05 Freestar overheats only when heater on high

[BrunoWilimek]

I am helping out my former service manager with this concern. he now works at the other Ford dealer in town and has a customer with this problem. He called me when he had exhausted all his technicians ideas, as he knows I spen a lot of time on the pro-tech website. The Freestar has about 70,000km(40,000 miles) on it. Since hitting a deer and having the condensor replaced, it has this weird symptom. Only with the heater on full blast, the temperature guage momentarily climbs into the hot zone and then drops back down. This has been verified in the shop. ECT bears out the temperature is actually climbing. Thermostat and temp sensor have been replaced. All heat exchangers have been checked for obstructions and cleaned out as necessary. If heater is turned down to a more normal setting, this problem does not occur. Hotline is no help. Temperature PID shows around 240 F when problem occurs. The Service Manager wonders if the heater is drawing so much heat from the engine at maximum that it causes the thermostat to close prematurely, causing this symptom. Any thoughts on that, or any similar experiences? /forums/images/%%GRAEMLIN_URL%%/scratchhead.gif

[Bruce Amacker]

the temperature guage momentarily climbs into the hot zone and then drops back down. This has been verified in the shop. ECT bears out the temperature is actually climbing.

I can't comment for sure, but on a smallblock Chevy with a blocked heater core or plugged heater hose passages, this will happen. Does the heater work to it's fullest? Is there a water control valve in the system? I'd be looking at flow through the heater core. Without it, the coolant flow does not circulate properly and the stat gets cold pockets behind it, causing this exact symptom.

 

Was the cooling system bled with a vacuum bleeder? Air pockets could also cause this.

 

Good Luck!

 

/forums/images/%%GRAEMLIN_URL%%/grin.gif

[BrunoWilimek]

Thanks, Bruce. I have read your reply to Mike(our old S.M.) and he is going to check those things out. /forums/images/%%GRAEMLIN_URL%%/thumbup.gif

[BrunoWilimek]

I did some looking on the inford website and found a previous posting on the same concern. A dealer in New Brunswick had 2 Freestars doing the same thing and hotline was no help and he replaced the same parts as Mike's shop. Another tech posted a reply stating that the CHT sensor was mounted in a hot spot on the cylinder head and hotline told them to move it to a different hole(must have been a smarter hotline guy). The first tech tried it and it worked. Who woulda thunk it? /forums/images/%%GRAEMLIN_URL%%/cheers.gif

[rgarver]

I had a 04 freestar that would go to 250 degrees or more on scanner above 70mph, below 70 it was ok. Dash gauge would also go to hot which was customer complaint,but van never showed signs of overheating. Hotline had me replacing thermostats,cylinder heads and the fix was to move CHT sensor to rear cylinder head. No one at hotline could give me a good explaiation of why it read so hot in the front head and why it didn't become a problem until 40k miles.(just out of warranty)