The rest of the day was spent messing with the coolant system. A coolant-bypass hose was added from the head to the water pump to better replicate the factory setup, but after putting everything back together, I realized all I’d done was effectively short out the radiator. Since the work was already done a test drive was run and the findings were interesting. With the bypass hose the car <em>still</em> runs too cool, though warmer than before. Unfortunately I’d changed two things at once so didn’t know what was doing what: adding the bypass hose, and installing a new thermostat with only three holes drilled in the housing. With both mods coolant temperature was up to 70 deg C (158 deg F)… better, but still too low. As an experiment I pinched off the bypass hose with a C-clamp, and the coolant temp actually got cooler – huh?
Fed up with the aftermarket housing, the stock Honda unit was dug up and things got a bit clearer after seeing how it’s made. Seems that Honda uses a two-stage thermostat, one that gates coolant locally within the block and head until the thermostat opens. Once warmed up, that local circuit (which the aftermarket unit does not have) closes and the engine then gets coolant from the radiator. The radiator and ducting have more than proven their effectiveness so it’s up to me to manage that capacity. I can either fabricate a thermostat housing or adapt the Honda part. The reason for the aftermarket housing (having assumed that the designer knew what he was doing…) was because three things were needed to be at the inlet of the water pump: the cooling fan switch, the return line from the turbo’s water-cooled jacket, and the header tank. The factory part had only two inlets which is why it was sat aside.
The question is whether the Honda unit can be adapted to work, but since it’s “free” it’ll be modified to see how it works. There’s two issues: one inlet is smooth-bore, expecting a hard line with an O-ring, and the other is that I need three inlets but have only two. I don’t know what type of plastic the housing is made from; will it stick to adhesives, or will drilling and threading cause it to crack (or worse, work for months and <em>then</em> crack?) In order to use the smooth-bore port, the ID will either have to be threaded with a fitting or plugged. I just don’t want it to fail far from home… Maybe an aluminum manifold that’s a press-fit, glued into the smooth port so the plastic housing doesn’t have to be drilled or tapped.
In other news, header wrap is on the way, along with some big bad-ass brake parts – no more messing about. I’m on-call next weekend and have to stick around home, but the above gives plenty to do. There’s a reason why it’s called “shake-down drives” or “R&D.” I’ll probably start taking it apart – again – this week, spreading the task over several days to lessen the sting of doing it for the third time…