Hey all,

Went for a drive last night in the woods and had my first overheating experience with my new/old truck.

Conditions: Unloaded, up and down hills, paved roads under 45mph and a little 2nd gear rough-roading. I wasn't watching the gauge closely so i can't say when it first happened, but at some point the heater wasn't heating and the gauge would jump up nearly to 240 and then drop to about 140. the radiator cap had released at some point - i assume the issues with heat and temp changes are related to air in the system. Coolant was 1.5gallons low when i refilled it today. No puddle under the truck.

Replaced the rad cap, since it's a whopping $7 and refilled with low-silicate fluid.

Ran great again on highway today heading home at 65mph - jumps to ~195 and then drops to ~185 like normal.

First things to check? Fan clutch? T-stat?

Considering a switch to electric fans if the clutch is shot. I understand they don't keep up with towing loads? I don't tow a lot, but there's a once per year trip to the desert (late august too) Denver to Nevada with probably 13k behind the truck. Otherwise, most of my driving is unloaded or with loads that fit on the flatbed. I do tree work, this will hopefully change as the season picks up.

Thoughts? I'm getting 16-18mpg now and any increase would shave a bit off the bottom line at 3.65/gallon when diesel's CHEAP!! I know, I know, I bought a 6 speed 4wd with a **** flatbed. It's no civic, but I'd like to do what i can...

Thanks all!
Charlie

 

Remove and clean the radiator.
You will find, if you look hard, the overflow bottle will leave an oil film and it sucks into the radiator on the drivers side , then dust collects and plugs it.

Very common unless the bottle has been rmoved and a hose run up and over the motor to inside the frame.
your overheating issue though was low collant.

 

Charlie, what are you checking for?
The heater not working and the temp gauge jumping indicates low coolant.
You filled it back up and it's back to normal. 185-195 seems just right to me.
No need for a fan clutch. But, might need to figure out where it's leaking. (water pump or ??)

 

A properly operating thermostatic fan clutch should come on whenever the air temp coming over it from the radiator hits a certain temp. That would benefit towing as well as off roading and traffic jams. That being said if the radiator is clogged with dirt then the air will not flow through it and not activate the fan or if it does the fan cannot pull air through the dirty radiator. Electric fans will never move as much air as the stock fan and when you are pulling hard you need every bit of that airflow. The stock fan when not engaged use very little horsepower, in the tenths, so that will not be affecting your mileage.

Rick

 

Give your current fan a spin by hand when the engine is cool. It should not spin freely, no more than 5 turns. If it spins freely, that indicates that the viscous clutch is not functioning.

This is what j-fox is referring to above. The radiator can get clogged by the oily mist coming out of the puke bottle/crankcase vent tube that is on the front of the engine. The fan circulates that oily mist and it tends to stick on the radiator fins, and attract dirt. This continues until the radiator is clogged and air no longer circulates through it well. It is not easy to tell if the radiator is clogged from the back, they tend to clog at the front like in this picture:

 

I was given to believe that if the rad was plugged with gunk it wouldn't flow right at speed either, is that true? The PO said he had cleaned it out, but based on the quality of other work i've seen from the fellow so far...

I guess i also don't understand how off-roading would ever provide enough air through the radiator to activate the clutch if it relies on that flow.

The fan isn't "locked" at regular operating temp (opened the hood immediately after shutdown) but it doesn't spin freely. It doesn't fully freewheel cold either. I don't ever hear the fan kick in, but this truck is so loud it's not a huge surprise.

@redliner: if there's a leak, it's not making it to the ground. Oil looks like oil, no mayonnaise. The loss of coolant came from overheating last night, there was coolant all over the area of the radiator cap, sprayed up under the hood and on the battery.

Just trying to understand! Sounds like cleaning is the first line of defense. Would a cracked shroud make much difference at low speeds?

 

Generally, the fan clutch engages at idle/slow speeds/stop and go driving. The engine gets warm due to no air flowing thru the radiator. Clutch locks up causing the fan to pull air thru and keep things cool.
Once cool, it goes to free-wheeling again.
At hwy speeds, it mostly free-wheels since air is being forced thru the radiator.
This is "generally". The clutch will lock during extreme conditions also (towing, weather, etc).

The redneck method of checking? With the engine cold, try to wobble the fan blade. It should not be loose and wobbly.
Spin the blade by hand. It should be pretty darn tight. If, when cold, I can reach in and give it spin and the fun turns more than one full revolution? I'd consider that needing another one.
If you are holding a fan clutch in your hand. Look for oil leakage around the shaft. If wet, it's bad.
If it's dry, try to turn the threaded nut by hand. If it's REALLY hard to turn by hand, and it's dry? Good fan clutch.

The only time I ever hear mine engage is. HOT summer time, on the interstate, running 75ish, with the a/c blasting, and pulling anything behind me (boat).
When I start up an incline it sounds like a small jet engine fires up under the hood. Top the hill and it'll get quiet again.

 

The fan clutch never totally disengages.

 

Mine is definitely easily turn-able by hand, though it doesn't revolve freely hot or cold. and I think the issues cropped up while i was off the highway, so maybe i'll do a rad clean (need to install a new condenser for the ac anyhow) and go do a slow drive again and see how he does before i drop a bunch of cash on a fan clutch.