GM’s Worst Engines: Why The 1981 V-8-6-4 368ci Engine Was a Failure 

My uncle worked for a large Cadillac dealership in the early 80s. He told me for a time the service department each week did dozens of disabling jobs of the system. Once deactivated, the 368 was a solid and reliable engine.

I had my Arco station back at this time and we had a number of customers with these engines. These people were not concerned about MPG, they wanted smooth. After many trips to the dealer with no improvement they came to see me. Disconnecting the brown wire at the transmission would keep it in V8. My customers were happy.

I remember when I was a kid my aunt and uncle bought a brand new 1981 Cadillac Coupe Deville with that engine. After they picked it up at the dealer they stopped by our house to show us the car. And the car started giving problems in our driveway. They had to get it towed out of our driveway.

I had a '81 Sedan DeVille with a 8-6-4 368. I locked it into 8 cylinder mode and drove it 340,000 miles trouble free. It required just routine maintenance.

We had a 1981 Fleetwood Brougham; grey exterior and grey, button-tufted velour interior. The most beautiful car and the most comfortable car ever. We had a toggle switch installed that was mounted under the dash. We kept it in V8 mode while in-town use and flipped the switch to the V8-6-4 mode on the freeway. Ran like a top for 10 years. Absolutely no issues with that engine. The car was a delight. Too bad it wasn't just a V8-4 engine.

The actor here is Don Matheson who is probably better known for his character Mark Wilson in Land of the Giants. He also guest starred in an episode of Lost in Space where he uttered the immortal line, "Crush, Kill, Destroy!

Great marketing pitch and (seemingly) great idea. Car makers still are struggling with cylinder deactivation, so it is not a trivial problem.

The current displacement on demand engines GM has now still SUCK! Oil changes are absolutely critical for these engines or they blow up.

I worked on dozens of these cars back in the day and even owned an '81 Eldorado that I drove for years. Wonderful vehicle. Yes, some computers suffered from RF interference causing the 8-6-4 feature to act strange at times. It was a isolation problem. Nothing to do with the functioning of the rocker arms or fuel injector, which BTW simply cut it's pulse-width in half (in 6 cyl) and shut off entirely (zero pulse width) in 4 cylinder. It worked excellent. As a test, I un-pluged the oil pressure (governor pressure) switch on top of the transmission ( you could easily reach it) causing it to remain in 8 cylinders all the time. The fuel economy at a steady 70 mph went from 16 mpg in 8 cylinder, to 26 mpg in 4 cylinder. It was wildly effective. It is my personal opinion these cars got a very unfair rap and were truly ahead of their time

The time, money and energy to get a few more MPGs was counterproductive in so many instances.

Basically CAFE helped wreck Cadillac. In just 9 years 5000+ pound cars with 8.2 liter engines became 3400 pound cars with 4.1 liter engines and lost as much as 38 inches in length and 8 inches in width to boot. Such a radical change took Cadillac from what it did best, making enormous luxobarges with reliable gas-guzzling engines, to having to downsize drastically while trying to maintain some semblance of power and prestige. The technology just wasn't there fast enough, and a whole bunch of bad engines along with tiny, cookie-cutter cars destroyed Cadillac's reputation. The more reliable 4.5, 4.9, and Chevy-powered Fleetwoods of the time were helping to dig them out of the hole, but it was too little too late, especially once the Northstar head gasket debacle occurred.

I owned a 1981 Seville with that engine with it disabled . Not fast but smooth and trouble free , Two tone as you have pictured in video , silver and burgundy . Very elegant car. You either loved the look or hated it ,,I loved it .

More than 40 years later the advice to anyone buying any vehicle, new or used, is to avoid Cylinder Deactivation (or whatever name given it to hide its presence). Whether it is GM, Honda, Ford, Mazda, Mopar, VW, BMW. Mercedes Benz, Hyundai, or others, ... avoid high mileage versions with CD.

The 4.1, 4.6 and diesel were all steaming piles but the engine used for V8-6-4 was based on the L61 which was a decent mill. The problem with this car was the engine management system which was not up to the task, the basic engine was fine.

GM has always rushed things to market without proper R&D. They have been doing this for decades and still are to this very day.

