I recently picked up a 99 f150 4.2l 4x4 and it had ecu codes that were fixed by replacing fuse #23 (o2, cam sensor, egr, etc.) and now for some reason im having cooling problems. the temp level on the dash panel will heat to normal temp.

However, after a few minutes of being stable operating temp it will continue to rise to red triggering the red lamp on the panel. It is not over heating, coolant temps are normal (210 range after a long ride). When this happens I can pull over, kill the engine and the gauge levels out back to normal temp range. Start it back up and it rises again after a few minutes.

This all occurred after replacing fuse #23 and I have no engine codes whatsoever. What should I do?

Thanks,
Randy

 

Before reading all my ideas you might want to search some here. I think I read an old thread on this very same topic.


If the '99 4.2 has two temp sensors (like my '98 E250 4.2), one for the computer and one for the gauge, your trouble may be isolated to the sensor for the computer. It can be checked with a multimeter. One thing you need to check is the resistance between the terminals of the sensor. The other is the voltage from the wiring harness.

I understand that the ECT sensor provides the input to the computer. The CHT is for the gauge only.

As you look at the motor from the grill side looking to the firewall; the ECT (Engine Coolant Temperature) should be to the left and a little higher than the CHT (Cylinder Head Temperature). The sensors are both in the front, on top, and just right of center.
The CHT is easier to get to on my vehicle.

You should clean the terminals and the connectors. I used pipe cleaners and contact cleaner. The pipe cleaners are less likely to bend terminals and the contact cleaner leaves little to no residue after it dries.

Replacing a fuse sometimes is a 'band aid' action. Something other than the fuse failing may be the cause of the burnt fuse. It would be a good idea to check all the circuits fed by that fuse. Wire insulation, connectors, terminals, and the devices on the circuits. Resistance, voltage, and cleaning. I've been using heat shrink tubing instead of tape to repair bad wires. Cut the wire, remove about half in inch or less insulation,
clean, thread the wire through the tube, do a tight 'western union' splice as opposed to a pig tail, solder is best, then bring the heat shrink tube over the splice, and then 'shrink to fit'. Two heat shrinks tubes works very nicely some times, as long as you can get the second over the splice and tube.

 

I should mention that I picked up the vehicle knowing it had problems, I didnt pay but dirt for it and was anticipating putting some decent money into getting her going. In my effort to fix all the other engine codes I traced it to fuse #23 which was absent, by simply adding that fuse all the other engine codes disappeared and this issue started.

I had been using the truck intermittently for the last few weeks including pulling a heavily loaded trailer a few hundred miles with no traces of it overheating or the temp being outside "normal".

Earlier I pulled a sensor from the drivers side rear firewall, it was a temp sensor of some variety but no coolant came out when I pulled it. The ohms dropped as I heated it with a soldering iron however I never tested the circuit as I dont know what voltage range I am looking for.

Any further help would be appreciated.

 

I'm in a similar situation with my E250, I picked it up for $1200 knowing it had some issues. Got used tires for $120 by selling the near new front ones at the same time then sold the shelves and tool box that came with it for $250. so far so good

I found a thread that is similar to your trouble with the OP (original poster) solving his issue by fixing a wiring problem on the trailer light circuits. So you you may have needle in a haystack thing here.

https://www.ford-trucks.com/forums/1...ode-p1299.html


Bad thermostat, air pocket, and other ideas

https://www.ford-trucks.com/forums/4...ode-p1299.html


Here is a good one, it mentions your fuse and gives some other ideas

https://www.ford-trucks.com/forums/6...ple-codes.html

another

https://www.ford-trucks.com/forums/1...mp-sensor.html

 

engine coolant temperature sensor - F150online Forums

Coolant Temperature Sending (CTS) unit on the right it may be a CHT (Cylinder Head Temperature).


Engine Coolant Temperature sensor on the left, I removed mine and got a good spray of coolent


The Haynes seems no better then the Chilton as far as specifically identifying these sensors. What little I know of the on line Motocraft manual indicates it is far superior. I plan to return my Haynes manual and maybe even the OB2 Techbook. Then I will bet the online subscription and then buy the CD manual or paper one from that web site.

 

Ill drag the laptop down to the truck and see what I can find in reference to those posts. Thanks a lot for your help!