Old thread, but I finally bypassed my heater core last week - but at the engine like a few here have done. The problem I have with bypassing the heater core up front is that hot coolant is still flowing through the heater lines just below the dash. If you drive at night or on a cloudy day, just feel how hot the corners of the dashboard are once the coolant is up to temp. It's this additional heat that bakes the adjacent vent tubes, further heat soaks the dash, and ultimately reduces A/C cooling. Bypassing at the front is only keeping the HVAC box cooler - it's not preventing your dash vents from baking due to the adjacent coolant lines.
I installed a simple, but rugged inline ball valve between the engine and heater feed. This is way easier to service than fixing loose clamps buried under the front clam. By blocking at the engine and having no flow through the heater lines, my coolant now hits operating temp about 5 minutes faster thanks to the t-stat opening sooner. The radiator still does its job and my coolant temps peaked at 190° this weekend in lower 90s ambient temps, which is the same as before. This still isn't hot enough to trigger the recirculation pump upon shutdown, but if I ever hit upper 190s, then I'll just open the valve and let the pump do its job.
How's my A/C? The A/C is definitely colder and doesn't heat soak after 15 minutes like before. I didn't record numbers before this mod, but I'd safely say the A/C blows at least 10° colder during long drives! Some of that improvement is also from insulating the outer vent arms with Reflectix. The dash will still bake on sunny days, but at least the insulation barrier cuts back on thermal transfer to the long vent feeds. The two inner vents don't have as much surface area as the outer ones, so I left them alone.
Last edited by +TSRAGR; 08-01-2017 at 01:11 AM.