The 368 Cadillac V8 is in the same engine family as the ever so reliable 472 that was inroduced for the 1968 model year. The 368 is a good engine, but, the additional electronics with DOD gave it a bad rap. Cadillac should have kept the Olds Rocket 350 as their primary. That engine had MPFI, and was very reliable !

I owned a '80 CdV with the carbureted 368, it was the sweetest running carbureted engine I ever had. I dailied it in and out of Boston for a while and it never missed a beat, never overheated. I thought the torque was adequate. Shame that Caddy tossed the baby out with the bath water, and rushed out the hideous Hook & Tow 4100, which maybe did more to damage their reputation than 8-6-4.

compared to the HT-4100 & the North Star the 864 was a bloody jewel !!! If I could find a 1981 Eldorado with the 864 I would snap it up.

In 1981, my dad bought a beautiful triple black Eldorado with the 8-6-4. After owning the car for several years, the 8-6-4 turned out to be one of the only things on the car that was NOT problematic. His Eldo was built without one of the crank bearings and it took the dealer nearly 3 months to find it!

I remember those being advertised when I was a teenager. Seemed like a great idea in theory, and I can’t fault them for trying it. However, the execution was just amiss. What a shame for a car brand I’ve always rooted for, since I was 7 years old.

The Olds diesel, the V-8-6-4, the HT4100, and don't forget the Cimarron, LOL. Yes, Cadillac was really stumbling in the early '80s.

My '77 Sedan DeVille with 425 was adequate, but seemed heavy and fairly slow compared to my '80 Sedan with 368. The '80 was light and responsive, and had terrific balance and handling. Later I had an '84 Fleetwood with HT4100 that was predictably a slug, and then an '86 Fleetwood with the Olds 307 was only mediocre. Dad had an '83 Seville with HT4100, not superb, but better than the RWD C-body. Friends of the parents bought an '81 Coupe new with the V8-6-4, liked it and had no problems until it was traded about 1986. My biggest lament about the V8-6-4 is that it basically meant the end for the fantastic 368. My 1980 Sedan now seems like it was a unicorn, and I seem to remember topping 20 mpg on highway trips!

When these were introduced I totally understood the concept. The ancient Olds 88 I was driving at the time practiced it's own form of cylinder deactivation, particularly in wet weather.

The Cadillac 4.9 is not too bad. The Northstar COULD have been great with hardened steel inserts in the block to anchor the headbolts and better gaskets in the skirt and oil pan. So, I declare the carbureted 425 was the last GREAT Cadillac V8.

". . .if you can believe 429 CID was too small . . ." The Beast of Turin enters the chat - "EACH of my 4 cylinders is 427 CID" (1910 FIAT racing car. Has 4 cylinder 28L engine - still exists and is driveable)

We had some family friends who were big GM people,, we were Ford people,, and in the early 80's his wife had 2 bad Cadillacs in a row and he had 2 bad Corvettes in a row so the next thing we know she's got a Town Car and he's got an 85' Ford Bronco with the 5.8 HO 4 barrel and from then on he was a Ford guy,, and for the rest of his life...

One of my cousins bought a 1981 sedan Deville with the six cylinder option, white with a blue interior. I rode in it many times, and it was a most pleasant and reliable car for him. I guess it wasn’t overly fast, but certainly it would carry, several people in comfort and I never noticed it being overly slow.

I had a limousine service that used the Fleetwood 75 as our corporate transportation vehicle. The cars were great as they could move 5 people comfortably on velour seats (in the rear) and leather in the front. The divider was manual, the rear passengers could control the a/c as well as the radio and there were 2 seats that you could open (un- fold) and you then had seating for 5 in the rear. This was called the formal limousine. The engine was an 8-6-4, and it was just the worst for gas mileage and dependability. In our fleet we also had a Sedan De’Ville with a 4100 engine in it and everyone preferred the 4100 to the 8-6-4. I was able to have the 8-6-4 disconnected to just run as an 8. I was able to buy 3 1984 ‘s with 3000 miles or less for 25k or less from an investment banking firm. Running them just as an 8 cyl. was great. No great mileage but lots of comfort and lots of room for luggage and people. It was also great to use around Wall Street . This was before the stretch limo became popular. I ended up selling them all and making a profit from them. Caddy came out with small limo that were awful and soon we converted to all Lincoln town cars. They were great. The best thing about the caddy was driving in lower Manhattan. You could make it around the tight curves which you could not do with a stretch limo. Also the FDR drive had a weight limit of 6000 lbs at 96th street going south. These cars were about the worst caddy ever offered.

