98 Sable - Baffling Overheating Problem

This one is a real doozy and I'm going to try to condense this as much as possible.
About three weeks ago, the water pump went out on my '98 Sable. A couple of
the impellers were broken off. The temperature climbed a little, but never got over about 85% of maximum. I shut her down really fast to avoid engine damage. Coolant rolled out of the overflow tank (there is no visible radiator cap on this car, by the way.)
After replacement, everything was fine for a couple of weeks. Then, about 23 miles into my 38.5 mile commute to work, after the temperature had remained steady and normal the whole time, I was going about 70 miles per hour and the temperature slowly started to climb, but not nearly as fast as it did when the water pump went out. I had time to judge what might be happening, but it continued to slowly climb so I pulled into a restaurant and shut it down and lost coolant through the overflow tank.
I checked for blockage of airflow, but didn't see any. I removed the thermostat before driving it home. I made it about as far as I'd come on the way to work, and the temperature climbed again. I had to pull over about 900 yards from the house. The mechanics at the shop found a plastic ice bag between the condenser and radiator where I was unable to see. I would have checked for that myself, but I never imagined anything could blow up into that little space and I would have had to stick my face under the car and look up in there. I would have if I could have imagined, but I just didn't. They pulled that out and installed the new thermostat I'd purchased, then test drove it and sent me on my way. They gave me the bag, too. It had not been melted, so there shouldn't be any plastic clogging the fins of the radiator.
On the way to work that same afternoon, the temperature again remained steady and very normal, then started climbing again, this time about 17 miles into my trip, just like it did when I'd had the ice bag embarrassment: just slowly creeping up. I pulled over again and watched the water roll out of the overflow tank again.
Now at none of these points did the car ever get into the "danger zone" of overheating. At the most, it hit about 85% of the maximum reading on the gauge. My dad taught me well. When it starts overheating, kill it quick!
First, a few key points:
1. The car has approximately 153,000 miles on it, but has been very dependable.
2. This car has never been one to overheat. It's always run just dead on normal, even in heavy traffic and in the hottest part of the day, just right at 45% up the gauge. It's never even hinted at even climbing a single hair over 45%. I even tested it one day by letting it idle on a hot day at 105 with the air conditioner on for 30 minutes and the temperature didn't climb at all.
3. I'll be driving along and the temperature will be normal for 20-25 miles, sometimes more, sometimes less. Then suddenly it'll start climbing. It doesn't go up, then down, then up more then back down, then up even more, then back down. It just starts slowly creeping up and doesn't stop.
4. The engine cools down VERY quickly after it starts getting too warm. The mechanic said that once the temperature climbed, he turned the key off and let it coast for just a bit. He started it back up and the temperature had already returned to normal. And no, the temperature gauge is not malfunctioning. Indeed, when the temperature gauge is up there, there's no mistaking the coolant boiling out onto the ground, or the hot, steamy cloud rolling out from under the hood.
I got it back to the garage and here's what we know so far:
1. It's been flushed and reflushed and reflushed again. The mechanics believe the system is clean.
2. It's been pressure tested and pressure tested again. There are no leaks.
3. The new water pump was replaced with another new water pump.
4. The new thermostat was replaced with another new thermostat.
5. The mechanics say I do not have a blown head gasket.
6. The mechanics say my radiator is not clogged up. (The radiator that's in there now is a new one I had installed back in December of 2003.)
7. The mechanics say my heater core is not clogged up and that the recall work to provide a bypass route around the heater core has already been installed.
8. The mechanics checked to make sure the lower radiator hose was not collapsing.
9. The mechanics say there are no air pockets in the engine.
They're out of ideas. They're now outsourcing opinions on iATN, which is absolutely fine with me. I'm glad they're doing that instead of just telling me they give up. But I haven't worked in a week now because I require my car during working hours. I'm posting here to absorb all possible ideas from those who might have run across this mysterious behavior in a car before, particularly a Ford/Mercury. It doesn't seem to be to be caused by any common problem and everybody involved seems to be at a loss.
Any ideas will be appreciated to no end.
Thanks, Matthew
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On 7/12/04 1:25 PM, in article snipped-for-privacy@4ax.com,

Does it have electric radiator fans? Are they coming on?
Where did the broken impeller blades go from the water pump? If they are still in there somewhere, they could be causing an obstruction.
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a message in news:rec.autos.tech which read:

Wow, I thought I covered everything. Yes, the fans work.

The impellers were recovered. I saw them sitting beside the water pump.
Matthew
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Matthew wrote:

Not sure about which years, but i though some had 2 speed fans As i recall. Maybe its not going on high speed if that's the case? If thats the case, it could be the fan or the IRM (relay module).

I assume the system was pressure tested and a new radiator cap put on? Maybe you should pull the radiator and have it boiled out at the radiator shop and have them inspect it closely.
Bob
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posted a message in posted

Do you think the fans really make a difference when I'm going 70 miles an hour down the highway?

