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When I’m on the highway the temperature gauge on my 1994 Plymouth Voyager will go all the way to the H and then come back down immediately. When the car is parked and idling, the radiator will bubble and over flow immensely. It will over heat sometimes at city speeds, but not at often as it would on the highway. I have a brand new thermostat, and all of my hoses leading from my radiator have pressure and heat.

It’s only been doing this since I fixed the thermostat a week or so ago. The car has since gotten another new thermostat and has been flushed out multiple times. I changed the thermostat because my engine was running cold. We checked it and it looked to be the original.

  • Was the thermostat installed in the correct direction? Have you checked that the radiator is nor blocked both water and air? – Solar Mike Nov 22 '17 at 5:28
  • Hi M. Ty. Please try to give us more information so we can help you - The make, model and year of the car in particular, plus anything else that may be helpful - for example, how long has it been doing it? Did it do so before you replaced the thermostat? If not, what prompted you to change the thermostat? – Nick C Nov 22 '17 at 16:27
  • It’s a 1994 Plymouth Voyager. It’s only been doing this since I fixed the thermostat a week or so ago. The car has since gotten another new thermostat and has been flushed out multiple times. I changed the thermostat because my engine was running cold. We checked it and it looked to be the original. – M.Ty Nov 23 '17 at 6:54
  • Sorry for lack of info, I have never used this site before – M.Ty Nov 23 '17 at 6:55
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Do you mean when the radiator cap is taken off, you will see bubbles overflow and gushing out? That means that the head gasket is shot. Also the fact that your car overheats is very likely due to a corroded radiator or a shot fan or fan clutch, or it can be something as benign as low fluid, or air in the coolant system.

But your thermostat is behaving erratically for it to ping up at the H and then quickly fall back down. Car seems to have issues compounded on top of it.

  • My radiator is fine, nothing wrong with it. Im only losing fluids when the car boils over. There is no sign of a leak anywhere and I just took it to a shop for a diagnosis. They could not replicate the overheating so it came back inconclusive. That’s why I’m here now – M.Ty Nov 23 '17 at 6:58
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I have had those symptoms when the water passages in the block were plugged with rust. Of course this means an old iron block, your car has the age ; iron block ? My rust was caused by the radiator cap not sealing. The water that boiled out was brown with rust.

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Try a new, high quality radiator cap. Your system is not pressurizing. If it was pressurized it wouldn't boil, assuming the appropriate thermostat and fluid level.

The pressure is getting out somewhere, you just need to find where. Where does the water come out when it overheats?

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