4.0L OHV & SOHC V6 Tech General discussion of 4.0L OHV and SOHC V6 Ford Ranger engines.

Overheating issue

  #1  
Old 12-11-2018
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Overheating issue

I have a 2005 ford ranger 4.0 only has 60,000 on it this morning was going to work and the temperature gauge shot up and coolent light came on so I pulled over opened the hood and coolent was shooting out of the cap on the resivor, you could hear it bubbling in the radiator and then it blew the cap off of the resivor and was pushing coolant out of the radiator cap. Both upper and lower hoses were sucked flat. Could this be the thermostat getting stuck closed. Thermostat houseing was changed maybe 5,000 miles ago
 
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Old 12-11-2018
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Welcome to the forum

Yes, could be thermostat failed, but could be rad cap failed as well

You are running an overflow cooling system
As the coolant in the engine warms up it expands in volume, 1 gallon becomes 1.5gallons
This expansion is what creates the pressure in the cooling system
Rad cap is usually rated at 16psi, so at 17psi it is pushed open and hot coolant flows over to the overflow tank, this happens every time you drive more than 15-20minutes
The hotter the coolant gets the more it expands so the more coolant is sent to overflow tank

When you shut off the engine the coolant cools down, and as is shrinks in volume the pressure in the system drops, if any coolant was sent over to the overflow tank then the pressure will drop to -1psi
In the center of the rad cap is a smaller valve, when pressure gets to -1psi this valve is pulled open and SUCKS coolant from the overflow tank back into the radiator, this keeps the coolant level in the radiator topped up, always.

IF..........the center valve is not working, or overflow tank has debris inside, then coolant can't be sucked back in, so every time you drive there is less and less coolant in the engine, until it overheats.

The sucked flat rad hoses points more to rad cap(overflow tank) issues, but doesn't take thermostat off the table
As pressure in the engine side drops below 0psi and to -1psi then -2psi, ect.......it in essence creates a vacuum in the engine side, if it can't suck in coolant, or air, then the outside air pressure starts to collapse the larger hoses, the rad hoses show it first

Get new rad cap

Drain overflow tank and make sure it is clean inside, then check overflow tank hose to rad cap opening, must be air tight
 

Last edited by RonD; 12-11-2018 at 10:12 AM.
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