Hey everyone,

I have a 2002 3.0 with 186k on it. It's been having this issue for about a year now but it's worsened because of the cold weather. My truck will get up to operating temperature (about 3/8 of the way up on the guage) but it has trouble sustaining this temperature once I get moving.

I was driving today on a long downhill slope with the heat on in the cab. My temp guage dropped below the 1/4 mark until I turned the heat off.

The heat has never been hot since I replaced my radiator a year ago. I also replaced the thermostat and did a core flush at that time. The heat will get pretty warm but not like it used to.

I just did a coolant replacement a week ago after an upper engine rebuild. The thermostat seemed fine when I inspected it during the rebuild. I've also tried to bleed all air out of the system.

The hoses under the hood don't get very hot either. It's like my coolant just can't stay warm unless my truck is under load with no heat on.

Any ideas as to what this could be? I was thinking there might still be air in the system or possibly a weak water pump. I'd love to hear your thoughts!

 

Check the fan clutch

When engine is cold(sat overnight) open the hood and spin the fan, should be hard to spin, called "cold lock"
Start engine(hood open), should hear fan pulling air because its cold locked but that should go away in under 10 seconds, but turn engine off in 20seconds
Spin fan again, should be easy to spin, unlocked
If not replace fan clutch


The fan clutch doesn't pull air thru radiator when it's unlocked or blow much air around engine bay, this allows the engine to heat up much faster
On the front of the fan clutch is a bi-metal spring, this is heated up by RADIATOR HEAT, not engine heat
So as the center of the radiator heats up the fan clutch will slowly start to lock the fan blade to water pump shaft, so fan pulls in and pushes out more air to cool radiator

If outside temp is cold then fan clutch may never lock, no need to
If its broken and locked all the time then over cooling is the result
And it has a "fail safe" mode, which is to LOCK when it fails, so over cooling but NOT over heating, which is "safer", fail safe

Thermostat should be a 190-195degF model, not 180degF

 

Thanks for the info Ron.

I tested it and it seems the clutch is bad. I replaced the fan clutch and water pump while I was at it but now the problem is worse.

The new fan clutch seems to be doing the same thing. It doesn't sound loud like a typical stuck clutch but it never disengages either. No matter what it's always hard to spin. At higher RPMs on the highway my engine Temp drops drastically to near zero. Also, I can't get any cab heat at all now unless I'm idling.

Is it possible the new clutch is also bad? I'm positive I did the install correctly but now my symptoms are even worse than before. Any help is appreciated.

 

TStat stuck open? Or airlock in coolant system?
Park truck pointed uphill or jack up front end,
idle engine with RadiatorCap OFF & Heat MAX until TStat opens to purge air,
then let cool down & top off radiator; may need to do this a couple of times.

 

Yes, new fan clutch can be bad

Cold engine, open hood spin fan, should hardly turn
Start engine, count to 10, turn engine off
Spin fan again, should be easier to turn, if not, new fan clutch is bad, 100% B A D

New used to mean "tested and working"

New now means "YOU TEST IT, we will replace it if it doesn't work"

 

Thanks again for your help, Ron.

I've replaced the fan clutch again, it's still causing the same issue. I know it's disengaging, as I can hear it "calm down" a few seconds after starting the engine. If I try spinning it a few seconds after startup it is easier to spin but it's MAYBE half a turn.

The fan clutch I'm using is from Autozone and is a "heavy duty" clutch. Everything I can find from Advance/AutoZone/NAPA is either Severe or Heavy duty. Should I be using a "standard duty" clutch? I wish I could just use an OEM but I can't seem to find any anywhere online.

My engine will sometimes be at operating temperature, sometimes not, can't figure out why. I'm currently sitting in idle after a long drive and it's sitting at 1/2 of operating temperature, where as it was at full operating temperature before I left. I've done as a much as I can to ensure no air is in the system, so it has to be the clutch considering this worsened issue started after the repair.

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Just coming back and updating old threads with the solution I found.

Essentially, my problem had several causes. A coolant leak in the lower intake manifold was causing coolant to spill into the cylinder. This was causing a large amount of engine cooling lol.

After fixing this issue, I still had almost no heat in the cab but engine would stay around normal operating temperature. I replaced the thermostat with a 192 degree duralast. I also jacked the front of the truck up and ran it with radiator cap off and no-spill coolant funnel attached. After a few minutes of this, heat returned to the cab.

Lastly, I replaced my duralast fan clutch with a used OEM one. The aftermarket fan clutches are hypersensitive and tend to engage before the engine is at full operating temperature. This causes bogging on the engine, lower mpg, and cooler running temperatures. I would not recommend using aftermarket fan clutches. Hope this helps someone.