Hi guys, i have been lurking on this forum for a couple of days now and all can say is that there is a wealth of info here.

I am considering buying a late 80's Fleetwood because i always liked the look and roominess. The only draw back is fuel economy.

I currently have a 1987 Suburban i use for camping and pulling my 22" boat. I has a 6.2 diesel and a 700r4 transmission. I have had this truck for over 5 years and other than oil changes and fuel/air filters, its been maintenance free and a great truck. But even better is the fact that fully loaded with camping gear, 4 adults and towing my boat i get over 28 mpg.

Now i know allot of people look down on the 6.2. some say its not powerful enough, some that it breaks cranks and crack's heads. But that has not been my experience with it and the 3 other trucks i had with one.

I was thinking that if i can get 28 mpg with the Burb, with proper gearing, i should be able to easily beat that on a lighter and more aerodynamic Fleetwood. I was thinking about the 6.2 because of it's simplicity and very good MPG. I know the 6.5 is more powerfull but i dont think i need more. If its fine for my Burg, should be more than enought for the Caddy.

Anybody did this before ?

PS:Please dont tell me the 6.2 is this or that, i dont care...i like it.

Thanks guys !!

Whomever rebuilt your suburban transmission is the reason you have a good story instead of a bad one. Diesel economy is hard to beat and you will not likely do that with a gasoline car.

The only issue is you WILL have to replace the rear axle eventually. Most of the 81(?) to 90 D bodies had a spindly 7.5" axle (ones with the 4.1L V8 and 307 Olds V8), which won't live too long with the 6.2L torque unless you are always very gentle on it.

I would recommend a 9.5" axle out of a Limo, with 2.93 gears, or find a car with the 8.5" rear, but the 9.5" would be far more durable. If you need more gear, the 3.42's ARE out there in the 9.5", just harder to find. This would yield acceptable towing capacity (likely exceed that of the Suburban if it is a 1/2 ton, and excellent fuel economy. The shorter tires of the Fleetwood bring up the gearing as compared to what is on the Suburban.

You would need to find a place to put the water separator, the fuel filter, feed it LOTS of air, get a diesel radiator with the engine oil cooler or add one external in front of the engine radiator. Get a radiator out of a 7L 77-79 Deville/Fleetwood, unless you can find a larger one. Heck, the one in the Suburban might fit too. Do some measuring, they did use large ones too, but might be taller. The best is the 96-99 C/K2500/3500 truck radiator from the 454 or diesel. If they fit, they are the best you can get with factory parts.

Sounds like a good swap.

Ok, what you don't want to hear: Don't use a 6.2L, get a 6.5L TD! Or drop a 6.5L turbo on your 6.2L, make it fun! Just kidding. The military beats the tar out of 6.2L (HD versions) engines and they take it. Just they suck on glow plugs. Oh yeah, you'll need to add a WAIT light somewhere when you hook up the glow plug controller.

See if Dal can get you the diesel "NON CATALYST" underhood engine sticker so you don't have any issues with emissions testing. And you will need to pull the cats and run a large dual exhaust, diesels love to breathe.

Check the dampener (the rubber in the middle dry-rots, and that's what makes them kill cranks). I'm sure that some of the parts could be borrowed from the 5.7 diesel cars to help with things like f/w seperator and "wait" light, but they were based on the Olds block, although that could be usefull info as well because the Olds 307 was used in the Cads in the mid-eighties. If it uses corp. SBC cradle, then the early nineties models were equipped with those for your engine-bay parts needs. I've never seen or heard of this kind of wap before, so I'm here for simple reference on parts-cars, but I hope that you find it useful anyway. PRG04

5.7 diesels had crappy water seperation -use the gear from the truck. But I'm sure the WAIT or PLUGS lamp can be gleaned from the appropriate cluster. I saw an olds diesel cluster with tach on ebay a while back -must be a rare option even on those cars; did Cad offer a tach on any cars?

