boiling radiator fluid ... PLEASE HELP!

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Richard Lange 2

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Location
little elm, TX
A year and a half ago I changed my water pump and thermostat. Truck has been great ever until the beginning of this summer. Now when I crank up my AC on the way home from work, eveything is great until I get about half way home (15 miles). Then I start to smell radiator fluid. When I get home the resevoir top has popped up and fluid is everywhere. The fluid that is still leaving the radiator and going to the resevoir is bubbling (maybe even boiling???)



I did a flush 3 weeks ago and it was fine until today (50/50 mix like the directions say). Then I got the same result of popped top and fluid everywhere. I am at a loss. The fan is turning. Cold air is blowing. Heater works fine. Fluid is moving back and forth. Why would it get so hot that that it bubbles and blows the cap off the resivior?



Autozone does not think its the thermostat or the water pump. Thinking it maybe the sensor that controls the thermostat.



Any ideas? What about a 180 degree thermostat instead of the 192 that is comes with the truck?
 
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oh ... and the temperature gauge on the dash board moves like it is supposed to, but I have not seen it get above the little key shape in the center. So I do not think it is stuck, but does anyone know if a bad thermostat would not tell you the truck is overheating when it really is. And if so then then, the othe issue is why is the truck overheating?
 
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My guess would be the thermostat...dont use the ford replacement..they are notorious for failure...

the movement of fluid you see may just be from the bypass...



edit; have you ever replaced the radiator cap ? Stay with the 192 ts

if the cap is failing what is comming to the resivoir may have the appearance of boiling
 
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It could be a bad thermostat or even a bad radiator cap. The worse case sceanareo would be a blown head gasket, that would get real pricey $$$.



If you are only putting water in your radiator that can cause premature boil-overs. The coolant/antifreeze also raises the boiling point to prevent boil-overs.



Replace the Thermostat yourself, have the cap and cooling system pressure tested.



...Rich
 
no I have not replaced tha cap, but the guy autozone suggested that. somthing about the presuure not being right. It seats tights, when I screw it on ... do you really think that could cause it?



DO you think the 180 degree would be better? Autozone has the EOM themostat by Duralast. Is that what you are suggesting to avoid? Any suggestions on what is better? the last one I got from O'Reillys, but I am sure it is whatever the EOM part they had.





I have been using the 50/50 mix that is suggested in the manual. where can I get it the cap tested? I think the part is less than $20, so I may just buy it and try it.
 
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Sounds to me like a cap. The cap is releasing fluid to the overflow resevoir a lot faster than it should.



If it was a thermostat, you would see a rise in engine temp(and then the radiator cap would release as designed when the pressure rating was exceeded). There is no sensor that controls the thermostat. The thermostat itself has has bimetalic spring that opens and closes when heated or cooled. AutoZone or other parts store should be able to test the cap. Of course, you would have to take it to them in something other than the ST because the cap will be under pressure when hot...
 
I think I am going to replace the cap at lunch. It has been taken on and off over 20x in the past 2 years in dealing with my water pump, thermostat, and now this. So I imagine even if it is not bad, it could be there very soon.



If this still does not fix the problem, then I will change the thermostat. For an 01, 2 wd ... does anyone know if I need the thermostat with or without the O-ring? Autozone had both listed for my truck.





As for the sensor. The guy at Autozone showed me the sensor, but I think it may be what tells the truck to kick on the fan? Let me know if I am smoking some crack on that? I know just enough about cars to really screw them up ;)
 
Your guess is probably right, the guy at AutoZone is showing you the sensor that controls the electric fan. Do verify that the fan is running when the truck gets hot though. If they are not, then that will add to the proclem.



I agree with everyone else in thinking that it is probably the radiator cap that is bad. The cap is designed to hold the system at a specified pressure which also raises the boiling point of your coolant. If your cap is not holding the specified pressure then it is releasing the coolant prematurely to flow into your overflow tank which it is it is overflowing the tank when the engine gets hot.
 
We don't have an electric fan.



There is a coolant temperature sensor.



Stick with the 192.



Get the pressure test done, it will verify if the cap is failing or not.



You need the t-stat with the o ring.
 
I agree that there is a coolant temperature sensor, but I didn't think we have an electric fan. Let us know how the new cap works out.
 
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A closed system runs at 13 psi, thats what the radiator cap opens at. A 50/50 mixture of antifreeze/water at 13 psi raises the boiling point to 237 degrees F. If the water was boiling that is damn hot, I have had it happen in my Bronco a few times.



I would change the thermostat and the cap. Thats why it sucks that we have those idiot gauges instead of analog gauges. Also at that temp the hoses get real soft, inspect the hoses also.
 
IMO if the temperature guage is working properly and does not show an overheat condition, then it appears that the radiator cap is venting based on pressure. The radiator cap doesn't understand temperature. Either the cap is venting at a lower than rated pressure or the system is pressurizing above the nominal value. he pressure is increased in a closed system based on the temperature. If the temperature is in the normal range then I would expect that the cap is venting at a lower than designed pressure. To see if you are venting prematurely, loosen the radiatior cap and run the trac as normal. If the temperature is within the expected values the radiator will not "boil over' but it will allow the fluid to expand in the reservoir.













 
bad thermostat,bad cap or maybe a block passage somewhere in the motor. Have the system back flushed and see what color the antifreeze is coming out. Hope you get the problem fixed. Good Luck!
 

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