04 RAM 1500 4.7L 4x4 Overheating At Highway Speeds Only
I bought an 04 Ram 1500 w/ 4.7L in November. All was well until recently. The other day outdoor temps reached excess of 80 degrees and my truck overheated on the way home from work. I wasn't paying attention to the gauges, but the "Check Gauges" light and warning bell caught my attention and I noticed the temp gauge just below the RED. I immediately exited the freeway and cranked the heater. The temps came back down to normal in a few minutes.
Normal has always been when the temp gauge needle is just below the half-way mark.
It seems as though this only happens when it is warmer (~70 degrees plus) and at higher speeds (~65mph+).
Driving in town at slower speeds or idling the temp gauge runs at a normal level.
Here is what I have done so far...
- Checked coolant level. OK.
- Replaced thermostat.
- Replaced water pump.
- Checked hoses. Seem to be OK. No leaks or blockage or collapsing..
- Removed radiator and flushed internally with a hose. Flow seemed OK.
- Cleaned radiator exterior of any debris.
- Burped system. (Purged air).
- Ran for 5+ hours with a radiator Super Clean/Flush product.
After all of this it has not overheated to the point that the "Check Gauges" light comes on, but it does run warmer at times (~3/4 mark on the temp gauge). Of course at this point I usually slow down, crank the heater, or pull over to keep it from getting any hotter, so i am not sure if it would truly overheat now.
My next steps will be:
- Checking the new thermostat (in a pan of boiling water with a thermometer to make sure it opens correctly).
- Possibly the fan clutch (although I would think that the air flow caused by the truck moving at 65 mph would be enough)
- Lastly a radiator.
One more side note...I have been running straight water (no antifreeze) due to all of the work I have been doing on it. (Didn;t want to spend a bunch of money on antifreeze, just to drain it later) I know antifreeze/coolant has better thermal transfer than plain water, but I don't think that coolant would keep it from overheating at reasonable temperatures and normal daily driving. Am I wrong inthinking this?
Is there anything that I am missing/overlooking or other words of advice?