My 98' F150 SC 4x4 5.4L has 193,500 + miles on it. Today we rented a 2900 lb. GWR U-Haul open trailer (5x9) to haul some brush. The temp was 85 degs. and the AC was on MAX. It was down hill all the way to the facility, dumped it off and came back home to get another load. On the flat hwy the engine slowly started loosing power. The transmission started slipping. I looked at the "Edge Evol." I have and it said 208 cyl. head temp. and 109 degs. IAT temp. We then had to climb a step hill and the truck had very little power. Once we got up the hill, I took it out on a level road to cool-it off at 50 mph. The temp. slowly came down but still was slipping.

Strangely the brake pedal also got mushy after picking up the trailer the day before. 2 years ago, all hoses replaced, system was flushed, cleaned and filled 60/40 coolant to water ratio (resp.) for MN winters. It felt humid outside, but the weather says 37 % humidity today. Humidity can't make your engine overheat can it, not in my experience. It's been running great otherwise without the trailer. We pull a 4000 lb. boat with no problems, although it's been 2 years since we've use it. All the fluids are full. Most often we are towing in cool weather here in Northern MN. I always notice a big difference in power when it gets hot out.

Is the engine just tired, sorry for the length here but, what the hell? Opinions please.

 

Im not sure 208 head temp is high. How did the inlet air get to 110 if the ambient is 85 ? Im not sure you have a real problem, but what kind of inlet air system do you have ?

 

Did you check to see if the outside of the rad core might be plugged?
Transmission slipping is not a good thing,is the fluid burnt?

 

To put some guidelines in place; towing like discribed is out of trans lockup.
This will raise the transmission fluid temperature the radiator has to deal with along with coolant temperature.
Add to this the A/C load the radiator will be subject to from the heat generated by the condenser air passing through the radiator.
This could also raise the intake air temp of the intake tube as influenced by the engine bay heat passing through.
208 is not very far out of line if you consider what the thermostat age might be, what the road speed was and condition of the radiator.
No doubt there might be an issue but consider the general operating conditions.
The radiator may be starting to get an accumulation of sludge beginning to restrict flow and reducing total capacity under the total of the towing conditions and the ambient outside air temp.
As the truck ages, things begin to show up.
Good luck.

 

Factory IAT sensor and intake. Inlet air temp sensor is under the hood where heat from the engine affects it until you get moving along. Once the truck gets moving that hot air moves out of the engine compartment lowering the under hood temp. I watch the "Edge Evol" always for my ambient air temp. When it cools down at night (50s-60s) the engine has seemingly twice the power opposed to hot days. Engines love that cool rich air. I wonder if that big difference is a sign of long engine life/high miles?

 

No, I'll check that now. Maybe, with all the rain we've had up here the bug population has sky rocketed, especially the moths.

Tranny newly rebuilt with new converter 2 years ago by a very highly rated shop and by the teacher of the Vocational schools mechanics dept. Has a new "Midwest" torque converter, an upgrade from stock with factory stall speed. I was figuring that the heat in the rad was raising the trans temp and causing viscous slippage in the converter because of higher fluid temp. Fluid not burnt, I had full synthetic fluid installed upon the rebuild. I googled humidity and found that it can aid in the overheating process strangely enough? That was news to me.

 

Good point on the lock up, hadn't thought of that yet.

I installed a newer thermostat (the fail open kind) when I flushed the cooling system and installed a new heater core.

I checked "Rock Auto" quickly and and found the 4x4 s use a 2 row rad. The coolant was down about an inch in the reservoir tank and there are no leaks, topped it off with a little water.

In your experience can high humidity along with high ambient air temps aid in overheating?

I wonder if that high heat under the hood could affect the IAT and lean out the engine making it run hot? I'll double check that bug accumulation on the front of the rad. Up here, there usually isn't a long enough summer to get that much stuck in it bug wise.

