To ebay radiator or not to ebay radiator?
 

I'm going to be driving my Miata 1400 miles from Flagstaff, AZ to Tacoma, WA this summer. I did this same trip last summer and the temp gauge was reading past 12:00 in 85-90 degree ambient temps most of the way. Thus, I'm looking to upgrade my cooling system for this next trip. My plan is to replace the thermostat, flush the cooling system, switch to 70/30 mixture instead of 50/50, and possibly purchase a higher capacity aluminum radiator (my current radiator is an OEM replacement which I installed about a year ago). I also plan to do some track days this summer, so I think a larger radiator would be a good investment regardless.

I'm wondering if it's worth it to spend $250+ on a name-brand radiator, or if I should take my chances with a $100 aluminum radiator from ebay. I'm concerned there would be fitment/longevity/efficiency issues with an ebay radiator, and I can't afford to be stranded 700 miles from home puking coolant all over the highway. However, from what I've read, ebay radiators don't seem to have that bad of a wrap. Anybody have experience with ebay rads? Will I be saving $150 now only to run into trouble later (or immediately)?

have ebay. works well. Werf the cap it comes with and install a new OEM one. If you have time, install it and drive it for a while, make sure it is ok. Like, don't throw it in and hit the road as soon as you tighten the bolts up, so if it does fail you have a chance to go plan B.

I dont know what AZ weather is like, but if stereotypes ring true, you could run at or close to straight water due to feezing not being a concern.
i went csf because good deal, but i hear allot more recommendations than failure on ebay units. A reroute would be a good idea for trackstuff though.

CSF or the Koyo Hyper V VH060650

Any real benefit of crossflow vs downflow?

It depends on if the cross flow is multi-pass.
If it is then...
Yes crossflow is better.

Cross flow single pass might be slightly better as the tubes will be longer horizontally than vertically.
Heat rejection tends to be higher if the liquid stays in the heat exchanger for a longer period of time.
This is super simplified but correct IMO.

Not freezing =/= not corroding. By all means dispense with the antifreeze, but anti corrosion is good.

Make sure you have good ducting/seal up the gaps so air is moving through the rad.

Picked up a CSF. Going to go with 30/70 mixture and see how that treats me (can't go with only water in Flagstaff, temps routinely get far below freezing in the fall/winter/spring at 7000 ft).

I like Honda blue antifreeze. In comes 50/50. So diilute it 50/50 again with distilled water and you have 75/25, good to 10*F

With lower than recommended dilution, how does that affect the corrosion inhibitors in it? I guess they keep working down to a certain ratio, but I have no idea what that ratio might be.

If I was running very low ratios of anti-freeze, I'd be looking to top up the ratio with an inhibitor. Having seen a recent photo of a water pump impellor that had completely corroded away, I'd place corrosion prevention before maximising coolant heat transfer.

There is a lot of opportunity to improve the efficiency of a radiator by ensuring that all air entering the mouth exits through the radiator, not around it, under it, or out through the bumper skin ...

If you haven't boiled it by now, the bigger radiator will probably be enough by itself to bring the temps down, without dropping the ration below 50/50. Making sure the sides and bottom of the radiator are sealed would be my next step, even if that didn't (and it would not) seal it completely. Then I'd complete the sealing if I thought I needed more cooling.

If that still wasn't enough, I'd be looking at the thermostat and water pump next, ensuring that there was plenty of flow into the radiator when the thermostat was open. The absolute last thing I would do would be think about the coolant heat transfer.

But YMMV.

Good points. I ran the 50/50 for a few years and just dropped the % last summer. I did not see any difference in temps at the track. I may bring it back up.

The Honda does seem to have lots of inhibitors, which is why I like it. I can’t quantify that statement, however.