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Cadillac CTS First Generation Forum - 2003 - 2007 Discussion, 2003 CTS thermostat in Cadillac CTS Coupe, Sport Sedan and Sport Wagon Forums; The t-stat stays closed till the engine reaches it optimal temperature then opens to let the fluid cool through the ...
  1. #31
    Sammy Z's Avatar
    Sammy Z is offline Cadillac Owners Connoisseur
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    Re: 2003 CTS thermostat

    The t-stat stays closed till the engine reaches it optimal temperature then opens to let the fluid cool through the radiator. If the T-stat is weak and the spring opens too soon, the fluid will cool too fast and the engine runs cooler and burns more fuel. I don't think it's doeng any damage, but it will put your mileage in the crapper. I have the 3.2 and i ger 23 m/p/g combined. (25 when it's mostly highway)

  2. #32
    ryanducati is offline Cadillac Owners Member
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    Re: 2003 CTS thermostat

    Maybe it's not your thermostat?
    When I first bought my car, the check engine light use to come on when I put in cheap gas, I brought it to the dealer and they said the thermostat was bad... I have not replaced it. I had them reset the light and switch to premium gas. The light does not come on unless someone borrow's my car and puts in the cheap gas.

  3. #33
    grinder419 is offline Cadillac Owners Member
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    Re: 2003 CTS thermostat

    You wouldnt happen to know what code you had when your check engine light came on? I'm thinking my 16 mpg mostly highway is a good indicator that my thermostat is jacked.

  4. #34
    ewill3rd is offline Cadillac Technician
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    Re: 2003 CTS thermostat

    P0128 is the DTC for "coolant temperature too low for closed loop".
    The computer knows what the Coolant temp should be and if it stays below regulated temperature for too long the code will set.

  5. #35
    grinder419 is offline Cadillac Owners Member
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    Re: 2003 CTS thermostat

    Quote Originally Posted by ewill3rd View Post
    P0128 is the DTC for "coolant temperature too low for closed loop".
    The computer knows what the Coolant temp should be and if it stays below regulated temperature for too long the code will set.
    So I have gotten the P0128 come on 4 out of 7 days in the past week, but its been snowing in Washington. And my car sits outside where its freezing during the day. I keep resetting it til it comes on again, but like I said I'm getting bad MPG so do you think it is the thermostat?

  6. #36
    Sammy Z's Avatar
    Sammy Z is offline Cadillac Owners Connoisseur
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    Re: 2003 CTS thermostat

    I'd say it was the T-stat, wait for a nice day and replace it. Make sure you buy some Anti-freeze to replace what you loose.

  7. #37
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    Re: 2003 CTS thermostat

    Quote Originally Posted by Sammy Z View Post
    The t-stat stays closed till the engine reaches it optimal temperature then opens to let the fluid cool through the radiator. If the T-stat is weak and the spring opens too soon, the fluid will cool too fast and the engine runs cooler and burns more fuel. I don't think it's doeng any damage, but it will put your mileage in the crapper. I have the 3.2 and i ger 23 m/p/g combined. (25 when it's mostly highway)
    I agree and I get identical mileage down here in the Lone Star State(2003 CTS 3.2 Auto, 50k mi), but I get the P1028 when it gets "cold" down here and I do not let it warm up before I kick on the heater.

    Not really a problem in Houston as that is only 10-12 times a year at the most and I can stand those temps, but I have been thinking of doing some seriouis maintenance now that it has reached 50k mi.; might as well regasket and change the thermostat and clean the engine and bay.

    .02

  8. #38
    ghettomike's Avatar
    ghettomike is offline Cadillac Owners Master
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    Re: 2003 CTS thermostat

    Quote Originally Posted by grinder419 View Post
    So I have gotten the P0128 come on 4 out of 7 days in the past week, but its been snowing in Washington. And my car sits outside where its freezing during the day. I keep resetting it til it comes on again, but like I said I'm getting bad MPG so do you think it is the thermostat?
    if the code is comming up while running the engine should have had time to heat up. change the t-stat... you wont have anymore issues, currently you are running your car cold all the time...not good at all for it.

