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Cadillac 4100 Engine

edzeb76cedzeb76c Posts: 5
edited March 2014 in Cadillac
I have a beautiful '84 Eldorado Convertible with
76K on the engine. I bought the car 3 months ago,
and the dealer gave me a 1 year warranty on it. It
just blew a head gasket, leaking coolant into the
oil which ground up the valves. The dealer, whom I
have found to be honest, has promised to do
whatever is necessary to return it to perfect
condition. I know that these engines have had
problems, and I want to know what other
owners/mechanics recommend to keep this from
happening again. Also, can these engines be
reliable, or, should I get rid of the car when it's


  • andre1969andre1969 Posts: 23,549
    You might want to find out how much it would cost to swap in a more reliable engine. The Oldsmobile Toronado and Buick Riviera, cousins to the Eldorado, had Olds 307's in them from 1981 to 1985, and that is a pretty good engine. In 1979, all three came with an Olds 350, but I think Cadillac went to a Caddy 368 block in 1980, and then the notorious V-8-6-4 based on the same block for 1981.

    I don't know how much would be involved swapping in an Oldsmobile engine, either a 350 or a 307 (hell, a 403 would probably fit, too!), but in the long run should be a lot more reliable than the aluminum Caddy engine. I know Buick-Olds-Pontiac all had the same bolt patterns for the transmission... Cadillac may have, too.

    Good luck!
  • Thanks to the folks who responded to my question about the Caddy 4100 engine. Now, I have another one about the same topic - has anyone out there done an engine swap with this car? How involved is it? Is it a bolt-in, with readily available parts from a junkyard, or, am I looking at a very expensive and difficult job.
    Also, I still would really appreciate it if anyone with experience with these engines could give me a straight answer as to their reliability if they are well cared for. There are a lot of mid 80's Cadillacs running around, so there must be some trick to keeping them running without major engine work every few thousand miles.
  • andre1969andre1969 Posts: 23,549
    If they're well cared for (not driven too hard, oil and coolant changed regularly, not overheated, etc), they will probably last, but I would change stuff like the coolant and hoses more often than I would an iron block.

    I think the main reason you see so many mid-80's Caddies running around still is that the mid 80's was the end of Cadillac's heyday. When the Eldorado and Seville downsized for 1986, they lost a ton of sales, and reliability went downhill. When the DeVille downsized for 1985, sales were good, but the cars just didn't last, and they looked too much like a Buick or Olds. On average, the 1979-1985 Eldorado sold about 3x as many units per year as the 1986-current models. The margin isn't as wide with the Seville, but still significant. The DeVille sold well for a few years, and I think still sells fairly well, but not like the old RWD model did.

    I still see a lot of older Caddies around, too. Most are driven either by senior citizens, who probably are gentler on their cars which may explain their longevity.

    As far as replacing the 4100 with a different engine, I believe any Buick, Olds, or Pontiac V-8 will bolt right up to the transmission. It would be best to get an engine as close to the same year as your car, though, for emissions concerns. Your best bet would be if you could find a 1979-80 Toronado or Riviera with the Olds 350. You may have to replace the engine mounts, but I don't know...they may be the same. Back then Buick, Olds, and Pontiac shared a lot of components and it was easy to swap internal parts among the three, while Chevrolet parts were not as interchangeable. Cadillac tried to stand on its own as the flagship, but I have a feeling a lot of their parts are easily interchangeble with Buick/Olds/Pontiac.

    I've never done an engine swap, but may do so in the future. I have a 1985 LeSabre with an Olds 307 that my grandmother gave to me. When the engine goes, I'm thinking about putting an Olds 350 or 403 in it. But right now, the current engine is still going strong at 150K miles, and I have a feeling the engine may outlast the car! This would be an easier swap, though, because it's still swapping an Olds smallblock for an Olds smallblock.

    If you want, the next time I see my mechanic I'll ask him how hard it would be to swap an Olds engine into an Eldorado.

    Good luck with your car...I love those Eldorado convertibles (and the Toronado/Riviera ones as well)...beautiful cars!
  • corlt1corlt1 Posts: 29
    The 4100 is basically the same engine as the 4.5 and the 4.9. It had a very lightweight aluminum block with cast iron heads. The block studs went fron the bottom of the block up through the heads and tyied the entire assembly pretty tight together.

    The original water jackets in the aluminum blocks were very porus and therefore leaked coolant which gave the engine a bad rep for overheating (due to coolant loss) then blowing head gaskets. Around 1985 to 86, Cadillac started using Nikelsill (pronounced like Nickle Seal) into the water jackets to take care of the filling the porus areas know to cause leakage.

