dr bob

I sometimes get similar symptoms after changing coolant or otherwise drain the level down some. Seems like my thermostat needs to be in actual contact with hot coolant before it decides to allow flow through the radiator. So my recovery procedure is to fill the reservoir to the top. Heater valve vacuum hose removed or temp slider at full-hot to aloow collant to circulate through. Then pull the little vent hose from the top nipple on the radiator to allow air to escape, put it back when water comes out. Start the engine with the reservoir FULL, reservoir cap off, and let it idle for a bit to warm up. Watch the gauge to see when it comes up close to normal temp, be sure the reservoir is FULL the whole time, then rev the engine some while kneading the top hose. Engine revs give the water pump a chance to pull any air through and deposit it in the reservoir. Kneading may be enough to push some water around to get the thermostat contact and get it open.

I put a new thermostat in when I did the TB/WP/Etc project last spring, with slightly different temp results than what I'd been seeing previously. I followed the burp-and-puke protocol above, and it came up nicely. On the S4+, fans running is the confirmation that you have coolant flowing through the radiator. No flow, no fans, and the temp will continue up to overheat if not caught in time.

bureau13

Interesting...I did lose some coolant and refill recently (stupid me not clamping the upper rad hose tightly after re-tensioning the timing belt, etc). Unfortunately, I don't really know if current behavior is different from before, since the temp gauge wasn't working back then.

bureau13

This problem is fixed. I drained and replaced the coolant (Zerex G-05/distilled water plus a bottle of Water Wetter), replaced the thermostat and rear thermostat seal behind it, and I get temps no hotter than midway, sitting in traffic (no functional aux fan...still need to address that, and ambient temps around 70F). Moving, it was right around the lower hash. I'm not sure which part of the work had the greatest bang for the buck, but my money is on that rear thermostat seal. There was so little rubber left it looked like the seal was missing at first, although it turned out that the metal part was still there.

Word to the wise, stuff something in the hole to the right and down from the seal (looking at it from the front) when you attempt to pry it off with a screwdriver. It plopped right down that hole, I had to fish it out with an extendable magnetic thing-a-majig. I'm fortunate I was able to get it, because I couldn't feel it with my fingers at all.