Forget about the coolant issue for now. My radiator leaks and I fill it with at least a quart every few days. Low coolant will not throw a code but a bad sensor will. You MUST check your codes.

 

As long as it's a coolant leak outside the block, and not under the heads, that's the least of your problems. A small leak like that may indeed be hard to find. It'll take a cooling system pressure test to find it. There used to be radiator caps with Schrader valves on top which would allow you to pump the system up with a bicycle pump. These apparently were removed from the market because too many people were damaging heater cores and radiators by not paying attention to the pressure they were putting on the system. Anyone could see where this might be a problem for vehicles still under warranty. There are pressure testers available, but they're a little pricey. I was close to buying one until I found a pin hole in a bypass hose on my old T-Bird. So, as far as your leak is concerned, it's small, and will take some time to find, short of replacing ALL hoses to make sure it isn't a pin hole in rubber somewhere.

Now, as for the CEL, the ECM has detected something is wrong. If you're not burning a horrible amount of fuel, it probably isn't the ECT (Engine Coolant Temperature) sensor. These normally cause "limp mode" when they fail, and the ECM will dump ENORMOUS amounts of fuel in the engine, and retard the timing, because it has no idea how hot the engine is. Dumping in the extra fuel will keep it running cooler because of richer, less complete, combustion. Retarding the timing will also keep it running cooler. This keeps the the truck running until you can get it home or to a service center. You didn't say anything about abnormally low fuel mileage (4-6 mpg on a 5.0) so we'll move on to another possibility.

If there's a delay from the time you start the engine, say 10 minutes or about 5-6 miles, chances are the O2 sensor is telling you the mix is lean or the O2 Sensor is no longer switching. Not switching does not necessarily mean that the O2 sensor is bad. Not switching could mean either constantly lean or rich exhaust. Typically, for the price, most replace the O2 sensor if that's the code the ECM is throwing.

Another code that will be delayed would be an EGR/EVP code. The EGR is not opened until the engine is warm, above idle, and vehicle moving. It is for economy at cruising speed and emissions reduction. When the ECM tells the EGR to open, there is a sensor on that which gives a feedback to the ECM to let it know that it did indeed open. If that signal (EVP [EGR Valve Position]) does not follow the command, the ECM will turn on the CEL. If it is because the valve is actually stuck and not moving, this will result in reduced economy, or surging idle, or even random miss and rough idle. You may even get some pinging due to lean conditions, which will also cause an O2 not switching code.

Most any other code that will turn on the CEL and keep it on usually results in a very poorly running engine, if it will run at all. In your first post, you said the truck is running fine, so chances are you have codes for EGR, O2, or maybe ACT (Air Charge Temperature). The ACT is down on the manifold in the #5 intake runner (front right facing the front of the truck) and sends the air temperature in the intake to the ECM. This allows the ECM to compensate for air density based on temperature, as well as vacuum level (MAP).

You've been told repeatedly to pull codes, and I'll simply re-iterate that we won't be able to give you a direct answer without the code(s) that is causing the latched CEL. I'm sure you have a paper clip readily accessible. You have time to come in here and read, so that means you have time to go to www.fordfuelinjection.com and read. You're travelling home from school, so that means you have a warm engine when you get home. It'll take all of 15 minutes of your busy schedule to pull the codes. You get off work some time after school, and go back home to sleep. I don't think missing 15 minutes one night is going to hurt you if you're young enough to still be in school. Besides that, the first test is done without the engine even running, so it ain't like you've gotta drive to do the testing. Most of it, you do sitting in the driver's seat.

So, again, pull the codes, then we can help you. We could all guess from now on, and have you replace one sensor at a time at great expense to you, and much frustration to us. Or, you could take 15 minutes, pull the codes, and we can give you educated recommendations on what to target first with some educated information.

 

Old_Paint, thanks for the info

The whole code thing, i really dont have time, it sucks. Do i need to get the codes when the light is ON? or will it show when its not on?

Oh, and im posting and reading IN school lol, cant exactly walk outside and work on my truck

 

When the light comes up, it stores the code in your computer until the next time you clear out the codes, so you can check them ANYTIME before you clear the codes (lose power to the truck for several minutes).

 

Good to know, thats what i wasnt sure about, cause it wont come on until about 20 mins of driving or so

 

go to fordfuelinjection.com there is a whole article on how to pull codes and a seperate list of what each possible code is...its very simple to do...the hardest thing is me being impatent and not wanted to sit through the codes and count...but really 5 mins it not bad to have a good running truck...

 

just get a code reader. they're like 30 bucks. and i'd change the o2 sensor. i bet that will clear that light.

 

where can you buy the code readers? its NOT OBDII

 

you can get them at any auto parts stores... all OBD I testers are the same just make sure it says ford...they do the exact same thing as a paper clip...the only difference is they beep each time it blinks as well...instead of just flashing...

So IMO the testers are worthless....I bought one and dont even use it...

 

Y'know for $30 you can get a tester that reads out the codes on a display, instead of a flashing light/beeping noise... Thats what I got at Kragen, best $30 I ever spent.

http://www.partsamerica.com/ProductDetail.aspx?MfrCode=EQU&MfrPartNumber=3145& CategoryCode=3389

 

nice...i dont have a krager anywhere near here (Naples, SW FL)...I went to discount/advanced and autozone both had the exact same orange POS model so I picked it up....useless...one that actually displays the codes would be nice!!! I might go to kragers website and see what I can find....I need a reader that can read both OBD I for my 95 and OBDII for my 01...I heard that certain models can actually test transmissions and other various parts??? Is this true...I think the Snap-On one was one of them...I saw it in another tread about testing the tranny...

 

http://www.iequus.com/product_info.php?product_id=3140

OBD1 and 2, covers all powertrain and emissions, no ABS or SRS though. NAPA number 700-2541 on sale at $379.00. On backorder per the website.

 

....or you could use a piece of wire and take the 30$ and buy a case of beer!
Itch

BTW....Great post Old_Paint. I think it would take me twice as long to type that out, than it would to pull the codes!

 

My thoughts exactly....maybe even more than one case!

 

x2 on Old Paint's post.

Beer is good, and if you're staring down a $300-plus all-singing, all-dancing code reader, I'd be tempted. I'd certainly resort to a paper clip and a pencil.

But $30? If invested in quick and easy access to codes (I found one at Murray's Discount) that 30 bucks will do good things for you not just now, but for a lot longer than a whole case of premium beer. A well cared for truck will run a long time. Remember you only rent beer...