Overheating 1999 Mercury Mountaineer (Ford Explorer) 5.0L V8

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Imran - 23 May 2006 23:54 GMT

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.

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Fred 2 - 24 May 2006 03:54 GMT

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 think was a
faulty collant gauge sensor or something even on new vehicles. A
coworker had this problem on a new vehicles and the dealer changed a
minor part.

>I have a 99 Mercury Mountaineer 5.0L V8 that recently started
>overheating (or thats what the gauge is telling me). The "Check Gauge"
[quoted text clipped - 16 lines]
>
>Any recommendations of what to try next would be appreciated.

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ross - 24 May 2006 06:59 GMT

>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??

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.

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Imran - 24 May 2006 16:55 GMT

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.

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JohanB - 25 May 2006 03:24 GMT

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.

> I have a 99 Mercury Mountaineer 5.0L V8 that recently started
> overheating (or thats what the gauge is telling me). The "Check Gauge"
[quoted text clipped - 16 lines]
>
> Any recommendations of what to try next would be appreciated.

Reply to this Message