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1998 Cadillac Deville, 1987 Fleetwood Brougham
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Discussion Starter #1
Alrighty. Here's the deal. I just bought this 1998 Cadillac Deville about 45 days ago, but for the last 4 weeks, I've noticed it has had cooling problems, and I parked it. What happens is, it overheats when going under 65, but when going over that speed, it fluxuates between 228 and 239. At this point, I had already replaced the damaged radiator cap, and thermostat.

Today, I replaced the water pump with all gaskets and belt. It slowly got up to the opening temperature of the main thermostat (180) as opposed to before that point. So I was getting very happy. After running for 30 minutes, it stayed at 215 degrees. Ooooh man, I was REALLY happy. Soooo, I take it out for a spin, and while driving it goes down to 210!! But . . . I take it out on the highway, do about 67 for appx. 35 seconds and it jumps from 210 to 242 within seconds . . . . I get off on the next exit to go back home (since this was just a test run) and within 30 seconds, it's back down to 217 . . . . Soo, uh . . . what's going on?? The water pump fixed things (the old one was beat up and rusted; the hose, ouch.. bad) . . . so what's with this?

I did spray a lot of water near the fans . . . I'm thinking the fans didn't kick on because moisture go into the motors. The only thing I can think of that may cause this issue (besides that) is the temp sensor (screwed into bottom block) or . . . the fan sensors . . . what are some things I can look at that may cause this very interesting issue. Go slow, it stay cools . . . go fast, it gets hot . . . but if you slow down, it drops quickly to normal operating temperature....


REPLACED

.. water pump w/ o-ring and housing gasket
.. water pump belt
.. thermostat
.. radiator cap
.. bottom radiator hose without inner coil to keep it open w/ new clamps
.. nothing is leaking

Thanks everyone!! And if this question was already answered before, please forgive me. Just give me a link to read and I'll do that tomorrow. For now, the car will sit and cool and dry out overnight. I spent 8 hours working on it . . . I am tired. I'm now gonna grab dinner and watch tv. Phew!!
 
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You didn't by chance purchase this car in Palm Harbor, FL did you?. Ok, I'm gonna shoot it to you straight, your head gaskets are blown and you are in for a very expensive repair. Have a nice day. :ill:
 

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White Diamond '03 DHS (with DTS floor shift)
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Head gaskets are a very distinct possibility, but before you condemn them, check the purge line for coolant flow. If it is plugged, you could have the symptoms you are experiencing. Also be sure that the cap is holding pressure and that the tensioner is providing enough belt tension. If those things are OK, get a coolant test kit to check for exhaust gases in the coolant.
 

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1998 Cadillac Deville, 1987 Fleetwood Brougham
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Discussion Starter #4
My head gaskets??? That doesn't make any sense. I've been working on Cadillacs for 10 years, and that doesn't many any sense. I've had a blown head gasket before, and never had this problem. It overheated no matter HOW fast you were going, and when I broke the engine down, I found 3 cylinders full of water. This engine is not pinging, not banging, not showing any signs of lost integrity. It looks awesome, and it's not leaking. A major sign of a blown headgasket is leaking FROM the head gasket. And as I said, the cooling system is SEALED. Nothing is leaking. The more and more I think about it, it's probably the restriction in that bottom radiator hose. I'm going to make adjustments to it and see what that does. This hose did not come with an inner aluminum coil, and it was a little too long. I was too excited about getting the job done, and I'm sure that once I get above 1100 RPM, the flow is slowed down by this 20% restriction at the bends. I'll let you guys know in a few days . . . If I bought another lemon, I'm going to be pissed. This car is beautiful inside and out. :( Thanks for your responses, anyway. I'm going to do other tests before I . . . *sigh* . . . consider the head gaskets . . .
 

