Repeating Cadillac STS-V Intercooler HX Tests

I went back to rerun the test on the new Intercooler Heat Exchanger (Flexalite 45321) for confirmation of the original test, Initial IAT2 times with New HX – woops

Here was the test data from that test, suggesting the new HX is not as effective as the original:

My method plan was to rerun the test this weekend after the car has had a week to work the air out of the intercooler loop.

Current configuration:  Flexalite 45321 heat exchanger in the place of the OEM radiator type heat exchanger, no other heat exchanger in the circuit, no inline tank added.

What I found today was that the intercooler IAT2 temp never got below 131F, which is worse than the baseline above.  Unfortunately, test1 today I fumbled the mouse at the end of the test and lost all the test data by accidentally closing VCM Scanner (doh).  The STS-V was heat soaked before the test, starting at 156F for the IAT2, and was able to cool down to 131F and was still dropping slightly on highway runs.  But it was not getting to a steady state of under 120F as the OEM did.

I also got the impression there is some interplay between A/C on or off and intercooler IAT2 temps although I am not clear why.  My intuition is that A/C on would run the radiator fans and improve air flow and so lower IAT2, but on the ‘back’ of the loop where I normally do acceleration runs, I noted that when I turned off the A/C the IAT2s fell 5F quickly.

Now I’m not worried about performance runs for the STS-V when heat-soaked, but this does give us a way to test the efficiency of the intercooler cooling system, since it is presented with the greatest heat load.

After a break I’ll get back on to test2 and try to bring back a data stream this time!  Stay tuned.


Okay, refueled and reran the test loop.  I have added the retest new HX data to the previous data table.  I have also added in some data lines from Jaimie’s STS-V.  Jaime has an 07 STS-V with the 45321 HX in place of the OEM, a Frozen Boost front-mounted heat exchanger, and he has an aftermarket intercooler pump instead of the OEM pump.

Retest of New HX appears to confirm previous test

My conclusion is that my config is still running hotter than I want.  My plan is to return to the OEM intercooler heat exchanger, and add a new ZZP S3 front mounted heat exchanger under the bumper in series with the OEM hx.  So, another install weekend then hopefully more data.

Also, I found on the retest that the area I was in led to a decrease in the IAT2, not turning the A/C off.  The issue is that there is a zone of cooler air at the top of my test loop due to getting off the highway and I saw a drop in IAT2s in that area with the A/C left on during the retest.


6 thoughts on “Repeating Cadillac STS-V Intercooler HX Tests

  1. Only read four pages and that was a lot to try to digest. Do you believe, not that it is hindsight, that these changes and the grief associated were worth it to the car?

    Not knocking at all, just asking what your thoughts are in hindsight. Being old as dirt I just had a proper tune and said to myself to put the extra time/$/energy into the ‘company’ drag car.

  2. I like getting measured results and documenting what I find. I was disappointed that the IATs didn’t improve, but that is why I tested, to verify or not.
    Meanwhile I am having fun and learning more about my V.
    Up next is OEM hx + S3 fmhe and new tests.

  3. Thanks you for the courtesy of an answer; by the way, what is hx + S3 fmhe?

    I am a Dominator carb, adjust valves etc. guy and the new stuff is way beyond my scope.

  4. Thank you for commenting.

    I have a ZZP brand front mounted heat exchanger (fmhe) coming, called the S3. It is used for supercharged cobalts originally as a stage 3 component. It is relatively light and will fit under the front bumper on the V. Tim C is modifying it slightly for this purpose so it is a ZZP S3TC as I like to quip.

    I plan to test with the oem heat exchange (hx) back in, and the S3TC, so OEM+S3TC FMHE.

    See the article:
    Cadillac STS-V Intercooler cooling – gathering more parts

    I am also looking at a custom fill tank from RX Performance and trying to source a small inline tank for our Vs.

  5. Well if they make a significant difference let us know. I was going to upgrade my intercooler for a larger capacity and said, ‘what for?’ I don’t race the thing and punch it from time top time but anything over about 130 takes a while – these are not CTS-V’s.

    But I really like the thing a lot; to be honest, it may be a lot slower but I like it a lot more then the CTS-V.

  6. Will do. I feel pretty good about the repeatability of the results so far, and I am excited about the new install, once the parts get here.
    I want to see if I can get the intercooler temps down between runs. I am hoping for steady state of 20F over ambient, but we’ll see.
    I have a couple of other things I want to experiment with on the topic of intercooler cooling, but one step at a time.

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