85 Eldorado overheating

[SSallday]

Hi everyone, I would like to start by introducing myself. I own a 1985 Eldorado with the reinforced 4100 motor. The motor has been good to me until a couple of weeks ago. I was traveling up a very steep hill and the temperature light came on. I was able to get the car home since the issue occurred about a minute down the street from my house. The coolant was boiling and spewing out  from the radiator cap. This issue only occurs when I travel up this steep hill. The car could idle for an hour and it won't overheat. I've already replaced the thermostat and checked the coolant level so I'm guessing it might be the head gasket. Has anyone experienced this problem?

[TJ Hopland]

I was able to get the car home

Was what every former 4100 owner told me about when they got rid of theirs when I had mine many years ago.

That isn't good for any engine but when you get an engine with mixed materials and cylinder sleeves its really not good. 

Where are things at now?   You refill and everything seems ok?   Usually when these had issues it wasn't a minor maybe its bad maybe its not sort of thing like it cold be on some other engines.    The low tech way to check for a head gasket issue is to start out with a dead cold engine.  Squeeze the upper radiator hose.  If its hard remove then re install the radiator cap.  It should now be soft.   Start er up and let it idle.   Periodically check squeeze the upper hose.   It should stay soft till you get some real heat in the engine which usually requires driving it to get a load on it.   By the time it gets hard it should be hot enough to be pretty uncomfortable to touch.  If its hard before its really hot its a head gasket.   

If it never gets hard even after a drive you have a bad cap or a leak somewhere and the test won't work.   Also maybe is the reason it boiled over.   Water being mixed with antifreeze only raises the boiling point a few degrees so you don't really have much headroom over the 200 ish degrees the engine normally runs at.   What gets you into the 250 boiling point range is the 15 ish pounds of pressure regulated by the radiator cap.   Any sort of a leak including the cap not working properly you are back to 212 boiling point.    Gaining 12 degrees above 'normal' temp on a 35 year old car going up a hill?   Pretty likely so without the extra range gained by the pressure it just boils.

So hopefully it is just some sort of leak but you do know the engine got warm.  Even though it may not have got much over 212 before it boiled boiling coolant is a crappy coolant and can't be pumped by the water pump so you for sure had some really hot spots and uneven temps in that engine which with the mix of materials this had is never a good thing.   Hope it turns out to be fine because these are not cheap to rebuild and good used ones just are not around anymore.   Swaps are also difficult with this car because a lot of the needed donor parts are no longer laying in junkyards like they used to be.

[76eldo]

I have a lot of past experience with the HT4100 and also with Northstar's.

Engines like the 4100 have a lot of known issues and problems.  There are a few different things that can happen that lead to an overheat condition on the 4100.

1.  Hopefully it's this one... Low on coolant due to a leak.  A leak from a hose, water pump, or the radiator.  That's just common old car stuff and easy to find and fix.

2.  Coolant loss from under tightened manifold bolts.  This is bad.  Check your oil on the dipstick.  If it's clean or even just dirty black oil, that's good.  If it's gray in color, that's coolant and oil mixed together which is also know as the milkshake of death.  At this point your engine is toast.

3.  Coolant loss from head gasket(s) which can be seen as coolant seeping down the sides of the block from the head/block joint.

4.  The last one and what i think you have... Combustion gasses and heat blowing into the cooling parts of the head and/or block from head gasket leak.  You can have water leaking into the combustion chamber which causes a white smoke and a sweet exhaust smell, OR it can be blown out the other way and allow exhaust gasses to pressurize the wet side of the engine.  The classic sign of this is exactly what you had described.  The engine only overheats when you push it or when you are climbing a steep or prolonged grade.

So you need to do some diagnostic work and then decide how much you love the car.  If you have bad head gaskets and have overheated it even once, it's not advisable to just do a head gasket job.  The entire engine should be rebuilt and the block and heads checked.  It's an aluminum block with cast iron heads.  Not sound engineering and I really don't know why they didn't make the entire engine from aluminum.  There were many other deficiencies as well and if you google HT4100 problems you can read all about it.

The other alternative if you want to try to buy some time is to purchase a product called K-Seal.  It's a known pour in solution that is not too expensive and may seal up your gasket problem for a while.  When you install a new Jasper engine you also have to replace the engine oil coolant lines and radiator to be able to have the warranty.  This fix is probably going to be a lot more expensive than the car is worth unless its a really mint loaded Biarritz convertible.

Good luck and please report back once you have decided on a path.