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1998 Cadillac Deville, 1987 Fleetwood Brougham
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Discussion Starter #5
And no Destroyer, I didn't buy the car in Florida. ;-P . . . but, I did a coolant test and there is nothing coming out of the exhaust (which is common on the high-side) and I know in the manifolds, it could be non-detectable . . . but I'm hoping it was that restricted bottom radiator hose. I was going to fix it later, but figured the restriction wasn't great enough to be a problem . . . PERHAPS, I was wrong. Again, I'll check in within a few days. :)
 
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My head gaskets??? That doesn't make any sense. I've been working on Cadillacs for 10 years, and that doesn't many any sense. I've had a blown head gasket before, and never had this problem. It overheated no matter HOW fast you were going, and when I broke the engine down, I found 3 cylinders full of water. This engine is not pinging, not banging, not showing any signs of lost integrity.
Mistake no. 1 is to compare it to any other car you had before. The Northstar motors unlike most others can actually be driven for quite some time with bad head gaskets and coolant wont mix with the oil, it wont always overheat but it will see temperatures like the ones you are seeing, they wont ping or bang and will appear to drive and sound good.....BUT in time the situation worsens, the overheating will occur and with more frequency until its unusable.

The more and more I think about it, it's probably the restriction in that bottom radiator hose. I'm going to make adjustments to it and see what that does. This hose did not come with an inner aluminum coil, and it was a little too long. I was too excited about getting the job done, and I'm sure that once I get above 1100 RPM, the flow is slowed down by this 20% restriction at the bends. . . .
Dont want to see you spending all sorts of time and money "figuring out" what it could be and then find its the head gaskets anyway but it sounds like you will find out the hard way, much like I did. I and several others here (and I do mean several) have gone through the same situation. I do hope you are right though. Good luck with that.

. . If I bought another lemon, I'm going to be pissed. This car is beautiful inside and out.
Mine was beautiful inside and out as well but I decided to get rid of it rather than dumping that kind of money into a car that clearly wasn't worth it. Mine was a '98 model. I now drive 2 reliable (thus far) Lincoln Mark VIII's.
 
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And no Destroyer, I didn't buy the car in Florida. ;-P . . . but, I did a coolant test and there is nothing coming out of the exhaust (which is common on the high-side) and I know in the manifolds, it could be non-detectable . . . but I'm hoping it was that restricted bottom radiator hose. I was going to fix it later, but figured the restriction wasn't great enough to be a problem . . . PERHAPS, I was wrong. Again, I'll check in within a few days. :)
I hope you are right and I am wrong in this case. Either way, let us know how it goes. :thumbsup:
 

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94 ETC,97 STS
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As Destroyer said, forget everything you think you know about head gaskets.

Have an exhaust gas test done before you do a lot of replacements. If it's positive you know it's HG's. If it's negative you can treat it as a regular overheating problem.

The best place is a radiator shop. Quicker and cheaper than a mechanic.
 

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Sedan de Ville, CTS
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Mistake no. 1 is to compare it to any other car you had before. The Northstar motors unlike most others can actually be driven for quite some time with bad head gaskets and coolant wont mix with the oil, it wont always overheat but it will see temperatures like the ones you are seeing, they wont ping or bang and will appear to drive and sound good.....BUT in time the situation worsens, the overheating will occur and with more frequency until its unusable.

Dont want to see you spending all sorts of time and money "figuring out" what it could be and then find its the head gaskets anyway but it sounds like you will find out the hard way, much like I did. I and several others here (and I do mean several) have gone through the same situation. I do hope you are right though. Good luck with that.

Mine was beautiful inside and out as well but I decided to get rid of it rather than dumping that kind of money into a car that clearly wasn't worth it. Mine was a '98 model. I now drive 2 reliable (thus far) Lincoln Mark VIII's.
Bad news on Mark VIIIs: air shocks are about $900 EACH. I could be wrong, but that is plus labor.

I love the look of the Marks, but I have avoided them because of the shocks. I just turned down a 2002 Continental with 7000 miles on it. Again, I was afraid of shocks.
 

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1996 Deville (sold), 2000 Mustang GT
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Bad news on Mark VIIIs: air shocks are about $900 EACH.
Bad news on Devilles and Sevilles; The road sensing suspension shocks are 1000 dollars a piece and about 450 for each shock sensor.
 
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Bad news on Mark VIIIs: air shocks are about $900 EACH. I could be wrong, but that is plus labor.

I love the look of the Marks, but I have avoided them because of the shocks. I just turned down a 2002 Continental with 7000 miles on it. Again, I was afraid of shocks.
That is ridiculous!. I replaced the whole air ride suspension with NEW conventional strut conversion for $380 plus 2 hours of my time on my '95. Why? Even though there was nothing wrong with the air ride, I found it annoying. My wife's '98 still has it but that car only has 19k original miles so I'm not gonna mess with it.
 

