Diesel Swap Gone Right: Kevin Lambert’s 1980 Cadillac Coupe De Ville

Sometimes, I come across something that makes me do a double-take. For instance, Kevin Lambert’s 1980 Cadillac Coupe De Ville. Normally, I would think it was just another old Cadillac. But Kevin made this car cooler than any Caddy I’ve ever seen by completing a Duramax diesel swap for motivation.

Most engine swaps involving a diesel are simply done to get a truck moving again. A lot of those swaps might have been hastily accomplished and the under-hood appearance less than show quality. And that’s alright for some guys. Not so for Kevin, as the Caddy looks factory delivered. But the quality of the workmanship aside, I had to ask, “Why a Caddy”?

An Unconventional Diesel Swap

“I really fell for this two-door coupe,” says Kevin. “I’ve always been a four-door hard top and four-door sedan guy, but something about the colors and the body lines pulled me towards this car. The interior was immaculate, and I had never seen a full-size sunroof in one of these. It was weirdly optioned.”

diesel swap

Kevin told me that the car has a leather interior, ASTRO roof, factory CB radio, air suspension, and the pièce de resistance when he first found the car, the much-maligned 350 Oldsmobile diesel. I know there might be one or two people that like that old rattletrap engine, but c’mon…

“This was the first and only one I have seen optioned like that,” Kevin quipped. “Since it had a diesel in it already, it also had hydro-boosted brakes, the bigger fuel tank and fuel neck, all the badging, and the glow plug wait-to-start lights. The car spent most of its life in northern California, so it was one of the most rust-free cars I’ve seen.”

coupe deville

Easy loading, although there might be a better way to do this.

Kevin found the car a few years ago while he was in college and looking for a comfortable daily driver that wouldn’t break the bank to drive and maintain. “I had been combing Craigslist and Facebook Marketplace and I was trying to find a VW or Mercedes or diesel,” says Kevin.

The car was listed by a kid who was working for a junkyard. It had a phone number listed and it said it was a diesel. Kevin called the number and set up a time to go check it out. He packed up an old Suburban, rented a trailer, and away he went. However, when he arrived at the junkyard, it was clear that the situation was not properly explained over the phone.

Out of one and into another.

The car was actually in the yard getting picked over for parts. When he asked how it ran, they said ‘It runs great, just needs a battery’. Kevin laughs that this should have made him turn around, but he decided to still consider the car. A few cosmetic pieces were missing, like bumper fillers, the factory CB radio, and trim pieces, but the car looked complete enough and it was rust-free, so he made an offer. “I think I paid $800 for it and a loader operator picked it up and loaded it onto the trailer and we headed home,” Kevin states.

Long story short, he soon learned the age-old sales trick that “just needs a battery” really translates to “the engine is completely seized up”. With this new-found information, he pulled the factory Olds 350 diesel out and tried to save it. “I had the crankshaft turned, found new rods, started buying parts, had the block honed, and then, I learned the heads were cracked and I decided to cut my losses,” he says. “To get the car running I had a good running 396 big-block with a Turbo 400 from another project and decided to drop that into the car.

diesel swap

The Need For The Diesel Swap

He drove it with the big-block for roughly two years and it did what it needed to do, but a carbureted big-block is far from anyone’s idea of an economy ride. He started to think about installing a 6.2- or 6.5-liter GM diesel, as he felt it would have similar enough external dimensions to a big-block and would fit in its place.

Kevin relays, “I had bought a 6.5-liter engine from a friend and was planning to get it ready to use for my diesel swap. Once again, I learned that ‘it ran awesome years ago’ means, ‘I don’t know man, I haven’t turned it over in years’”. Once again, Kevin learned a hard lesson as this engine sat for several years full of coolant and was frozen solid. At this point, he had a zero and two record with diesels and decided to postpone the project for a while.

An Unexpected New Beginning

Fast forward two years, and Kevin is in the process of starting a prototyping and CNC machine shop with some of his former college classmates. He had found a 2006 GMC van through a friend and decided to go take a look. It was a service van from a small company in Boston. It had high mileage, but it was motivated by an LBZ Duramax with a 4L85e transmission. He made an offer and drove it home. After a few years of service as the shop truck and his personal mode of transportation, it was totaled on the interstate when a tractor-trailer load of hay bales fell off the trailer right in front of him. He had the van hauled home and after a few hours of measuring, he figured he would pull the engine and see if it would fit in the Caddy.

The engine is completely stock, but when he started the diesel swap in the car, he had to switch from some van-specific parts to truck parts. Things like the intake Y-bridge, fuel rail drain lines, fuel feed and return lines, dipstick, intake horn, and thermostat housing all had to be swapped. Luckily, he was able to find used parts to replace all of these components. His goal was to have as many OE parts on the engine as possible to ensure that he would be able to find replacements far into the future. But there was one part that had to be modified.

diesel swap

“When it comes to the oil pan, That’s been a project itself,” Kevin laughs. “I am on my third iteration of modifying a cast aluminum pan. There needed to be a significant amount of cutting and welding done to make the pan clear the front frame section. I was able to retain the windage tray and lower bolt-on pan, so capacity is marginally affected. The engine mounts are off-the-shelf Duramax diesel swap mounts made for 1990s GMC trucks.”

Kevin had the 4L85 transmission rebuilt and the only thing he had to do was convert to an old-style GM shift lever for the selector. The transmission crossmember is a combination of two stock crossmembers welded together to support the 4L85. The factory Cadillac 7.5-inch rear is still in service, has a Positrac with 2.56 gears and a factory sway bar, and utilizes the factory air level-ride suspension.

The Details Matter With This Diesel Swap

The electrical connections for this diesel swap are made via the factory van harness which has been modified to add in cruise control and instrumentation outputs. “I sent the harness to standaloneharness.com, and Ken Wolkens took care of the slimming down and adding the options I requested,” says Kevin. “Every dash light in the car works and is activated from the ECU. The cruise control takes advantage of the original brake pedal switch and blinker controls. The torque converter unlocks with a press on the brake pedal and works with the stock pedal switches. The speedometer is driven by a Dakota Digital PWM connected to a cable drive box and is adjustable. The air conditioning control is integrated into the stock vacuum-driven hysteresis controller and works flawlessly.”

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Kevon’s Caddy is definitely something different, and when push comes to shove, different is not always a bad thing.

Do you want to read about more Readers Rigs? All you need to do is click here. I want to see your trucks. If you would like to share yours, I want to hear about it. Since I started this series, I have received more than a few candidates, but I still want to see more — I can never get enough. If you want to see more trucks built by you the readers, send a few pictures of your truck showing the engine, interior, and exterior, along with all of the pertinent information, and I’ll make you internet famous. You can send your submissions to DieselArmy@powerautomedia.com.

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About the author

Randy Bolig

Randy Bolig has been working on cars and has been involved in the hobby ever since he bought his first car when he was only 14 years old. His passion for performance got him noticed by many locals, and he began helping them modify their vehicles.
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