Worst Engines of All Time: Cadillac HT4100 - Why is it so bad? How can you preserve yours?

Learn some more details about a troubled Cadillac engine and how to best preserve yours in the event you own one.

[blautens]

In the early 90s, I needed a cheap driver once and almost bought an older Cadillac with this engine from a flipper (here in south Florida, low mileage cars like this from the elderly are all over). I asked him if the HT4100 was reliable (this was pre Internet, and I had no experience with it) and he thought for a second and said "it is not - this one works fine, but it won't for long, if I'm being honest". I was stunned and grateful.

[mark_osborne]

I thank GM from the bottom of my heart, these engines provided this old mechanic with probably a million dollars of revenue over the years, there was a period of about 5 years where they are pretty much all I worked on

[litreho]

As a heavy line mechanic for Cadillac in the 1980s, I worked on several of these HT4100 engines. The most common issues with customer cars with this engine were oil leaks, mostly intake manifold. Also, overheating and warped blocks. Worth noting, the crankshaft flange only had 3 Torx screws that secured the flex plate to the crankshaft🤣. Also, this engine had such low vacuum that it wasn't enough to run the vacuum accessories of the car. So GM put a belt driven vacuum pump in with the other accessories in front of the engine (what a joke!). Cadillac should have kept the Olds Rocket 350 for these cars through the 80s!! The best engines Cadillac ever had were the 472 and 500 V8s. Honorable mention is the 425 and 368 derivatives of the 472....

[JAMESSTEINBREN]

It's always refreshing to be able to listen to someone with real knowledge on a subject, wax poetic on the character both good and bad on a love-hate platform. I've always wondered about how Cadillac people felt about the HT4100 and now I know! I'll look for a 4.5 or 4.9 Deville.

[giggiddy]

You are really pumping out lots of wonderful, long, videos. You're now at the top of my list. Thank you for your time and please keep them coming.

[gerardmills]

The diagnostic system was amazing....all the code resets and real time data....plus the sequence to clear it all out....is great...once you learn how to do it. A lifesaver

[Martmns]

I remember even in the first few weeks and months after these terrible engines came out in the 1982 model year, coming across numerous 4100 engines and especially bare engine blocks in scrapyards, Not wrecking yards where parts are salvaged, but actual metal recycling SCRAPYARDS.

[roundsrapid]

I never was a big fan of GM, but they played a big part in my life. They had a wiring plant in my hometown, and my uncle worked there for 20+ years, from the mid ‘70s on. He passed away recently at 75.

[rtwice]

Although I spent the first 13 years of my career as a mechanic at a Ford dealership (1983-1996), I did occasionally work on other makes of cars. Usually something taken in on trade by the used car department.

One of those times came when they had taken a Caddy in on trade with a seized 4100 engine. It was a beautiful car owned by a reality company that was used to haul prospective buyers around town to look at property. Somehow, no one ever changed the oil. At 59, 000 miles the engine locked up. So they traded it in on a Lincoln Town Car. The used car manager asked me to get it running.

We got a replacement engine from a local wrecking yard. It wasn't terribly difficult to swap, but I could never get the damn thing to idle properly. The internet wasn't widely available then, so repair information on that engine was hard to come by. I tried all the tricks I would use on a Ford with poor idle quality. I ended up swapping the TBI off the old engine which seemed to fix it. I guess the ECM didn't play well with strangers.

[klwtherd]

This kind of video is exactly what i like on this channel. We all can basically agree that this motor is NOT good at all. But still, some people love these year Cadillacs and want to buy one. So instead of just badmouthing it to death, it's better to help the lovers/owners of these cars know how to preserve them to minimize damage and issues. Please do a video on the onboard diagnostics. It would be well worth your time.

[HomerJ]

When I graduated from college in 1986, I bought a 1983 Coupe DeVille with this engine. It didn’t have much power but it was so smooth and quiet. I absolutely loved that car. Unfortunately, less than a year after I bought it, I was hit by an F-150 at a high rate of speed. The car was totaled. I replaced it with a new 1988 Chevy Corsica.

[DSP]

"The party arrives when you do" -- love that! Another very informative overview. Thank you, sir.