My Cousin Bought One For $500 In 2000. Had 130,000mi. Ran Perfect. 8 6 4 Still Worked As Intended.

Oh, The early eighties and the overreach with electronics by almost all manufactures!!!

My dad and I were talking about the V8-6-4 and the HT4100 grenade. He joked that Cadillac went from "The Standard Of The World" to "The Terror Of The World"!

When I heard Mazda had 2 cylinder deactivtaion, it remiinded me of this engine.

My father had one of these, and it was nothing but trouble.

The American car industry never was the same, once the government put their hands on it.

At least the base engine was solid. So if the engine was made to stay in v8 mode, it was solid

Even today I won't want an engine with cylinder deactivation. The fundamental problems are still there. I had a neighbor who was a mechanic and he worked on these. Or I should say he replaced these.

Still better than the crossover garbage people drive today

The V8-6-4, 368cid, was still a good, sound engine with torque and adequate power. All you had to do was reach under the hood and yank one plug. Problem solved. You got a true, Cadillac big block V8 that ran on all 8 cylinders. So, what's the fuss? I had one, unplugged the V8-6-4, done. Simple.

A common "fix" for this engine was that many people who bought it would disconnect the wiring, turning the V8-6-4 into a regular V8 engine. That's what I've heard anyway, not sure how true that really is. After all, one can't believe everything they hear.

I had a 1981 Eldorado Hess & Eisenhardt custom convertible with V864. I worked flawlessly and most time was spent in 8 and 4 cylinder modes. The 6 cylinder mode was more for transition. I guess I got a fluke since my Eldorado always ran well. Great video as usual Adam.

It bugs the hell out of me when sources degrade this engine. In all honesty it was last Cadillac engine that was any good, being an all iron block and heads, and its roots were from the reliable 472, 500 and 425 engines prior. Just delete the cylinder deactivation and you have the same 368 from 1980. Cadillac was forced to do this to meet cafe standards, when they saw that it was a failed system, option B was even worse in 1982 by resorting to the HT 4100.

A sound robust engine married to a technology that was introduced years before it was ready for prime time. What they should have done instead was make TBI std across the board on the 368 and installed a more robust version of the 200-4R automatic overdrive transmission which would have bumped highway mileage into the mid 20's and got them to 1984 when the new smaller FWD C-body cars were being introduced and more development time on the HT4100 V8

My uncle had one of them in his Fleetwood, what a hunk of junk.

Everything Ive seen from MANY good automotive youtube channels shows that the current generation of GM AFM/DOD engines have horrible reliability and longevity. And just like the V864 of old the only real fix - after replacing crapped out lifters - is to disable the feature. Some things never change at GM.

Nice. There is a beautiful 1981 Eldorado for sale near me. It has the V8-6-4. Been for sale for months.

My uncle had 1. The 8/6/4 system kept giving him trouble. As he put it, it seemed to 'hunt' between power modes. The dealer simply told him to use the in dash button feature to turn the system off each time he started the car. No issues after that, as it was in V8 mode all the time and he claimed it actually got better mileage with the system turned off!. He traded it in for a 89 sedan DeVille, his 1st FWD car. What I will say is if you look at the valvetrain set up in an untouched 8/6/4, it was incredibly complex. Given how bad Delco electronics were in this era, I can't believe it even worked at all!

Thank you Adam for this video! In the mid 90s i lived next to a fella with an 81 Coupe Deville with the 8-6-4. He loved that car and took great care of it. Oddly enough; he never had any trouble with his. I think he got very lucky!! Thank you again for your videos!!

My Dad was a Cadillac man and owned a '76 Seville still in 1981. We went to look at the new Cadillacs and a salesman opened the hood on an 8-6-4 equipped vehicle. My Dad's response, "That looks like a whole lot that can go wrong." I'll never forget it as he shook his head and walked away. Way to go, Dad!

It is tough to make a variable displacement engine that lasts. Have a friend who had an Oddessy with the V6 which shut off two cylinders in eco mode. He got rid of that van with only 60k miles due to it turning into an oil burner. Plugs kept fowling out.

