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Discussion Starter #1
Hello,
I'm new to the Cadillac forum and made my first post in the new members section.
I am looking to learn more about the HT4100. I have heard that it was the worst engine Cadillac made, and one of the worst engines in existence among all carmakers, and I'm curious to find out why.

I know they were aluminum heads on a cast iron block, and the two metals would heat up at different rates. Is this the source of their problems? Sounds like a blown head gasket waiting to happen. If I remember correctly the GM diesels of the time suffered from that too- (5.7 and 6.2)- what was GM thinking?

Where there other problems with the HT4100 as well? I've never owned one so I'm totally new to them. I still see Caddies loping around here with that ominous badge- right by the front wheel, so it makes me wonder.

Could someone enlighten me about these engines? I notice the cars that have them in seem to sell dirt cheap (under a grand). There's an 85 Eldo in the paper with 73K on it, for $1650.

I was just in a car accident, so I am left without a car, and am looking for a Caddy. My budget is limited however, at 3 grand, which leads me to the older cars. I've been thinking maybe 80's to early 90's Broughams.

If anyone has any thoughts, I'd appreciate it.

Thanks,
Jon
 

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Azriel said:
Hello,
I'm new to the Cadillac forum and made my first post in the new members section.
I am looking to learn more about the HT4100. I have heard that it was the worst engine Cadillac made, and one of the worst engines in existence among all carmakers, and I'm curious to find out why.

I know they were aluminum heads on a cast iron block, and the two metals would heat up at different rates. Is this the source of their problems? Sounds like a blown head gasket waiting to happen. If I remember correctly the GM diesels of the time suffered from that too- (5.7 and 6.2)- what was GM thinking?

Where there other problems with the HT4100 as well? I've never owned one so I'm totally new to them. I still see Caddies loping around here with that ominous badge- right by the front wheel, so it makes me wonder.

Could someone enlighten me about these engines? I notice the cars that have them in seem to sell dirt cheap (under a grand). There's an 85 Eldo in the paper with 73K on it, for $1650.

I was just in a car accident, so I am left without a car, and am looking for a Caddy. My budget is limited however, at 3 grand, which leads me to the older cars. I've been thinking maybe 80's to early 90's Broughams.

If anyone has any thoughts, I'd appreciate it.

Thanks,
Jon
The Highly Troublesome 4100 was made of an Aluminum block with sleeve liners and iron heads. The problem was that the seal between the sleeve liners and the block would not seal correctly or the head gasket would blow. Everyone was told to use the Coolant Suppliment but few followed directions.

I have seen several HT4100's that have been taken care of with over 100k on the clock. Then you get the ones like my 84 SDV that needed an engine at 79k because it was not maintained by the previous owner.

IMO, the HT4100 was good if maintained properly. It was underpowered for my taste and the way I drive however it did get great fuel mileage.

If I were you and was after a Brougham I would get one with the 5.0 engine. Well maintained 4100's are hard to come by these days.

BTW, there is a Black 85 Brougham down the road for sale. I would have grabbed it but it's 4100 is tired.
 

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Azriel said:
Hello,
I'm new to the Cadillac forum and made my first post in the new members section.
I am looking to learn more about the HT4100. I have heard that it was the worst engine Cadillac made, and one of the worst engines in existence among all carmakers, and I'm curious to find out why.

I know they were aluminum heads on a cast iron block, and the two metals would heat up at different rates. Is this the source of their problems? Sounds like a blown head gasket waiting to happen. If I remember correctly the GM diesels of the time suffered from that too- (5.7 and 6.2)- what was GM thinking?

Where there other problems with the HT4100 as well? I've never owned one so I'm totally new to them. I still see Caddies loping around here with that ominous badge- right by the front wheel, so it makes me wonder.

Could someone enlighten me about these engines? I notice the cars that have them in seem to sell dirt cheap (under a grand). There's an 85 Eldo in the paper with 73K on it, for $1650.

I was just in a car accident, so I am left without a car, and am looking for a Caddy. My budget is limited however, at 3 grand, which leads me to the older cars. I've been thinking maybe 80's to early 90's Broughams.

If anyone has any thoughts, I'd appreciate it.

Thanks,
Jon

Hi Jon,

I have an 83 Eldorado with the 4100 that has been very well maintained, oil changed every three months (1200 - 1500 miles) and all other problems taken care of promptly and so forth. Loping is a good term for how we get around though, very slow and really lousy mileage, I avg around 11. I am in the process of exploring my options in regard to engine swap, possibly for a 5 or 5.7 gm engine. I have not been able to find anyone with much good to say about the 4100, but in its defense my mom drove this one for almost 20 years and it never let her down.

