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85 eldo conv (yes HT4100) overheating

Started by Tom Forsberg, March 21, 2010, 08:51:20 AM

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Tom Forsberg

I have a 1985 Eldorado Biarritz Convertible with the infamous HT4100.  I bought it used with 59K.  I have had an 84 CDV so I have been around the block with this engine, IE feeling failed main bearing knock in steering wheel.  However, this engine has a new intake manifold gasket.  The engine runs excellent, and no signs of any coolant in the oil etc.  Have sent oil sample to Blackstone for analysis.  However, I drove for about an hour yesterday and it ran great.  Sat idling in traffic (making it work to go up any type of hill) etc and all was well.  However, when I got back into my driveway after a bit of very slow speed driving through a residential area, the dreaded Stop Engine Temp light and the chimes went off.  I shut the car off immediately and it was boiling over (yes I did not sleep well last night thinking about the head gaskets after this happening).  The previous owner had disclosed this to me that it overheated once and I have the receipts for a new thermostat, coolant sensor etc. which was less than 5k ago.  I started it up, took it out again on the highway last night and drove around all without a problem.  I have the manual to invoke the self diagnostics to display the coolant temp live while driving and while it's in celcius, the engine was running at 212-224 degrees (had to convert the celcius) with no warning lights.  I was corresponding with a mechanic on-line who said its probably a head gasket.  This does not make sense to me.  How does a head gasket cause overheating,  I always thought it was the reverse...Overheating kills the headgasket?  Has anyone else ecnountered this problem?
1956 series 62 CoupeDeVille

TJ Hopland

After the light came on and it cooled off was the coolant low?

The way a bad head gasket causes overheating (and then a worse head gasket problem) is that anytime the cylinder pressure is greater than the cooling system pressure what ever is in the cylinder gets pushed into the cooling system.   The cooling system should only be in the 10-16 psi range because the radiator cap regulates / bleeds off any more than that.  The cylinder on the compression stroke reaches 100-200 psi.   Just right there you are going to get a 'squirt' of air/fuel mix pushed through the leak into the cooling system.  Next thing that happens is the spark plug fires and bang you now have 1000's? of psi in there so you get another blast of basically exhaust gas getting pushed into the cooling system.  On the intake stroke when the cylinder is under vacuum is when you have a chance that the 15 psi in the cooling system will push back into the cylinder.   These air bubbles build up in the cooling system.  Several things happen.  Lets say there is a bubble stuck along the edge of the cylinder and head gasket.  Air is not as good at heat transfer as liquid is so there is going to be a hot spot in the block there that may weaken the metal or the head gasket or cause detonation (pinging) that will cause more heat and so on.  You could get an air bubble at the coolant sensor.  Sensor is designed to read coolant, not air so your reading will not be accurate.   You get an air bubble in the water pump, impeller blades are designed to move liquid not air so you dont get any flow.  This caused the coolant to boil in the hot places and makes more air and pressure... you can now see the death spiral, especially on an aluminum engine that cant take the abuse like cast iron could.     The bit about basically exhaust being pushed into the coolant after the plug fires is the reason shops will often take their exhaust probe and 'sniff' around the radiator cap with the engine running.  The only way to get hydrocarbons into the coolant is through a bad head gasket so its a good test.

I dont mind the 4100's so we wont get into that but Im sure others will (assume the fetal position with flack jacket and swat team gear on!).    Back in the day EVERY 4100 failure I heard about was due to overheating.  All the stories were the same.  Light came on but I made it home.  You said you shut it down immediately which is good but you also said that the previous owner got it hot so that may be when the damage was done.  Early on the reason for getting hot could have been a 'defect' but they got those pretty well worked out and taken care of. Back then we were all used to cast iron that could take a bit of abuse.  Now days most engines are aluminum and head gaskets go all the time and most people dont seem to care.  Even back then look at the chrysler 2.2's.  Those made the 4100's look un stoppable.

Somewhere here in one of the many 4100 bashing threads someone posted some photos of a national re builder that apparently still does quite a few of these motors.  There are a few local shops for me that last time I checked told be they still do a few also so if you choose to or need to there should be good options.    You may not need a rebuild but I would pull the motor from the car.  You get a better look at things and more room to work.  If its determined that the gasket can be replaced then you can just do that and put it back in (but while its out maybe some new seals and gaskets and a clean up).  If it can be fixed then you got it out already.  Its been a while but I think some of the head bolts are on the outside of the block so they can be a problem and if they are its much easier to deal with them out of the car.  If its not the 4100,4.54.9 thats like that then its the N star.  I know is was some aluminum caddy.   
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Tom Forsberg

 The coolant in the reservoir was at about the same level it has been and the radiator was full to the top as I was watching it while the engine was running to make sure there was good flow through the radiator and I saw 2 of the top fins and coolant was flowing well.  I have been watching it very closely as I know missing coolant on this is a bad sign.  I also changed the oil a few days ago and it was not milky or bubbly.
Thanks for explaining this to me, truly appreciated.

