So I'm having an issue with my 98 4.6 Expedition. Bought it 2 years ago, had 220k on it. Only driven it to 230k so far and started noticing rust in my reservoir. I already had a very slow leak in my radiator so I replaced it myself. No change after a home flush. Changed the water pump (blades were clearly rusted on it) but still no change. The heater core was disconnected when I got it and I haven;t done anything to it. Here's my issue though, the damn thing keeps overheating with the thermostat in it. I've tried 2 different thermostats and the overheating wont stop. Without the thermostat there's no overhearing at all.

Also noticed that the radiator doesn't seem to be hot when the car overheats. Almost as if it isnt getting water with the thermostat in. Not sure what to do. Already purchased new radiator hoses and will put them in today but I'm certain that isn't it since it runs fine without the thermostat (stil rust in water but no overheating)

Any ideas???

 

A blown head gasket can cause the thermostat to not function properly. I have had a blown head gasket in a car and it would cause the temps to go way up then sometimes cool back down. You can checked for exhaust gases in the coolant.

 

My bad, forgot to mention that I tested the exhaust, oil, and even got it a compression test to make sure it didn't have a blown head. Everything is clear.

 

Not to sound insulting, but it sounds like you could be installing the t-stats backwards.

 

I agree with alloro. And same sentiments...

Are you using a Motorcraft t-stat or an aftermarket? One thing I have learned with vehicles is use OEM even if its "X" amount more. I've had 3 aftermarket t-stats fail and seen 2 others on Chrysler/Mopar fail. Always OEM on t-stats and I always put themin boiling water to test before installing.

Also, when engine overheated or gauge shows it does, where is the needle sitting between H and C? Have you used an IR gun and got a temp reading to confirm?

 

No offense taken. Thermostat was installed correctly. Checked to make sure they're working properly. Both were OEM.

agree with alloro. And same sentiments...

Are you using a Motorcraft t-stat or an aftermarket? One thing I have learned with vehicles is use OEM even if its "X" amount more. I've had 3 aftermarket t-stats fail and seen 2 others on Chrysler/Mopar fail. Always OEM on t-stats and I always put themin boiling water to test before installing.

Also, when engine overheated or gauge shows it does, where is the needle sitting between H and C? Have you used an IR gun and got a temp reading to confirm?[/QUOTE]

 

I would try to perform coolant flush, but weather may make it impossible.

 

If radiator is still cool relative to a hot engine, clearly you don't have any coolant circulation. The only thing to really plug this is the thermostat and with rust still in the system, you have more issues to fix.

As also stated, do a complete flush after removing the t-stat. Maybe consider leaving it out if necessary, weather permitting.

 

Agreed do a complete thorough flush of the entire cooling system. Also since you've already got the cooling system open why not replace the heater core. I'll guaranty it's clogged. Also be sure to replace the blend door on the HVAC box while your there. You don't want to do this job twice. I would recommend replacing the heater hose as well. It would be a real shame to do all this work and have one or both of them blow out next week. Then your back at square one. Also I would recommend getting a coolant system vacuum puller if you have access to an air compressor. That way it'll pretty much guaranty that (if used correctly) you won't have an air pocket trapped in the cooling system. As that too will cause an overheat condition. Plus you'll know if you are going to have any leaks in the system before you add the coolant.

 

Paredneck is so right, I bet you have an air pocket that's restricting the coolant flow. I've had so many of those issues with my daughter's Mini, even though it has a air release plug in a high spot on the top rad hose.

It just too easy to avoid.