Overheating 4.6L

[saefjordan]

Hi Guys:

I have a 2007 ST Limited 4.6L V8 with 77k on the clock. This past Saturday I was driving it down I-696 in about 90 Degree weather when it started to overheat. I had the A/C ON and was going about 75 mph when I noticed it. I quickly slowed down and turned the air off and the HEAT on high to try to cool it down a little and eventually it did. Temp dropped down and I continued to drive it only a couple miles further but I noticed the Fan was engaged the whole time.

When I drove it home on the same route, I noticed that I didn't overheat again but when I turned the A/C it did the same thing after 5 minutes. Once I shut it off it actually made it home without the fan running or it overheating though the outside temperature had dropped 20 degrees due to heavy rain. I checked the coolant level when it was cold and the reservoir was EMPTY! I replaced it with 50/50 blend coolant to the FULL COLD line, and started it up. Ran it for 10 minutes, and then another 10 minutes with the A/C on. Underneath the vehicle I can find NO SIGN OF LEAKS. A week before this I drove the vehicle 500 miles over two days.

I did replace the thermostat about 2 months ago with an Advanced Auto Parts Generic Brand Thermostat rated for 195 Degrees. I did overheat once right before I changed it. (the reason for changing it)

1. So, where did my coolant go? I didn't lose much when I changed the thermostat.

2. If it is a head gasket, what are the signs I should be looking for?

3. Is there any way it could be leaking when I am driving and not just parked? Ie, does the coolant flow through the transmission in a way that it wouldn't leak unless I'm driving?

4. Why would this be overheating when the A/C is on?

Any help is truly appreciated. Thanks.

 

[88racing]

Do you have efans or a fan of clutch?

Check the radiator+condenser fins for bugs and crud....make sure they're clean

 

[stylin99]

I had the same thermostat failure last week. Overheated sitting in a parking lot. Luckily I noticed before it boiled over. CHanged the thermostat and its fine now.

You may have been boiling the coolant out of it when you were beginning to overheat with a bad thermostat, and then it just got worse from there. You will probably see some coolant stains where it boiled over. Just refill it and check for a couple weeks religiously and make sure its not leaking or spewing out somewhere.

Overheating an engine repeatedly is never a good thing. If it was doing it at highway speeds, you really must have puked all the coolant out of it!

Does the truck run ok with correct coolant level? The only other possibility is that you're leaking internally into the engine, which would be obvoius, by lots of white smoke, or drastically reduced power levels. It would be rare for this on a newer Sport Trac, but not ruling it out.

Update: and it overheats with a/c on because its an accessory that's drawing energy from the engine when the a/c clutch kicks on. Making the engine work harder, creates more heat. With the A/C clutch off (such as at wide open throttle), it doesn't drag any at all on the power level of the engine, or make it work any harder.

 

[BigV]

It could be ur fan it has two speeds one is high for when the ac is on if it isn't on high it may have caused it to overheat. When the head gasket goes the coolant goes to either the oil or exhaust. Check ur oil if its a caramel color its in the oil if you see white smoke from exhaust its in the exhaust. I am willing to bet it ovetheated and pushed out the cap while u were driving.