Let me know if you find out any good resource areas, and I will do the same...

Kerry
 

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1995 ETC, 75 Deville, Cad500 powered 73 Apollo, 94 Mark VIII
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I have a thought... maybe you should get a 1981 or before Cadillac with the 368/425/500/472 series of engines. They seem to be pretty reliable and are bound to be cheaper. If you can find one in good shape go for it..
 

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Discussion Starter #5
Hello,
I was thinking the same thing- pre 80's- there's a 79 Coupe Deville in the paper for 2800, says it's in real good shape. Is it worth that?

Thanks,
Jon
 

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Discussion Starter #7 (Edited)
Hello,
Thanks for the NADA link. It said a 79 Coupe DeVille is worth $2000 to $4000- I didn't think it would be that much. I see them for $2000 in Auto Trader.
 

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ga_caddy said:
Everyone was told to use the Coolant Suppliment but few followed directions.
What's this Coolant Suppliment, and where do I get it? My Eldo has the 4100 and has 131,7xx miles (although I think it's a rebuilt engine, last owner had no clue), so maybe I should put it in. Is this a major thing, or can it be done for less than $300?

Thanks.
 

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Hello serdriver,

You can buy it for $15 or so. There are six round pack of some kind of
brown stuff, look like dried mud or some sort.

About HT4100, I had a HT4100 (83 Eldorado) and took care of coolant as GM suggested. I had never had any engine trouble. It is not powerful, but my impression is that it is a good engine to run and easy to work on.

serdriver said:
What's this Coolant Suppliment, and where do I get it? My Eldo has the 4100 and has 131,7xx miles (although I think it's a rebuilt engine, last owner had no clue), so maybe I should put it in. Is this a major thing, or can it be done for less than $300?

Thanks.
 

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100 said:
Hello serdriver,

You can buy it for $15 or so. There are six round pack of some kind of
brown stuff, look like dried mud or some sort.

About HT4100, I had a HT4100 (83 Eldorado) and took care of coolant as GM suggested. I had never had any engine trouble. It is not powerful, but my impression is that it is a good engine to run and easy to work on.
As stated, the key to the 4100's long life is proper maintenance especially coolant changes (although oil changes are also important!).

The coolant has anti-corosive components which wear out (even though the coolant could look clean and green)after 1+ years. Consequently, the coolant must be changed every 24 months at a minimum per the factory SM. Change the thermostat at the same time.

The pellets are just BarsLeak and prevent coolant leakage only; they do NOT prevent corrosion.

There is an improved replacement gasget which should be installed if you have the engine apart.

If your 4.1 is history, you can rebuild it or install a 4.5 (a bored and stroked 4.1) which is physically the same, but you will have to use many components off of the 4.1 (manifolds, etc.) so that the computer "thinks" the engine is a 4100. More performance BUT less gas mileage.

My '88 Allante with 110,000 miles has a 4100; 16+ mpg in town with A/C on. Since I am not in "race mode" when I use the car, the 4100 is fine.

Brian Bray
 

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Regarding Lack Of Power, I Owned An '84 Eldo 4 Or 5 Years Ago. I Installed The Throttle Body Assembly From An '81 368 Cu. Inch Engine. I Used The Two Injectors From The 4100. Onto The Replacement Throttle Body. The '81 Unit Had Much Larger Throttle Bores But The Same Exterior Dimensions. Had To Use The Thick Base Gasket From And '81 So Throttle Blades Would Not Hit The Intake Manifold At Wide Open Throttle. Used The Trottle Position Sensor From The 4100 And Adjusted To '84 Specs. If I Recall I Had To Change The Cruise Control Servo To A Chain Attachment Type To Retain Cruise Function. Bumped Timing 2 Degrees Up . Was Much Improved Regarding Off Idle Snap. Would Bark Tires From Rest!. Freeway Performance Was Better And Got Same Mileage. At Higher Altitudes At Wide Open Throttle Was No Better But No Worse Than Before. As One Would Understand The Engine Could Only Take So Much Air At Wide Open Throttle. Ideally The Bore Diameter Of The Intake Manifold Should Match The Throttle Body Throttle Blades, But Because Of The Serious Time To R&r The Manifold, This Was Not Done To Mine. Did Not Affect The Smog Testing At All. Was A Much Nicer Car To Drive After That.
 