It wasn't the engine,it was the fuel injection that failed,the 1980 had the same engine and it was a great car but GM thought that the HT 4100 would be the way to go, but I think that engine was crap.

Adam, I’d like to hear you comment on something you may have mentioned before, that was that GM had been planning to reduce the size of their C-bodied cars, regardless of whether CAFE had happened. You, or whomever I heard speaking on this, said that the C-body’s dimensions were at the maximum size and that this was no longer tenable, or necessary in the market conditions of the 1970s. Thanks for all your excellent work; I check daily for your newest programming.

45 years later and GM still cannot figure it out.

Thank you Adam. I watched the video and I realized something. GM was successful with its downsizing in 1977-1979. They tried to do it again in 1985-1987 and it failed. They did it for the same reason fuel economy and government standards. I think the reason it failed the second time is they cars got too small and they no longer had divisional brand identity that stood out. GM then spent all that money correcting the downsizing in 1989-1992. That cost money, market share and time. It is interesting the 1977 new B and C bodies had the dimensions of the 1973-1977 midsized GM cars. They became the new definition of full size. Over time the engines and fuel economy got better. Cadillac however had a series of engine disasters from this engine in 1981, the HT 4100 and finally got on a good streak with the 4.5 and 4.8 liter V8 only to get back on another bad streak with the Northstar V8. The Oldsmobile diesel V8 is not winning awards and it did not help as it hindered adaptation of diesel V8's and it was under powered, and not reliable. The 1980's was not a good time for Cadillac. Thank you for talking about this engine and how this type of engine exists today.

People who do not change their oil on a regular basis, get what they deserve. Same goes for transmission fluid and filter (not talking about flushing).

We had a Seville with this engine. Going downhill, the fuel economy number would shoot up, but on the way back up, the opposite was true. I liked the bustle back styling but the engine didn't seem as nice as it should be. We had a 425 before this. Sadly, the Seville got traded in on a 4100 Fleetwood which was kind of underpowered. I had an 89 FWD Fleetwood with the 4.5 and it was much better in that configuration than the RWD Fleetwood. Today, Caddies have engines that are not unique to the models. So sad. I love the Lyriq, but again, it lacks the heart of a real Cadillac. I could have a dream car, it would be a 64 Cadillac Eldorado convertible.

My parents owned one of these in the early 2000's. My dad got it cheap and ripped the v8-6-4 out, slapped in a 400 sbc and never looked back... My mom said the car would idle itself up to 40mph. I don't know how we ever lived through my childhood.

Just another example of GM putting something out before it has been fully tested and developed. The computing power just wasn't ready yet.

It sounds great on paper

Thanks for this one, Adam.. I remember well watching in absolute horror as Cadillac proceeded to just completely self destruct as a brand during the early 1980s.. It was sad to watch, and it was a nadir that took decades for Cadillac to climb out of.

Adam, I'm always impressed by how much detail you go into. This is a video that wears many hats, but the topic is spot on. I always wondered if this engine could be successful with better electronics; however, I didn't realize that their idea of fuel injection was basically a carburetor. There's essentially nothing you can do...

Everybody I talked to than owned these back in the day had the system unplugged. I'm not sure how the limos did it, but they were geared differently and didn't have a MPG sentinel to tell if the system was working or not. Maybe GM tricked the system on the Limos, who knows 🤷

They should have gotten rid of the 6 cylinder mode and kept the V-4-8 until they had cars which were small enough for the 4100. They could have made up for the annoyances of the system with extended warranties and total deactivation for customers who insisted. Either would be better than an underpowered engine that won't stay in one piece. It could also have been a positive learning experience for GM and certainly a less painful one than the early 4100s. It must have taken an army of yes-men to get the 4100 approved when it was so obviously a disaster in progress.

I have a 2012 EXL-V6 Honda Accord that has turned cylinders on and off flawlessly for 12 years and 150,000 miles. How did any leader at GM keep their jobs during this time?

The EPA was so concerned about the PPM, they failed to understand if you use LESS gas, you have less "M" for the "PP" to matter. It was the EPA that killed mpg in the 70s. Most American small block V8s BEFORE the EPA stepped in got 20+ mpg on the freeway. (Excepting the L79 or Boss 302, LT-1, and other HYPO engines or course).