    Then another problem occured called gasket walk, in which the constant heating expansion and cooling contraction, took it's toll on the heqad gaskets. The result was coolant leaking inot the engine oil. When you pull the dipstick and the oil looks like a thick chocolate pudding, you have water or coolant in the oil. This happended to me in a 1987 Eldorado with the HT4100. I had it fixed by Cadillac and the car ran fine until I sold it at 98,000 miles to a co-worker that is still driving it at around 115,000 miles.

    The prevention for gasket walk is to change the coolant every 12 to 24 months and add 3 of the GM graphyte pellets to the radiator (not the overflow tank) every 12 to 24 months. The pellets disolve and keep the gaskets lubricated and prevent gasket walk. The reason for the blown head gaskets is that the very light aluminum block expands and contracts at a very much different rate then the cast iron heads, so the poor head gasket in the middle gets worn away until it blows allowing coolant to leak.

    Another NEW factory and recall fix made around 87 to 88 was to add new head gaskets impregnated with graphyte. If you change the coolant every 24 months as per the manual, add in the 3 pellets (also in the manual), you will not have a problem again. Also, keep the factory desingnated thermostat and DO NOT USE a lower temporature T-Stat. Contrary to popular belief, the higher temperature is more constant and will eliminate stress on the gaskets. When a lower T-Stat is used, the engine runs cool at highway speeds, but heats up in traffic. This heating and cooling contributes to the head gasket heat cycling problem.
    The HT4100 runs hot and many Cadillacs, especially the transverse mount FWD models have an aux. oil cooler to help cool the engine block. I have found that you should always use a Delco oil filter. There maybe be some better filters out there, but I had the oil changed at a Mobil Quick Lube and they used a Mobil filter on the 87 Eldorado. Several times, when driving at high speed or accellerating pretty hard out of the toll plaza on the interstate, the engine started to knock. After shutting off the engine, and restarting, the problem would disappear. I found out that the Mobil filter has much smaller oil passage holes than the factory Delco filters and was causing the engine to starve for oil when driven hard or at continued high speed.

    There is nothing wrong with the HT4100, 4.1L, 4.5L or the 4.9L engines. They were a reveloutionary light weight design made at a time, when America was thrust into a downsizing time due to numerous fuel shortages. If you want to have your engine repaired, do so with the knowledge that there have been some revisions and upgrading of parts over the years that effectiveley cured the bad rep on that engine. I had mine repaired and it's still running well today for a co-worker. I would not have sold it to a co-worker if I had any quams that it would fail him.
    My only concern is that this engine is SO UNDERPOWERED for such a heavy car (and expensive to repair), that an engine swap is probably a wiser and cheaper choice. Since the 4100 was used in both transverse FWD, RWD and longitudinal FWD, there are too many variations when considering this engine for a swap.
    If you decide to do an engine swap, this should be fairly easy as the 1979 thru 1985 Eldorado, was essentially the same as the Olds Toronado of those years. I wish to leave out the Riviera, since most came with the Buick 3.8 L V6 and some were even turbo charged (known as T-Types), although some did come with the Olds 350 V8.

    Since the Toronado and Eldorado, used only V8 engines, I would confine myself to just these makes. The Cadillac did offer a nice 368 cu. in. V8 (although also expensive to fix and purchase) in this same chassis. Some Olds 350 V8s also found their way into the Eldorado. The Olds 403 is the same exact external size as the 350 so it too could be considered. ALL will bolt up to your transmission.

    What ever engine you choose, keep in mind that the small block Olds engine was made from 1964 thru 1987, so there are plenty of parts available.

    The easiest way to accomplish this swap is to find a 77 to 85 Olds Toronado donor car in a junk yard. Get the power steering, A/C and alternator brackets, nuts and bolts and the entire engine if it's running or repairable. Most likely your existing A/C compressor, power steering pump and alternator will fit, but the brackets are different.

    Whenever you need a fan belt, water pump or a spark plug, buy it for the correct year Olds Toronado. Even adding the cost of buying the Olds engine and having it rebuilt would probably be cheaper than rebuilding your 4100.

    Keep us updated and the best of luck to you. I hope this helps.
  • To andre 1969 & corlt l - thanks a lot for the info on preventitive maintainance & engine swaps. As I mentioned in my first posting, the dealer from whom I bought the car has promised to do whatever is necessary to make it right. He has the car right now, and is supposed to start work on it this week. I will met with him this week and ask him if he'd prefer replacing the 4100 engine with an Olds 350, or, if he wants to rebuild the 4100. Either way, I'll pass on to him the info about the new type gaskets & Nickelsill (in case he doesn't already know about them) & I'll make sure I use the pellets if he rebuilds the 4100. I'll let you know what happens if/when I get the car back. Again, thanks for your input.
This discussion has been closed.