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Brian,
You are very correct. The GM coolant supplement is actually "Bars Leak". It is probably the best cooling system sealant you can buy. I swear by it, but it will usually not seal a blown head gasket in a 4100. It is much cheaper to buy at an auto parts store or "Auto Zone" than the dealer. Probably the majority of 4100's didn't have their coolant changed every 2 years as recommended by GM let alone have the coolant supplement added.
I have owned four 4100 Coupes. Of them, the one that made it the farthest was an '84 with 129,000 miles. I bought it at 66,000 miles and changed the coolant every two years and oil every 3,000 miles. It blew a head gasket causing coolant to leak between the head and block out the back of the passenger head. However, I didn't know of the need to add the coolant additive until after it blew the head gasket (two years ago). I just stripped the car of good parts that interchange with my other '81-'84 Coupes.
My other 4100 cars were all bought with bad engines at just over 100,000 miles. Another of my '84's and my '82 both had worn out camshafts (103,000 and 113,000 miles respectively). Because of the cost of 4100 parts and its low performance, I installed a '72 Olds 350 in the '84 (bolts right in with 350 Olds diesel parts) and a '80 368 (103,000 miles from an extremely rusty '80 Coupe; bolts right in) in the '82.
The last of my '84's had its first engine replaced at about 56,000 miles. The second engine went around 100,000 miles. This engine "locked up". The original owner, had the transmission rebuilt 6 months earlier and was not about to put another engine into the car.


Brian Bray said:
As stated, the key to the 4100's long life is proper maintenance especially coolant changes (although oil changes are also important!).

The coolant has anti-corosive components which wear out (even though the coolant could look clean and green)after 1+ years. Consequently, the coolant must be changed every 24 months at a minimum per the factory SM. Change the thermostat at the same time.

The pellets are just BarsLeak and prevent coolant leakage only; they do NOT prevent corrosion.

There is an improved replacement gasget which should be installed if you have the engine apart.

If your 4.1 is history, you can rebuild it or install a 4.5 (a bored and stroked 4.1) which is physically the same, but you will have to use many components off of the 4.1 (manifolds, etc.) so that the computer "thinks" the engine is a 4100. More performance BUT less gas mileage.

My '88 Allante with 110,000 miles has a 4100; 16+ mpg in town with A/C on. Since I am not in "race mode" when I use the car, the 4100 is fine.

Brian Bray
 

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4100

Alot of the used car warranty companies won't even provide a protection plan for cars equipped with the 4100 engine. Yet I have seen a select few roll in as trade ins with 150k + miles on them (not saying that they are allways the original engine or anything). Also regarding Bars Leak... the stuff works good on small leaks but we had a 94 Deville with a pretty hefty drip on it so we doubbled its doseage of sealant (2.5 bottles of Bars Leaks), plugged the engine block solid. The stuff got in there and sealed up eveything, the engine overheated and cost us one used 4.9L in repairs. Be carefull.
 

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Re: 4100

Slick Black Cadillac said:
Alot of the used car warranty companies won't even provide a protection plan for cars equipped with the 4100 engine. Yet I have seen a select few roll in as trade ins with 150k + miles on them (not saying that they are allways the original engine or anything). Also regarding Bars Leak... the stuff works good on small leaks but we had a 94 Deville with a pretty hefty drip on it so we doubbled its doseage of sealant (2.5 bottles of Bars Leaks), plugged the engine block solid. The stuff got in there and sealed up eveything, the engine overheated and cost us one used 4.9L in repairs. Be carefull.
I owned mine a total of 2 hours and it hydrolocked
no biggie it needs a 500 anyhow
 

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Re: 4100

Slick Black Cadillac said:
Alot of the used car warranty companies won't even provide a protection plan for cars equipped with the 4100 engine. Yet I have seen a select few roll in as trade ins with 150k + miles on them (not saying that they are allways the original engine or anything). Also regarding Bars Leak... the stuff works good on small leaks but we had a 94 Deville with a pretty hefty drip on it so we doubbled its doseage of sealant (2.5 bottles of Bars Leaks), plugged the engine block solid. The stuff got in there and sealed up eveything, the engine overheated and cost us one used 4.9L in repairs. Be carefull.
Obviously, Bars Leak is not a panacea. It will not seal up a leaking head gascet and it won't stop a substantial leak. The real key to the 4100's long life is the frequent coolant changes so the anticorrosive ingredients of the coolant are always present. The lack of anticorrosive ingredients in the coolant is more of a factor in causing engine failures than lack of using Bars Leak, but both are important.

As I understand, the material in Bars Leak remains small while in a liquid state and then expands when it is exposed to the air. As it leak out, it is exposed to the air and expands and seals the leak. I've also used Bars Leak successfully to temporarilly seal up a radiator leak; granted, sealing up a radiator is different than keeping an engine from leaking.

In moderate amounts, for very small engine leaks, it seems to work great. When the corrosion has occurred, no amount of Bars Leak will seal up that sort of problem.

