Pressure Way Off Towing With One Tire

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techdude99

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When driving my '19 Expedition 4x4 without a trailer, all tire pressures are stable. After attaching my dual axle Featherlite car hauler that's loaded (5000 lbs total weight,) the driver's side rear tire of the Expedition jumps from 39 Psi to 59 Psi. This just started happening after the trailer sat for a year. The trailer tire pressures remain normal.

The brake controller is set to 6 and seems fine. I don't see anything obviously wrong with the disks and drums on the truck and trailer.

I'm leaning toward sticking shoes on the trailer as the cause.

Any troubleshooting suggestions would be appreciated before I start tearing things apart.

Thank you.
 
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JasonH

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If you have one of those infrared guns you can get an instant temperature measurement of the trailer hubs and tire temps after trailering. Elevated temps suggest higher load or insufficient lube. Not sure how you would get the load on one side of the axle. They have scales for that, but most public ones give you total axle, not each side. Maybe measure fender drop on the side that is heating up to see if it's being subjected to higher loads.
 
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techdude99

techdude99

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If you have one of those infrared guns you can get an instant temperature measurement of the trailer hubs and tire temps after trailering. Elevated temps suggest higher load or insufficient lube. Not sure how you would get the load on one side of the axle. They have scales for that, but most public ones give you total axle, not each side. Maybe measure fender drop on the side that is heating up to see if it's being subjected to higher loads.
Thank you. I appreciate the suggestions.
 

Meeker

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I'm having a hard time believing you get that much pressure increase from temperature (it would be very very hot). Do you have TPS on your trailer tires too? Is there a possibility that when you're towing, a sensor on the trailer is interfering with the left rear sensor on the Expedition? Like they have the same code or something?
 

JasonH

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Thank you. I appreciate the suggestions.
One other thing I neglected to mention, direct sunlight will heat tires and change the tire pressure. So if you fill a tire when it's cold out, and ambient temps increase, the tire pressure could indicate much higher than you expect. Even while towing, the side in direct sunlight may show higher temps than the side in the shade.
 
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techdude99

techdude99

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I'm having a hard time believing you get that much pressure increase from temperature (it would be very very hot). Do you have TPS on your trailer tires too? Is there a possibility that when you're towing, a sensor on the trailer is interfering with the left rear sensor on the Expedition? Like they have the same code or something?
No trailer sensors. I do need to get some before heading down to Sebring next week.

One other thing I neglected to mention, direct sunlight will heat tires and change the tire pressure. So if you fill a tire when it's cold out, and ambient temps increase, the tire pressure could indicate much higher than you expect. Even while towing, the side in direct sunlight may show higher temps than the side in the shade.

I've noticed that as well. They the sunny side is always more but I still can't account for the extra pressure in the one tire. I took the truck to Costco and they found a very small pinhole on that tire between the sidewall and the tread that couldn't be fixed. Could it be from too much pressure when it was heating up or a defect?

Since I'm towing the Camaro down to Sebring next week, I swapped my OEM 22" Hankook's over to some new 18" Goodyear's from an F150 takeoff. I'll set them to the max pressure of 51 PSI and do a 20 mile test run with the Camaro on the trailer before I leave to see if there's a change.

Is there a possiblity that the Expedition's stability assist is kicking in too much and overheating that corner?
 

JasonH

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I would say dragging e-brake, but it doesnt seem to happen when unladen. Try the fender drop measurement. If there's substantially more load on one side that would be the first clue.
 

RacerBX1

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Tire pressure will increase/decrease by 1 psi for every 8 to 10 deg F in temperature change. The OP’s saying 20 deg F change, so that would mean a 160 to 200 deg F change in temperature and that is something that would be noticed just walking by. Is the pressure measured from a gauge or the monitor in the vehicle?
 

GlennSullivan

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Certainly Very Strange, especially because of the one side only.
Does this happen when the unloaded trailer is connected or only when the trailer with the car is connected and you drive for awhile?
I assume you are testing with a known accurate tire pressure gauge and not relying on TPS for info.
With the trailer connected, have you verified that the rear wheels of the truck and all trailer wheels spin freely by jacking the back of the truck and each side of the trailer?
You mentioned installing 18" wheels with different tires, does this still occur with this different rear wheel / tire combo (assuming with different TPS)?
 
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