[geofjones]

The 4.5 was ok, the 4.9 was great! I had a 93 De Ville 4.9. Great gas mileage, a hot rod for performance. a pleasure to drive. Car had a few troubles, no internal engine problems. Trans gave trouble, gas mileage dropped from 28 mpg average to 20. Traded it off at 245K miles in '05 for a new Le Sabre. Another great car!

[SedanChevy]

Honestly, I think this engine and the reputation it earned- for being a grenade and a total slug in terms of performance- was the biggest straw that broke the Cadillac back. The Cimarron was a disaster, sure, but the 4.1 ruined what would've otherwise been great '82-'85 Cadillacs. I think it turned off a lot of buyers who happily left and went to Lincoln... which ironically had a 302 that wasn't much more powerful than the 4100. As shown by the Brougham that ran into '92 (albeit with the Olds 307 in '86 and the Chevy motors in '90), the cars themselves were great and honestly hold up very well even now 30+ years later. In particular, I feel the '80 redesign for the Coupe DeVille produced one of the most handsome cars of the era, but unfortunately any year aside from the 1980 is saddled with poor engines. I can't blame shoppers in the early 80s for shunning these cars, no matter how good they looked or how comfortable they are.

The 4100 should have been held off until the downsized cars arrived for 1985- by then the engines had sorted through a lot of problems. I think the Chevy 305 or even Olds 307 would have been a much better option during this time after the V8-6-4 was deemed unacceptable. Even limiting cars to the 4.1 V6 or even the 3.8 probably would've hurt their reputation less. That being said, the 4100 did become what I would consider a good motor in the 4.5 and 4.9, which are nice to drive and have a much better reputation.

[JeffKing]

The growth in the channel is fantastic - well done Adam!

Great “Porch Chat” as always. Another classic engine!

[robertmayeriii]

I cannot tell you how thrilled I am to find this video that you have made! I’m seriously considering purchasing a 1986 Cadillac
Sedan Deville Limousine Hess and Eisenhart

[bigdogpete]

Your knowledge of these cars is why this channel is exploding. Experts are hard to find. I really enjoy the calm demeanor and well presented material. Thanks.

[NVzla]

I had an 83 Fleetwood with that engine, and I beat the hell out of that car. It leaked everything, had a throw-out bearing holding tension for water pump/alternator and other junk. It lived, never overheated, and ran fine. I graduated to a 4.9 93 DeVille, and after 2 transmissions, I happily saw I drive away to get parted out. I still have a 6.0 368 V8-6-4 in an 81 Fleetwood, still running but of course, cylinder deactivation is permanently deleted.

[rileysteve]

Years ago I worked for a firm on Atlanta's south side, whose fleet colors were Dove Gray. We had a Cadillac hearse from 1986. I do not recall who did the coachwork. Anyway it had a 4100 in it. We just hated it, not so much for lack of dependability, more for the lame power output. That engine combined with the weight of a Fleetwood 75 chassis and specialized coach work was completely overwhelmed. I really enjoy your in-depth reviews and knowledge. Thank you!

[Paramount]

Thank you so much for this video! This was the most comprehensive summary of the issues plaguing those of us who owned 4.1 Cadillacs. I had an 85 Sedan deVille just like the one you pictured and I absolutely loved the car as a whole. It was smooth, very quiet and extremely pleasant to drive. My 4.1 had been rebuilt before I got it, but I did have issues:

1. I suddenly lost the oil pump while driving. Fortunately I was on a quiet residential space and I shut it off within 5 seconds of the oil light going on. I towed the car back to my house and dropped the pan, what had happened was one of the large steel pins that the pump gears ran on had slowly worked downward, allowing the shaft to disengage from the distributor. I bought a new Cadillac oil pump at the dealer, it was an updated pump from the 4.5. This issue made me lose trust in the car.

2. It was very sensitive to plug wire condition. Once the wires started to go bad it would slam into a lower gear very harshly, at first making me think that the trans had gone south. I drove out to a very dark place at night and watched sparks go all over the wires. I replaced them and the problem went away, only to reappear maybe a year later. New wires again solved the problem.

3. My 4.1 and many others I heard had a dull thumping sound in the engine. Somewhere I read or was told that it was camshaft end play. I don't know, but it sounded bad.

4. My thermostat went bad twice. Not bad enough to overheat and turn the light on, but when I parked and shut it off I could hear coolant boiling. I kept the coolant fresh and used the tabs. This was promptly repaired on both occasions.