Overheating deamon?

2002 LS V8 3.9 201k miles.

Darndest thing. For the second time in about 4 months, the engine tried to overheat. I quickly turned on the heat to help cool it down and as before, the engine temperature went to back to normal. I tuned the heat off and it drove just fine.

The thermostat and all that plastic housing around it was replaced about 6 months ago. There is plenty of coolant and no leaks.

Thoughts?

Did you happen to notice if the cooling fan was running when the heat gauge indicated high? Did the cylinder head temperature warning come on, or are you going off of just the gauge?

-Rod

Did you happen to notice if the cooling fan was running when the heat gauge indicated high? Did the cylinder head temperature warning come on, or are you going off of just the gauge?

-Rod

Hi Rod,

I am going off the gauge. Im pretty sure the cooling fan was on. It didn't get hot enough to activate the warnings because I heard the hydraulic fans running louder than usual. Then I noticed the gauge just above 3/4 when its usually at 1/2.

2002 LS, 3.9 V8, 230k miles.

Okay, back to this. I replaced the thermostat about two weeks ago. That seemed to calm things down until recently. The running/trying to over heat is back. The aux fans whining alerted me that its starting to run above normal. The temp gauge slightly high. I kept it from overheating by cranking the heat up. It was running warm and I needed gas. It was shut down for a few while pumping gas. On restart, it ran normal. Same situation on a few other instances. so:

*When it starts running warm, just shut it down for a few and it runs normal.
*Whenever its running warm the air blows cold. Prior to that the air is warm.
*The coolant level in the degas bottle is normal.
*No leaks.
*Its been intermittently misfiring as if a coil is going bad but no CEL.
*it's not misfiring and running hot at the same time. No misfires today.
*Cold snap in TX, but its a garage car

I' am sure there is a bubble or two from me replacing the thermostat, but that should not cause this condition... I [did] let it warm up with the filler and degas caps off to bleed out as much air as I could and the heat blew hot. Its been doing fine until recently.

Aux water pump?

Thanks

The blowing cold air when running hot comment sure makes it sound like a trapped air situation.

-Rod

The blowing cold air when running hot comment sure makes it sound like a trapped air situation.

-Rod

Okay, but I have to mention that way before this incident started, I would only get heat when the rpm's were up (i.e. highway operating speeds). when I come to a stop and the rpm's drop, the air would turn cold. I could rev the engine at a stop and the air would start warming.

My recall of the purpose of the Aux pump is to keep warm coolant circulating when the engine is idling, such as at a stoplight, etc. Considering the behavior before the overheating started, it would be reasonable to spend a bit more time troubleshooting the Aux pump to confirm whether or not it is working properly. A thermal imaging camera would be pretty useful for troubleshooting this issue....

-Rod

My recall of the purpose of the Aux pump is to keep warm coolant circulating when the engine is idling, such as at a stoplight, etc. Considering the behavior before the overheating started, it would be reasonable to spend a bit more time troubleshooting the Aux pump to confirm whether or not it is working properly. A thermal imaging camera would be pretty useful for troubleshooting this issue....

-Rod

I took it in and the Aux pump is definitely dead. problem is that they want $280 for the part. The Lincoln dealership want $245. So I am shopping around for a cheaper price.