Cooling and fluctuating temp question

Discussion in 'Street/strip 400/430/455' started by jaystoy, Apr 20, 2022.

  1. jaystoy

    jaystoy Well-Known Member

    Fresh rebuilt 455. Has one season on the motor. Took the car out today. 50 degrees here in Connecticut. 180 degree thermostat. Put new thermostat in this winter, along with a new aluminum radiator. I have bled the system. Temps will hover around 180, then quickly go up to 195 then back down to 175 or 180 and back and forth. Running a heavy duty clutch fan, new. Fan fits perfect in the shroud, both in diameter and depth. Everything is new. Or, is 195 nothing to worry about?

    Second, would dual fans do any better job cooling?
     
  2. CJay

    CJay Supercar owner Staff Member

    Does it evenentually level off?
     
  3. jaystoy

    jaystoy Well-Known Member

    No, it may stay pegged at 180 for 5 minutes or so, I glance and it is 175 or 195. Dont get the fluctuation. Was thinking a stingy
    air pocket, But i have bled it a few times
     
  4. FLGS400

    FLGS400 Gold Level Contributor

    Not saying that this is your issue or the cure, but I had a similar problem with my 400. When I last installed the thermostat i put an excessive amount of RTV on the gasket, which when cured mostly blocked the port for the bypass hose. This past time I did things differently and it went away. The last time I had it out, it stayed between 175 and 190 with a 180 degree thermostat, in 75 degree weather. No quick fluctuations.

    Mine would quickly climb to 200-210 when decelerating, then quickly come back to 170-190 when idling or steady cruising.
     
  5. CJay

    CJay Supercar owner Staff Member

    The best way imo, to remove any air pockets is to crack the gauge fitting while I fill the cooling system. Once antifreeze comes out the fitting, I know there are no air pockets
     
    BadBrad likes this.
  6. jaystoy

    jaystoy Well-Known Member

    I use, and have used 3 times, that bleed bowl that gets mounted to the radiator opening. I run it until all bubbles are gone. Is a 180 thermostat not full open until 195? That fan clutch sounds like a turbine. Maybe switch to dual fans?
     
  7. Lou Perfetto

    Lou Perfetto All Throttle/ No Bottle

    While the car is idling and up to temperature with the cap off, do you see any air bubbles coming up from the coolant? Also, are the air bubbles constant? Maybe even just a little bit once in a while but does not seem to stop?
     
  8. 87GN_70GS

    87GN_70GS Well-Known Member

    Drill a 1/8" hole in the thermostat flange. This will slow down the action of the t-stat opening and closing
     
  9. Max Damage

    Max Damage I'm working on it!

    It should stay at 180 if the thermostat and the gauge are accurate. 195 is not a problem, but it seems odd that it fluctuates? maybe double check the actual coolant temp with a second gauge or Infrared thermometer? I also use Jason's method of bleeding because it's high up in the system, so you know when the coolant gets there you are good.
     
  10. TORQUED455

    TORQUED455 Well-Known Member

    What type of temp gauge are you using and where is the thermocouple installed?
     
    Max Damage likes this.
  11. jaystoy

    jaystoy Well-Known Member

    Using auto meter sport comp. installed directly near the water outlet, eddy intake. I will check again for bubbles. I will check with infrared gun
     
  12. TORQUED455

    TORQUED455 Well-Known Member

    Picture of intake?
     
  13. BadBrad

    BadBrad Got 4-speed?

    Of course, tough to check when you're driving - but do you have a collapsing hose? Even at idle I've seen this. A spring in he lower hose is s good idea.
     
  14. Mark Demko

    Mark Demko Well-Known Member

    No, wont help.
    Change the thermostat again.
     
  15. Lou Perfetto

    Lou Perfetto All Throttle/ No Bottle

    I still think you have a air problem. Let me explain. If you are running a mechanical temperature gauge it is a capillary tube driven gauge. For it to work properly the probe needs to be Completely submersed-in the coolant. That will allow the fluid in the capillary tube to expand and push the bellows in the gauge head to move the needle on the gauge face. If it is not completely submersed, the fluid will contract and give a lower reading. That's why I believe you are building an air pocket in the motor. As your RPM increases or decreases will dictate whether the probe is fully immersed or not giving you the fluctuation in the readings on the gauge.
     
    Mark Demko likes this.
  16. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    I think it is the particular thermostat. Sometimes, it is hard to get a good one. Sounds like that particular thermostat is sticking, and not operating smoothly.. A 180 stat should just begin to open at 180*, and be fully open at 200*. It should open and close just enough to keep the coolant temperature as close to 180* as possible. That is how a thermostat is supposed to operate. That's why if you see the temperature increase to more than 20* over the stat rating, the thermostat has lost control of the system temperature. That will happen if there is a deficiency somewhere else in the system, bad radiator or fan clutch. It is normal for the thermostat to cycle a bit when warming an engine up, but a good stat will stabilize at a running temperature.
     
  17. Max Damage

    Max Damage I'm working on it!

    If it's an electrical gauge you might also be seeing fluctuations in the electrical system rather than temp...

    A lot of these "Sport Comp" Autometer gauges appear to be electrical...
     
  18. TORQUED455

    TORQUED455 Well-Known Member

    If the thermocouple is installed in the port directly to the passenger side of the thermostat housing, then you likely have no cooling system issue. The actual water temp at that location will bounce around, so your gauge is not lying, and this is normal. If this bothers you, move the probe to the port on the front of the intake to the driver's side, and see what happens. If it's already there, try a different thermostat.
     
    FLGS400 and Mark Demko like this.
  19. jaystoy

    jaystoy Well-Known Member

    Lots of great input here, thank you. Yes, it’s an electric gauge. I can snap a pic of the intake this weekend. Thinking Larry may be correct. Change thermostat might be in order. It never use to do this. I want to try and purge again.
     
  20. jaystoy

    jaystoy Well-Known Member

    So i ponied up. I pulled the water pump. It was a no frills off the shelf water pump. So i ordered TA's high flow pump. Wow. What a nice piece. Painted it and installed it. Questioning the 180 degree stat, i swapped it out with a high flow stat 180 degrees. Anyhow today, warmed it up for any leaks and bled the coolant. Geez, i went the opposite. No more fluctuation but now it struggles to even come close to 180, stays around 170. Ugh! I might take the heavy duty fan clutch off for the lighter duty one.
     

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