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  • Thermostat vs no thermostat

    OK, run a race motor so I don't have heater system to worry about. I always warm my motor to 160 degrees 30 minutes prior to race time. I like to heat soak the engine before a race. I top off the radiator then head to the grid. Sometimes on the first lap the temp will shoot up then come back down almost immediately. I think the thermostat is cycling. I can turn the fan on for a lap and then it cools down and I turn the fan off for the rest of the race 190 to 200 degrees.

    Now my question is should I even run a thermostat?
    I don't like a thermostat on the inlet side of the water pump. I think this is a restriction to the flow. Also it does not pressurize the block and head.

    Can I eliminate the by pass hoses, and thermostat and put a restrictor in the upper radiator hose outlet. This will put a small amount of pressure on the block and head to reduce cavitation.

  • #2
    The thermostat provides a restriction just the same as a restrictor in the upper radiator hose. It's a loop, so as long as the restriction is somewhere it's going to cause a pressure drop through it (higher before it, lower after).


    As for a temp spike, sounds like you maybe haven't bled the system all the way and an air pocket is making it's way out?

    I wouldn't eliminate a thermostat, but if you wanted less restriction or more constant flow you could drill out the jiggle valve to a 3/16-3/8" hole (or multiple smaller holes if space is running low). I think I'd go that route before ditching it entirely.


    What kind of temps are you seeing when they shoot up?
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    • #3
      It will run up 230-240 then drop back down. This will happen in about 5-6 turns on track. If I see it and turn on the fan it will drop back down and stay at 190-200 for the rest of the race, with no fan. At one race it pushed water out. I came off track filled with water went back out and finished race. I have bled the system of air. This started last year at BIR, I cooked a motor there.
      This may happen once on a weekend maybe not.

      I just thought a restrictor in top would be better than at the bottom.

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      • #4
        Originally posted by rioredstang View Post
        It will run up 230-240 then drop back down. This will happen in about 5-6 turns on track. If I see it and turn on the fan it will drop back down and stay at 190-200 for the rest of the race, with no fan. At one race it pushed water out. I came off track filled with water went back out and finished race. I have bled the system of air. This started last year at BIR, I cooked a motor there.
        This may happen once on a weekend maybe not.

        I just thought a restrictor in top would be better than at the bottom.
        Almost sounds like a head lifting with the temp shooting up that fast. Or the thermostat is sticking badly.


        I'd drill a few bypass holes in it just so you always have some cooling, but never "full bore" cooling.


        It doesn't matter where in the system the restriction is, but I'd keep the pressure higher in the radiator since it's still pretty hot going in there. But the static pressure output of the water pump probably isn't all that high.
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        • #5
          I've never had that kind of problem with my car on track, except when I come in and check hot tire temps & pressures last weekend.. of course that's because I came off the track hot and didn't take any time to cool the engine down.
          soon as I got to the grid, I shut off the engine so I could hear dad yelling temps and such, and I could hear the coolant boiling inside the engine. I turned the ign back on and temps were 230+.
          I immediately started the engine and let coolant circulate, and it was back down to 210 or so in under a minute and was at 200 by the time I idled around to the paddock at the back of the track.

          BTW, that's with stock radiator, thermostat, and NO ducting. heater hoses are just looped back into each other, which I need to remove. that's not doing anybody any good.

          It definitely sounds to me like you've got an air pocket or sticking thermostat.
          when you bleed the system on the KA, you have to jack the front end of the car pretty high in the air to get all of the air out of the system.
          hope some of that helps.
          Originally posted by SoSideways
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          • #6
            What and where is the temp. sensor that your readings are from?

            Also, a pretty good write up on Pirate4x4 on cooling systems.
            http://www.pirate4x4.com/tech/billavista/Cooling/
            S12 || N13 || S13 || B16

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            • #7
              I usually bled the system very good each time. I deleted the heater hoses and that's when this seems to have started. I built a new motor and ran one session to break everything in. Temps were fine. But wait, I think I just got it. I built a new motor, new oil pump, front cover. It had a thermostat already in it. I have been running a nissan thermostat but I did not change it. I bet it has been sticking. Man am I ever dumb. I thought I was running my 180 degree stat but who knows what they may have in it. I bought a good cover but who knows.
              See talking to some one may turn on a light or kick in a brain cell sometimes. I probably have chasing my tail and burning parts all this time due to not properly checking parts while building the motor.
              THANK YOU ALL FOR ALL YOUR INPUT. THIS IS A VALUABLE SOURCE KNOWLEDGE.

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              • #8
                Yep, definitely seems like a thermostat issue. Replace it with a new Nissan one and see how it goes. I never saw the need for lower temp thermostats personally on track. A stocker is going to be wide open within half a lap anyway.
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                • #9
                  I always open up a couple holes ~3/16 in the thermostat, makes everything easierd
                  I am SKULLWORKS

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                  • #10
                    Just open the thermostat in a pot of water ....stack aspirins in it till thermostat compresses on them and it jams open then rush it into the car right quick and bolt it in.

                    Air pockets will come out, and the aspirin will just dissolve as the coolant circulates allowing t-stat to return to normal operation.

                    No drillings

                    Plus ur KA wont get headaches.

                    Easy bleeding.
                    Last edited by ZorRtwice; 04-23-2012, 07:31 PM.
                    Time is the school in which we learn; Time is the fire in which we burn.

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                    • #11
                      Or it will just open as the engine comes up to temp...
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                      • #12
                        Point is if its NOT opening due to improper bleeding. Ive tried many times to bleed KAs and it will get dead hot with one hose ice cold as if there is a flow obstruction. I tested 3 different parts house tstats and an oem nissan tstat same issue even with maticulous bleeding.


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                        • #13
                          Wont let me edit on mobile... Anyway the easy way for me was to remove tstat entirely or use the aspirin method heh


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                          • #14
                            Whats the hole drilling crap I am hearing of? Is this a joke?

                            You definitely want to keep the thermostat or the engine will run cold. Drilling holes through it will adversely affect how long it takes for the engine to warm up - if at all. Normal operating temperature (N.O.T) MUST be reached so the clearances inside the engine are correct. If you want to run the engine cooler then you can use a thermostat that opens earlier. Standard Nissan SR20 thermostats start to open at 76.5C while Nismo ones open at something like 65C.

                            I used to work at a workshop which ran several IPRA race cars and my boss had always run the vehicles without thermostat. The water temps of the vehicles on race day during winter were WAY below N.O.T. Something like 60ish C. We ended up blocking parts of the radiator up to bring the temps up. Its not ideal.

                            Just run a thermostat. I've never seen one jam up in a properly maintained cooling system.


                            Originally posted by Def View Post
                            Or it will just open as the engine comes up to temp...
                            I dont know about KA's but on SR's if you put a little too much sealant on the thermostat housing it can jam up the bleed/check valve resulting in a massive air pocket where the thermostat is not actually bathed in coolant but just air - resulting in a situation where it never opens and your engine overheats. It happens.
                            Last edited by tez; 04-24-2012, 04:21 AM.

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                            • #15
                              You'd need way too much, like WAY too much RTV to seal the jiggle valve.

                              I guess it could happen, but I've never run into that issue and I've installed quite a few S chassis thermostats. Also never had a problem bleeding the system in the probably couple hundred times I've done.
                              '18 Chevrolet Volt - Electric fun hatch for DD duty!


                              DefSport Koni Sleeve and Spring Perch Buy!!!
                              http://www.nissanroadracing.com/showthread.php?t=5902

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