Good Luck,

Brian

[SSallday]

I drove it about 4 hours on the highway without overheating. It doesn't like the one steep hill that I have to travel on. Is it possible that the air conditioner would cause an issue? The A/c was running both times that it overheated. It drives me crazy to think that the gaskets are bad and it's a shame that GM didn't engineer the 4100 differently.

[TJ Hopland]

When its warmed up try carefully squeezing the upper hose to see if its building pressure.  I say careful because it should be around 200 degrees.   If its not hard there is no pressure and it will boil over around 212 degrees which like I said earlier is only 12 degrees over the 200 its normally running at.   AC + hill could easily add that 12 degrees.   You need the pressure to raise that boiling point to around 250.  Gives you some headroom for hills and ac.   

IF its not hard the first thing to try is a new radiator cap.  Those are cheap and easy.   If a new cap doesn't let it build pressure then you have a leak somewhere.    You can get a pressure test kit for $50-100 these days and that is a great way to find the leak.  Its a hand pump and gauge that attaches in place of the cap.  You can put the system under pressure with out the danger and hassle of a running, hot, and noisy engine.   

[76eldo]

You really need to figure out if you are losing coolant.

[James Landi]

I've owned four, yes, four 4100's--  they all absolutely needed serious, professional radiator cleansing , as the core gets crusty, and heat transfer/cooling is reduced.  Since the engine has so little horse power, hardly enough to pull the car up a hill, those are the times when they begin to overheat.  The comments about blown head gaskets are right on target, but if, as stated in earlier posts, you're not spewing coolant when  the engine is cold and gradually warming, you're likely still ok. I will caution you that if your entire engine is not thoroughly and aggressively  flushed by a professional cooling system technician of accumulated coolant tablet gunk, and your radiator is not changed or the core is not chemically flushed by an expert, you can expect a disaster, as the head gasket will blow, and sometimes the front main crankshaft bearing will wear to the point that you develop the 4100 "death rattle."  Get the cooling system and engine professionally flushed, and by the way, DON'T EVER use any other "stop leak" product -- use only the GM tablets. Oh, and another" by the way," is the radiator shroud still in place??? If removed there won't be sufficient cooling air for those times when the engine is taxed. Hope this helps.  James

[76eldo]

James,

I agree about getting the radiator flushed or professionally cleaned out but I would never aggressively flush or even backflush one of these engines.

I open the petcock and drain out all of the old stuff with the car warmed up and heater on, and the cap off.  Then I fill with water.  Then let if flush by dribbling in hose water and the old stuff comes out of the petcock.  Once it's all running clear, let it drain out and refill with 50/50 coolant and 6 crushed up pellets adding the pellets gradually.

What the pellets do can quickly be undone by harsh flushing as far as pressure or chemicals.  You can see if the radiator core looks all crusty by looking inside through the filler neck.

The crucial info is, is the car losing coolant.  If it's not, then it is possible that it could be just a cooling system issue as in bad radiator flow, or bad water pump.

Brian

[Eric DeVirgilis CLC# 8621]

I've owned many HT4100s and none of them overheated while ascending steep grades with the air conditioner running, regardless of how high the outdoor temperature. The problem is not due to "engineering" per se, but to a defect.

Bryan has outlined the probable causes very well. I would only add that the head gaskets or engine block could be damaged in such a way that hot exhaust gasses are entering the coolant stream without resulting in coolant entering the crankcase which tends to be the most common symptom of HG failure in the HT4100.

Northstar engines on the other hand rarely introduce coolant into the crankcase when they develop HG issues. Instead they exhibit the exact same symptoms of the '85 Eldorado - ie: overheating when the car is under load but could otherwise operate all day (in cooler temperatures) on in flat areas without exceeding maximum operational limits of engine temperature.

Sorry to say this situation doesn't sound good and if the head gaskets are indeed bad, you're probably looking at engine replacement as these engines do not like being taken apart at this age. 

[Tom Forsberg]

I’ve owned several 4100’s, most of the 84/85 vintage... loved the styling of the era, and frankly was never in a hurry to get anywhere and the only fear I had at the time Was merging onto a freeway!  But what can I say, I Have a sense of adventure and always migrate to the unusual...I had to have a 76 eldo with fuel injection or my 81 with the V864!

To everyone’s point the very worst thing you can do is overheat these engines!  When my 85 eldo convertible overheated I was sick to my stomach and was ready for the funeral procession.  After assuming the worst (head gasket) I tested it with a kit and that was not it.  Next I replaced the thermostat.   Then it dawned on me... Sometimes the most obvious thing is staring right at you.   Those old cross flow radiators are notorious for plugging up.  That was it in my case.  I replaced the radiator and never had another problem.  You might want to check into that.

