Overheating Issue Suggestions?

[DirtyDeedsInc]

I have an overheating issue on my '06 GT that's got me stumped. Went for a 150+ mile drive a couple weeks ago. Didn't notice any issues (wasn't looking either so who knows) until I was on my way back after the car had been sitting an hour or so. When I got to highway speed, 70-80MPH, temperature gauge started climbing from straight up (normal 12 o'clock) to high temp. Even set off the high temp idiot light twice. Turned A/C off and heater on and that kept it just out of the red while I was in middle of no where. Once I got to the next town and slowed down to 40MPH, needle came back to normal straight up position. Got through little town, sped up and climbed rapidly to almost red. Stopped and bought a thermostat thinking I'd be changing it on the side of the road. Managed to get home and let the car sit overnight. Next morning changed the thermostat as well as oil and fuel filter just because it was time. Coolant was nice and clean and oil was nice and black, no water in it. Next drive was 28 miles and everything seemed fine. Car sat for 3+ hours and drove home, started overheating on the way. Topped off coolant reservoir and figured it was from burping the air out but it wasn't empty, just very low. After that was just a little bit of local driving with no issues, until I go to airport for work. Before I've made it 20 miles I'm turning off A/C and turning heater on to keep temp out of the red. When RPM drops from 2500 to 2000, gauge goes back to normal. Doesn't climb until I start accelerating to 80. Didn't have time to see if it was low on water again as I got there just in time to check my bag and walk through security.

What I've done or checked so far: Water pump isn't leaking, fans come on sitting at idle, coolant looks good, t-stat has been changed, radiator outside is clean, no water in engine oil or tranny and hoses are Mishimoto silicone. Radiator cap is original but I'm not losing water as far as I can tell and it only overheats between 70-80MPH, cools down some at 60 and gets better the slower I go. I'm guessing pump sucks water from bottom radiator hose and I have not checked to see if it is collapsing somehow. Hoses were put on so long ago that I can't remember if they have a spring inside. No water puddles or coolant smell when sitting at idle. Car has 201k miles on it. It has tried to overheat before but that was from sitting in traffic for hours in August in Houston Texas or Lake Charles Louisiana and cooled down when I got on the highway.

I'm stumped. I figure if it was a blockage it would get hot all the time or at least run hotter than usual. Radiator cap would also keep it hot and I'd be losing water. T-stat is new. Have not seen any leaks in the system. I think if it were the water pump it would either be leaking or doing it all the time. I've changed the water pump on an Expedition with the 4.6 and dread doing it again. I've also done many searches on Google with no luck except for maybe a collapsing hose. Bad sending unit on temperature gauge would probably screw up all the time, not just like I've described. I'm thinking about adding a temperature gauge anyhow though. I've never seen a water pump impeller wear out but I've also never got a car to 200,000+ miles before either, especially being the original owner.

Does ANYONE have ANY ideas on what I've missed or should check next?

I have to go to Houston in 2 weeks for a week and really don't want to break down there or on the way. I'll also only have 2 days to work on it between when I get home and when I leave again. I don't want to drive my truck there as it gets 12-13MPG (6.2L w/4.10 gears) and I'll be too tempted to run over some idiots car. Plus the loud exhaust on my Mustang has woke up drunks that were about to side swipe me in Houston. Thought about driving wife's old MKX but I hate the lack of power in it and gas mileage is less than the Mustang.

 

[Dino Dino Bambino]

What you've described suggests to me that your radiator isn't dissipating enough heat as you increase the load on the engine (higher road speeds). I suggest you drain the coolant, remove the radiator, and do the following:

1. Pressure wash the outside of the radiator to remove any grime that could be stuck between the fins and obstructing airflow.

2. Flush the inside of the radiator with a garden hose until the water comes out clean.

3. Cap off the bottom radiator outlet, fill the radiator with diluted vinegar, and leave it to soak overnight. The acetic acid in the vinegar will strip away any limescale that could be deposited inside, especially if someone added tap water to the cooling system sometime in the past.

4. Flush out the diluted vinegar with the garden hose and reinstall the radiator.

When you refill the cooling system, use only Motorcraft Gold coolant concentrate with distilled water. Leave the cap off the expansion reservoir, start the engine, let it idle, and turn on the heater. This will circulate coolant and evacuate the air. Gently squeeze the upper radiator hose a few times until all the air is evacuated and you no longer see air bubbles inside the reservoir, top it up as required, replace the cap, and go for a drive. After the engine's cooled down for at least four hours, check the coolant level inside the reservoir and top up if necessary.
Hopefully this process will solve your overheating problem.

BTW, replacing the water pump on the 4.6 3V is as easy as it can possibly get. With the drivebelt still in place to prevent the water pump pulley from spinning, remove the four pulley retaining bolts, remove the drivebelt, remove the four water pump retaining bolts, and pull the water pump out. Reinstallation of the new pump is the reverse of the removal procedure. Just make sure the block mating surface is clean, and lightly coat the water pump rubber o ring with clean engine oil to prevent it from galling when you put the pump in the block.

 

[DirtyDeedsInc]

Hadn't thought of vinegar, that's an excellent idea. I have used filtered tap water and I do live in Limestone County so that could be something. Water was coming out clean though when I had a catch pan under it swapping the thermostat. Of course that doesn't mean that the guts don't have scale. Outside of radiator has been washed regularly.

Issue I had with the water pump on that Expedition was that it would not budge no matter what I hit it with. Also nothing to pry against. Ended up pouring cold water on just the pump and that shrunk it enough to knock it off. Wasn't nearly as easy as swapping one on an old Windsor block.

