1999 Deville Temp spike on highway
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Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, 1999 Deville Temp spike on highway in Past Cadillac Vehicle Discussion; Hey guys, Im new to this forum. I know there are hundreds of threads on the Northstars overheating and what ...
  1. #1
    Abottino24 is offline Cadillac Owners Member
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    1999 Deville Temp spike on highway

    Hey guys, Im new to this forum. I know there are hundreds of threads on the Northstars overheating and what not, but i think my situation is a little different than most. I bought this car a year ago off a friend. It has been owned by older men since brand new. always babied never beat on. Since ive owned it ive never seen the temp go about 222 no matter what. It would jump to 222 while sitting in traffic but fans would kick on and drop it right back down to normal opperating temp of 199. On the highway, it would never get above 201. In the past 3 months ive noticed it loosing a little coolant every so often. I just kept topping it off, never had a problem. However i was noticing it would jump up to 222 a little more frequent while idling. I had a trip planned to drive to new jersey last weekend so i went to Jiffy Lube to get an oil change and figured id do a coolant flush. caddy small.JPG As you can see the coolant that came out was a wierd color. I drove it out of there and back home with it running perfect. no Temp spikes with city driving. The next day i go to get on the highway to start my trip and about 25 miles down the highway i look down and temp is at 246. I was shocked as ive NEVER seen this. I watched it rise to 255 then 265 then at 270 with all the warnings i decided to pull over. I shut the car off and let it cool down back to 200 then i tried to turn around. 3 minutes later back up to 280 which actually cut out the engine. Got it towed to my mechanic. He says the air wasnt bled from the system and i was acctually low some coolant. he also says they used thier universal coolant which when mixed with Dex cool creates a mud. anyways he said i was fine and problem solved so i picked it up and drove it for the past 2 days around city and on highway. Well last night while crusing at 50 i look down and temp read 228. it quickly dropped back down to 205. Again this morning while cruising at 70 on the highway it jumps to 234. Falls back down to 200 then back up to 228 then back down and up to 224. This is worring me because ive never seen it above 222 and that was only at idle. I dont know what jiffy lube did but im afraid to take this thing anywhere. any ideas?

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  3. #2
    Submariner409's Avatar
    Submariner409 is offline If it won't run, stick on fender vents
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    Re: 1999 Deville Temp spike on highway

    You're in the wrong Forum - your car has a Northstar engine, 4.6L, so this belongs in either Northstar Performance or Deville.

    I'll flag it for the Forum Moderator.

  4. #3
    Abottino24 is offline Cadillac Owners Member
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    Re: 1999 Deville Temp spike on highway

    oops sorry, i didnt even realize what forum i posted on. How do i change it?

  5. #4
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    Rolex is offline Super Moderator
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    Re: 1999 Deville Temp spike on highway

    I'm going to put this in DeVille to see if they can help. Good luck OP and welcome to cadillacforums!!!!
    The above post is my 2 cents....nothing more.

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    Re: 1999 Deville Temp spike on highway

    just sit tight and a mod for this forum will move it.

    That said, you have all the symptoms of a failing HG, not to mention it is a '99 (worst offenders). get a block test kit and check for exhaust gases in the surge tank after the next overheat episode.

  7. #6
    MRneatfreak- is offline Cadillac Owners Fanatic
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    Re: 1999 Deville Temp spike on highway

    Even then the block test isn't 100% foolproof. The blue liquid on mine never really turned yellow, just sort of greenish blue, even though temps are through the roof on the road but fine in the driveway for the first 15 minutes. My point being is the block test isn't cut and dry. I would also do the leak down test, and check the cyls for coolant inside. I'm in the same boat you are with my other 97.

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    MRneatfreak- is offline Cadillac Owners Fanatic
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    Re: 1999 Deville Temp spike on highway

    Also if you are sure everything is sealed up and there are no air leaks like a crooked radiator cap etc.. and after the car gets hot and you shut it off, and you hear air gurgles in the overflow tank. You have to know that it is sucking air from somewhere (heads) and that there is a problem.

  9. #8
    Abottino24 is offline Cadillac Owners Member
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    Re: 1999 Deville Temp spike on highway

    Ive noticed while driving on the highway at 70, after about 15 min off straight highway, the temp will go from 190-194 and quickly climb to 217-221 then drop fast back down to the 190-194 mark. Almost seems like the thermostat is getting stuck then opening at the same temp?

  10. #9
    Submariner409's Avatar
    Submariner409 is offline If it won't run, stick on fender vents
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    Re: 1999 Deville Temp spike on highway

    Wrong. Normal. You get off the highway and the engine dumps a LOT of heat into the coolant very quickly, and because you're not moving at 65 there's little or no airflow through the radiator - so the temp goes to about 224, fans go to SLOW, the fans turn OFF at 213 and the cycle repeats.

    Once again: the thermostat begins at 188 and is fully open at 206. From there on out it's all dependent on your vehicle speed and/or your length of time in traffic.

    Read the articles on cooling system operation in the Cadillac Technical Archives up ^^^ in the black bar, and in the stickys in Northstar performance, and in the Cadillac Tech Tips in Discussions............and in every tenth thread in here and in Seville for many, many years.

    Click my username, open the profile. Two albums, six pages of Northstar stuff in the left column. Lots, including an annotated temp gauge, for your engine.

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