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Help! thermostat mystery!

bones66

Member
Joined
September 5, 2010
Messages
36
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0
City, State
Bozeman MT
Year, Model & Trim Level
1994 4dr 4x4
hey all i was swapping my thermostat yesterday getting prepared for the montana winters. i was running a 160 thermostat for the summer and just picked up a 190 for the winter. the thermostat swap went as well as could be, i can get the three bolts out without messing with the belt fan etc. anyway got the swap done and went to bleed the system. Then the problems started. the heater works great blowing warm air, the fill tube going to the block is nice and hot and the radiator is super warm as it should be, BUT the lower hose is still cold as can be and the engine temp is barely hitting the N of normal. the temp will go up to the n and then you can watch it dive back down to cold like the thermostat is opening super low. i went ahead and took the thermostat back out and boiled it to make sure it worked. put it back in and still having the same problem. my local mechanic told me to get it warm shut it off and pop the cap to fix this. been doing that for the last 24 hours and im seeing small amounts of bubbles but the lower hose is still cold and the temp gauge is not rising. need this for work and dont know what to do!
 






Sounds like what happens when you swap in a 160 thermostat after using a 190-195.

Proper 'burp' procedure for the cooling system is to only tighten the cap to the first click, leaving it loose for air to come out, and with the radiator almost full, run the engine until the temp gauge goes up then goes back down. Let the engine cool completely, fill the radiator back up almost full, put the cap back on halfway, and do the same thing again. After doing this twice the air should be purged and you can fill the radiator and overflow tank and should be good.

If the thermostat isn't opening all the way no matter what, you would probably want to try getting a new radiator cap. OEM Motorcrafts with the 16lb rating are the best and they are inexpensive, but an aftermarket one is ok if you're stuck.

Also make sure you're using a rubber gasket around the thermostat, to create a seal. If it's just in there loose coolant will flow past it and pressure will never build up.

I'd also say you should probably just use a 190-195 thermostat all the time in such a climate as Montana, the use of a 160 degree thermostat is usually for searing-hot climates like the southwest, where 100-plus degrees days can last the summer and really affect the cooling system.
 






thanks bud. we hit 80-90 here in bozeman pretty regularly here in the summers, so i wanted to be safe with such a wild temp swing. i think i got her fixed. this morning went out cranked the heater and let it sit running for awhile. shut it down and i could see a ton of bubbles flowing into the resivior. checked the levels topped off then about an hour ago warmed it up and went for a drive. the temp gauge got to the R of normal and the lower hose is warm and pressurized so i think im good to go. the thermostat is the oe motorcraft one. i wouldnt be suprised if im going to need a new radiator cap soon as ive been taking it on and off for a good while now. thanks for the help man
 






Well busted out my infared thermometer. Lower hose is 120 running perfectly
 






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