walk up to me since I've owner her wanting to buy her or wanting to know how old she is. One fellow thought she was brand new... which surprised me given the condition of the paint on top of the hood (guess he didn't see that...)
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Old 08-23-2005, 11:04 PM   #10 (permalink)
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Re: 6.9 IDI vs. 7.3 IDI

Well I know you can sleave them it but you can usually find another core cheaper than getting it sleeved. Head studs are cheaper and easier to replace.
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Old 08-24-2005, 07:16 AM   #11 (permalink)
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Re: 6.9 IDI vs. 7.3 IDI

As for running WVO, some fuel systems are better for that operation; I think bosch is the injector pump you would need.
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Old 08-24-2005, 12:36 PM   #12 (permalink)
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Re: 6.9 IDI vs. 7.3 IDI

There is no difference with the use of WVO. The stanadyne DB2 pump is not preferrd for WVO systems, but Magyver and some others are successfully running WVO with a heated system...even if you do blow up a pump they are replaceable for $250-500, it won't take long to be money ahead at today's fuel prices. The 6.9 is my favorite, I'd plan on replacing head gaskets and glow plugs. If you don't have to pull the heads you're lucky, but some haven't had to,
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Old 08-24-2005, 12:54 PM   #13 (permalink)
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Re: 6.9 IDI vs. 7.3 IDI

Just my 2 cents, but if you are going to use the truck for commuting, I believe the deciding factor should be the transmission(ie gearing) and not the motor. The older trucks do not have an overdrive transmission and in my opinion are not good highway cruisers. If you are going to make a reasonably long commute, I would recommend you be sure and get an overdrive transmission. I think both motors are excellent and you can expect years of service from either one.
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Old 08-24-2005, 08:59 PM   #14 (permalink)
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Re: 6.9 IDI vs. 7.3 IDI

My dad had an '85 6.9L F-250 2wd. When he gave it away three years ago, it had about 225K miles on it, IIRC. Virtually problem-free and it had a very hard life.

My brother has a '93 7.3L (pre-Powerstroke) that he bought a couple of years ago. It's been nickeling and diming him to death but once he gets things ironed-out I believe it will be a fine truck. For some reason, it does not have the power of the 6.9L my dad had.
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Old 08-24-2005, 09:58 PM   #15 (permalink)
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Re: 6.9 IDI vs. 7.3 IDI

For those suggesting the 6.9 Ford actually built a few, very few 1987's with the ZF 5-speed. 1987 they also went to the revamped cab and 4x4's got a real front axle. Otherwise you are looking at 88 and up 5-speeds or 89.5 E4OD's.
By the way every auto supply house has the wrong part listed for the early 7.3 glow plug controller. They all try to give you the 6.9 "WET" controller instead of th "DRY" one that is only available at the dealer.
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