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99 z28 runnin hot

This is a discussion on 99 z28 runnin hot within the General Help forums, part of the LSx Technical Help Section category; i went back and read the archive posts and still haven't been able to diagnose the problem. stats on the ...

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    99 z28 runnin hot

    i went back and read the archive posts and still haven't been able to diagnose the problem. stats on the car are as follows- 99 A4 Z28 all stock except HD trans, was sprayed with nitrous before i bought it.
    whats happening- temp fluctuates between 215 and 230 while driving and it's very sparatic. it may jump to 230 and back down to 212 in a matter of seconds. I've driven for at least 30 minutes in the city which would have been about 15 miles and it never got over 230 but it use to always sit right under 210. fans stay on after the car is turned off but only for one or two minutes.

    so far i have tried- new radiator cap, coolant flush, fill cooling system from cold start

    i thought maybe thermastat but if that wasn't opening would i be able to drive for 30 mintues without hittin the red???? any help would be appreciated this is my only car and I don't like not knowing if it's gonna sh*t on me at any time.


    small side note, when it was running(over 210) i had the cap off the radiator & was squeezing the hose that went to the waterneck/thermastat and the collant level in the radiator would rise when i applied pressure to the hose. does that mean that the thermastat is not open?? again thanks in advance for input it is all good!

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    Quote Originally Posted by MillerTime View Post
    i had the cap off the radiator & was squeezing the hose that went to the waterneck/thermastat and the collant level in the radiator would rise when i applied pressure to the hose. does that mean that the thermastat is not open??
    You were also creating a restriction by squeezing the hose.

    How about this?
    Engine temperature: Overheating and coolant loss may be due to rough surface on radiator filler neck. Neck should be sanded smooth and cap replaced.(1999-2000)
    I also believe that the gauge was altered in 1999 to not show the constant temp fluctuations. Are you actually overheating, or is the gauge at fault? Have you tested the thermostat in hot water?

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    I haven't tested the thermo in hot water yet, prob a good measure to take next. I was wondering if the guage was functioning correctly also. suppose I could stick a thermo in the coolant to see if the guage is accurate. it never got past 230 that's what was strange to me. in my past vehicles, once you got that much past your normal running point, you were only a matter of time from the red.

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    Being that 99 and up got crap for coolant gauges I would hook up a scanner and see what the temps are really doing, but the t-stat and coolant cap are a good place to start if the temps are really going that high.

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    Yes I would do almost the same as the last post. Hook up to a scan tool that let's you view live pids. Once that is hooked up go drive around waiting for your guage to fluctuate as it does and watch pid values to see if they are telling you the same. That temp. sensor could be bad besides the fact that the guage could be off on top of the sensor going bad.

    Another quick check is find one of your friends that has a temp. gun and shoot the coolant with the cap off while runnong and up to temp. to see if the guage is still acurate.
    I've seen cars that were almost 20 degrees off.

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    Definitely overheating if the fans are staying on after the ignition is shut off - happens when the PCM sees 284*.

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    thanks for all the replies. the problem is not remedied yet but the causes are being narrowed. should have the new thermo installed late tonight after it cools off. is a heat gun or scan tool the only way to get an accurate coolant temp? i was hopin i could roll up to parts store( Chinazone or O'heilly's etc.) and have them check it while running?? i don't know anyone with a heat gun or scan tool that i know of. when i got home tonight the guage read about 230 when i shut the car off, fans ran for 1 or 2 minutes.... didn't feel excessively hot under the hood. plus within about 5 minutes or less the guage was down to about 218-220 when i turned the key forward(without starting) to check the temp. i did put on a new cap. no dice. has anyone had a water pump go out on them and/or do these sound anything like symptoms of a failing or weak water pump??

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    Quote Originally Posted by 2001NBMZ28 View Post
    Definitely overheating if the fans are staying on after the ignition is shut off - happens when the PCM sees 284*.
    got me worried now, i guess if i blow the engine, good excuse to buy a new one. now to figure out which bank to rob to get the money

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    also some of the archive posts i read talked about cats bein clogged and causing overheating. anyway to determine that other than pullin them off or looking for glowing red manifolds???

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    check to see if the radiator/condenser is being blocked.(grass,leaves,wrappers...ect) corvettes (C4's and C5's) have this problem because they suck up a lot of crap and when people dont clean the crap off it runs hot.

    i have taken a 1 gallon milk jug out of the front of a corvette.

    u can determine if a cat is clogged by checking for exessive backpressure. at the o2 sensor hole

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    i'll check that out tonight when i put in the new stat. somethin could have gotten hung up in there

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    also check your coolant temp sensor, it may be actying wirery

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    I never did see if your fans are engaging correctly. Are they cutting on at all? If not, there's your problem.

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    Pressure test the system and replace the stat..you can rent a tester at autozone for free.

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    thanks to everyone for the advice and tips. The problem has finally been REMEDIED!! about 4 o'clock in the morning friday i installed a new thermastat, then in the morning i went n got some coolant to replace what i lost. Also i bought a thermometer so I could test the coolant temp to make sure the guage was accurate. So i ran it til it hit operating tempurature made sure it was full of coolant and correct temp, everything looked great. Went for a spin and all was well! again thanks to everyone for the help. I'm sure i saved hundreds of dollars in diagnosis and unneccessary parts.

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    Quote Originally Posted by MillerTime View Post
    thanks to everyone for the advice and tips. The problem has finally been REMEDIED!! about 4 o'clock in the morning friday i installed a new thermastat, then in the morning i went n got some coolant to replace what i lost. Also i bought a thermometer so I could test the coolant temp to make sure the guage was accurate. So i ran it til it hit operating tempurature made sure it was full of coolant and correct temp, everything looked great. Went for a spin and all was well! again thanks to everyone for the help. I'm sure i saved hundreds of dollars in diagnosis and unneccessary parts.
    Don't be afraid of the bottle!!! Be afraid of your tune!!!

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