 

[moooosestang]

Is it actually overheating? Do you have a gauge to read head temps or a tuner to log them? It really shouldn't get cooler the slower you go. I mean unless you are doing 80 in 3rd gear the whole way it should run cooler at speed.

 

[RocketcarX]

Is it actually overheating? Do you have a gauge to read head temps or a tuner to log them? It really shouldn't get cooler the slower you go. I mean unless you are doing 80 in 3rd gear the whole way it should run cooler at speed.

This. What does the data from the car indicate?

 

[Midlife Crises]

My first thought is water pump.

 

[moooosestang]

My first thought is water pump.

yeah, maybe the propeller has come loose or just corroded to nothing. would make sense that going faster wouldn't help cool the motor if water flow isn't increasing.

 

[Midlife Crises]

corroded

Yes. The impeller can erode and the clearances increase . The pump becomes less efficient.

 

[Dino Dino Bambino]

Yes. The impeller can erode and the clearances increase. The pump becomes less efficient.

Yeah, an impeller that's been eaten away by severe corrosion certainly wouldn't pump much coolant but that should never happen if you're using the proper coolant mix since it also contains a corrosion inhibitor.
I've changed water pumps four times in my lifetime on other cars I've owned and never seen worn impeller blades. The usual failure mode is worn pump shaft bearings that eventually break through the shaft seal and cause coolant to leak out through the weep hole.

 

[Laga]

Is it actually overheating?

But an engine produces more heat at highway speeds than moving in traffic. My oil temps never approach 210°F in traffic, but will always hit 220°F at 80 mph. This happens in both my pony and pickup. A clogged radiator has the same effect as a bad water pump.

 

[Dino Dino Bambino]

But an engine produces more heat at highway speeds than moving in traffic.

That's true but at highway speeds, there should be more than enough ram airflow through the radiator to keep the engine cool without even needing a fan.
In slow moving traffic and at sustained high engine rpm on a road course, the oil and coolant temperatures will rise. The former situation will be due to reduced ram airflow through the radiator (hence the need for a fan), and the latter will be due to the engine producing more heat.
At highway speeds cruising in a high gear with the engine at low rpm, the oil temperature as well as the coolant temperature should be at its lowest. If the engine overheats in this situation, the commonest cause is either a clogged radiator or an aftermarket radiator of insufficient cooling capacity. A lean air/fuel mixture is another cause but is less common.

 

[RocketcarX]

Yeah, an impeller that's been eaten away by severe corrosion certainly wouldn't pump much coolant but that should never happen if you're using the proper coolant mix since it also contains a corrosion inhibitor.
I've changed water pumps four times in my lifetime on other cars I've owned and never seen worn impeller blades. The usual failure mode is worn pump shaft bearings that eventually break through the shaft seal and cause coolant to leak out through the weep hole.

As a veteran tech I can tell you impeller blade can erode, especially cheap steel ones.

 

[moooosestang]

But an engine produces more heat at highway speeds than moving in traffic. My oil temps never approach 210°F in traffic, but will always hit 220°F at 80 mph. This happens in both my pony and pickup. A clogged radiator has the same effect as a bad water pump.

My head temps would disagree. my head temps are 180F at highway speeds and only creep up to 200f in traffic when the fan kicks on bringing them back down into the 180's. I have a 160deg thermostat and my fan temps have been changed in my tune. I also have 4.10 gears so i'm turning high rpms at 70-80. I have no idea how hot my oil is getting.

 

[DieHarder]

Why you're in there change out the thermostat (cheap troubleshooting step and will eliminate it as an issue). If it's sticking partially open that could contribute to the symptoms you're seeing.

 

[TexasBlownV8]

Why you're in there change out the thermostat (cheap troubleshooting step and will eliminate it as an issue). If it's sticking partially open that could contribute to the symptoms you're seeing.

What about removing the thermostat altogether and test it that way? (Or would this cause issues, at this time of year)

 

[DirtyDeedsInc]

I'd think the water pump impeller being eroded would cause issues no matter what, but I also haven't raised the RPM at low speeds. Transmission is an automatic. Since it's been acting up, I haven't been driving it hard. I may just change the water pump as preemptive maintenance since it's the original anyhow and has 201,000 miles on it. I'll also try distilled vinegar in case of lime deposits in the radiator. Thought about monitoring with a tuner last drive I took but: 1. Tuner was in the trunk and I was in a hurry., 2. Wouldn't the tuner be getting its information from the same sending unit for the factory temp gauge? Radiator is also original factory.

 

[DieHarder]

I'd think the water pump impeller being eroded would cause issues no matter what, but I also haven't raised the RPM at low speeds. Transmission is an automatic. Since it's been acting up, I haven't been driving it hard. I may just change the water pump as preemptive maintenance since it's the original anyhow and has 201,000 miles on it. I'll also try distilled vinegar in case of lime deposits in the radiator. Thought about monitoring with a tuner last drive I took but: 1. Tuner was in the trunk and I was in a hurry., 2. Wouldn't the tuner be getting its information from the same sending unit for the factory temp gauge? Radiator is also original factory.

The sending unit (Cylinder Head Temp - CHT) in a GT is in the passenger head. It's not actually in a water jacket but near one. If you want to read actual water temps you'll have to move it which is what I did during my DOB upgrade or add a standalone gauge/sensor and plumb it into one of the radiator hoses with an adapter (easier - see below).