Yet another coolant leak (Page 4/5) cvxjet NOV 06, 10:27 PM quote Originally posted by Patrick: Bill, I'll be 68 next month... but I refuse to get "older". You should start>>>SUBTRACTING!!! css9450 NOV 07, 08:25 AM quote Originally posted by Cliff Pennock: Now the thermostat itself doesn't "click" in place. It just "floats" and is held down by the cap. This might also be the reason why I can't get the original cap to close since the thermostat might not be far enough down the housing. I had a thermostat which wouldn't click into place, in fact it was sort of sitting there on the little ledge it was supposed to click into. Consequently, it sat too high in the thermostat housing and made the cap not seal correctly and small amounts of coolant would leak around the cap once the car got good and hot. Ogre recommends a small amount of silicone brake grease to lube up the O ring on the thermostat. I tried that on mine, and with a little wiggling it suddenly clicked into place like it had never done before. And no more leaks! I suspect there are a lot of manufacturing tolerances between old AC Delco, new AC Delco, Gates, Stant, Motorad, etc and whomever else makes thermostats and caps for our cars. theogre NOV 07, 08:54 AM quote Originally posted by Cliff Pennock: I removed the cap and thermostat just so I could make a comparison. Just to clarify: The "new" cap takes no effort whatsoever to close, while the "original" cap apparently takes more elbow grease than I can supply without modding something. New is MotoRad, Old is "Real" GM/Stant. (Stant made a lot of caps for Big 3 & relabel for them.) The old cap Rivet in center doesn't allow the seal part to rotate freely. Either was made that way or likely has enough rust to block this. Forcing it On like that makes the rubber to "twist" & simply may not seal or rip it and never seal. New cap may not seal because T-stat house edge is f'd & letting coolant out. If true can try scraping etc to get rust & other crap off the sealing face. May need a new cap even then. After cleaning, Coat that w/ Permatex Green label Brake Grease to prevent more rust w/o "eating" the rubber. Silicon oil/grease if can't get that brake grease. "height" different may not matter for some T-stat houses. Has to do w/ actual design all parts & Tolerance Stacking. Cliff Pennock NOV 07, 09:44 AM quote Originally posted by css9450: Ogre recommends a small amount of silicone brake grease to lube up the O ring on the thermostat. That actually did the trick. 👍 I used a little bit of bearing grease and the thermostat went in quite easily. Now both caps closed easily as where before, I couldn't get the old cap to close now matter how hard I tried. But with the old cap, it still leaked. It doesn't (seem to) leak with the new cap however. I've only driven it a few block so the engine isn't at temperature yet so I will check if this has solved the leak next time I need to run some errands. theogre NOV 07, 09:54 AM quote Originally posted by Cliff Pennock: That actually did the trick. 👍 I used a little bit of bearing grease and the thermostat went in quite easily. Now both caps closed easily as where before, I couldn't get the old cap to close now matter how hard I tried. But with the old cap, it still leaked. It doesn't (seem to) leak with the new cap however. I've only driven it a few block so the engine isn't at temperature yet so I will check if this has solved the leak next time I need to run some errands. Wrong Grease. Get a new cap before opening weeks to months later. Any "Normal" & Syn oils/greases has chemical to prevent hard seals but those "eat" brake & coolant rubber parts. Once they get on those rubber parts, washing won't help even if you wash right now. theogre NOV 07, 10:06 AM Need a pic of both cap's top to see label on them. Cliff Pennock NOV 07, 10:30 AM Yeah I'll put on the proper grease shortly. I first want to find out if this stopped the leak or not. Patrick NOV 07, 03:59 PM quote Originally posted by Cliff Pennock: I used a little bit of bearing grease and the thermostat went in quite easily. Now both caps closed easily as where before, I couldn't get the old cap to close now matter how hard I tried. Putting a lubricant on there was the right idea, but... quote Originally posted by Patrick Here: I had the thermostat removed for a few days... and when I went to reinstall it, this is what I saw. Anyone care to guess what's going on here? I do know what happened... I'm just testing your knowledge. quote Originally posted by Patrick: I've been putting grease on the Fiero's thermostat O-ring for decades (for easier installation into the housing), and never had a problem. Even when I pulled this thermostat out last week, the O-ring appeared to be fine. It wasn't until I left the thermostat out of the engine for several days that the O-ring had an opportunity to swell up. Lesson learned! theogre NOV 07, 06:34 PM When installed w/ wrong grease... Cap or o-ring will try to swell etc but pressure keeps them in shape. When the part is open/removed after, the pressure is gone & swell/warp then. Depending on oil/grease used, Can be just minutes to a few hours before you see the problem & have new part handy or can't drive until cap is replace. Cliff Pennock NOV 09, 02:20 PM It looks like it's no longer leaking from the thermostat housing. 🥳