A properly rebuilt 4100 with the improved head gasget and regular coolant changes AND Bars Leak is a dependable engine. The problem is that most of us acquire a vehicle AFTER one or more owners has neglected the proper maintenance and no amount of coolant changes and/or Bars Leaks after the fact is going to prevent an eventual problem; it may postpone it for a while, however.

Brian Bray
 

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Being the nice guy that am, I will not give my personal opinion of the HT4100 motor here.

I will just say that I have had the unpleasant experience of buying several of them after they were abused by their previous owners.

The last good one I had I put it in a 83 Sedan Deville and Gave it to my stepson.

I did not know about thew bars leak although I was told long ago to change the coolant once a year, on those motors.

I will buy some and put it in his car before it does what it does best! :fan:
 

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I have an 83 Coupe DeVille with 104k on the clock and it runs fine. I just religiously change fluids at specified intervals and keep a close eye on fluid levels. Problems start occurring when you don't use the coolant tablets.Most people didn't know you needed them and that's where all the problems started.
 

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Yeah I never knew about the tablets before I read about them on this forum.

But now that I think of it, I've never had one leak oddly enought, all the 4.1 that came my way all started knocking severly after awile. previous owners must not have changed the oil ever!
 

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Hi all, I'm new here to the caddy forums. I have been reading about this coolant additive for the 4.1 and 4.5's. Exactly what is this additive called and where do I get it from? I have a '85 Fleetwood Brougham with that damn 4.1 and I have been pretty good with changing fluids on time but I did not know about the additive for the cooling system. I flushed the cooling system last August (so around 6 months ago) new thermostat, gasket, etc. My question is should I get this additive ASAP and add it to the cooling system or wait until i flush the system in 6 months? Any help would be great. Thanks guys.
 

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AElayyat said:
Hi all, I'm new here to the caddy forums. I have been reading about this coolant additive for the 4.1 and 4.5's. Exactly what is this additive called and where do I get it from? I have a '85 Fleetwood Brougham with that damn 4.1 and I have been pretty good with changing fluids on time but I did not know about the additive for the cooling system. I flushed the cooling system last August (so around 6 months ago) new thermostat, gasket, etc. My question is should I get this additive ASAP and add it to the cooling system or wait until i flush the system in 6 months? Any help would be great. Thanks guys.
It is kind of funny to hear all the bad comments about the 4.1 since it was last in production in 1987 (..ok....1988 in the Allante..). If they are STILL showing up on used car lots and being driven around by people they couldn't have been all THAT bad if they've lasted 20 years at this point...!!!!


If your 85 fleetwood brougham is still running good then that "damn" 4.1 has provided pretty good service for 20 years....!!!! Not bad I would say especially if it hasn't been cared for as specified.....if you read the owners manual or the service manual the use of the coolant supplement is outlined there....


The coolant supplement or sealer is just that....sealer. You can purchase it at any GM dealer....ask for the GM coolant supplement pellets at the parts counter. They come 6 to a card. You need all six in a 4.1. Or, if it is easier or quicker then stop by a Walmart or Aco or other autoparts store and find the BarsLeaks "golden seal" brand cooling system stop leak or sealer. The best Bars product is the "golden seal" powder in the clear tubes. Use two of the tubes in the 4.1. Put it directly in the radiator. I would recommend doing it now to provide maximum protection for the system. It is not hard to do...just remove the radiator cap when the system is cold and put the sealant powder into the radiator and reinstall the cap. It is usually easier if you suck some coolant out with a turkey baster and squirt it into the coolant recovery bottle. You'll likely have to crush the coolant pellets up to get them in the rad end tank due to clearance with the intank oil cooler.

The same company that makes the coolant supplement for GM for the pellets markets the material under the BarsLeaks brand so it is the same stuff...just do NOT use the "liquid aluminum" type sealants or any other brand as they can cause other problems. Check the BarsLeaks web site for other details.

You should realize that the factory installed the cooling system sealer in the sytem when it was first assembled...as does just about every automaker. The BarsLeaks supplier supplies cooling system sealer to a WIDE variety of automakers for OEM use. It is very common in the industry for sealling incidental and nuisance leaks and is very effective in the case of the 4.1 engines where coolant could get into the oil in the event of a gasket failure... After 20 years of use this is not an impossible situation to occur.


I would NOT recommend "flushing" the cooling system or adding any sort of corrosive or caustic cleaners or anything to the system. Just drain and refill occasionally with fresh 50/50 coolant/distilled water to refresh the system. That is all that is required. People always put it off until the system is a disaster and then blame the engine for being intolerant. If they would just do a simple drain and refill every two years the system would be like new now (20 years later....)
 
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