 

The higher humidity doesn't affect heating as much as the higher ambient.
High humidity would tend to help cool the cylinders to some small degree.
The IAT is mounted in the intake tube just after to filter so would be subject to engine bay heat especially at lower road speeds when air is not being forced by road speed.
Higher IAT sense would tend to help lean out the total A/F ratio and be part of the loss in power. It's a normal action.
Be sure there is no air trapped from the core replacement job.
I did replace my radiator single core with a 2 core from Rock Auto several years ago just for heavy towing along with a aux trans cooler with it's own cooling fan on it's core.
.
Depending on the gross load, hill incline, road speed, how long pulling in the load situation, and ambient temp., the trans outlet temp can go as high as 260 degrees at the outlet of the converter before it gets to the cooling system coil in the left top side of the core.
I have cooling monitor at the converter outlet to see all this in real time as the load conditions change.
IMO a pan gage is looking at fluid temp after the fact and won't see the but the average pan temp only.
.
Something to think about is the trans fluid temp is still not cooled to far below the cooling system thermostat operating level at any given time.
The AUX cooler after the radiator does the rest of the cooling for the trans.
The average temp drop across most cooling cores is still only about 30 to 45 degrees unless the cooler is huge in area and has a lot of air flow through it.
As fluid returns back to the trans. it still goes to lubing and cooling internal parts before returning back to the pan so it can still pick up more heat at those points.
To close on all this, the PAN; even using a larger pan does not cause the overall fluid temperature to drop a noticeable amount.
What it does do is delay from a cold start the total time the system takes to stabilize to the same temperatures it would normally run at per the load conditions.
The fluid normally an take temps of as high as 280 but if run to lo long and to often that high it begins to break down. With known conditions like that, the fluid should be changed often.
Good luck.

 

My particular model has OE: Rad, Trans cooler, PS cooler, and oil cooler.

Q: Is the OE radiator an aluminum core with plastic ends or a cooper / brass complete unit.

 

Even in Minnesota you sometimes need to cough up for a new radiator. It must have been darned hot under the hood to affect your brake fluid too. Time to at least turkey baster the reservoir out and put in some new dot 3.

 

I'm sure the Rad could be replaced and make a sig. difference in cooling after 14 years of operation. The brake were gone over about 4 years ago and bleed. I may have blown a wheel cylinder but will have to check removing the drums and WC dust caps to see.

I took it out last night to return the trailer once the once the outside temp. cooled down. The engine temp did start to rise a bit going up mild hills while towing. Once the trailer was dropped off the truck ran cool: 194 cht and 72 degs. outside air temp. The accel. pedal was still low on response. Going down a 3rd of the way before acceleration could be felt. When cooler outside, the response is much improved.

 

Update: I drove 30 miles up the hwy for a ride (no trailer) and on the way back, I noticed the CHT was down to 180 and mostly stayed there. Once I got back into town the CHT went back to about 194 with temps in the low 70's. I watched the CHT while driving and it didn't jump suddenly (indicative of a bubble in the cooling system) so I'm thinking it may be a bad thermostat again. If the rad was bad it may not have ran so cool on the hwy. I've seen those water pumps that have literally lost there impellers due to corrosion, and mine is original as far as I know and not leaking so that doesn't seem likely. Could a quality thermostat that I installed have gone bad already in just a few years. It may have been stuck open on the way home when it stayed at 180 degs.

Opinions please:

 

You can't really trust the gage to give accurate temp.
The normal thermostat should run the cooling between 194 and 200.
I had one that ran 185 for I don't know how long because I never looked at it with my monitor setting.
Took it out and everyhting was clean as new but thermo was still operating to low in temp.
Put new in and it now runs 194 to 200.
There is a suttle difference in how the motor ran before and after.
One was a bit more low end torque under the cooler running with extra fuel. After the temp adjustment the torque seemed to move up just a bit.
Next item is improved fuel mileage as the engine is not being fueled as rich with higher cylinder head temp it now runs with the new thermstat.
Good luck.

 

The gauge in question was not the OE temp gage in the dash. It is the "Edge Evolution" gage that's plugged into the PCM under the dash with pod mounted a-top the dash near the window and has been quite accurate in my experience. I installed a new temp sender back 7 years ago, doubt it's that.

 

I don't know maybe I missed your using the monitor.
It should be good.
I use the same one and get a lot of data over the long term with it.
Usually have the spark advance, the instant mpg and average mpg and now the CHT dialed up.
I had been watcing the IAT in place of the CHT and found in very cold winter temps the running IAT temp begins to go different than the upper console temp by some noticable amount indicating one or the other does not track well at very low temps.
While running, the IAT is subject to the cold outside air intake and normally is not very dfferent than the console indicator until below about 20f are encountered.
Btw since you have the monitor notice the next time your driving in OD at light throttle, watch the spark advance.
When you see it go over 35 degrees in sort of a rapid jump, that is the EGR opening when it is supposed to under those conditions.
As soon as you apply more thottle it will pull back into the mid to lower 20s as it's supposed to do.
Good luck.