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1984 Eldorado 4100
1984 Cadillac Eldorado Biarritz
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8 Posts
Discussion Starter #1
Hello, my name is Alex and I recently purchased a 1984 Cadillac Eldorado Biarritz with the horrid, faulty, problematic HT4100. I’m really starting this thread to learn and grow as a mechanic and to learn more about my car. So, so far, this is what I know!
There are very obvious stains in the coolant overflow tank (oil I later determined) so the first thing I did was drain the radiator, replace the coolant, and then did a basic oil change (the high mileage stuff for the old boat😂) and she was running good! Had good power. (respectively) and was shifting and riding smooth as ever. I went and got the windows tinted (35% on the front two, 5% on the sun strip, and 5% on the backs, as this is what’s legal in Nevada) and everything was fantastic! I started planning the build (she’s gonna be a Slab) and then... I noticed more oil in my coolant. After asking my buddies and such, we determined that the head gasket, and probably most of the hoses and valves, are leaking, and thus, putting oil in my radiator and into my coolant. So, head gasket kit here we come! I’m gonna start actually taking her apart tomorrow morning, so after that I’ll post again and update. Any pointers on anything at all Links or other wise would be appreciated!
-Alex M.
576414
 

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1984 Eldorado Biarritz
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Do you have staining from oil or discoloration from sealant tablets? Before tearing the motor apart I would pressure test the cooling system. Head gasket failures that let the coolant and oil contaminate each other are very rare on this car. Of far greater importance is the opposite of your supposed problem; that is coolant in the engine oil.
 

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1984 Eldorado 4100
1984 Cadillac Eldorado Biarritz
Joined
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8 Posts
Discussion Starter #3
Do you have staining from oil or discoloration from sealant tablets? Before tearing the motor apart I would pressure test the cooling system. Head gasket failures that let the coolant and oil contaminate each other are very rare on this car. Of far greater importance is the opposite of your supposed problem; that is coolant in the engine oil.
Hmmm, I didn’t know that about these engines, thank you sir. However, and I’m sure you’ll agree once I explain, I still plan on doing the full head gasket kit. Since 2008 the car has only been driven 22,000 miles. The other week she flipped to 133,000 miles. In any case, the reason that’s pertinent is because I have a couple of phantom leaks that I haven’t been able to identify coming from mid engine. So isolating and replacing all of the oil lines is first and foremost. But when the car wasn’t being driven is just sat, so I have a sneaky suspicion that finding this lovely concoction in my coolant overflow tank means I should just go ahead and commit to the project before she blows on me and I have to do a 350 swap before I’m ready. Thank you for the advice and let me know what you think. Also, as you can see in the second picture, it’s pretty caked in there. I’ve also run my finger along the inside of the radiator itself and all I got was this coolant/oil mix.
F5D051C4-5962-44B3-8E93-5F11A5DF6E75.jpeg
I’m gonna get better pictures of the coolant tank itself when I pull it off tonight. Just gotta finish prepping the project area when I get home so I can pull of my hood in the morning.
576437
 

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1984 Eldorado Biarritz
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Ok, so definitely oil in the coolant. The tank to me looks consistent with the residue from the recommended sealant tablets.

Before condemning the head gasket, I would take the lines off the oil cooler in the radiator and block them, run the car and check for further oil intrusion. The oil cooler is submerged in coolant and a leak there is more likely in this circumstance than head gasket. You want to avoid taking the heads off this engine if you can as you will break stuff, especially if it’s your first one.
 

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1984 Eldorado 4100
1984 Cadillac Eldorado Biarritz
Joined
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8 Posts
Discussion Starter #5
This is the progress so far, I’ve decided to just go ahead and do the whole top end, I got wires, cap and rotor, upper and lower radiator hoses, and spark plugs. I’m gonna be replacing all of the vacuum hoses as I go, just labeling, and taking them into auto zone to get cut and replaced. Tomorrow I take off the carb and label, and disassemble my distributer while marking the corresponding wires as they go to the plugs. Any advice on disassembling the carb?
576626
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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68,043 Posts
That's not a carburetor - it's throttlebody fuel injection.

You are going to NEED either a GM/Cadillac/Helm paper service manual set (used, eBay) or subscribe the car to www.alldatadiy.com, the online GM/Cadillac service manuals.

All your wiring, ignition, fuel, vacuum, etc.., etc. schematics are in there.
 

