Oil Cooler Testing and Diagnosing High IATs
What if adding an oil cooler can actually make the car slower?
Continuing where we left off from the last post, it was time to start looking really hard at the oil cooler as the culprit for overly high IATs on track. As a refresher, we have a 2018 Golf R that is APR S1 tuned, equipped with a 19 row Setrab oil cooler (with iAbed plate, the included Mocal 180F inline thermostat, and all fittings converted to -10 vs the original -8 parts) and a newly installed APR IC that only improved the IAT delta over ambient by 10 degrees… and was still seeing at BEST 45F over ambient in a session on track. Average was 55F.
We started by pulling the bumper and installing a TON of aluminum HVAC sealing tape around the edges of the radiator/intercooler/etc. We also fixed one of the flappy bits that was kind of bent outwards on the driver side. We did this pre-emptively and in an attempt to save time and having to test 4 times vs 3 times. Sealing the cores is almost always beneficial, though we had doubts that it was the true cause.
So then we taped some cardboard covers over the front and back of his oil cooler. The idea is to just not allow air to pass through the cooler, getting heated up, and then flowing into the intercooler behind it. Not a permanent solution, but a quick and dirty test to verify if IC temps improve to "normal".
Attached are some photos of the process... Also just realized I never got any great pics of ALL the aluminum tape applied. It was down at the top and sides as well as the bottom as viewed from the front. We also sealed the radiator from the top on the back side below the stock airbox piece. You can see the gap in one of the attached photos that was covered up afterwards.
As for the DATA, we performed back to back testing. First with the cooler blocked off:
Results: Highway pull IATs down to within 12F or so of ambient. Highway steady cruising (A/C off to clarify) - IATs stable between 15-20F above ambient. Another highway pull: IATs down to within 10F of ambient.
So obviously something we did helped. Now was time to pull the CAD designed block-off plates (Cardboard Aided Design) and re-test again.
With the oil cooler UNBLOCKED/cardboard removed:
Results: 35 to almost 40F over ambient when cruising. First pull ended at a little over 25F over ambient, with the second pull being nearly 30F over ambient.
So we've finally figured out that the oil cooler is the problem (placement, size, etc). Obviously a bunch of people run them, and many people run them in this very same location (including Area Motorsports, who recommends placing it exactly where this one is). I do think that being located on the passenger side is less than ideal because that is the cold side of the intercooler - if that side gets heated by hot air from the oil cooler, it's got no chance of ever coming back down.
Mounting on the driver side would still allow a better [lower] delta-T if the pass side stays cooler, but realistically the correct option is to duct the existing cooler down and under the car or relocate the oil cooler somewhere else which is very tough on a DSG R.
Venting downwards isn't great for aerodynamics, but it is probably the lesser of two evils when there are coolers occupying both fenders already. Also mounting on the driver side would likely screw with the ambient temp readings, and I suspect would likely give false "good" results (will look like IATs dropped by say 10F, when in reality the AAT went "up" by 10F), though the AAT could be relocated without too much effort.
Also it is worth noting that oil temps indicated on dash with the cooler UNblocked, were stable 185-190F the entire time. When the oil is closer to 250-270F entering the cooler on track... it will be throwing a LOT more heat into the intercooler. I can see why people might not see any "problems" on the street and then without running data think everything is fine on track.
I’m not necessarily surprised that the oil cooler can affect IATs, what surprises me is the fact that nobody has “discovered” just how bad it really is while logging, etc. I would have suspected maybe 10F more than typical, not 25F over ambient (comparing the track log vs most of the other samples).
Next step is prototyping a solution for further testing… Check the next blog post for details!
