Overheating 1999 Mercury Mountaineer (Ford Explorer) 5.0L V8

I have a 99 Mercury Mountaineer 5.0L V8 that recently started overheating (or thats what the gauge is telling me). The "Check Gauge" light has come on, but turning the heat on seems to make the gauge read cooler.

The radiator is barely warm, but definitely not hot, and no coolant is boiling when it's reading hot. When it's warm, there does seem to be some gurgling around the heater valve - possibly the heater core.

To try to cure this problem, I have changed the coolant and thermostat

- but nothing helped.

To my knowledge I am not leaking any coolant.

When I changed the coolant, I left the radiator cap off to burp the air. When it heated up (and I presume the thermostat opened) coolant sprayed quite violently from the radiator top. I thought coolant level should drop when the stat opens??

Any recommendations of what to try next would be appreciated.

Reply to
Imran
Loading thread data ...

Put an OBD-III scanner on it and scan the sensor readouts while the engine is running and see what the coolant sensor readout is. The coolant sensor for the on board computer is not the same one for the coolant gauge.

I know that some late 90's 5.0 liter had a problem with I th>I have a 99 Mercury Mountaineer 5.0L V8 that recently started

Reply to
Fred 2

I am going to assume your gauge is reporting correctly because of your boilover at idle. Your cooling system should be able to keep up at idle and not spray coolant out the radiator top.

Since you did the thermostat, you could have a radiator problem or a water pump problem (radiator not getting warm).

Drain your new coolant , pull the lower radiator hose off the radiator, stick a garden hose in the top of the radiator, and turn it on pretty hard. Water should flow out the lower hose opening strongly, and should not back up out of the top of the radiator. Backyard mechanic method, but if you are getting a good flow of water thru the radiator, then the rad is good enough not to cause overheating, at least at idle and low speeds.

If the radiator is flowing well, then you may have a more unusual problem where the water pump impeller isn't working, it's free spinning on the water pump shaft. In that case, there is nothing to circulate the hot coolant, the coolant in the engine starts boiling cause it gets superhot, and you get the geyser effect when the thermostat FINALLY gets hot enough to open. So if the radiator tests ok, I would replace the water pump.

Reply to
ross via CarKB.com

The boilover happened when the radiator cap was removed. With the cap on, no boilover occurred.

With the cap off, if I do a fast idle, I notice the coolant level drops in the radiator - which leads me to believe that the water pump is functioning.

Reply to
Imran

How many quarts did you put back in ?

I always loosen heater hose to let the air out when filling it

With the block empty after removing t-stat all you fill is the radiator , not the block.

Reply to
JohanB

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.