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  • Engine Cooling - How to?

    Looking for advice here from some of you guys who are MUCH smarter than myself:

    I am having a very difficult time sorting out my cooling system.

    The Problem(s):
    Car overheats after 2-3 "hot" (IE. At speed) HPDE Laps. Ambient Temperature from 60-90.

    Coolant temperature Jumps from ~210 to ~250 almost instantly

    Coolant overflow tank is ALWAYS full after this happens. I can usually sense when coolant temp is about to "jump" by noticing the overflow tank overflowing. The motor pushes out coolant even when this "overheat" condition does not occur, just more slowly.


    Car will drive and run fine under normal around-town driving
    Car will drive fine and run a HPDE if ambient is cool. Did a HPDE in March where ambients were in the 50's and had no trouble. (maybe car was better back then and something has changed since?)


    Car Setup
    S13, Stock Bumper, Fenders
    no splitter, chin spoiler, ect. just plain bumper. factory undertray is missing
    LS1 with stock waterpump, heads, ect.
    Aftermarket fiberglass hood with vent directly above radiator cap (i can take it off with the hood closed)
    LS1 has a 160 degree thermostat that IS working.
    Coolant Temp read from 2 different sources (stock gauge in driver side head, aftermarket gauge on waterpump housing)
    Heater core is bypassed
    factory steam vents from LS heads are directed into a surge tank. surge tank is connected with a "T" to the heatercore outputs
    Radiator is a KA24 Style Megan racing aluminum radiator. (think, mishimoto)
    Fans are Altima fans adapted to the radiator. Shroud is perfect on top and bottom but slightly too wide, so about 1 inch on each side gap facing the front of the car
    radiator cap on radiator is sealed with a 42 psi cap (no spring to release pressure). the output where the overflow tank was originally connected is plumbed to the surge tank.
    surge tank has a 24 psi radiator cap that vents to the factory overflow tank

    Tests
    Compression check shows within 5% across the board
    Leakdown test passed on #1 and #2. Got lazy after that point.
    Pure water/waterwetter does not help
    pressure under the hood is POSITIVE. Taped up vent inhood and drove and the tape pushed OUT and eventually blew off


    Any ideas? My next step is to call griffin or another radiator shop and try to get a bigger/better radiator and more powerful fans with a matching shroud.
    1992 LS13
    385whp/370tq

  • #2
    small head gasket leak? mine cools just fine with a $100 ebay radiator (16x26x3) and a spal 16" fan. my water expansion from cold to 210* is around 1 pint, if that (18psi cap)

    i highyl doubt its just insufficient radiator if its shooting from 210 to 250. that sounds like coolant being pressurized by cylinder. i'd say try the dye in the coolant test.
    Originally posted by Jason M
    I have no chance to win without the Giken...

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    • #3
      Josh is right, there might be "Air" in the coolant system.. I mean gaz .

      I am not sure the heater core by-pass is a good idea. Basically its like having a port to a radiator with no radiator between. It would be detrimental to the flow in the engine. If you meant you blocked them off ok.

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      • #4
        this is an ls1, what are your oil temps?

        Most PM answers: F 17X9 +22, R 17X9 +35

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        • #5
          Sounds like a small head gasket leak to me...
          Originally posted by SoSideways
          I don't care what color they are as long as they are LONG AND HARD.
          '04 G35 Sedan 6MT- The DD
          '96 240SX- The Track Toy

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          • #6
            Could you explain the die-in-the-coolant test?

            On a LS, looping the heater core hoses is the way everyone does it. Come to mention it, the heater core was hooked up when i was not having this issue in march. In march I did not have a surge tank and it was pushing out ALOT of coolant though. I just had to monitor it between sessions.
            http://ls1tech.com/forums/conversion...ater-core.html

            Oil temps never go above 190. I have a oil cooler and the T-stat opens at 180.

            Guess the consensus is to leakdown test all the cylinders or try a hydrocarbon test?
            1992 LS13
            385whp/370tq

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            • #7
              Quick test for head gasket prob. Remove the radiator overflow cap and smell. It will smell like fuel if you have a head gasket prob. My overflow tank would smell like race fuel when the head gasket failed.

              Hydrocarbon test would confirm.
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              • #8
                Again, hydrocarbon test. If you let the car sit for a while (after it's completely cool) does the radiator have any pressure in it? My head gasket had a small leak that was forcing combustion pressure into the coolant system. It would overheat if I didn't bleed off the excess pressure every now and then, but there was always residual pressure in the cooling system even days after I last ran the engine.

                I was able to re-torque my head and the problem went away. Maybe you can do the same? Shouldn't be too difficult without cams in the way haha.

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                • #9
                  When our lemons car lost a hg at a race, the engine would build pressure in the cooling system any time the engine was running- hot or cold.
                  Easiest test there is to pull radiator cap on a cold engine to bleed pressure, put cap back on, then fire it up. Let it run for 30 sec or so and pull rad cap. If you have pressure again, then you've got a bad hg.
                  Originally posted by SoSideways
                  I don't care what color they are as long as they are LONG AND HARD.
                  '04 G35 Sedan 6MT- The DD
                  '96 240SX- The Track Toy

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                  • #10
                    o2 sensor ?? had a z31 with a bad o2 could drive anytime if I kept it below 2500-3000 rpm, but as soon as I passed that rpm instant boil.
                    Weak fuel pump,fpr, or clogged injectors another possibility...
                    Last edited by slidewayzagain; 08-31-2012, 08:02 AM. Reason: bad typo

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                    • #11
                      I would think there would have to be a gas in the coolant system to bring the temperatures up almost instantaniously. It seems as though a temperature jump that significant and that quickly through a closed system filled with only a fluid would take an extremely large amount of energy. Probably more than the engine could produce in a short time period. My vote would be that the combustions gases are getting into the coolant system, the only thing that seems off is that the compression test looked good. Hydrocarbon test would be the way to go.

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                      • #12
                        LS1's natrually run hot though...at least in my experience with them they do. 230+ isn't out of the question on them when getting beat on.
                        'Slicks on a car show me you care - broken axles show me you're trying'
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                        • #13
                          Well, yall were correct. Hydrocarbon test indicated the headgasket was blown:


                          So, I started pulling the heads off. This motor is MUCH easier to work on in a 240 than in a vette or f-body (especially)




                          and, this is what i found:




                          And, the headgasket:
                          1992 LS13
                          385whp/370tq

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                          • #14
                            Is that from an oil galley to a water jacket? I don't think that was your failure. That might just be the carbon gasket getting nasty over time exposed to water.

                            It's usually hard to see a failure like yours on a gasket in my experience, as it only flows combustion gasses when really hot, and othertimes it's sealed up.
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                            • #15
                              You don't normally EVER see headgasket failures on LS motors...even if junkyard engines with gaskets from 3 motors ago with a turbo (trust me, I know)
                              'Slicks on a car show me you care - broken axles show me you're trying'
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