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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.

Pᴀᴜʟsᴛᴇʀ2
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M.Ty
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3 Answers3

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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.

Lump Coon
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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.

blacksmith37
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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?

Tim Nevins
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