OE coolant reservoirs on S13's are notorious for embrittling and cracking, as most of you are aware. I scored a new one when my car was @ P1 because Tony accidentally put his finger through it. I rocked it for about a year (really 1 HPDE and 3 Solo events), and figured out recently that I needed the space it occupied for my oil filter canister. So I traded it to a friend for a BMC heatshield and found an alternative at Summit Racing:
Moroso 1-Quart Coolant "Overflow" Tank, P/N MOR-63657 (http://store.summitracing.com/partdetail.asp?autofilter=1&part=MOR%2D63657&N=700+115&autoview=sku) - $28.95
Moroso "Overflow" Tank Mounting Bracket, P/N MOR-63401 (http://store.summitracing.com/partdetail.asp?part=MOR-63401) - $6.95

While not as blingy as most other alternatives, it should do the job nicely, and cheaply.

Here it is, out of the packaging:
http://i116.photobucket.com/albums/o20/2Fass240us/Project_240/CoolantRes/Moroso_01.jpg
It comes with a draincock (uh huh huh huh) and a 90° hose barb. The configuration shown on Summit's site is the draincock on bottom, but I decided to put mine on top as a means of adding coolant, and using the hose barb on bottom to route the line in from the radiator neck. I did this to match the OE configuration where the overflow goes into the bottom of the reservoir:
http://i116.photobucket.com/albums/o20/2Fass240us/Project_240/CoolantRes/OEReservoir.jpg

I tried this as a potential spot:
http://i116.photobucket.com/albums/o20/2Fass240us/Project_240/CoolantRes/Moroso_02.jpg
But wasn't comfortable with the way the silicone hose bent to make the turn:
http://i116.photobucket.com/albums/o20/2Fass240us/Project_240/CoolantRes/Moroso_03.jpg

So I test-fitted and found a new spot:
http://i116.photobucket.com/albums/o20/2Fass240us/Project_240/CoolantRes/Moroso_04.jpg
http://i116.photobucket.com/albums/o20/2Fass240us/Project_240/CoolantRes/Moroso_05.jpg

Mounted:
http://i116.photobucket.com/albums/o20/2Fass240us/Project_240/CoolantRes/Moroso_06.jpg
http://i116.photobucket.com/albums/o20/2Fass240us/Project_240/CoolantRes/Moroso_07.jpg

Draining the distilled water & Water Wetter into the new tank:
http://i116.photobucket.com/albums/o20/2Fass240us/Project_240/CoolantRes/Moroso_09.jpg

Detail of the hose into the barb on the bottom:
http://i116.photobucket.com/albums/o20/2Fass240us/Project_240/CoolantRes/Moroso_08.jpg

Added the draincock (this word gets me every time!) to the top:
http://i116.photobucket.com/albums/o20/2Fass240us/Project_240/CoolantRes/Moroso_10.jpg
The tank has a vent hole in the top that should be sufficient to bleed pressure in the event that coolant does overflow into the tank, so I don't need to keep the draincock open.

I like this mounting location because it's discreet, but realize that this won't work if you have pop-up motors. So this spot (or close to it) would only be an option in cases like mine, or if you swapped another front end on the car. Might work for S14's too, but I haven't messed with one to know for sure.

No issues from hard track usage last month, which means it should stand the test of normal driving. Of course, the real test is if you actually have an overflow situation, so I guess I have nothing conclusive to add quite yet.

-Andy

thank you, I might grab one of those.
YW, glad to be of assistance.

would it be an issue that (from the pictures) the top of the tank is lower than the top of the radiator? it seems that the radiator would try to equalize and fill up the tank.

would it be an issue that (from the pictures) the top of the tank is lower than the top of the radiator? it seems that the radiator would try to equalize and fill up the tank.

The spring in the rad cap keeps the coolant in the radiator....

The spring in the rad cap keeps the coolant in the radiator....

but after it releases back into the overflow it will not return into the radiator... right?

I think its a cool idea... there are cheaper alternatives like using a smaller one from another car... but this is really clean.

Does summit carry a clear reservoir? If they did, I would use it and mount it a little higher...

I like.

The spring rad cap only keeps stuff in the radiator until the coolant gets hot enough (i.e. high enough pressure) to force its way past. The reverse is also true - coolant will only "return" to the rad until it cools enough that the spring closes it up again.

So how do you tell how full it is? Seems risky unless you're always popping the cap to check when the engine's cold...

As it sits, the bottom of the new reservoir is not higher than the return to the neck, which I think the OE one may have been (anyone care to check?) So if water exits the radiator neck to the new reservoir, it will not return.

I might be able to add a "sightglass," but had no plans of doing that currently.

It's also important to note that this might not be a long-term solution if I get the dual-pass C&R eventually.