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98 Eldorado
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Discussion Starter #1
Well I'm still driving my '98 Eldo with just the usual upkeep expenses. More serious problem just recently started. I drive around town on a daily basis with a little highway. Average speed around here is 55mph. Car runs great. I still have to add coolant every month or so but don't get the low coolant message. Mechanics have checked for leaks, pressure checked, etc. No problems found. OK so here's the problem. About two months ago I took a run up I-87 with speed between 65 and 75. Stopped at a rest area and when I left I floored it to get back onto the thruway in heavy traffic. The temp guage started to rise to the 1 o'clock position then to the 2 o'clock position. I slowed down to 60 and temp started to drop. Slowed to 55 and it dropped to normal 12 o'clock. Stopped at a gas station and had to add about two or three quarts of coolant. Everything was fine after that. Yesterday, 2 months later, exact same thing happened. Never overheats around town. Oil is clean, no leaks found in coolant system. Could the thermostat be bad or are you going to say HeadGasket is going?
 

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Just dealing with the overheat, I would chalk that up to fluid flow. You were almost a gallon low, faster RPM, Faster flow, but not enough fluid in system to meet the demand. You need to stay on top of the level, check it more often, I would be suicidal if I let mine get that low, nevermind the fact you are nursing another problem.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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You need to let the system settle for a couple of days after adding coolant to halfway up in the surge tank, COLD. Then, get to a GOOD radiator shop and have them test the airspace over the coolant in the surge tank for the presence of exhaust gasses.

Cross your fingers, caress your credit card, call Jake the stud man (^^^ banner ad), and cross your fingers again. Not good symptoms.

A properly operating Northstar cooling system will NEVER - NEVER need to be "topped up".
 

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04 Deville, 11 DTS Premium, 00 Deville (sold), 02 Deville (sold)
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You need to let the system settle for a couple of days after adding coolant to halfway up in the surge tank, COLD. Then, get to a GOOD radiator shop and have them test the airspace over the coolant in the surge tank for the presence of exhaust gasses.
NAPA has the Exhaust gas test kit it will run you about $50
 

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98 Eldorado
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214 Posts
Discussion Starter #7
Well today the outside temp is hovering around 68 degrees so figured I would have some fun. I drove around town for about twenty minutes, in and out of traffic to make sure temp was up there. No overheat. Got on the highway and did a couple of WOT's to simulate what I did on those two overheat situations. Then I continued on the highway at 70 mph for about five minutes. No overheat. Got home. Checked the coolant level and all was OK. The first time I had the overheat problem, the outside temp was hovering over 90 degrees. Second time it was around 85 degrees. Guess I'm safe as long as I don't go on any long trips in hot weather. ???????
 

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1997 Eldorado
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637 Posts
Well today the outside temp is hovering around 68 degrees so figured I would have some fun. I drove around town for about twenty minutes, in and out of traffic to make sure temp was up there. No overheat. Got on the highway and did a couple of WOT's to simulate what I did on those two overheat situations. Then I continued on the highway at 70 mph for about five minutes. No overheat. Got home. Checked the coolant level and all was OK. The first time I had the overheat problem, the outside temp was hovering over 90 degrees. Second time it was around 85 degrees. Guess I'm safe as long as I don't go on any long trips in hot weather. ???????
WHAT! 68 man your lucky
 

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2010 DTS
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87,544 Posts
Mitch, outside temperature should make no difference. The engine was tested in death valley. IF it is a head gasket it will slowly get worse. I'd test it.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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Whether the ambient air temperature is 20 or 100 degrees the engine should run in the thermostat/fan operation band: 188 to 224 degrees, 20 mph or 120 mph.

As Ranger posted, these things have very healthy cooling systems. IF you are continually adding coolant to keep the level at halfway up the surge tank, COLD, then you have one of two problems: A system leak or failing head gasket(s).

If you cannot positively document a leak, then test the airspace in the surge tank for exhaust gas.
 

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90 Eldo -SOLD-, 98 ETC -SOLD-, 86 XR4Ti Track Car, 07 Ranger
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Mitch, do you have the plastic connector piece between your front bumper and your radiator support or if when your hood is up can you look and see the ground between your radiator support and your front plastic bumper?

I second getting the $50 block tester, it'll tell you in 10 minutes if you have a big problem or not.