In 81 to best thing to do (I did with my mothers Seville); go to the dealer and disconnect that stupid 8-6-4 garbage-was only a plug on the transmission. Then, the engine went back to normal. The 82-85 HT4100 was awful and underpowered. At 90 k perfectly maintained miles my 85 Eldo dropped dead. Close to $4000 to redo the engine. In hindsight I should have replaced it with a V8 350.

And, lest we forget, to add to the misery in this time period, Cadillac also introduced a re-badged, dolled up Chevy Cavalier known as the Cimmaron. Dark days indeed for Cadillac. In the meantime, Lincoln overtook Cadillac in prestige and desirability.

Ah yes, GM's favorite method for ruining an otherwise amazing, reliable V8- cylinder deactivation! The fact that this concept failed in 1981, and has continued to have so many issues even on the modern LS V8s, is really a major frustration to those of us who really typically like GM V8s.

Cadillac sold a lot of Lincolns in those years.

I was gonna Mention VICE GRIP Garage. Derek did get it running. He removed all the smog disco equipment and the throttle body and put a Holley carb on it. Ran smooth after that

IMHO 1977 to 1985 best looking Cadillacs of all time.

They should have made a V8, 10, 12, lol

My buddy’s dad had a new one of these when we were in college, we used to love to screw around with it and watch the instant MPG readout go from 0 to 99 😁 That was a long time ago, but I still remember the six-cylinder operation was pretty crude.

Sounds like a good idea but not practical at least then.

Our government should reward all companies who create efficiencies, at all methods of production and energy, instead Forcing Companies to Government standards. I never could understand why Our Federal government does this. Products like this cause problems for everyone. It still exists to this day. Just Crazy.

i think cylinder deactivation should be driver choice like a slap shift, both of those would be great in a vehicle.

I was a Cadillac Master Craftsman when these were new... Mostly disabling the V8 64 systems... They failed regularly...

Every current engine manufacturer that uses cylinder deactivation that I can think of has a problem with it. GM, Ram, and Honda. Not just drivability or vibration, but valve train longevity.

My mentor was a master collision tech refinisher, and was a used car man as a second form of income. He said he found that he filled his lot with Cadillacs in the mid 80s with engine issues. He said in the early 80s Cadillacs had devolved into merely a nice place to sit. Along with dozens of diesel Oldsmobile 88s and 98s, all of these bad Cadillac V864s HT4100s received used Oldsmobile 350s sourced primarily from rusted and crashed Cutlasses. They were a cash cow for him.

On Vice Grip Garage, Derek did later get his 81 Cadillac running with a new ECM.

They only offered it 1 year. That should be telling. For the GM premier marque to have so many engine problems is pretty inexcusable. After 8-6-4 it was the disastrous HT4100 that couldn't be disabled.

A wonderful summary, Adam. I never had the joy of driving one and would have liked to just for the experience.

Still better than the HT4100. You could at least deactivate the 8-6-4 problem, but the 368 was actually decent in its conception. The Aluminum block, cast iron head 4.1 was a disaster. Cadillac should have gone with the 350 Olds in all their models.

Drove mine across the country both directions and averaged about 27mpg’s. It was a pain to keep working and the vibration in 6 cylinder mode didn’t feel great but it kept on going.

Most Cadillac buyers back then wouldn't even consider a V6. Too bad it was the best engine available.

My Aunt and Uncle bought a 1981 Sedan DeVille. My Uncle complained so much about the engine (8-6-4). They would not keep it long before they traded it in for a Grand Marquis

Just deleted my 2015 4.3 v6 in my silverado, it runs smoother and gets just as good of mileage maybe even better. It would shake and vibrate when in 4 cylinder mode, and will lessen the life of your engine.

I have a V-6 3.5L engine in my Honda. And it switches between 3, 4, and 6 cylinders. Even though, it is all wheel drive, and weighs 4,000 pounds. It can cruise along at 70mph, with the AC blasting, and get 30 mpg. Stop and go traffic, is another story. It loves gasoline in those conditions. PS It has active motor mounts, and active sound control for the cabin, via the sound system.

