One more cooling system problem with my friend's Sonic. The car had been losing coolant for a few weeks, not much at first, and quite a bit (1 or 2 litres a day) recently. I looked at it for him a couple of days ago and noticed that the throttle-body coolant pipe was leaking badly at the thermostat housing. I didn't replace this plastic pipe when I did the other work a few months ago - it sealed well for several months, but obviously I should have replaced it at the time.
He bought a new one yesterday, and we installed it this morning. It's a poor design in my opinion - a fairly rigid plastic pipe with some preformed bends in it. It was a bit of a pain to fish under, through, and around various hoses and wire bundles, but did seem to fit well in the end. It may get installed early on in the factory. A run of rubber hose would be a lot easier to work with.
It has a plastic clip the snaps into place to retain the one end (which has an O-ring) in the thermostat housing. The other end attaches to a short rubber hose which is connected to the throttle body.
The old pipe was quite brittle, and the end with the O-ring was missing, and yet didn't seem to have snapped off in the new thermostat housing. It seems weird to me that it didn't leak worse that it did. I assume I would have noticed if it was missing when I replaced the old thermostat housing, Did it just dissolve?
Anyway, this did nothing to make me like plastic parts in cooling systems, subject to frequent huge temperature swings. The coolant could drop to -30 C here in the winter, and then hit close to 100 C after driving some. That's got to be hard on plastic.
I would guess that the purpose of this assembly is to bring the throttle body up to temperature during cold weather - probably helps fuel vaporization to have warm air entering the combustion chamber.
Here's a link to the part - my friend bought from a local dealer, though, in the interest of getting it done sooner.
https://www.rockauto.com/en/moreinfo.php?pk=9913560&cc=1501879&pt=48150&jsn=1303