Quote from: TJ Hopland on March 21, 2010, 09:56:53 AM
After the light came on and it cooled off was the coolant low?

The way a bad head gasket causes overheating (and then a worse head gasket problem) is that anytime the cylinder pressure is greater than the cooling system pressure what ever is in the cylinder gets pushed into the cooling system.   The cooling system should only be in the 10-16 psi range because the radiator cap regulates / bleeds off any more than that.  The cylinder on the compression stroke reaches 100-200 psi.   Just right there you are going to get a 'squirt' of air/fuel mix pushed through the leak into the cooling system.  Next thing that happens is the spark plug fires and bang you now have 1000's? of psi in there so you get another blast of basically exhaust gas getting pushed into the cooling system.  On the intake stroke when the cylinder is under vacuum is when you have a chance that the 15 psi in the cooling system will push back into the cylinder.   These air bubbles build up in the cooling system.  Several things happen.  Lets say there is a bubble stuck along the edge of the cylinder and head gasket.  Air is not as good at heat transfer as liquid is so there is going to be a hot spot in the block there that may weaken the metal or the head gasket or cause detonation (pinging) that will cause more heat and so on.  You could get an air bubble at the coolant sensor.  Sensor is designed to read coolant, not air so your reading will not be accurate.   You get an air bubble in the water pump, impeller blades are designed to move liquid not air so you dont get any flow.  This caused the coolant to boil in the hot places and makes more air and pressure... you can now see the death spiral, especially on an aluminum engine that cant take the abuse like cast iron could.     The bit about basically exhaust being pushed into the coolant after the plug fires is the reason shops will often take their exhaust probe and 'sniff' around the radiator cap with the engine running.  The only way to get hydrocarbons into the coolant is through a bad head gasket so its a good test.

I dont mind the 4100's so we wont get into that but Im sure others will (assume the fetal position with flack jacket and swat team gear on!).    Back in the day EVERY 4100 failure I heard about was due to overheating.  All the stories were the same.  Light came on but I made it home.  You said you shut it down immediately which is good but you also said that the previous owner got it hot so that may be when the damage was done.  Early on the reason for getting hot could have been a 'defect' but they got those pretty well worked out and taken care of. Back then we were all used to cast iron that could take a bit of abuse.  Now days most engines are aluminum and head gaskets go all the time and most people dont seem to care.  Even back then look at the chrysler 2.2's.  Those made the 4100's look un stoppable.

Somewhere here in one of the many 4100 bashing threads someone posted some photos of a national re builder that apparently still does quite a few of these motors.  There are a few local shops for me that last time I checked told be they still do a few also so if you choose to or need to there should be good options.    You may not need a rebuild but I would pull the motor from the car.  You get a better look at things and more room to work.  If its determined that the gasket can be replaced then you can just do that and put it back in (but while its out maybe some new seals and gaskets and a clean up).  If it can be fixed then you got it out already.  Its been a while but I think some of the head bolts are on the outside of the block so they can be a problem and if they are its much easier to deal with them out of the car.  If its not the 4100,4.54.9 thats like that then its the N star.  I know is was some aluminum caddy.   
1956 series 62 CoupeDeVille

76eldo

#3
There are a few problems with doing the head gaskets on HT4100's.

First, NEVER rotate the engine for any reason with the heads off.  This will cause the liners to rise up and become dislodged from the O ring seal at the bottom of the liners.  Make sure your mechanic knows this.  Cadillac has a special tool that bolts on to prevent this from happening.  I know all about this because I did it.

Bolting the heads back down...  The threads in the block can easily become damaged.  Make sure the threads are cleaned out and blown out with a thread chase ( not a tap).

I had an 85 convertible that I bought with a "totally rebuilt engine, done by the best mechanic in town" a few years ago.  2 weeks later an external coolant leak developed in one of the areas where the head bolt leaves the head, goes external, and threads into the block.

I tore it down, and the head gaskets were badly corroded, indicating that the "rebuild" was a joke.

