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HT4100 4.1, 4.5, 4.9 Discussion, Did I miss anything? in Cadillac Engine Technical Discussion; 86 Fleetwood d'Elegance Cooling system service: All new hoses Drain and gently flush system. 50/50 mix of long life HOAT ...
  1. #1
    watajob is offline Cadillac Owners Member
    Automobile(s): 86 Fleetwood d'Elegance, 92 T/A 'vert, 04 Sierra, 08 Rondo
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    Did I miss anything?

    86 Fleetwood d'Elegance

    Cooling system service:
    All new hoses
    Drain and gently flush system.
    50/50 mix of long life HOAT coolant, (Peak Global Lifetime and distilled water)
    6 tabs
    Bottle of Water Wetter
    180 'stat
    New cap but down to 10 PSI

    Oil Change:
    15W/40 Rotella (decreased hot knock)
    Pure One filter
    Bottle of Lucas break in additive

    It's a weekend driver and will be garaged, (heated), for winter.

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  3. #2
    ehall's Avatar
    ehall is offline Cadillac Owners Connoisseur
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    Re: Did I miss anything?

    Isn't spec for a 195 thermostat? Why the 180? It will just take longer to reach operating temperature

  4. #3
    watajob is offline Cadillac Owners Member
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    Re: Did I miss anything?

    Yes it is. However, the ECM goes into closed loop at approx. 155, so all will still function well and it will just run a little cooler, which in this case, I believe, is a good thing.

  5. #4
    aeronca36606 is offline Cadillac Owners Enthusiast
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    Re: Did I miss anything?

    Looks to me like he is concerned with the high temperatures and pressures these engines where designed for. I am also old school with respect to this. However lowering the thermostat temperature and lowering the radiator cap pressure may cause him some trouble.

    He should be ok while cruising down the road. He will experience lower operating temperatures. However the first time he gets stuck in stop and go traffic in hot weather, The lack of airflow will let the engine temperature to rise to the turn on temp of the radiator cooling fans.

    The Peak Antifreeze has a boiling point of 265 degrees with a pressure cap of 15 PSI at a 50/50 mix.
    One PSI = 3 degrees temp rise in boiling point.
    So 265 degrees - 15 degrees = 250 degrees boiling point with a 10 PSI cap.
    The radiator cooling fans switch on low speed at 223 degrees and high speed at 241 degrees.
    Now that doesn't allow a whole lot of room between high speed turn on temperature and coolant boil over with the 10 PSI cap. About 9 degrees. Whereas with the 15 PSI cap there is a 24 degree margin.
    Now if one could reprogram the BCM to lower those Fan turn on temps, than the lower thermostat temp and lower cap pressures would make sense.
    All this is with the A/C off. With the A/C on the cooling fans are also overridden by the needs of the A/C system and the cooling fans will come on at low speed much earlier.
    I also wonder if it is harder on the engine to go through a wider temperature swing between the 180 degree thermostat limit and the fan turn on temps. Will those heat cycles be any harder on the aluminium block and steel head. (Different expansion coefficient between metals) Probably not.
    The Fuel Injection system is also optimized to run at the higher temps although i suspect that a 180 degree thermostat won't make a lot of difference.

    Interesting discussion and thoughts.

  6. #5
    watajob is offline Cadillac Owners Member
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    Re: Did I miss anything?

    Your presumption about my fear of heat with this engine is correct. I'm thinking a Hayden adjustable fan switch, a coupla' relays and we can forget about the BCM / A/C controls on the fan.

  7. #6
    aeronca36606 is offline Cadillac Owners Enthusiast
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    Re: Did I miss anything?

    That would work. But you may have a problem with the A/C. The compressor is controlled by the BCM. Removing control of the Radiator cooling fans by the BCM will set at least a trouble code.F41 cooling fans trouble. This will light the Cooling Fan Problem tell tail light when the engine is hot. (you could remove the bulb to stop that). It may also interfere with the A/C clutch and keep the A/C from engaging. You can test this by disconnecting the smaller of the two connectors that go to the Fan Control module. These connectors are right next to the Battery. The wire colours will be Dark Green and Brown. When you disconnect this connector, It will cause the Cooling Fans to run whenever the ignition key is turned on. It will also keep the computer from knowing whether the fans are working and set the code 41. You can then test to see if there will be any ill effects on the A/C system. The connector you are disconnecting is the Fan enable wire and the Fan feedback wire.
    On my 1985 Deville Diesel it will disable the A/C. But the Diesel is a unique vehicle and has a few differences in the BCM firmware. I will have to give it a try on my 1985 Gas Deville later on today.

  8. #7
    watajob is offline Cadillac Owners Member
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    Re: Did I miss anything?

    I'm jealous. I perused the FSM last night for quite sometime and couldn't find all the info you gave me. In fact, the cooling fan section is pretty worthless. Then again, GM's FSM are constructed in a very weird manner as one section refers you to another, which refers you to another, etc., until you get to the info you want/need, in some other chapter that has nothing to do with what you originally started out looking for. I really don't want to read the whole thing, cover to cover!

  9. #8
    aeronca36606 is offline Cadillac Owners Enthusiast
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    Re: Did I miss anything?

    I did get a chance to try disconnecting the fan control module on my 1985 Gas Coupe Deville. The A/C worked just fine. I did not get the engine very hot. It is cool for once here in East Tennessee! There still may be an issue when the BCM calls for Fans and the feedback circuit doesn't respond correctly. This condition will light the Fan Trouble light and may then interfere with the A/C. But i do not know. Anyway if the fans are switched on earlier, Then the computer may never call for the fans anyway. Now if you could find a Temperature switch that was normally closed until it reaches the high temperature you want, Then it could be plugged directly into the previously mentioned connector. The fan control module is triggered by grounding or un grounding the control line. Technically speaking the computer doesn't turn the Fans on it actually turns the Fans off. The Fans automatically go on at full speed until the control wire is grounded. The computer does this until it senses a need for the fans. It then releases the control wire and the fans go on. If you where to remove the BCM completely the fans would run at full speed.

  10. #9
    watajob is offline Cadillac Owners Member
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    Re: Did I miss anything?

    Lordy! Too complicated for a dummy such as myself. How about as big a pusher with a pancake motor as fits, mounted in front of the condenser with said fan switch set to about on at 205, off at 190? Also, someday, a set of digital gauges in as close a color as I can find to match the digital dash.

  11. #10
    aeronca36606 is offline Cadillac Owners Enthusiast
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    Re: Did I miss anything?

    That would work!

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