Best of luck to you!  And don’t give up if you like your car.   Later model 4100s can last just as long as any other engine.   Just keep changing out your coolant every 2 years and replace the coolant tablets.   

[SSallday]

First off, I appreciate all of your responses. I want to clarify what has been done to the car. The radiator and cap were both replaced. I threw the tabs in from Cadillac once the new radiator was installed. The coolant level has not changed so I'm assuming that there isn't a leak.

[Eric DeVirgilis CLC# 8621]

  Later model 4100s can last just as long as any other engine.   

I wouldn't go that far - not by a longshot.

Granted, owners who regularly had the cooling system serviced had far better luck than those who didn't. However no amount of coolant changing could prevent bearing wear which was also common on the HT4100 due to the undersized mains used in this engine. Another problem was soft camshafts which again, no amount of servicing could prevent although the camshaft problem seems to have been corrected by 1984.

Another problem is the small oil returns that become clogged resulting in large accumulations of oil in the valve covers causing oil leakage because they were not designed to retain this quantity of oil.

In a nutshell, the HT4100's recorded ailments are many, compounded by the fact that major disassembly is likely to result in terminal damage to major engine components due to their fragility and the galvanization of dissimilar metal composition of hardware and and engine parts. After nearly 40 years, intake and head bolts are so "welded" together that it's nearly impossible to extract bolts without breaking chunks off of the engine block. Ask me how I know. 

Beautiful cars otherwise but I have washed my hands of HT4100 Cadillacs.

[James Landi]

Hi Mike,

So having changed out the radiator, I wonder about the status of the radiator shroud that was a key component for cooling. Is it all intact as it was originally designed?  and the fan clutch? Also, you might consider installing an electric temperature gauge as the telltale (aka idiot light) may be providing you with a false reading.  In any case, do "baby" your engine.  My 83 Eldo clocked 315,000 miles before it developed the death rattle.  Some of these engines did last and last, but for the most part, those were well maintained, babied, and lived in the warm flat lands.   Happy day,  James

[Eric DeVirgilis CLC# 8621]

For the most part, I think the exceptions to HT4100 (often short) longevity are cars that have high mileage accumulations over a relatively short period of time, ie: high "highway" mileage. This is not surprising as it's common for cars that are operated this way to perform very well despite some eyebrow-raising mileage accumulations.

Start and stop driving in traffic and short trips (especially in cold weather) is far more detrimental to engine wear that steady speed highway cruising where the engine never has a chance to get sludged up and hot/cold cycles are limited.

Once we had a customer stop in with an '84 Fleetwood with over 400,000 miles. I jokingly asked how many engine replacements the car had. I could see he was visibly puzzled by this inquiry, responding that the engine is original and that Cadillacs "run forever" oblivious to the HT4100s reputation. As it turns out, he was from Tennessee his job involved 50,000 miles of driving a year (car was 8 years old at the time).  That's the reason the engine lasted as long as it did - mileagewise.  Age however, is another story...

[79 Eldorado]

It seems like all the bases have been covered but knowing the actual temperature as James Landi brought up by installing an actual gauge cannot be overstated. Most of the "Tell tale" idiot lights don't come on until 260F from what I recall. Cadillac really let people down by not having at least a gauge option IMO. Even the Toronado (at least in 1979) without even having the full gauge package had a temperature gauge.

One other tool which can help is an infrared pyrometer (I would still want a gauge). If you don't have one you would be amazed at the number of things it can help you diagnose. A sticking caliper will generate more heat so you can get a relative comparison, bearings going bad can be hotter, temperature before and after a catalytic converter or comparison of 2 on a dual exhaust.

I hope you figure out the issue. I love these cars but knowing the Olds 350 was only offered one year in this body style is why I bought the 1979 (California also carried over to 1980). I now know through this forum that the 368 wasn't that bad either as long as the 8-6-4 was disabled. I wish I knew that long ago because one of the most beautiful Eldorados I've ever seen was in a Niagara Falls junk yard for parts. At the time I couldn't understand why until I opened the hood and saw the 8-6-4 option. The interior of that car was like showroom new. That was years ago now.

Scott

[bcroe]

I agree, get a temp gauge and keep an eye on it in stressful situations. 
And I would get a new radiator, check if larger radiator for a 368 or 350
car is a possibility.  Another possibility is having a high performance
radiator built to fit, extra fins, extra rows, at a price.  All mine have this
sort of upgrade, and the temp gauge pretty much stays glued to 185,
where the thermostat opens. 
good luck, Bruce Roe