The sad thing is that they still hadn't learned completely from this design. I mean newer AFM engines are a lot better but they still can run into issues, particularly if oil is not changed enough (and I had a Silverado with AFM -- 2013 year --- and apparently found out later that I needed to change the oil about every 3,000 miles). Mine only started having issues after about 200k miles so I got quite lucky in some respects but got rid of it after that. I imagine the 1981 design was far worse though.

Fast forward and V8 cylinder deactivation is relatively common. They had the right idea, they just didn’t have the technology.

I feel the Northstar is a bit categorically different than the prior engines it's compared to. From my experience it's not the catastrophically problematic, already in its early years (original owner / second owner, still in warranty, etc.), that some of these predecessors seem to have been. My family have had 3 or 4 ('93 STS & '98 STS for my parents, '08 DTS for sure for my granddad, I think the '08 DTS replaced a DTS a few years older... but that was a long time ago now) and the most significant repair I'm aware of was the water pump on the '98 just before it was traded for a CTS4 in 2010/11.

I remember the smart thing was to swap this engine out with a 350 olds motor

Never understood why they did this goofy solution instead of just using that 350 olds gas engine out of the previous Seville. It made more power than this larger 368 and probably got better mpg than this silly solution.

I 83 I had an 81 Coupe de Ville with the 8 6 4 de-activated and the car ran flawless for years

My best friends father just HAD to have a Cadillac after his older brother bought a 1982. He couldn’t afford a new one so he bought a used 2 year old 1981 Coupe De Ville. What a lemon! This thing spent more time back at the Cadillac dealer than it did in his own garage. The V8/6/4 was one of the myriad of issues. I drove the car to Florida and back from Wisconsin and got a whole 17 miles per gallon. I had a friend who owned a 1968 Coupe de Ville and it got 16 miles per gallon on the highway. The 1968 would run away and hide from the 1981. After dealing with the mechanical issues for a little over a year, the Cadillac ended up on a Ford dealerships used car lot.

The sad thing is they used the excellent and highly reliable 425 as the base model engine before they shrank its displacement and added this awful variable displacement system to it. But what you ended up with, after you rip that trash off, is a big block iron block engine with absurdly small displacement for its size, which, if you were crazy enough, could take insane levels of boost via turbo or super charging. However superchargers and turbochargers designed for this application are quite scarce.

Ironically I’ll be daily driving a 1972 Cadillac DeVille soon. I don’t care the economy is not the best, I care about having something that is fun, comfortable stylish and cheap for parts and repairs. Being im a mechanic they are the best choice. If they were built to last 50 years then I would rather put in the time and money in them to last another 50 years. There’s no reason to buy a new car. They don’t last long and they cost a lot of money both in purchase price and repair costs. Automakers messed up. Bad

As a result of 2 gas shortages in the 70s, there were kits available to permanently deactivate cylinders in a V8.

With respect to the highway MPGs of your previously owned Cadillacs, keep in mind that in 1974 the Federal Government established the national 55 mile per hour speed limit in response to the oil crisis of the early 70s. Driving at 55mph was supposed to save fuel. So I’d be curious to know if your Cadillacs actually got better mileage at 55 versus 70. In the end, studies showed the fuel savings of the 55mph law was negligible.

A friend had a Coupe De Ville with this engine- I drove the car once, it worked OK, went from 8 on starting then down to 4 on the road. He said it got 30 MPG, but he did trade it after one year for a Sedan De Ville with a conventional engine. I guess he dodged a bullet. But, he didn't have any trouble with it while he had it.

To downgrade it's previously excellent Bendix derived Oldsmobile Electronic Port Fuel Injection to pi55 and Dribble Throttle Body Injection was the beginning of the problem for the 368. General Motors with the Cosworth Vega and 5.7 Olds and the 8.2 Liter, that Bendix system was successful on three different engine families, Chevy, Olds and Cadillac. Bendix merchandised Three different Port EFi systems starting, 1975. The roll out was on 121 cube 16 valve Vega(75), 350 Olds(76), and 500 Cadillac ( optional, 76 I think) and then as a continued option on the downgraded 425 Cadillac ( for 77-79). Somewhere, some one did a Budget cut move to TBi in the early 80's, and that continuous supply of fuel to disabled cylinders did the worst to the 368 Modulated Displacement V8. For GM to ruin the 368 ship, for a hapworth o' tar...tragic!