They put a new cap on, yeah. The radiator is fairly new. It was installed in 2003. I've never heard of one stopping up that quickly, but I suppose anything is possible.
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On 7/12/04 6:51 PM, in article snipped-for-privacy@4ax.com,

I wouldn't think so. It wasn't clear (at least not to me) from the earlier posts what your speed is when it overheats. This whole thing is sounding more and more like an obstruction somewhere in the water jacket.

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E. Meyer wrote:

Strange. Is the engine performance dropping off any when this happens? Maybe the engine running lean and then overheating? Changed the fuel filter lately? I would think it would set a code. (have you had the codes scanned ?).
Other off the wall ideas. Collapsing radiator hose? Partially plugged oil pump screen? Have you had the plugs out and do they look normal?
Bob
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Hi Just thought I would let you know that a similar situation happened to me. I found the problem too late to help me. One or two of the ports from the engine block to the head filled with corrosion until it restricted the flow enough to cause the engin to overheat no matter what I did. I found this problem after I pushed it one time too many and lost the motor. I was overly curious so I started to take the motor apart and found the problem. You might mention this to the garage. Mine also flushed fine as the water just flowed through the uncloged waterways.
wrote:

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On 12 Jul 2004 17:51:25 -0700, snipped-for-privacy@adelphia.net (Ford Man) posted a message in news:rec.autos.tech which read:

Did it overheat in the same way I'm describing? Doing fine for about 20 or 30 miles down the highway, then suddenly climbing?

What would the solution have been to clear out the corrosion? Seems like if flushing won't get it out, then I might as well consider it a head gasket job or something since they'd probably have to do some major work to tear it apart and clean out whatever's clogging it. Might as well replace those gaskets while they're at it, huh.
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Matthew wrote:

when the impeller in the old water pump broke; did you get all the old parts out???? if not that might be your problem.. they was floating in the system and blocking the flow??? take the pump off and put the hose in there and blow it out(the pump and the engine) if you cant account for all the broken plastic parts that might be the problem???? did the new pump also break??? on my 96 contour its got the plastic impeller and there was a crack in it and the shaft would turn and the impeller would just stay there and no pump any coolant... all the pieces were inside the pump and never broke away...if it did i would have hunted for all the pieces of plastic.....
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=========Anyone check for exaust in the cooling system? Your first overheat could have caused a head gasket to go....
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news:rec.autos.tech which read:

The head gaskets are fine. The test was done to check for exhaust in the cooling system, and another test was done to check for coolant fumes in the exhaust. Both were negative. And the car never actually overheated. It was headed that way, but I shut it down before it actually happened.
Thanks, matthew
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news:rec.autos.tech which read:

I called in for an update on the situation and of the 15 replies they received from iATN members, 13 of them voted for head gasket problems. They're doing a pressure test for that now. I should know something this afternoon. Good god I hope it's not head gaskets! That's never cheap work.
The only baffling thing is the fact that the oil has no water in it.
Matthew
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posted a message in

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It doesnt have to- to be a head gasket. it could have a small leak from the combution chamber to the cooling system. That would also cause your boiling over without it being "overheated"
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Scott M wrote:

You might want to check this out:
http://www.cartrackers.com/Forums/live/Ford/132.html
Bob
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posted a message in news:rec.autos.tech which read:

Thanks for the link. I'm hoping that maybe they might find the problem now, but if they have to pull the engine to replace all the freeze plugs, that's going to be one hella expensive job.
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Matthew wrote:

Good luck on what ever you have to do. My philosophy is do the cheap stuff first before you move on to the expensive stuff. I am afraid your on the road to expensive stuff. SOmewhere around the mid 90's, they changed something in the 3.0's that caused internal corrosion problems. I am still not quite sure the how and the why of this. It did not seem to affect the earlier ones. If they have to do the freeze plugs, they need to change them all which is an expensive proposition due to access. Pulling the heads is no cheap operation either. Let us know how it all comes out.
Bob
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news:rec.autos.tech which read:

Yeah. My dad corrected me on that. But the shop said after the tests that the head gaskets are okay.
Now they're pulling the freeze plugs to see if there's any gunk built up in there. If those are clean, they're going to pull the radiator. THey would have done the radiator already, but according to their book it's a 6 hour job. When I had the radiator replaced before, they started working on it at around 8:30 or 9:00am. I went and picked it up at 4:10pm and I only had to wait that long because I was waiting for a ride to take me to pick it up.
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Snip>
Thanks,
Hmmm, it seems all bases have been covered already, except - I assume this is an automatic transmission vehicle? If so, a malfunctioning transmission could be what is caiusing overheating of the cooling system. I had the same symptoms with a Dodge I used to have. Never really suspected it as a cause till it started slipping so bad I could feel it. The overheating tranny overheated the trans fluid and since it was cooled through the radiator, it caused the engine coolant to overheat.....fixed the trans, no more overheating.
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