Cooling System Specifics & Questions

Discussion in 'Troubleshooting & Diagnosis' started by jtherrien, Sep 19, 2017.

  1. jtherrien

    jtherrien Member

    Mar 27, 2016
    Hey all,

    I am running a sbc350 with 11.4:1 compression. It has been driven on the road only a few times. Currently, it has the acclaimed NastyZ28 $90 Carquest aluminum radiator, stock 78' thermostat, and radiator cap. I believe it is an "open" cooling system, since there is a coolant overflow tank on the passenger side, and the cap of that reservoir has a vent hole. Car runs 160-180 at idle, but just a short drive later it will jump to 220 (the beginning of the "red" on the U14 gauges). Temp sender is on driver side. Temp sender is new.

    I have a few questions about the fundamentals of cooling systems and how they pertain to my application:

    1.) What is a "closed/pressurized" and what is an "open" system? Does opening the radiator cap to "burp" the system of air bubble matter if this is an "open" system? Are our cars considered to have an "open" system?

    2.) My current thermostat is original to my '78 305 so it goes without saying that it could afford to be replaced. I see conflicting information in these threads about whether to run a 160 or 180 or 195 (stock?) thermostat- what do I purchase?

    3.) Follow up to question 2... What is my optimal operating temp? I pulled over and shut it off @ 220, but should I not be worried? It was not "puking fluid".

    4.) What PSI radiator cap should I be running, and does it matter?

    5.) If 220 is too hot, what is my plan of action? Burping the system? Thermostat? Taurus fan?
  2. rchydzik

    rchydzik Veteran Member Lifetime Gold Member

    Nov 13, 1999
    Colbert, WA USA
    1-A 78 should be closed. The 15 psi cap keeps the system under pressure. If the pressure exceeds 15psi, it allows flow into the overflow bottle. Coolant will expand when heated, so the overflow bottle captures that expansion. When the engine is shut off and cools, the vacuum in the system pulls the coolant back into the radiator. It's "closed" in the sense that the overflow bottle captures the expansion rather than simply overflowing.

    2-I would use a 180 degree thermostat. 160 is a little too cold. 195 might be too hot with high compression.

    3-With a 180 thermostat, operating temperature should be 180-200F. 220 seems hot to me.

    4-15 psi

    5-The best investment I made in cooling was a good water pump. Stewart-Warner. Expensive, but works really well. A clutch fan and shroud should work well for you.
  3. larrylarry

    larrylarry Veteran Member

    Dec 22, 2011
    San Antonio Tx
    Also the overflow tank / puke tank will remove any air in the radiator. I consider 220 to be hot but all new cars run at 210... 180 is more gooder. I run an electric fan without a shroud but one should be used, mine doesn't seem to need one.
  4. Rdobbs1977

    Rdobbs1977 Huge Guns N Roses Fan

    Dec 1, 2014
    220 is too hot.

    Rad cap does matter. For each size radiator cap you get, you can gain 3 degrees of cooling, so yes replacing your rad cap can with another one can help.

    A 180 thermostat will help your cooling too. I like 195s on a street car but if i had cooling problems, then i'd not be opposed to the 180.

    You might have air in your block, not uncommon after a build (assuming you just did one). yes, removing the cap with motor running and burping it 'might' solve your problem. Built a drag only 383 last year from ground up. Idled like yours but when i hit it, the gauge went completely to the right. Burped it, problem solved.

    Would not recommend on a street car BUT......I've found an electric water pump with elec fan (obviously) cools better than the mechanical fan w/shroud. Trade off, when the elec pump goes you may not know it before its too late and you're using more voltage.
  5. Joekool

    Joekool Veteran Member

    Feb 4, 2002
    Hollister CA USA
    Where do you take your temp reading? If it is from the cylinder head, 220*f isn't all that hot, if it is at the thermostat or nearby on the intake then 220 is too hot.

    The thermostat will only regulate the min coolant temp, it wont do anything to change the max temp at all.

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