Engine Temps,Thermostats, and Jiggle Valves (1 Viewer)

Aug 13, 2013
Chandler AZ
At the risk of embarrassing myself (I should be used to it by now), and in the spirit of saving YOU from the same troubles...make sure your Thermostat Jiggle Valve is at the TOP!

For sometime (too long) I have been unhappy with my engine temps. They were never bad/too high (never exceeding 205F) but they would sit in the low 190's (190-194 for most drives) and fluctuate a lot, particularly when standing still idling. And this was regardless of ambient temps (50-110F). I am in AZ so we have quite the range. I had a previous cruiser that I drove across the country that didn't even break 194, ever...so I knew that lower temps were possible. Generally I tried to live with it - rationalizing that there is variation in thermostats, temp sensors, fan clutches etc....but still it bugged me.

Well last night I tried my third thermostat! When I disassembled I noticed immediately that the old thermostat had its jiggle valve at about ~30 degrees (maybe more!?) instead of straight up 0 degrees. I put in a new thermostat anyway, and this time made sure it stayed up at 0 degrees. Having a new o-ring/gasket for the thermostat helps keep it still while I bolted on the inlet cover. Topped off with 50/50 Toyota juice and went for a test....I didn't do any elaborate burping (me of the hundy).

I was so happy! 186F - nailed. I could get it to go DOWN (to 184F) by reving the engine but it soon settled at 186 again (like <30 seconds). I drove hard...3.5k rpm for extended periods 186F....I got up to 188F when drove hard and then stopped and let it idle, but again, it would soon settle back to 186F (less than a minute). Ambient temp last night while I was driving according to the dash was ~65F, cooler I know, but even at that temp I would see 190F easily on my old 'stat.

So...to be fair I can't tell you if it was the new thermostat or the position of the jiggle valve... but the behavior was different (as far as what the engine temp did relative to driving/rpm)...so I think rather it was the jiggle valve.

I understand that the jiggle valve lets the air through/out...and perhaps I had an air pocket around the coil of the old thermostat, or at least my temp sensor which is near by. Either way...I am happy to have this finally licked!

Hopefully this helps you. Our hundreds really should stick close to 186F. I know the thermostat is stamped 82C/180F but operating 186F seems to be the spot?



Oct 30, 2018
West Texas
I know this is an older thread, but glad I found it. I just replace my heater Ts, all hoses and OEM thermostat. I filled it back up with T red in a 50/50 mix with distilled, de-mineralized water. Temp on my scangauge was running 187+or- a bit before the work. After the “work” it was running 200 to 204 at 75mph. I had burped the system and kept a check on coolant level.....couldn’t figure it out! Then I ran across this thread......repositioned the thermostat and now the scangauge has not shown over 188 degrees even on our 100 degree days......very pleased!
If you’re having overheating problems and you’ve recently changed your thermostat.....check the position of your jiggle valve!
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