  9. #39
    grinder419 is offline Cadillac Owners Member
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    Re: 2003 CTS thermostat

    I never have time to let the car warm up because i leave the morning everyday at 5:30 for work. But I will try waking up earlier when I get back and let the car warm up before driving. Ghettomike, you think the 16 mpg is a definate indicator with that code being thrown all the time that I need to spend the $500 or whatever to get the T-Stat replaced?

  10. #40
    vlbasten is offline Cadillac Owners Member
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    Re: 2003 CTS thermostat

    how do you remove the fuel rail? i already took off the Quick Connect Fittings(the metal collar), the hose are still connected tight, don't know how to disconnect from the fuel rail. do i need to relieve the fuel system pressure first? and how? thank you guys... waiting online to get back to work..

    Quote Originally Posted by carl langkammerer View Post
    My son and I replaced the thermostat in his 03 CTS TODAY.
    My wife also has an 03 CTS so I was very interested.

    It took us 5 hours to get it done with the GM Service Information (online) avaiable in the our shop. The SI says to remove the plenum and intake manifold but not the lower manifold on the 3.2L engine (different for the 2.8l amd the 3.6l). The lower manifold must be removed to remove the manifold on both of our 03 CTS's. With that knowledge. it is a 2.5 to 3.0 hour task. We played with the clearances between the head the rear of the timing cover and the lower manifold. After we ate lunch we removed the lower manifold and from there it was a matter of bolts.

    Our wasted time came from two sourdes: 1) the lower mainfold needs to be removed; 2) it is easy to remove the lower manifold if you remove the fuel rail and injectors so that the "manifold" comes out of the "V" in the center of the engine.

    Hope this helps from someone who has just done it!

  11. #41
    asoares is offline Cadillac Owners Member
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    Re: 2003 CTS thermostat

    I know this is a very old thread, but I'll add my $.02. If you disconnect any fuel lines, you'll want to FIRST make sure there is no preasure in the line and obviously that the engine is not hot (just in case there is a spill). To reduce the preasure, start your engine then pull the fuse for your fuel pump. I think the fuse can be found in the engine compartment's fuse box. Once the fuse is pulled, the engine will run out of gas and preasure. Find the fuse first prior to starting the engine. Remember: the engine will be hot from when you ran it so make sure the engine sits for a couple of hours to cool off before you disconnect the fuel line!!! If it spills, bye bye car! Gas is VERY hard to put out! IF a real machanic has a proper correct way to do this, please reply to the thread. -thx

  12. #42
    asoares is offline Cadillac Owners Member
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    Re: 2003 CTS thermostat

    I finally let the Cady dealer fix my car. I was going to do it myself but decided to pay the $530 to have them fix it. They wanted $630 but after some negotiation, I was able to get a discount from them. The overal result wasn't good. They replaced the thermostat and housing (housing cracked but not leaking), then they reset the code. After driving it for a couple of days, the engine light with the same error code came back on. After bringing it back to the dealer, they said they diagnosed the problem to being a faulty "coolant bypass valve". Since I told them to replace the thermostat without a diagnosis by them, I eat that cost. Good luck for you all, check the bypass valve first before going forward with replacing the thermostat. The replacement of the bypass valve should be easy but I hear it is a dealer part. See the this thread for the picture and info (thanks to Crh61483)):

    http://www.cadillacforums.com/forums...-2003-cts.html

    Also, my cady came back to me the after the thermo replacement at the dealer with a hissing coming out of the top of the engine. The repair tech didn't seat the vacum housing on top of the manifold correctly (they said they will fix if for free since they broke it)

  13. #43
    Braz60 is offline Cadillac Owners Fanatic
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    Re: 2003 CTS thermostat

    If anyone plans on changing their thermostat in the near future a step by step picture procedure would be very useful.

  14. #44
    r0k0 is offline Cadillac Owners Member
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    Re: 2003 CTS thermostat

    yeah detailed pictures would be awesome because im in the middle of doing mine and cant get the damn 2nd intake out so that the plastic intake off to take the T-stat housing out lol

  15. #45
    rjkone is offline Cadillac Owners Member
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    Re: 2003 CTS thermostat

    I am in the same boat..I think. Removed all bolts from the intake and the dam thing wont come out. It lifts about and inch or two on each side but keeps hitting the heads on either side. Any suggestions?

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