Temperature gauge jump
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From: Mesa
Temperature gauge jump
This morning when I got in my 2002 ford ranger 3.0 to goto work I noticed the air was cold and not warming up . I looked at the temperature gauge and it still registered cold like I just turned it on. Then about 5 minutes into driving it jumped to red line and the air inside the cab immediately got hot. The gauge hovered at red line for about 5 seconds then went to normal operating temperature and I did not have a problem the rest of the drive. Is this the thermostat?
Welcome to the forum
No, you have/had air in the system, cold heater is a sign of that
You may have a small coolant leak
Most Rangers use an "Overflow" cooling system, 2002 and up 2.3l used Degas system
When any liquid, like coolant, is heated up it expands in volume, this is where the Pressure in the cooling system comes from, expanding coolant
The radiator cap has TWO valves the larger one with the big spring, and a smaller one in the center, have a look
The larger valve is usually rated for 14psi pressure, as coolant heats up and expands the pressure will get to 15psi, at that time rad cap valve opens and sends hot coolant over to the overflow tank, this should happen every time you run the engine more than 10-15minutes, its normal
Thats why there is a COLD and HOT line on the overflow tank, to mark normal levels
When the engine is shut off the coolant cools down and SHRINKS in volume, when the pressure drops to -1psi, the Center Valve in rad cap is sucked open and coolant from overflow tank is pulled back into the radiator.
This makes the system Self Purging for air, if there was any air in the cooling system it would end up at the top of the radiator(high point), it should be pushed out as coolant expanded over 14psi and when it gets to Overflow tank it will bubble up to the top and be gone.
Thats why overflow hose is always at the bottom of the overflow tank
When engine cools down coolant is sucked back in to replace the air.
If there is a small coolant leak, then engine will lose some coolant yes, but what also happens is that AIR is sucked back in to the engine/radiator from the leak point as engine cools down because it is easier to suck in air than to suck in coolant from the overflow tank.
Could also be bad center valve on rad cap, or plugged overflow tank, these can get debris at the bottom so coolant flows in but can't flow back to rad
Over a few days or weeks more and more air ends up in the cooling system, and it ends up at high points in the engine, heater hoses and heads, also at thermostat
So you get what you describe, temp sender can't "read" hot air so gauge doesn't show warm up, and heater with hot air doesn't work, thermostat doesn't open when it should because hot air doesn't heat it up as fast as hot coolant.
Then when it did open a bit the coolant in the radiator rushed in and water pump could push it into the hot engine areas and thru heater core, temp gauge spikes because it could not "read" hot air but could "read" the hot coolant.
I would top up cold radiatior
And check overflow tank for debris, then fill it to COLD line, exactly
Drive it for a day
when it is COLD again open rad cap and check level, should be at the VERY VERY VERY Top, NO AIR at all
If there is air, then there is a problem
No, you have/had air in the system, cold heater is a sign of that
You may have a small coolant leak
Most Rangers use an "Overflow" cooling system, 2002 and up 2.3l used Degas system
When any liquid, like coolant, is heated up it expands in volume, this is where the Pressure in the cooling system comes from, expanding coolant
The radiator cap has TWO valves the larger one with the big spring, and a smaller one in the center, have a look
The larger valve is usually rated for 14psi pressure, as coolant heats up and expands the pressure will get to 15psi, at that time rad cap valve opens and sends hot coolant over to the overflow tank, this should happen every time you run the engine more than 10-15minutes, its normal
Thats why there is a COLD and HOT line on the overflow tank, to mark normal levels
When the engine is shut off the coolant cools down and SHRINKS in volume, when the pressure drops to -1psi, the Center Valve in rad cap is sucked open and coolant from overflow tank is pulled back into the radiator.
This makes the system Self Purging for air, if there was any air in the cooling system it would end up at the top of the radiator(high point), it should be pushed out as coolant expanded over 14psi and when it gets to Overflow tank it will bubble up to the top and be gone.
Thats why overflow hose is always at the bottom of the overflow tank
When engine cools down coolant is sucked back in to replace the air.
If there is a small coolant leak, then engine will lose some coolant yes, but what also happens is that AIR is sucked back in to the engine/radiator from the leak point as engine cools down because it is easier to suck in air than to suck in coolant from the overflow tank.
Could also be bad center valve on rad cap, or plugged overflow tank, these can get debris at the bottom so coolant flows in but can't flow back to rad
Over a few days or weeks more and more air ends up in the cooling system, and it ends up at high points in the engine, heater hoses and heads, also at thermostat
So you get what you describe, temp sender can't "read" hot air so gauge doesn't show warm up, and heater with hot air doesn't work, thermostat doesn't open when it should because hot air doesn't heat it up as fast as hot coolant.
Then when it did open a bit the coolant in the radiator rushed in and water pump could push it into the hot engine areas and thru heater core, temp gauge spikes because it could not "read" hot air but could "read" the hot coolant.
I would top up cold radiatior
And check overflow tank for debris, then fill it to COLD line, exactly
Drive it for a day
when it is COLD again open rad cap and check level, should be at the VERY VERY VERY Top, NO AIR at all
If there is air, then there is a problem
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