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  #1  
Old 04-24-2010, 03:59 PM
Jim Tighe - Deceased Jim Tighe - Deceased is offline
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Default Cadillac HT-4100 motor

For several years during the 1980's, Cad used a very small V-8 of about 250 cid. I have heard quite a few horror stories about this engine. Have any of you had experiences with it? If you found an otherwise nice car that had that engine, would you take a chance or not? Thank you for your thoughts on the matter.
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Old 04-24-2010, 04:33 PM
Keith Snyder Keith Snyder is offline
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The HT-4100 was a quickie replacement for Cadillac's ill-fated V8-6-4 modulated displacement engine introduced in 1981. Originally intended for use in the 1984 front-wheel-drive Caddys, the HT-4100 was quickly reworked and fitted to the full-size Broughams and DeVilles with the introduction of the 1982 models. The problems attributed to the V8-6-4 engine caused many people to have the system disabled but, when it was finally sorted out by GM, the problems were coming from a module supplied by an outside source. Once rectified, the V8-6-4 engines gave no real trouble and were used for a couple of years in the Series 75 models - but not the Brougham or DeVilles. The HT-4100 was a good engine, fairly reliable and trouble free but, when pulling excessive weight - as with a fully loaded 6-door climbing a steep grade - could balk. The real problems with these cars were the weak transmissions - especially noted in six-door limousines and some hearses. In addition, when used in these heavy cars, there was virtually no real 0-60 performance. In answer to your question, Yes, I would buy one if it was a low mileage, well maintained unit.
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Old 04-24-2010, 05:02 PM
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Mike Stevens Mike Stevens is offline
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Question 4100

Some other Cadillac buffs have not been so kind as Kevin. One highly regarded Cadillac writer has advised that if you are given a choice to get whatever is the other choice. Personally if the price was right and the car showed very good care I think I would take a chance on a 4100 car. Like anything else they can be fixed if broken. If you are willing to spend the $$$.
Mike
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Old 04-24-2010, 05:14 PM
Jim Tighe - Deceased Jim Tighe - Deceased is offline
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Keith, which tranny ( ies ) was/were used with this engine? Was it the 4sp auto/od unit?
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Old 04-24-2010, 10:47 PM
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Lawrence W. W. Wilson Lawrence W. W. Wilson is offline
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Jim, my answer to your question would basically be the same as Keith's........if you found a low mileage, well maintained vehicle with the 4.1 engine I could see buying it as long as you realize that you're not going to get 200K miles out of it. I know some people would agree with Mike's answer as well..........what softens me on the 4.1 is that I owned a 1980 Sedan DeVille with the 350 diesel engine...........which blew up on me at 66,000 miles in rush hour traffic in downtown Orlando. Fun. In 1989 I had a 1984 RWD Fleetwood Coupe with a 3.1 liter Buick V-6 in it [yes, from the factory] which got good gas mileage but had worse exceleration than the 4.1. The transmission in both of those cars was the TH200........now that was a crappy transmission. I think I have had to replace 3 or 4 of those over the years. The TH200 is what I would stay away from..............
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Old 04-24-2010, 11:21 PM
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so far the one in my FWD has been trouble free.but they tell me that it is a completely different engine they the Rwd one. I go for the condition like the rest you not in the fast lane of life anymore just don't pull it out in front of any buses
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Old 04-24-2010, 11:52 PM
Patrick J. Martin Patrick J. Martin is offline
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I owned a 1984 rear-drive Cadillac DeVille six-door limo with a HT4100 engine, owned it for several years as my daily driver, and would still have it if not for the car having gotten hit. In other words, my not having the car any more had nothing to do with the engine.

The car had something like 120,000 miles on it when it got hit, and the engine was still going fine. I was the third owner on the car, with the two previous owners being funeral homes, and when I got it, the glove box was full of receipts of work done on the car, which I went through, and it had always been a maintained car.

The 4100 was a real dog in the acceleration department, and on the expressway, the car topped out at 75, but the engine did perform wonderfully at its intended purpose of being good with gas mileage.

