Hi Guys .. I'm sure it's been said many times before but this forum ROCKS! I've learned soo much from this site.

My problem:

I have a 2003 1500 4.7L and I had an overheating issue last year, so I changed the rad (it was wicked plugged because I was trying to stop a heater core leak in the winter). Since then everything was fine until a few days ago when I was carrying 1200lbs and towing 3500lbs on a 95 Degree day then she started overheating. I probably drove it longer than I should have. Maybe a mile while redlined.
I must mention that I was running 87 fuel with octane boost added at the time. (It earned me 40 miles per tank) Since then I have not used the octane boost.

Today I was towing 3500lbs and it overheated again and again. It was a 90+ Degree day. I disconnected the trailer and waited till she was cold then travelled about one mile then she overheated again.

I have no visable leaks.

Symptoms:
1)While driving hot
a)Irratic idle .. stalls on occaison
b)with heat set to full - cycles from extremely hot air to ambient air and back
c)after cooling enough to add water it errupts when water is added.

2)While cold or idling
a)with temp reading normal - steam venting by rad cap
b)Minor irratic idle .. never quite stalls
c)nearly no cabin heat

Im my opinion my options are .. replace the thermostat (stock 195 but would like a lower temp one if i can find one locally tomorrow)
Replace the water pump - could be gummed up from previous attempt to seal heater core
Replace the fan clutch - I can rotate it with my hand (after engine overheat) very easily with nearly no effort.

In the last couple years I have replaced:
Radiator
Cold air intake
Exhaust manifold (drivers side)
Exhaust (minus converter)
Spark plugs
rad cap (18lbs .. upped from 16lbs)
Serpentine belt

Any .. and all suggestions would be greatly appreciated!!

 

Sounds like it might be a head gasket leak. How fast are you loosing coolant? Is your check engine light coming on when it idles rough?

 

I lose coolant pretty quickly.
Would my oil be sludge if my head gasket was gone and that much coolant was leaking into it? What are the symptoms and result of head gasket leak?
My guess is the thermostat is stuck closed then pops open at critical temp then my rad cant keep up and boils over?!

No engine light unless I redline temp.

 

I hate to say it, but a 4.7 that's been to redline temperature, if it didn't have a head gasket problem that caused the overheat, it has one now.

This is a reliable engine but one thing it can't take is heat! Much above 235* and the coolant gets very acidic, couple that with the fact the coolant lines were engineered WAY to close to the cylinder walls spells trouble with only a mild over-heat. What's redline temp? Like 260*?
Check the gasket, hope that's all it is and it isn't a cracked head(s)...

 

You don't have to have milky oil to determine that your head gasket is toast. All that coolant is going somewhere and unless you find the leak its being used internally. If not in your oil, then out of your exhaust. Do you have excessive white smoke or water burning out of your tailpipe? I hate to say it bro but only 2 or 3 of all the things you describe point to a failed HG, and you have listed just about every symptom except milký oil. Don't drive yourself crazy with this until you get the system pressure tested.

 

Ok, so I need to check compression right? Will that tell me what I need to know?

Back to the cause ... any ideas? What should I start with?
I have the whole day tomorrow to rip it apart if need be.
I'm thinking thermostat for sure .. then what? Pump or clutch .. or both?
Would a head gasket repair solve my issue or is it a result?

 

My rad cap is venting within 15 minutes of engine running .. I'm hoping THAT is where the coolant is going .. on the ground.
I have no smoke from tailpipe.

I am going to run the motor at 2000 rpm in my driveway and observe. Unfortunately I wont be able to work on it for a while after that.

 

I just ran it at 2-3K rpm for 15 minutes before it started leaking .. entirely from the rad cap vent tube .. it was pissing out of it .. maybe 1/2 gallon a minute. I heard a valve (presumably thermostat) open up just before cap started venting. Temperature guage read normal the entire test.

Idled quite well throughout test. Not perfect but didn't drop below 500rpm.

Small amout of white vapour and water from tailpipe when first started, gone within a minute or two.

I also hear a whine .. and a squeek coming from behind the rad.

There is a slight tick from under the front of the truck at idle.

Oil is clean and full. I run synthetic most of the time ... a dash of duralube on occasion. She barely burns any oil. Ounces per oil change.

The fan was easy to rotate by hand and would spin approx 1-2 rotations
When hot (earlier today) the fan was slightly harder to rotate and would only spin 1/2 rotation

Right from startup the 1/4 inch resevoir line from upper rad hose was spewing water into the resevoir and didn't appear to have any air.

 

I drive a 2001 4.7 Dakota @ 124K miles. I overheated towing our trailer, then weeks later it popped a lifter. So we tore the heads off and had them machined. The head gasket was toast! Coolant was leaking into cylinder #3 ,burns off and shows no sign in your oil. Every week I was adding coolant!! One sign was everytime i opened the cap (cold, of course) she would hiss at me like a snake!! Runs like a champ!!. My rear-end differential is gone also--whines more than my ex-wife!!! A junkyard will rebuilt the unit for $650 (warranty ) instead of another yard that has one for $400 used
Since I want to keep my truck I'll take the warranty this time!...So basically for $1300
-including gaskets- heads cost $480- I got me a new truck!!! GOOD LUCK !!

 

If you are overheating and loosing coolant and the oil level is fine and not milky then you are burning the coolant.

As everyone else has indicated, bad head gaskets and common issue