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4 minute(s) of a 731 minute read
6-29-2020
I've been doing lots of thinking, and a small amount of working. Some past sins are definitely compounding the issue, mainly my 'easy mode' heater core bypass.
Solved Issue 1: I learned how radiator caps work. This is the only car I've ever owned with a traditional radiator cap. The rest of my German/Euro trashbuckets have a radiator without a filler neck. Coolant is added to the pressurized overflow tank. They are much more complicated than I realized. Quite the 'duh' moment.
Solved Issue 2: The upper/outer sealing surface had some damage to it which may or may not have been preventing a complete seal. I took care of this with some fine grit sandpaper. Using my Mishimoto radiator cap I was able to get the system to seal, and open to the overflow tank when required.
Sorta solved Issue 3: The system normally comes with a 1.2bar (~16psi) radiator cap. The mishimoto radiator comes with a 1.3bar (19psi) cap. Given that my heater core install is aided by two piece of rubber hose; I'm not sure what pressure it will withstand. I'm nearly to the point where I'll remove the dash and do the heater core the right way and completely eliminate this weak point which has been a mild annoyance for years now. Doing the heater core the right way is supposed to be a huge pain in the butt, and I'm afraid of adding new rattles and squeaks; but it would be nice to fix this once and for all. Anyway, long story short, I replaced the 1.3 bar cap with a .9bar cap while I evaluate the system to prevent hot coolant all over my feet.
The system now holds pressure to 19psi and has no leaks. I still really don't have any idea what caused the 'spewing' issue. I'm sure the upper/outer seal not totally sealing didn't help, but I don't think the damage I found was new. To be 100% sure I wasn't dealing with an overabundance of pressure in the system, I did a block leak test which tested negative. Phew.
Outstanding issue 1: On my very first test drive after resolving all of these issues, it backfired and died out of nowhere and would not restart. I reset the ECU by unplugging the battery, and I also gave the PTU harness a good squeeze. It fired back up and hasn't given me any issues on a few drives since; but now I'll have that hanging in the back of my mind for a while. I guess this is one good argument for deleting the PTU altogether and upgrading to Audi coils.
Outstanding issue 2: The radiator doesn't seem to be sucking coolant back in from the overflow tank after cooling down. After the cooldown from my last hot weather drive I removed the cap and the coolant was down 2-3" (previous normal level with non-functioning overflow). I topped it up again and I'll check when I get home from work today. No leaks at all, and the overflow tank has coolant in it. Odd. I'm assuming the radiator should be filled to the tippy-top after a drive. I feel real silly not being sure about these questions after 12 years of ownership. Live and learn right?
I guess I should end on a positive note. It was ~92 on Saturday when I did my test drive observing the cooling system and coolant temperatures. AC worked well. It wasn't 'ice' cold, but it definitely made the interior cool. I'm using R134a with an R12 system; there will be efficiency losses which I was expecting. With ambient temps of ~70F the AC feels ice cold but I wasn't sure how it would perform in the heat. Thankfully it passed the hot weather test with flying colors. I'd guess the air temps were in the low 50's coming out of the vents.