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Discussion Starter #1
Hi guys,

New to the site. Looks fun here.

Here's the deal with my focus:

It overheats, but only when driven hard, or at high speeds. (75 mph) My wife was running late to work this morning, drove 75, and lo and behold, it overheated. Now the details:

It's a 2000 ZTS Zetec

I just replaced the coolant last week (largely because of this problem)

On long trips, I have noticed that sometimes the coolant boils over and escapes out of the resevoir, usually when stopped at a rest stop or something of that nature.

The heat barely works. You get enough to keep from freezing, but not exactly hot, and only if you put it on "recirculate."

6 months ago, I replaced the resevoir/cap.

My guess at this point is the water pump. I just wanted to get some input before doing that job.

Any help would be greatly appreciated!
 

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... I have noticed that sometimes the coolant boils over and escapes out of the resevoir,
My first guess is not the water pump.

My first guess is the new reservoir tank and/or the cap is not holding the required/normal pressure. A failure of the tank/cap can cause the coolant to boil.

My second guess is that the thermostat is not opening enough. You might consider replacing the t-stat with one that is temperature rated for your engine.

Coolant systems often get abused by some car owners when a problem arises; water is added or an incorrect type of coolant is mixed in.

When the car gets to normal operating temperature, you can grab the upper radiator hose and feel the Very Hot coolant running thru the hose. If you do not feel the Heat, my guess is bad T-stat. Water pumps do fail, but T-stat is more common and should be ruled out/replaced before the pump.
 

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Discussion Starter #3
My first guess is not the water pump.

My first guess is the new reservoir tank and/or the cap is not holding the required/normal pressure. A failure of the tank/cap can cause the coolant to boil.

My second guess is that the thermostat is not opening enough. You might consider replacing the t-stat with one that is temperature rated for your engine.

Coolant systems often get abused by some car owners when a problem arises; water is added or an incorrect type of coolant is mixed in.

When the car gets to normal operating temperature, you can grab the upper radiator hose and feel the Very Hot coolant running thru the hose. If you do not feel the Heat, my guess is bad T-stat. Water pumps do fail, but T-stat is more common and should be ruled out/replaced before the pump.
Thanks for the input! Is there a way to test the resevoir cap? It does look different than the old one - which, of course, I no longer have. I bought it brand new only 6 months or so ago...
 

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Is there a way to test the resevoir cap?
Not that I know of.

Put the suspect bad cap on another Focus [headbang]

Also, these plastic tanks usually fail after about 10 years. Mine was replaced just before I bought the car (it was 8 years old at the time). Did you replace it with a motorcraft/OEM part or with an aftermarket one? If aftermarket = higher chances of defective part.
 

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Discussion Starter #5
Not that I know of.

Put the suspect bad cap on another Focus [headbang]

Also, these plastic tanks usually fail after about 10 years. Mine was replaced just before I bought the car (it was 8 years old at the time). Did you replace it with a motorcraft/OEM part or with an aftermarket one? If aftermarket = higher chances of defective part.
Whatever they had at autozone. So yeah probably aftermarket. But it came with its own cap so you would think it would work ok.
 

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Likely a Dorman brand, and Autozone is great with lifetime warranty stuff, so if you have the receipt or phone number used when bought, they will exchange it. Call them and ask.

Lets pretend your T-stat is original so; just replace it... and call it preventative maintenance or call it fixing your overheat problem... or call it a waste of time and money. I call it fun.
 

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Get car good and hot and then let it sit for five minutes and then unscrew reservoir cap, you should get the hiss or pop that shows pressure still there, if not something is leaking pressure down. As good a cap test as anything else.

The caps can harden the seal to make hand tight not enough, I've had one where you had to very slightly overtighten the cap with pliers to seal it up right, but as long as that done cap working fine for years. I found it while working on car one day and heard the slight whistle of steam leaking after car sat for maybe ten minutes.
 

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Discussion Starter #9
Likely a Dorman brand, and Autozone is great with lifetime warranty stuff, so if you have the receipt or phone number used when bought, they will exchange it. Call them and ask.

Lets pretend your T-stat is original so; just replace it... and call it preventative maintenance or call it fixing your overheat problem... or call it a waste of time and money. I call it fun.
Good idea! It's original as far as I know. To be honest, I should probably do the timing belt/water pump anyway, since I have no idea when/if the previous owner ever did it.
 

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Get car good and hot and then let it sit for five minutes and then unscrew reservoir cap, you should get the hiss or pop that shows pressure still there, if not something is leaking pressure down. As good a cap test as anything else.

The caps can harden the seal to make hand tight not enough, I've had one where you had to very slightly overtighten the cap with pliers to seal it up right, but as long as that done cap working fine for years. I found it while working on car one day and heard the slight whistle of steam leaking after car sat for maybe ten minutes.
Yeah it just spins right off. However, I checked the coolant again yesterday and realized it was low. I then remembered that I never made sure to get all the air out of the system. So that's probably part of the problem. Obviously there's more going on there since the heat only sort of works.
 

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Zetecs self bleed and quick if you have all hoses in place properly. They are made specifically to do it, why all he extra hoses. The stat can be put in wrong to make them stack up air though. The small hole in stat outer periphery must be facing straight up to match the bleed hose port in the cover.
 
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