Thanks for making up this CTO list. Maybe this will help others....
My new '91 GW has been idling rough since I got it 4 months ago. the engine is stock exept for a 180 degree thermostat and champion truck plugs (4404 - the equivelant to RN12YC plugs. BTW they made no difference!) that I put in. I've got the 2150-3 (I think) carb. and this GW was manufactured for elevations above 4000 feet (The PO bought it new in Colorado). My initial mechanic said "some of them just run that way" (rough idle). So I've been busy trying to find the prob. on my own. Well, the other afternoon I hooked up my new timing light, tach meter and vac pump. I pulled the vac hose off the dist adv. plugged it and checked the timing. The mechanic had set it properly (17 +/-2 deg. BTDC (2150 w/ alt. comp)). Then I checked centrifigal advance and then cent. & vac adv.( all vac lines hooked back up. For a few minutes all was fine and then Whoa! The rough idle was back and my timing had about 28 degrees of extra adv. making total adv 45 degrees @ idle! It turns out the CTO switch controlling vac adv. was switching from carb ported vac (normal) to manifold (20" hg) vac when the temp gauge read 200 degrees. It isn't supposed to do this until it hits 220 degrees. I guess the extra adv. on the dist. makes the engine combustion less efficient and therefore reduced the heat output of the engine giving it a chance to cool. Anyway my engine temp is usually around 205 +/- 5 degrees w/ new fan clutch and 180 degree thermostat.
I'm pretty sure that my temp gauge is accurate (anyone know a quick way to check this?) So I printed out Bobs CTO page and started calling my parts stores. My '91 GW also uses the top 3 CTO switches on Bobs page. there isn't a lot of info in my TSM and Haynes to test these switches. I figure if I know one is bad I might as well replace them all (this is my daily driver and I'm trying to make it as reliable and smooth as possible also my city MPG is low... my city avg. is 7.5 mpg. ouch!).I found the prices varied widely (all 3 from the dealer $150! and a spec. order).
Brands: In my area Pepboys & Kragen carry Borg Warner while AutoZone carries Wells. Here's the cheapest I found:
220 degree 3 port: Borg Warner P/N EC970 @ PepB $10.49 (it is black instead of red and has "225" stamped into the bottom copper temp sensor)
155 degree 3 port: Wells P/N E901 @ Autozone: $15.99
115 degree 5 port: Wells P/N E960 @ Autozone: $19.94
This makes the total parts cost ($47) 1/3rd of the dealer parts cost.
At all the stores I called they are a special order. Pepboys takes 3 days while Autozone takes 1 day. I found the EC970 in stock at a PepB near me b/c it was a special order that never got picked up. I can vouch that it is identical to the original. My Autozone order doesn't arrive until tommorrow.
'91 GW "The Swank Tank"