Once I had the heads off, there wasn't much more to do to remove the engine.  I sent it out to a machine shop and found that the guy running the shop was an expert on HT4100's and rebuilt them cor Cadillac dealers in the 80's

Make sure you use the updated intake manifold gasket and seal set and spring washers from Cadillac.

These are beautiful cars, but the HT4100's can be a problem.  You may want to also consider a new Jasper engine.  If you do change out the engine, install a NEW radiator, and totally flush out the oil cooler hoses that run from the oil filter adapter to the radiator.  Be very careful when re-installing the hoses in the oil filter adapter.  Do not overtighten them, you split the aluminum casting ( yep, I did that too).

Hang in there.  Don't let anyone tell you the car is worthless.  If you like the car and it's really mint, fix it.

Good luck,

Brian

Brian Rachlin
Huntingdon Valley, Pa
I prefer email's not PM's rachlin@comcast.net

1960 62 Series Conv with Factory Tri Power
1970 DeVille Conv
1970 Eldo
1970 Caribu (?) "The Cadmino"
1973 Eldorado Conv Pace Car
1976 Eldorado Conv
1980 Eldorado H & E Conv
1993 Allante with Hardtop (X2)
2008 DTS
2012 CTS Coupe
2017 XT
1956 Thunderbird
1966 Olds Toronado

76eldo

I just noticed that you are in Phoenixville, Pa.

The rebuilder I mentioned was in North Hills, Pa.

You may want to check him out.

Email me directly at 76eldo@comcast.net

Brian
Brian Rachlin
Huntingdon Valley, Pa
I prefer email's not PM's rachlin@comcast.net

1960 62 Series Conv with Factory Tri Power
1970 DeVille Conv
1970 Eldo
1970 Caribu (?) "The Cadmino"
1973 Eldorado Conv Pace Car
1976 Eldorado Conv
1980 Eldorado H & E Conv
1993 Allante with Hardtop (X2)
2008 DTS
2012 CTS Coupe
2017 XT
1956 Thunderbird
1966 Olds Toronado

Guidematic


There is one thing that strikes me with this. You say that the engine temp is fine when you are moving well, on the highway. But when you do some slow driving, the engine gets hot. The coolant level stays the same, there are no leaks and no signs of oil or compression getting into the coolant?

This sounds like an airflow issue. Perhaps the fan is not operating like it should. It is supposed to engage when the temperature within the shroud gets to a certain point. If it is not doing that, then there will not be sufficient airflow through the rad, leading to higher temperatures.

When you are moving on the highway, there is plenty of airflow through the rad and the fan is not needed. This was a common malady with many cars in the 80's, not just with Cadillacs.

Remember, always start with the basics first before condemning something more complex, and still having the same issue afterwards.
1970 Fleetwood Brougham 68169
1985 Eldorado Coupe 6EL57
1988 Eldorado Biarritz 6EL57
1990 Brougham d'Elegance 6DW69
1994 Fleetwood Brougham 6DW69

Tom Forsberg

Thank You Mike.  You were dead on.  Replaced the radiator and the fan clutch, engine is now running 40 degrees cooler!  Thank you for your suggestion!!
Tom

Quote from: Mike Jones on March 21, 2010, 11:54:03 AM
There is one thing that strikes me with this. You say that the engine temp is fine when you are moving well, on the highway. But when you do some slow driving, the engine gets hot. The coolant level stays the same, there are no leaks and no signs of oil or compression getting into the coolant?

This sounds like an airflow issue. Perhaps the fan is not operating like it should. It is supposed to engage when the temperature within the shroud gets to a certain point. If it is not doing that, then there will not be sufficient airflow through the rad, leading to higher temperatures.

When you are moving on the highway, there is plenty of airflow through the rad and the fan is not needed. This was a common malady with many cars in the 80's, not just with Cadillacs.

Remember, always start with the basics first before condemning something more complex, and still having the same issue afterwards.
1956 series 62 CoupeDeVille

Guidematic


Excellent! Glad to hear it worked out for you.

Mike
1970 Fleetwood Brougham 68169
1985 Eldorado Coupe 6EL57
1988 Eldorado Biarritz 6EL57
1990 Brougham d'Elegance 6DW69
1994 Fleetwood Brougham 6DW69

TJ Hopland

Glad to hear you got it worked out with minimal expense.   
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Mark Pruett

Glad the radiator and fan clutch solved it. Another weak spot, which you might replace before it fails, is the heater valve in the heater hose between the engine and firewall. Cheap to replace, and it's prone to failure. Since it will leave a little coolant behind the rear passenger corner of the engine, it can be mistaken for an intake gasket leak.