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1998 Cadillac Deville, 1987 Fleetwood Brougham
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Discussion Starter #12
Destroyer . . . you might be right. Believe me, I am listening to you guys. I did more research and fixed the bottom radiator hose. I am finding all kinds of CRAP floating around inside my lines. I have been reading that a clogged radiator can do the same thing. And it quickly climbs when going uphill . . . which may indicate a cracked . . . *sigh* Sooo, I'm HOPING . . . it's the radiator. That's something else I can fix myself. If it's the head gasket . . . I hope someone can take payments. I don't feel like working on it. It'll take weeks around my work schedule. I can't afford $2,000 out-of-pocket right now, nor do I have credit cards with that kind of limit on them. I should have bought a new Cadillac. The $3,000 I spent on this car could have been a nice down payment. Now . . . (RANGER) mentioned checking a purge line . . . Since I'm still learning my way around this engine, where can I find this line at? Thanks! I have the 4.6L, 279 . . . if that helps. The last thing I'm going to do (and I promise) is buy a radiator . . . . if I still have the problem . . . then I give up; it's going into the shop for a head gasket replacement. I'm not about to use any cheap-**s band-aid fix (the amazing THERMAGASKET!!) and cause further harm to the engine.

Hey, at least by the time I get all this done, everything I replaced won't be a worry anymore. *wink* That's the upside.

I'll keep everyone posted.
 

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White Diamond '03 DHS (with DTS floor shift)
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The purge line is the 3/8" line that runs from the water pump housing to the surge tank. Remove it at the surge tank with the engine at idle (cold, so as not to burn yourself). It should have a coolant flow that will increase with RPM. If not, clear the clog, that is likely your problem. If it does have flow, the head gaskets are a likely suspect. Have the coolant checked for exhaust gases before throwing any parts at it.
 

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I really fail to understand why people just don't get an exhaust gas test done, and would rather throw parts and money at the problem. Annd then when their head gaskets are shot they have a big dilema because they just put all this money into a new cooling system and now have to shell out 3500 to fix the head gasket, i just dont get it.
 
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I really fail to understand why people just don't get an exhaust gas test done, and would rather throw parts and money at the problem. Annd then when their head gaskets are shot they have a big dilema because they just put all this money into a new cooling system and now have to shell out 3500 to fix the head gasket, i just dont get it.
Been there done that. I agree with you to an extent. I didn't know to get an exhaust gas test to tell if it was a head gasket and nobody here suggested it either. Like Mr. Fleetwood Fancy I thought a head gasket would reveal itself by coolant mixing with water, car running rough or white smoke out the exhaust. So, like him I listened to suggestions. I changed the water pump, t stat (twice), the belt on the other side of the motor, the radiator cap, etc.. Its funny cause after the water pump went in, I thought it was fixed but that only lasted a day or so, same with the other parts. After I spent over $1k trying to fix the problem did I finally realize it was the head gaskets. For awhile I figued ok this car just runs hot but when it started getting to 261 degrees leaving me stranded, it was just time to go.
 

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I really fail to understand why people just don't get an exhaust gas test done, and would rather throw parts and money at the problem. Annd then when their head gaskets are shot they have a big dilema because they just put all this money into a new cooling system and now have to shell out 3500 to fix the head gasket, i just dont get it.
I think part of it is denial. No one wants to believe it. Can't say as I blame them.
 

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White Diamond '03 DHS (with DTS floor shift)
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Northstar water pump is one of the easiest around. Starter is not bad either. Plugs are easier than a 4.9 or a 3.8. Head gasket diagnosis is the same as any other engine. They just respond a little differently when they begin to fail.
 

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1992 STS / 2005 MB G500 / 2003 STS / 2006 XLR-V
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I really fail to understand why people just don't get an exhaust gas test done, and would rather throw parts and money at the problem. Annd then when their head gaskets are shot they have a big dilema because they just put all this money into a new cooling system and now have to shell out 3500 to fix the head gasket, i just dont get it.
I agree 100 percent.
 
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