I installed a new fail-safe thermostat over the weekend. It worked for 24 hours, temps were 195-205 after the install.

Today driving home, both the realtime OBDII readout and the dummy gauge showed temps dropping steadily while at freeways speeds. Almost got down to 110. Temps were noticably low coming from heater core. Pulled into a gas station- > No leaks, and coolant levels are ok.

After 10 minutes, pull back on to the road, and temps get back up to the 195-205 range eventually. So the thermostat must have gotten stuck open, and the fluidyne kicks so much heat ass that underhood temps want to go to ambient.

What could cause this? Would a bubble in the system cause a thermostat to temporarily fail open? My last thermostat failed, by somehow warping itself, causing it to intermittently get stuck in the open position.

2gnt: '99 RS-T, killed by a toyota, pending rebuild...
Daily: Volt
Daily #2: '99 EVG ebike- STOLEN by PEDRO

I think I know what is going on here. The coolant system is working TOO well, so the question is what could cause that. If a new thermostat is failing open, and the old one was warped, something is subjecting the thermostat to stress. What if the bypass is clogged, and high pressure is thus forcing open the thermostat? The bypass on a stock 2g goes over the exhaust mani and into the heater core, then connects with the radiator outlet. On my car, the turbo coolant lines are inline with the heater core. Perhaps there is a partial obstruction in the turbo/heater core coolant line, causing high pressure at the thermostat, warping the old one and pushing the new one open all the time.

The car hits normal operating temperature if just sitting, because there is no air flow until the fans turn on. But when I drive, temps drop to the 140s-160s, b/c flow is always going on through the radiator.

I will have to find a shop that can do a high pressure flush of the turbo/heater core and test this.

2gnt: '99 RS-T, killed by a toyota, pending rebuild...
Daily: Volt
Daily #2: '99 EVG ebike- STOLEN by PEDRO

That's ok guys I'll just keep talking to myself ....

tumbleweeds blow through 2gnt


.... anyways I just realized an overpressurization in the bypass line would push the valve in the wrong direction, since it opens *towards* the motor, thus closing the valve. I think it might be due to cheap autozone failsafe thermostats. I think mine failed open permanently with 24 hours. This guy seemed to have the same problem, but his thread never had a resolution ->http://forums.2gnt.com/dcboard.php?az=show_topic&forum=5&topic_id=132505&mode=full


EDIT: ooo the jeep guys know their stuff - http://www.jeepforum.com/forum/f13/warning-fail-safe-thermostat-872316/index2.html Leaving that here in case anyone ever gets the same problem in the future.

2gnt: '99 RS-T, killed by a toyota, pending rebuild...
Daily: Volt
Daily #2: '99 EVG ebike- STOLEN by PEDRO

Nice job doing the research, Erik. If I had anything to input or knew on the subject I would have done so already.

I contributed to the Wiki.

Good thread for future reference.

P.S. I like your bike. I cycle everywhere in town no matter what. The DSM is just for road trips.

Yea I love biking so much more than driving now. NO TRAFFIC, home faster than by car in metro california.

So this is what happened to the "failsafe" thermostat within 24 hours :


It fails open almost instantly. I got the duralast one next (autozone gave me the wrong part number at first, thankfully it's in biking distance) and it has been operating perfectly.

2gnt: '99 RS-T, killed by a toyota, pending rebuild...
Daily: Volt
Daily #2: '99 EVG ebike- STOLEN by PEDRO