Duh, I misread your post. You want to put the diesel in a Cadillac. I get it now. Good idea. Weak point would still be the transmission. I sound like a broken record but a 4L80E out of a diesel vehicle (so it has a stand alone computer) would save a lot of headaches. These cars seem to ride better with more weight under the hood so that would be a plus. I know a few people who also swear by 6.2 diesels. It should work great. Since there would be a little electrical work involved, maybe you could upgrade the instrumentation. A real handy thing to have would be a precision ammeter to watch glow plug draw. That would be a plus for one of the sore spots. See you driving right by the gas station instead of stopping in.
What axle ratio does your truck have?

Can you put dual batteries on a D Body easily?

The 700 R4 was the std trans in the 6.2L on a lot of those trucks. Don't know reliability though. They weren't powerhouse diesels (150hp in the military version), and I can't imagine over 300 lb/ft torque, maybe a little more, but not too much. A 700 R4 should be able to live with it if setup properly.

Lots of good comments guys.

N0DIH :
Thanks for you input. I know the 7.5 axle is week, but i don’t plan on towing anything with this car, i have the Burb for that. As for the other stuff, fuel separator, filter and glow plug relay, I think the hood of a caddy is huge, plenty of space there. I also need space for 2 batteries. The radiator could be an issue. I will have to look more deeply into that. For the wait light, il just use the check engine light if it has one or hook up a LED somewhere.

Ape Man:
I know the 700r4 is week. But the main reason most of them die that i have heard of is people towing in OD. I have personally killed one like that a couple of years ago on my first truck. OD should only be used when NOT towing. Also, 700r4 after i think 85 or 86 are built stronger if i remember. I would probably use actual Oil pressure gauge, Volt and Amp gauges instead of the Idiot lights...actually, i could recycle that Oil idiot light in a Glow plug light. I don’t know what axle the truck has but i know its does not rev allot in OD at 65mph, i don’t know the RPM as i don’t have tach. I don’t have any testing what so ever over here in Quebec ;)


I have a couple more questions:
What transmission do the Caddy's come with ? If not 700r4, can one be fitted ?

What about engine mounts ? does it uses standard SBC mounts, i believe the 6.2 uses the SBC mounts, they are the same part number when looking them up.

Oil pan, i don’t know about that one...guess i will find out when i try to drop it. I know its bigger, around 8 liters of oil...Hopefully it clears the cross member and does not hit the ground...

Exhaust will have to be custom, 2 1/2 inch dual probably. I don’t think i will have issues with where the manifolds exit. I have a shop close that can do that...they did it a couple of years ago on my Burb. Is there enough space to run dual 2 1/2 ?

Again, thanks guys for all your knowledge :)

The 90-96 all came with 700 R4/4L60/4L60E, so install is no problem. Might need a 90-up crossmember, get one from a 94-96 and it supports dual exhaust. Not 100% if it fits in the older 77-92 cars, but should be very close.

The 7.5/7.625 (7 5/8") is used in the 4th Gen F-Bodies with that much power and survived a LOT of abuse (a friend of mine runs 12.2's on his with 4.10's). So I don't push replacing it unless the durability is needed. You probably get better mpg with the smaller gear, just don't hammer on it, or if you do, make sure the tires aren't hooking up! The more power I highly recommend the short ratio (higher numerically), as there is more ring gear surface area. The problem is under high torque/loads, the pinion tries to climb the ring gear and something breaks, either the pinion (likley) or a ring gear tooth. Something WILL give eventually....

3" exhaust fits fine, lots of room. Tailpipes might be limited to 2.5", but honestly, 2.5" duals will support a 473 CID engine @ 11.32 in the 1/4 mile, so don't fret needing massive exhaust. 2.5" is plenty fine.

Dual batteries would be easy. After you get rid of the charcoal canister there is plenty of room.
700 R-4 is at the mercy of a competent rebuilder. Sure, it can be done. The 307 cars used a 200 4-R transmission. These were used in the Buke Grand National so they can be made to hold up with torque also. The main ingredient is a hardned sun shell and updated pump. Weak transmissions can be patched just like crappy software. Still not something we can do on the weekends at home.
The oil pan will probably be a fabrication job. You can fit a nice 4 row radiator in the existing space. Consider electric fans instead of the clutch fan. They are hard on the alternator but there will be a lot more room to work with. You have to get fancy with a fan controller which comes on with high side AC pressure as well as engine temp but it might land up cooling better due to poor shroud to fan placement due to the swap.