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1984 Eldorado 4100
Joined
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8 Posts
This is the progress so far, I’ve decided to just go ahead and do the whole top end, I got wires, cap and rotor, upper and lower radiator hoses, and spark plugs. I’m gonna be replacing all of the vacuum hoses as I go, just labeling, and taking them into auto zone to get cut and replaced. Tomorrow I take off the carb and label, and disassemble my distributer while marking the corresponding wires as they go to the plugs. Any advice on disassembling the carb?
View attachment 576626
Your a life saver
 

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1984 Eldorado Biarritz
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Have you confirmed that the problem is the head gasket?

Throttle body: remove all fittings gently with a line wrench and do no more. There are no wear items inside of it that need replacing unless there are other signs of trouble

Rest of job: remove the 3 top valve cover bolts as carefully as possible as they're very easy to strip. Remove only the 5 nuts that hold each rocker assembly to the head bolt and take them off the engine as an assembly. They must be removed/reinstalled evenly, do not just loosen one side, do each bolt working from the middle 1 turn at a time. You will need a thin walled socket to reach the middle bolt. Do not unscrew the rocker pivots from the rocker arms under any circumstance. Remove headbolts with extreme care so as not to strip the threads, not a fun repair if you do. Before pulling each head off the engine, rap on it several times with a mallet to avoid unseating the cylinder liners. Are you changing the cylinder liner gaskets? Carefully inspect the coolant crossovers in the intake manifold for pitting on the sealing surface-if pitting exists you may be able to fix it with JB weld or the like. When putting the engine back together, use the GM retrofit intake gasket kit with spring loaded bolts.

You must acquire/borrow/steal/find the 1984 Cadillac GM service manual to effectuate this properly. What I see in the engine bay picture is a highly original car that has really not been tampered with-to be honest I really don't think that all this is necessary, but applaud your effort. Good luck!
 

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1984 Eldorado 4100
1984 Cadillac Eldorado Biarritz
Joined
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8 Posts
Discussion Starter #9
I realized my blunder as soon as I actually took a second to look at the part itself and read it. I automatically assumed that with a big ole air filter like that it must have a carb but I am obviously mistaken. I’ve found a video on disconnecting, disassembling, and rebuilding the whole throttle body itself. So I’m gonna watch that carfully as I take it off. I’m not gonna rebuild the whole throttle body because I haven’t had any problems with it. I’m just gonna take it off, clean it, and put it back on once it’s time. In the video I watched the lady used carb cleaner and Q-tips. Any better methods?
 

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1984 Eldorado 4100
1984 Cadillac Eldorado Biarritz
Joined
·
8 Posts
Discussion Starter #10
Have you confirmed that the problem is the head gasket?

Throttle body: remove all fittings gently with a line wrench and do no more. There are no wear items inside of it that need replacing unless there are other signs of trouble

Rest of job: remove the 3 top valve cover bolts as carefully as possible as they're very easy to strip. Remove only the 5 nuts that hold each rocker assembly to the head bolt and take them off the engine as an assembly. They must be removed/reinstalled evenly, do not just loosen one side, do each bolt working from the middle 1 turn at a time. You will need a thin walled socket to reach the middle bolt. Do not unscrew the rocker pivots from the rocker arms under any circumstance. Remove headbolts with extreme care so as not to strip the threads, not a fun repair if you do. Before pulling each head off the engine, rap on it several times with a mallet to avoid unseating the cylinder liners. Are you changing the cylinder liner gaskets? Carefully inspect the coolant crossovers in the intake manifold for pitting on the sealing surface-if pitting exists you may be able to fix it with JB weld or the like. When putting the engine back together, use the GM retrofit intake gasket kit with spring loaded bolts.

You must acquire/borrow/steal/find the 1984 Cadillac GM service manual to effectuate this properly. What I see in the engine bay picture is a highly original car that has really not been tampered with-to be honest I really don't think that all this is necessary, but applaud your effort. Good luck!
Have you confirmed that the problem is the head gasket?

Throttle body: remove all fittings gently with a line wrench and do no more. There are no wear items inside of it that need replacing unless there are other signs of trouble

Rest of job: remove the 3 top valve cover bolts as carefully as possible as they're very easy to strip. Remove only the 5 nuts that hold each rocker assembly to the head bolt and take them off the engine as an assembly. They must be removed/reinstalled evenly, do not just loosen one side, do each bolt working from the middle 1 turn at a time. You will need a thin walled socket to reach the middle bolt. Do not unscrew the rocker pivots from the rocker arms under any circumstance. Remove headbolts with extreme care so as not to strip the threads, not a fun repair if you do. Before pulling each head off the engine, rap on it several times with a mallet to avoid unseating the cylinder liners. Are you changing the cylinder liner gaskets? Carefully inspect the coolant crossovers in the intake manifold for pitting on the sealing surface-if pitting exists you may be able to fix it with JB weld or the like. When putting the engine back together, use the GM retrofit intake gasket kit with spring loaded bolts.