The horror stories regarding the HT4100 were not so much a result of any flawed design, but rather the result of most owners not following a slightly different maintainence schedule for the car. Most people just turn the key, and as long as the car starts, it gets no further thought. Well the HT4100 required its upkeep, and when it didn't get it, problems were had, some of them serious, and naturally it had to GM's fault for building such a lousy motor, and had nothing to do with owners ignoring what the owners manual said to do.

As I recall my HT4100 owners manual, it called for oil changes every 2500 miles instead of the more common 3000 miles, and whenever the coolant was changed, you HAD to add the GM sealant tablets to the cooling system. Other than those two quirks, and the fact that flooring it from traffic lights not only put undue strain on the engine, but also didn't accomplish anything anyway, I really have nothing bad to say about it.

The Cadillac V8-6-4 is also an engine I have experience with, and is also an engine that most people, even Cadillac experts, are mistaken about. The V8-6-4 was NOT a unique engine. What it was, was the Cadillac 368 V-8 fitted with a unique fuel injection system that would cut off fuel delivery to two cylinders, and then two more cylinders, when certain speeds were reached. Problems reported included cylinders deactivating too quickly resulting in a car with poor acceleration, a momentary but noticable hesitation when cylinders went offline, and some even reported fuel delvery being cut off entirely on occasion. The 8-6-4 fuel injection was governed by the car's speed, and simply unplugging the sensor from the transmission resulted in the engine acting as a full-time V-8 motor.

The 8-6-4 was a one year only system (1981), but the 368 motor it was fitted to was available in carburated form from 1980-1984. Additionally, only passenger cars got the 8-6-4 system in 1981, the commercial chassis in 1981 remained a carburated version. Any 1981 hearses that have the digital MPG readout display on the dash are ones that were converted from from sedans, not commercial chassis cars.
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Old 04-25-2010, 09:43 AM
Peter Jennings Peter Jennings is offline
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Well, as many of you know, I aquired a VERY NICE and exceptionally well documented 1985 Eureka Cadillac Limo style hearse from our friend Danny Ryder. When I got this car, I knew about the engine. It is not the original one that Danny blew up. The current one is also having issues. Using oil at a phenominal rate! Not much smoke, but some. A real BIG DAWG in the accel department, worse than my old 6 door limo with the 307 in it!! I can only imagine what it was like in its day during a service with a HEAVY casket in the rear. I looked at the possibility of replacing it with a 350 chevy, a very doable option, but the interface with the computer looks to be way too difficult. Looks that when the time comes, which will be soon, another 4.1 will go into the engine bay. Face it, its a hearse, not a vette. As often as its driven, a 4.1 will do.
So to answer directly, would I take the chance again? YES, if and only IF it were as nice and rare and as well documented as this car is. Otherwise, I doubt it.
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Old 04-26-2010, 08:35 AM
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I have had two of the 4.1 engines. One in a rear wheel drive 82 Eureka, and it ran great no issues, and still ran great the day I scrapped the car, major rust and electrical issues it had over 150,ooo on it. My 85 Superior FWD that I have owned for the last 10 years also has this engine. I have personally put 103,000 miles on it with only replacing the water pump and radiator (and normal tune up) and have never put in the tablets. This car still runs like new, gets 25 mpg, plenty of power, it will turn over the tires and I have had the speedo buried many times (stops at 85). This engine currently has 176,xxx. So in my experence I would not hesitate to have this engine.
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Old 04-26-2010, 09:50 AM
Jim Tighe - Deceased Jim Tighe - Deceased is offline
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Thank you all for the responses. My q was prompted by a car for sale locally, an '84 Cad sedan. Doubt that I would buy it anyway, but it does look nice. And, if, down the road, I would ever get another coach or limo, after Ron takes the M-M home, I know that quite a few of them still around from the '80's have that motor, so I just wanted some informed opinions. ( A woman I worked with in the '90's in Dayton had a mid-'80's Cad, and had to have the engine replaced twice in about a 3-yr span. She was not happy. )
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