Consistent intermittent temperatures spikes.
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Junior Member
Joined: Feb 2020
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From: Idaho
Consistent intermittent temperatures spikes.
I have been having some trouble with my truck for the past year or so and have not be able to figure it out. I have an 03 F150 with the 5.4 Triton in it. Approximately 285,000 miles on it.
I don’t have any performance issues with it, but within the first 15 minutes of driving I have the same thing happen. The A/C will be hot and then just randomly cut out to being ice cold, and the temperature gauge will start to climb. This will happen for about 2-4 minutes depending on the speed at which I am going. The lower the load the slower the climb. It will hit temperatures in the 240° range and then drop back down to 185-190°, at which point the hot air will resume and will be fine the rest of the drive. This doesn’t happen every time I drive but more often then not it is one each trip. I have preformed a flush of the coolant recently and changed the thermostat. On the rare occasion it will boil over and out of the radiator tank. Another detail is it is does have a light foam that builds only while driving but will disappear when the engine sits for a bit. It also has a hint of a gasoline smell to the coolant. I thought at first this was a possible head gasket, so I used one of the leave in systems stop leak treatments to try to get ahead of any possible small leaks or tears in the head gasket. I have checked my oil and it is clean as well other than normal build up on the cap. The dipstick is clean as well as everything else when looking in through the oil cap.
It doesn’t have any issues on longer trips. So I am just kinda lost for ideas at thus point that it could possibly be without having to open up the block and check the head gaskets. Please help?
I don’t have any performance issues with it, but within the first 15 minutes of driving I have the same thing happen. The A/C will be hot and then just randomly cut out to being ice cold, and the temperature gauge will start to climb. This will happen for about 2-4 minutes depending on the speed at which I am going. The lower the load the slower the climb. It will hit temperatures in the 240° range and then drop back down to 185-190°, at which point the hot air will resume and will be fine the rest of the drive. This doesn’t happen every time I drive but more often then not it is one each trip. I have preformed a flush of the coolant recently and changed the thermostat. On the rare occasion it will boil over and out of the radiator tank. Another detail is it is does have a light foam that builds only while driving but will disappear when the engine sits for a bit. It also has a hint of a gasoline smell to the coolant. I thought at first this was a possible head gasket, so I used one of the leave in systems stop leak treatments to try to get ahead of any possible small leaks or tears in the head gasket. I have checked my oil and it is clean as well other than normal build up on the cap. The dipstick is clean as well as everything else when looking in through the oil cap.
It doesn’t have any issues on longer trips. So I am just kinda lost for ideas at thus point that it could possibly be without having to open up the block and check the head gaskets. Please help?
Last edited by JHubner24; Feb 15, 2020 at 11:19 AM. Reason: Adding truck details
Senior Member
Joined: Jul 2004
Posts: 6,200
Likes: 39
From: Easton, Pa.
Some background to keep in mind;
The cylinder head temperature sensor is located in the driver side cylinder head.
It needs to be submerged in coolant full time.
If there is air in the system, that may cause the temp sensor to vary over a wide range.
This sensor signal is fed to the dash and is converted to analogue to drive the dash meter as well as to the computer.
If the computer gets a signal to high in temp., it can trigger the LIMP mode that will get your attention in a hurry from lack of power.
The meter has voltage applied on one side and reads according to the sensor resistance value vs temperature.
The coolant temperature should normally be 195 to 200 degrees, not in the 185 area.
As for your A/C action, the system normally cycles unless the system pressure varies because of a low charge condition because it also has a pressure sensor.
You could have two or more faults at the same time causing confusion.
Temp sensor wiring short to ground, a dash board issue, thermostat too low in temp., A/C issue, climate control issues etc..
Good luck.
The cylinder head temperature sensor is located in the driver side cylinder head.
It needs to be submerged in coolant full time.
If there is air in the system, that may cause the temp sensor to vary over a wide range.
This sensor signal is fed to the dash and is converted to analogue to drive the dash meter as well as to the computer.
If the computer gets a signal to high in temp., it can trigger the LIMP mode that will get your attention in a hurry from lack of power.
The meter has voltage applied on one side and reads according to the sensor resistance value vs temperature.
The coolant temperature should normally be 195 to 200 degrees, not in the 185 area.
As for your A/C action, the system normally cycles unless the system pressure varies because of a low charge condition because it also has a pressure sensor.
You could have two or more faults at the same time causing confusion.
Temp sensor wiring short to ground, a dash board issue, thermostat too low in temp., A/C issue, climate control issues etc..
Good luck.
