Put a rod across the top of a decent sized pot filled with water. With a straightened paper clip suspend the t-stat down into the water, dont let it contact the bottom of the pan. Grab one of the wifes kitchen thermometers (while she is gone--of course ) and use it to check the water temp as it comes up. Turn on the heat, and as the water temp gets to the t-stat rating, it will (or should) start to open. Run the temp up a little bit to confirm the t-stat is opening all the way.

I have chased that one myself after putting in a new t-stat. Sometimes, they are defective. LOL

 

allright update time ( and the truck still is not right) i just got it back from a rad shop and had the whole system flushed he said it was running fine with good heat in the back and front. i start to take it on the 9 mile ride home and all is going well then all off a suddun the needle goes all the way up to hot and the check eng light comes on and the truck is running like crap. i limp home and pull the code it is 1299 cylnder protecion. and the antfreez is coming out of the degas bottle a little??? what gives with this thing... i did the thermostat test in a pot of water and it works fine could it be a rad?

 

what year is the truck, how many miles....

running no t stat isn't good either. the coolant circulates too fast and doesn't pick up heat out of the block.

why was bars leak stop used? does th fan funtion properly? are the shrouds still in place? do both rad hoses get hot?

i am not a 5.4 guru but ask on the modular forum, but i thought there was a cross connect around the intake maybe it is a problem. sorry for the questions just looking into ideas.

 

I'm thinking you have a head gasket issue causing one or more the cylinders to leak into cooling system, pressuring and gassing it up and thus causing your vehicle to overheat and loose coolant out the degas bottle. I believe your vehicle is running ruff is due to a safety feature on the expedition called Fail Safe Cooling resulting from the gassing up of your cooling system. I'm not sure what year yours is but here's what the owners manual says about it for my 99. I'm thinking this has been your issue all along however flushing your cooling system has made it worse. One thing you might do is take the cap off your degassing bottle and see if your coolant smells like gasoline.

How fail-safe cooling works
If the engine begins to overheat:
the engine coolant temperature
gauge will move to the red (hot)
area.
the oil can symbol will illuminate.
the thermometer symbol will illuminate.
the Service Engine Soon
indicator light will illuminate.
If the engine reaches a preset over-temperature condition, the engine
will automatically switch to alternating cylinder operation. Each disabled
cylinder acts as an air pump and cools the engine.
When this occurs the vehicle will still operate, however:
the engine power will be limited.
the air conditioning system will be disabled.
Continued operation will increase the engine temperature:
the engine will completely shut down.
steering and braking effort will increase.
Once the engine temperature cools, the engine can be re-started. Take
your vehicle to a service facility as soon as possible to minimize engine
damage.
When fail-safe mode is activated
You have limited engine power when in the fail-safe mode, so drive the
vehicle with caution. The vehicle will not be able to maintain high speed
operation and the engine will run rough. Remember that the engine is
capable of completely shutting down automatically to prevent engine
damage, therefore:
1. Pull off the road as soon as safely possible and turn off the engine.
2. Arrange for the vehicle to be taken to a service facility.
3. If this is not possible, wait a short period for the engine to cool.
4. Check the coolant level and replenish if low.
Never remove the coolant reservoir cap while the engine is
running or hot.
5. Re start the engine and take your vehicle to a service facility.
Driving the vehicle without repairing the engine problem
increases the chance of engine damage. Take your vehicle to a
service facility as soon as possible.

If it's determined it is a head gasket as I suspect, here's a product you might try that could possibly save you quite a bit of money if it works. http://www.steelseal.com/ I haven't heard of anyone who's used this stuff yet so I'm not sure how well it works, but they sure make it sound good.

 

remember whe u could just removed the radiator cap and see bubbles and realized you were screwed?

perhaps compression checks could find a leak?

 

Yep, sure do. Life just ain't that simple anymore.

 

the truck is a 98, with the 5.4 the stat is back in and the system has been flushed and refilled. the truck heats up fine when it is in the driveway and light driving around the block but when you go on the big road the temp goes down and no heat then it shoots up and the code 1299 starts. it has me going berzerk!!! i have never had a problem like this

 

i also forgot i put 17 psi on the system for 1 hour and it did not go down theire is no water in the oil or smell or water from the tailpipe ....what gives????

 

Yes it could be a plugged radiator. It also could still be a bad t-stat that sometimes works right, sometimes doesn't. Your water pump could also have a broken impeller fin or two which will reduce the flow and cause high speed overheating but not idle/low speed overheating.

 

i did the water pump also when i did the thremostat and tested the thermo

 

After reading all this, I am beginning to suspect something . I dont know what triggers the 1299 code, or what sensor the PCM reads to determine that code. Somewhere there should be a detailed description of this code.

My suspicion is that it is not really overheating! I dont think you have said anything about symptoms that are overheating. Every vehicle I have ever had that actually overheated, it was obvious that it was by the smell, popping and crackling etc around the engine. Overheating engines blow water---very hot water/steam into the overflow bottle and is very obvious. You said you replaced the TS, so it should be functioning properly.

The PCM reads sensors for its information as well as the guages. On my 93 5.8, (I know you have a 5.4) there are 2 sensors for operating temp, one for the pcm and one for the guage. I replaced one of them because the PCM kept thinking the engine was cold and ran on cold-start all the time (gas was only ~$4 bux a gal ).

The 98 electronics are different, I am sure, but It might not hurt to check your sensors. Maybe you have, because I am totally surprised that anyone would do a scan and not suggest that. I would verify that it is actually running hot or switching to cold randomly. Maybe one more thing to consider anyway--LOL

 

His bottle is overflowing.

 

Yep, I saw that, but he says "a little ???". I was not sure just what he meant by that. Has he filled the radiator full and the overflow bottle full as well then run it until it heats up a little? If so, then a little overflow (through the vent tube) is normal if it is all too full. My question is that if it is really overheating then it should be almost blowing out the bottle----no doubt about it or question marks!! I am not "pickin" on him, just want to know the extent and particulars .

Head gaskets should either steam out the tailpipes or drip to the ground, depending which way its leaking. Either way, the water level will go down rapidly and should create steam--possibly lots of it. I havnt worked on modulars, but I would think a blocked passage in the head or block would make one cylinder run very hot and overheat the whole thing. Again, what does the PCM look at (what/where sensor) to kick that code?

 

(P1299 Cylinder Head Over Temperature Protection Active) Like I mentioned previously this is why your engine is running ruff when it reaches a certain temperature, because it's kicking in your fail safe cooling, which shuts down the firing of 4 cylinders and uses the air in those cylinders to help cool the engine.

 

a infrared temp gun would be usefule to see what's hot and whats not. not to mention they are just fun to play with. we have used them to tune mtorcyles to see that the exhaust temps are the same for carb setup, and spark for a quick way to see if a cylinder dropped out.