My Explorer overheated yesterday. Found a very loud hissing sound coming out from under the hood. Let it cool off filled it with antifreeze, started it up, started hissing again. Found the thermostat had broken. Replaced the thermostat. Filled it up again. After replacing the thermostat I found out the hissing sound was coming from the plastic thermostat housing. Replaced the housing. Again I refilled it with antifreeze. Started to let it warm up and noticed liquid dripping out of the exhaust pipe. Checked it out. Had a green color to it. Then I noticed the coolant resivor was full up to the cap. I did not fill it up past the full line on the side of the resistor. Tried removing the cap. Found out it had a ton of pressure under it. Bled off the pressure. Refilled it again. Did not put the cap back on. Tried starting it. Instantaneous geyser. Runs like it is missing on 1cylinder. No oil in the coolant that I can see. No coolant in the oil. Could this problem be caused by a blown head gasket of a crack in 1 of the heads or in the block? Any help would be greatly appreciated.

Thanks
Ralph

 

That motor has aluminum heads and an iron block, right? Could be a warped head, cracked head or bad head gasket. A cracked block seems less likely. There was probably still some water in the block since the leak was up high, whereas the heads may not have had much, if any water, in them. Pulling plugs should give you an idea which cylinder is having the problem.

Short of removing the heads and inspecting, I'm not sure how you would know exactly what the issue is. Even if it's just the gasket, the head flatness needs to be checked at the very least. When I come across problems like this, I like to be thorough to make sure I only have to do the job once so I would inspect everything.

 

Found out I was right. Blown head gasket. Dealerships mechanic asked me how long I had been driving it with a blown head gasket. Told it it got hot on Friday and shut down on it own. Replaced the plastic thermostat housing. And then it would not run correctly. Got it towed to the dealership to get it looked at and have them fix the problem. 3 days later the mechanic called and it was a blown head gasket. He said it was probably driven over a thousand miles with a head gasket that was progressively going out. Didn't know head gaskets could take that long to go bad. they say it toasted the motor. So this week they are putting a new motor in it. Lucky me.