Also, did you recently do any coolant system work and properly bleed the system? I know our system is 'supposed' to be self-bleeding but trust me, it does not always work, I recently re-bled my system after moving a hose to get to the alternator after I didn't bother at first and guess what, I got some bubbles out of the system, which again is 'supposed' to be self-bleeding. I find it funny there's a bleeding system procedure in the FSMs as well for my 98 Eldo...

Goodluck...
 

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1997 Eldorado
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637 Posts
Mitch, do you have the plastic connector piece between your front bumper and your radiator support or if when your hood is up can you look and see the ground between your radiator support and your front plastic bumper?

I second getting the $50 block tester, it'll tell you in 10 minutes if you have a big problem or not.

Also, did you recently do any coolant system work and properly bleed the system? I know our system is 'supposed' to be self-bleeding but trust me, it does not always work, I recently re-bled my system after moving a hose to get to the alternator after I didn't bother at first and guess what, I got some bubbles out of the system, which again is 'supposed' to be self-bleeding. I find it funny there's a bleeding system procedure in the FSMs as well for my 98 Eldo...

Goodluck...
how do you bleed the system?
 

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1992 STS / 2005 MB G500 / 2003 STS / 2006 XLR-V
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11,694 Posts
To the OP... you are having CLASSIC early headgasket failure symptoms. You need to follow Ranger and Sub's advice or you'll just end up finding out the hard way later.
 

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'99 SLS, '05 Deville, '87 Porsche 944
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299 Posts
To the OP... you are having CLASSIC early headgasket failure symptoms. You need to follow Ranger and Sub's advice or you'll just end up finding out the hard way later.
I'll second that. When I first bought mine I wasn't aware of the HG problems. For the first three months of ownership the car ran fine, apart from having to add coolant on a regular basis, also noting that when I would open the fill cap there always seemed to be pressure. Then the car overheated on me, once. I tested for combustion gases in the coolant reservoir and guess what. I continued to drive it for another month and had no further instance of overheating or need to add coolant. When I pulled it apart the gaskets were shot. Good luck!
 

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98 Eldorado
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214 Posts
Discussion Starter #15
My garage is closed 'til Tuesday so I'll have him pull an exhaust gas test next week and hope for the best. Stupidly, I never pulled the codes when I had the overheat problem. Checked this morning and I have one current, P1483, which is coolant system performance. Did a search here and a couple of comments on this code say it relates to the radiator fan not working. Took it for a 15 mile hard drive and checked the fans. One was running the other wasn't but I guess that's normal unless the engine is really hot. Could this be any way related to the overheat???
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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Normally, both fans run in slow as needed/commanded. The later fan control systems disable fans above 45 mph because they aren't needed: the airflow at speed is more than adequate.

Remember that any time you have some HVAC function set that calls for the A/C to run, both fans should run in slow. With the A/C system OFF, fans only run slow when the engine coolant temp goes to/above 224 and fast at 236.

If only one fan runs, something is wrong.
 

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2002 Cadillac Deville
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5 Posts
I have been having the same problem but i have a 02 Deville and it's sluggish at take off and when I get on the highway for five minutes it's overheats what do you think is causing this all my necessary fluids are full idk what to do it's becoming a hassle cause I'm late everyday to work cause I have to go down the access road
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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This thread has been dead for almost 8 years, but have you read it all? Have you studied the cooling system stickies in the Engines; Northstar forum?

Try to Google "cadillac forums 2002 deville overheating on highway" or something close.

Cooling fans don't run over 30 - 35 mph; not needed. You need to study up on the cooling system operation and the "purge line". It runs from the hollow bolt/nipple on the water crossover, then to the top side of the surge tank. It must flow a small steady stream at idle. Its function is to purge air and gas bubbles from the coolant so the water pump always sees "solid' coolant and doesn't airlock - instant overheat.

Have you inspected the water pump drive system? It's on the rear end (the driver's end) of the engine.

Proper coolant level is half full in the surge tank, cold. Never check/adjust coolant level with the engine hot.

It's all in these forums - but here are a few diagrams to get you started. Click to enlarge, use your browser <-- to back out. The diagrams are all for a 2002 Northstar engine.
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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20,214 Posts
I have been having the same problem but i have a 02 Deville and it's sluggish at take off and when I get on the highway for five minutes it's overheats what do you think is causing this all my necessary fluids are full idk what to do it's becoming a hassle cause I'm late everyday to work cause I have to go down the access road
======================
what to do
it's becoming a hassle cause I'm late everyday to work...................
either find and fix the problem - OR leave earlier -
 
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