What gives?
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HT4100 4.1, 4.5, 4.9 Discussion, What gives? in Cadillac Engine Technical Discussion; ...
  1. #1
    whereto is offline Cadillac Owners Member
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    What gives?

    Occasionaly,my 92 Eldo,4.9 will heat up to 230º briefly and drop right back down to 198º-207º in a mater of seconds.I live in AZ and run the A/C continuosly in the summer with no cooling problems.Have been told the fluxuating was no problem,but watching the digital dash read out drives me nuts, as you can watch each degree of change.Should I panic or not?

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  3. #2
    Ranger's Avatar
    Ranger is online now Cadillac Owners Member
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    Re: What gives?

    230 is too high. Maybe a sticky thermostat.

  4. #3
    whereto is offline Cadillac Owners Member
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    Re: What gives?

    Thanks for the feedback.How costly of a job to change thermostat? I live in a retirement community and your not allowed to tinker with auto.

  5. #4
    creeker is offline Cadillac Owners Connoisseur
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    Re: What gives?

    Quote Originally Posted by Ranger View Post
    230 is too high. Maybe a sticky thermostat.

    Is it possible it could be his water pump, this is one of the few weak points of a 4.9?.

  6. #5
    creeker is offline Cadillac Owners Connoisseur
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    Re: What gives?

    Quote Originally Posted by whereto View Post
    Thanks for the feedback.How costly of a job to change thermostat? I live in a retirement community and your not allowed to tinker with auto.
    What's the mileage on your car?.

  7. #6
    chubbyranger is offline Cadillac Owners Connoisseur
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    Re: What gives?

    Thermostat is a $5 part. If you get a coolant change while you're at it the bill should be ~$100-$150 (assuming $80/hour labor). If the water pump was failing I would expect to see slower recovery when the temperature surges and longer spikes in temperature.

  8. #7
    pocketpared is offline Cadillac Owners Fanatic
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    Re: What gives?

    My 92 Eldo 4.9 does the exact same thing. The water pump was replaced a year ago and the coolant was changed at the same time. Seems like when I'm running at speed then hit traffic it happens most often. I don't know if the thermostat was changed but the next time I do the coolant I'll have it changed and see what happens. Doesn't bother me.

  9. #8
    Ranger's Avatar
    Ranger is online now Cadillac Owners Member
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    Re: What gives?

    Water pumps fail by leaking. If it ain't leaking, it's not the problem. The tensioner could be bad and it might be slipping, but I doubt that.

    The other possibility is air in the system. If there is any I would wonder where it is coming from and IF there is, it should vent out after shut down IF the cap is working properly.

  10. #9
    HUF's Avatar
    HUF
    HUF is offline Cadillac Owners Connoisseur
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    Re: What gives?

    Quote Originally Posted by whereto View Post
    Occasionaly,my 92 Eldo,4.9 will heat up to 230º briefly and drop right back down to 198º-207º in a mater of seconds.I live in AZ and run the A/C continuosly in the summer with no cooling problems.Have been told the fluxuating was no problem,but watching the digital dash read out drives me nuts, as you can watch each degree of change.Should I panic or not?
    You should pay attention when it happens. Fans cannot bring the temperature down from 230 to 198 in seconds. It might be thermostat opening up late.

  11. #10
    drewsdeville's Avatar
    drewsdeville is offline Cadillac Owners Master
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    Re: What gives?

    If there are no other symptoms, leave it alone, there is nothing wrong with it as long as this is only on an occasional basis as you say.

    230 is not incredibly high. The cooling fans don't even begin to turn on until 224 degrees with the AC off. With the AC on, they only spin slow speed until 224. The engine warms up and when the fans turn on, you are seeing the temp drop. No big deal.

    Don't worry about that gauge. Idling with the AC on will warm any engine. People just aren't used to the large operating temp range of aluminum engines.

    Drive it and enjoy it.

    If you suspect air in the system, check the rad cap. If it's not holding proper pressure, your coolant will boil early.

  12. #11
    whereto is offline Cadillac Owners Member
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    Re: What gives?

    Thanks everyone for the feedback.No leaks,no pings runs strong.Going to replace the thermo.Just to put my little mind at ease.This puppy sets and idles with the a/c on when it's 118º in the shade,and the temp guage never goes above 207º.I'm still from the old school of "If it ain't broke,wait till it is."Thanks.

  13. #12
    behind-bars is offline Cadillac Owners Connoisseur
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    Re: What gives?

    If you cant work on autos in the community drive to an abandoned parking lot outside and do it; if you want to avoid taking it to a shop. The thermostat takes 5 mins tops to replace if the engine is cool. Just pop the upper hose where it runs into the top of the engine and it sits right there, may lose a bit of coolant but nothing major.

  14. #13
    steelybill is offline Cadillac Owners Enthusiast
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    Re: What gives?

    I had a Pontiac that did that for years. I figured that the temp sender was in a place where it was detected immediately rather than down-stream some place. It did it even after replacing the thermostat. I wouldn't get excited about it, but would replace the thermostat.

  15. #14
    carnut is offline Cadillac Owners Master
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    Re: What gives?

    I'll add my 2 cents and say its most likely air in the system. With the engine stone cold, remove the radiator cap. Coolant should be just under the cap and slightly overflow as the cap's removed. If its low, start the car and with a friend holding the idle speed around 12 to 1500 RPM and the heater display at 90 degrees displayed, watch the level until the thermostat opens and the coolant drops in the radiator. Once it drops add coolant until full to the top then quickly reinstall the cap before the friend lowers the eng. speed. Then fill the recovery tank to the proper level. That hi RPM top off should purge any air from the system. If the coolant is over 2 years old, its overdue for replacement anyway and a new 195 thermostat is good preventative maintenence as well as a new GM radiator cap. AND PUT YEAR AND TYPE OF CAD IN YOUR SIGNATURE PROFILE PLEASE!!

  16. #15
    whereto is offline Cadillac Owners Member
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    Replaced the thermo.(195) cost was $16.00 for the thermo,and $6.00 for the gasket.Labor was $40.00.Still runs up to 225º then right back down to 190º.Going to leave well enough alone.One thing does puzzle me,when doing the sqezze test,it only opened up about a 1/4".I checked one out of an Escalade and it opened at least3/4".Once again,thanks for your help.

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