You must acquire/borrow/steal/find the 1984 Cadillac GM service manual to effectuate this properly. What I see in the engine bay picture is a highly original car that has really not been tampered with-to be honest I really don't think that all this is necessary, but applaud your effort. Good luck!
I haven’t identified if it’s the head gasket or not, but I hear what you’re saying. I will definitely be careful with the head bolts as I’ve heard they can strip extremely easily, and I definitely don’t want to deal with that. I’m also kinda at a point where I’ve already spent the money on the full kit and everything, and, hypothetically, not have to pull anything off this intense ever in the future. I’m realizing that this might not have been the best engine to pull apart and learn on. But, I have confidence that it’s gonna turn out alright. I’m in the process of finding a manual as well. I’ll take a picture this weekend when I start actually pulling stuff off again. For now, the caddy sits and waits for another week until Saturday when I’ll actually have time to get wrenching again. Thank you for the advice and I appreciate the pointers. I’ll be posting the progress on the project as I go.
 

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1984 Eldorado 4100
1984 Cadillac Eldorado Biarritz
Joined
·
8 Posts
Discussion Starter #11
Have you confirmed that the problem is the head gasket?

Throttle body: remove all fittings gently with a line wrench and do no more. There are no wear items inside of it that need replacing unless there are other signs of trouble

Rest of job: remove the 3 top valve cover bolts as carefully as possible as they're very easy to strip. Remove only the 5 nuts that hold each rocker assembly to the head bolt and take them off the engine as an assembly. They must be removed/reinstalled evenly, do not just loosen one side, do each bolt working from the middle 1 turn at a time. You will need a thin walled socket to reach the middle bolt. Do not unscrew the rocker pivots from the rocker arms under any circumstance. Remove headbolts with extreme care so as not to strip the threads, not a fun repair if you do. Before pulling each head off the engine, rap on it several times with a mallet to avoid unseating the cylinder liners. Are you changing the cylinder liner gaskets? Carefully inspect the coolant crossovers in the intake manifold for pitting on the sealing surface-if pitting exists you may be able to fix it with JB weld or the like. When putting the engine back together, use the GM retrofit intake gasket kit with spring loaded bolts.

You must acquire/borrow/steal/find the 1984 Cadillac GM service manual to effectuate this properly. What I see in the engine bay picture is a highly original car that has really not been tampered with-to be honest I really don't think that all this is necessary, but applaud your effort. Good luck!
So, after some thought and finding out how much it is to resurface the heads ($400 at a local machine shop) I’ve decided to wait until I get paid on Wednesday and order the full owners manual (I found it for $25 here: Cadillac Eldorado (1971 - 1985) Repair Manuals) to do anything else on the caddy. I really don’t want to mess something else for no reason, especially if I really don’t have to do the head gasket, you’re right, I’m not gonna! So I’m going to wait until I get the manual, clean and organize for now, and then get back to it once the manual comes in. I do plan on taking your advice on checking the oil cooler first to see if that’s the problem. Also, because I have a full top end kit, I’m going to do a few of the gaskets I can, especially the intake manifold gasket, as I’ve heard they turn to dust around 100k miles which can cause coolant problems, so I’m going to unhook everything from the radiator and run it like that to see if I can eliminate the problem. That’s all for now, and thank you for the continued guidance
 

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1984 Eldorado Biarritz
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1984 Eldorado 4100
1984 Cadillac Eldorado Biarritz
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8 Posts
Discussion Starter #13
Progress so far: pulled all of the connections (carefully and without breaking anything) off of the throttle body and I’m gonna pull that as soon as I get the manual. I don’t really want to proceed without it. But I’ve also started pulling off the front panels so I can get to the oil cooler and check that as was suggested above.
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I’ve also disconnected the power steering container to get the fan shroud off. When I was following the fuel lines to try and figure out which of the lines went to the oil cooler, and my brother made a lovely discovery that the gasket for my oil pan is shot to hell, with pieces of it coming off around the sides. So I suppose we’ll have to fix that too.
 

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1984 Eldorado Biarritz
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The oil cooler on this car is inside the passenger tank of the radiator. You shouldn’t have to remove anything more then the shroud and battery to get it out. You should be able to test it with pressurized air with it in the car however. Have you pressure tested the cooling system?

Oil pan gasket is a bit of a headache-Defintley to be saved for later!
 
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