So, the truck only over heats (doesn't fully overheat, it's just that the needle goes above the 9 Oclock setting on the dash) if I'm sitting still through a long red light or at the drive up teller window at the bank WITH the AC ON and even then it doesn't always reproduce the same results. At all other times under all other conditions the truck operates fine. The radiator (original brass one) was professionally cleaned out (rodded out), new water pump, new resovior and black cap. The only thing that I can think of is changing out the thermostat for the 180F which I will do this weekend. The paper towls hug the radiator like they are supposed to so I know those fans are working correctly. I had to turn the heat on HIGH to get that needle to come back down below 9 Oclock. I will post back once I change out the thermostat.

Thanks

 

1. If you can use a scanner, the OBDII port will provide a more accurate coolant temp signal.

2. 180F is a good idea.

3. Test your viscous fan clutch. When warmed up, engine off, spin fan and release. If it goes one revolution or more that is freewheeling and the clutch is not providing power transfer when hot to send enough power to the fan. Should feel like peanut butter inside.

4. Turning the heat blower on does not add more water to the system, it is flowing inside there always. But it does send some air over the fins of the heater core, and just that little extra cooling is noticed. Which means you have some other reasons for not being cool. At freeway speed the 5280 feet per minute of air flow keeps rad cooler. Parked, you depend on the viscous fan and the electric fans, like 800 feet per minute. Clutch needs to be working well. Sinced rodded out, will assume little or no trash in front of radiator.

 

What about "new" fan clutch? Your overheating at idle is what the viscous coupling is designed to prevent. Yours isn't preventing it......

 

Many thanks for your response's. I did not have time to replace the thermostat but I will try to spin the fan clutch today once I'm home from work and will post back. Does the fact that the temp. does not rise while idling without the AC on have anything to do with the fan clutch not working properly?

 

its dangerous but while the truck is running you can take an old sweatshirt and push it into the fan very lightly. if the fan stops you need a new clutch. like i said it is dangerous so be careful!!!!!!!!!

Moderator note: This is so dangerous in that any fabric you introduce could be snatched by the serpantine belt and then pull your hand into the pulley path. Absolutely do not do this. You can test the fan clutch when truck is not running. At minimum power coupling a working clutch would still transfer 20% of the power. A wimpy fan clutch and a brand new clutch look just alike.

Many companies discipline employees for acts like this that endanger them and co workers. Your finger is worth more than the $60 fan clutch.

 

Maybe related. When you are running at 60 mph, you don't even need the fan, the 5280 feet per minute of airflow will take care of things. When you pull off the highway and idle, you have around 800 feet per minute of air flow from the fan. When you turn on the AC you have two fans that should come on at once and boost that to about 1100 feet per minute (on my truck), but again that is no where near the air flow flying down the road. The AC dumps a lot of heat on the radiator, so you might be just at the edge of what the system can handle, then add more.

The cooling system has a nimber of parts and a weakness can happen in one of more areas.

Easy things to check

Spin big fan when hot, engine off, should coast to a stop in under 1 revolution, ususlly less than that. Should not freewheel. Should feel like peanut butter inside. That is the fan clutch. If it is close to coasting one full turn it is time to swap it, too much fluid inside has been lost.

Electric fans on a D1 should both come on when AC comes on. Since they are electric, they should spin freely when off and spun by a screwdriver or knife blade.

Both big fan and electric fans should blow air toward engine. So they suck a paper towel against the grille on both left and right side. You can test electric fans at position 2 without engine running.

Coolant jug should be full to the midpoint line, and not loose coolant. Cap should be tight. If cap vents top of coolant jug will be wet (until it drys off from underhood heat). Cap can vent while driving down the road (sneaky).

If you remove radiator plug on top (only when cold) and point a flashlight in there you can see part of the top row of tubes. If you see sludge or white calcium, it will be thicker below. A good radiator will measure less than 10F difference top to bottom on the fins, sludge fills the bottom rows first, and they will be cooler. Raditaor can be blocked on the outside with mud and leaves and trash, which won't allow as much air flow, and the fan clutch may not get hot enogh to engage fully. Pull out that top rubber strip between radiator and AC condenser and look for trash.

So the quick check method:

Armed with pocket knife, paper towel, flashlight, rubber band, and adjustable wrench, and the hood is raised, engine off and cold.

1. Remove radiator plug and check inside for calcium. Replace plug if plastic it will break eventually. Refit plug carefully, it is a straight rather than tapered plug.

2. Remove coolant cap and inspect level. Re-tighten cap.

3. Spin electric fans, should spin freely.

4. Spin main fan, should stop in way less than 1 reveloution.

5. Key to position 2, AC on, electric fans should come on, and hold the paper towel to grille on both sides.

6. Turn AC off. Crank truck. Main fan should "roar" as it is fully engaged from cold fluid on one side. As it warms up, roar will decrease. Let truck idle.

7. Pull out rubber strip and look between radiator and condenser for trash. Replace strip, don't need to pull all the way out.

8. Switch off truck after the brief warm up. Spin main fan, should stop in under 1 revolution. Touch radiator fins top and bottom if no IR thermometer available. Bottom should be about same temp, should not be way colder.

9. Wipe grease from hands with paper towel.

10. Rubber band paper towel around coolant cap. Put knife in pocket and adjustable wrench back in the tool bin, flashligt to glovebox or center console. Go for test ride and when stopped remove paper towel to check for wetness.

 

Above 9:00 is a bad sign also. Use a scanner to read real temps. You will note my truck is at 235 while temp gauge is in the "normal" range. Rover gauges are not precise.

 

In the past when I've hooked my autos to an OBDII scanner from the local parts store, I've always done the diagnostic's with the engine off and the key in the "ON" position. I take it that I repeat the same steps to check coolant temps. obviously with engine warm.

 

No, that pix is with engine running. You'll get different readings at idle, underway at 60 mph, etc.

 

ok, sorry for the delay in responding but I"ve been out of town for work. This is where I"m at and what I"ve done. The truck does NOT overheat, needle goes above 9 o'clock then I turn AC off, unless the AC is on High and it's a really hot day and I'm sitting in traffic. All other conditions are ok. I've replaced the thermostat with the 180 degrees one, new coolant, no air in system as it's been bled properly, new water pump, both electric fans come on and suck air through the grill, there is no debris between radiator and condensor, the main fan blade will do almost one full turn by hand with truck warm and off, there is a 10 degrees difference in temp from bottom of the radiator temp and the top radiator temp( exterior heat of 176 vs. 166), new coolant. I've not hooked it up to an OBD scanner yet to check the actual temp of coolant but will do that tomorrow during lunch break with AC on high and hope to get accurate reading. The truck has not overheated yet but am concerned enough to want to fix it. I'll touch base again after my lunch hour when I hook up the OBD scanner to check coolant temp.

thanks for your continued help on this matter.