AVS 1 gal inline tank for the Cadillac STS-V intercooler loop

Got the AVS tank I ordered in the post today.  Very interesting.  Previous mention:  Cadillac STS-V inline flow-through intercooler tank

AVS tank in the box

I ordered this as a possible inline tank addition to my Cadillac STS-V intercooler coolant loop. Additional coolant would act as a buffer to temperature changes (both up and down). The stock system has 2.6 quarts. My system has the S3TC heat exchanger added, which holds 2 quarts, so it is running 4.6 quarts. The new tank would add 4 quarts, for 8.6 quarts total.

The tank has a drain at the bottom, 1/2″ NPT fittings that handily I have 1/2″ NPT to 3/4 inch hose barbs from my 45321 experiment to fit, and a 1/4″ NPT fitting for a gauge which I will either stick a stopper in or a temp gauge.

1/2" NPT to hose barb attachment added

I will have to decide whether to add the tank during in this weekend’s big install adjustments session, or wait and test with the new Spectre hoses in place first so I have a clean baseline, then redo the circuit with the tank in place. Notionally with the angle brackets on the bottom, this tank would just sit directly on top of the S3TC.  Choices are good.


This temperature gauge, with 1/2″ NPT fitting, 2″ probe length, and 0-220F temperature scale could work and hopefully be visible through the grill on close examination.  Hmm.

Cadillac STS-V inline flow-through intercooler tank

The Cadillac STS-V intercooler cooling system holds a total of 2.6 quarts of coolant.  That’s 0.65 gallons.  The benefit of having little coolant is that it heats up quickly, and it cools down quickly.  However, I wonder if there is more disadvantage to such a low coolant capacity.  The LS9 engine in the ZR1 has a small rectangular intercooler coolant tank inline to hold more coolant.  D3 offers a small cylindrical reservoir for the STS-V to hold more coolant and reports good results.

I have ordered one of these AVS tanks hoping I can find a good spot to fit it:

AVS 1 gallon aluminum tank

The tank is 15.5″ long x 3.5″ diameter with fittings at each end. The 1/2″ fittings will be a bit of a flow restriction for the 3/4″ inner diameter intercooler hoses.

For my next experiment I a hoping to use the OEM heat exchanger with a front mounted heat exchanger in series.  That in itself will add 1.9 Liters (2 quarts) of additional coolant inline.  But I’ll get the tank in hand and see if I can figure out a place to mount it for an experiment another day.  Then we can get some real data to answer this question.

Datalog analysis of Cadillac STS-V Ambient vs IAT1 vs IAT2

I have been planning new data-logging experiments and modifications, so I have been reviewing the datalogs I did last August in the summer temperatures.  For my next datalog I will attempt to capture comparative data to this info:

This screen is an HP Tuners VCM Scanner guage snapshot of parameters after a 0-60 run culminating at 65 mph.

Baseline from August

MPH (Temps in Deg Fahrenheit)

Item 0 30 45 60
Ambient 90 90 90 90
IAT1 113 117 113 106
IAT2 118 120 127 135
MAT 120 121 136 169

What we can see from this table, is that at the beginning of the 0-60 run the Ambient temp is 90F, and stays at 90F through the run.

IAT1: The IAT1, which is incoming air temperature as read in the intake air tubing, starts at 113F.  It has rapidly gone up to this value because the STS-V is stopped.  However, as the V accelerates to 30 mph it rises to 117F.   By 45 mph it has returned to 113F, and by 60 mph due to the incoming 90F air cooling it has resolved to 106F.  Conclusion:  heating of the incoming air at the IAT1 sensor does in fact effect the air temperature, and thus performance.   Conventional wisdom is that the incoming air is not in the intake tube long enough to become heated. Net Rise: -7F

IAT2: The IAT2, which is air after it has been heated by the supercharger and cooled by the intercooler, starts at 118F, a 5F increment over IAT1.  By 30 mph it has risen to 120F.  At 45 mph it has risen further to 127F, and by 60 mph has peaked at 135F.  Net rise: +17F.  Keeping in mind the IAT1 went down 7F in this time.

MAT: The manifold air temperature is a calculated value the engine uses to predict the temperature of air in the manifold.  It tends to go up at a higher rate than IAT2.  The MAT starts the run at 120F, is about the same at 30 mph at 121F, but rises to 136F by 45 mph and on to 169F by 60 mph.  Improvements in the IAT2 should have even greater improvements in the MAT value.  Net rise: +49F.

As a result of the high MAT temp by 65 mph as shown in the image, IAT temps are causing 3.6 degrees of advance to be pulled.  This begins at 59 mph when the IAT2 hits 135F and the MAT is at 157F at -3.2 degrees.
This was a video capture of the dashboard of the 0-60 run from August: