On my 2000 V10 6.8 with 256,000 miles. Newish to me.

I took it to Colorado hunting a few weeks ago. I live in S California. That's a tad less than 900 miles 1 way. It was just me in the Ex. I had all the seats except the front two out and maybe 1000 lbs of gear. On the steep mountain climbs it would overheat. The temp gauge would climb to red. I either pulled over or slowed way down to a crawl to keep it from getting too hot. I verified with an infrared gun when I pulled over. The thermostat housing read as hot as 230F once. Same temps on the passenger head. Upper hose and radiator read much cooler.

When I pulled over if I let it idle the temp would slowly go back down. I changed the thermostat in CO (seemed like coolant wasnt flowing past thermostat as gun showed much cooler temps in radiator hose.) Same thing happened on the way back. Same cause, symptoms and result of me pulling over and idling to cool off.

Just got a chance to run some diagnostics today. Started by checking the fan. It was hard to spin. It had been sitting for at least a week. Couldn't even get it to spin 1 blade to my hand.

Then used a head gasket tester by putting it on expansion tank. The fluid never changed color after letting it idle for 20 minutes or so. Using the gun the thermostat opened and the top of radiator was reading about 130f when the thermostat housing was at 175-180f. Decided to up the rpms and the top hose collapsed. Then I realized I had the tester in. Put the cap back on in place of tester and it did not collapse. May have been my imagination but it seemed ever so slightly flattened. So it seems no exhaust leaks in head/head gaskets. The fan also spun very fast the entire time the engine was coming up to temperature and I couldn't slow it down with cardboard. It did not sound excessively upon engine shut down either. So it seems the clutch is good.

Per the receipts from the PO the water pump was replaced about 1000 miles ago (due to an overheating problem.) I drove it about 600 miles before taking it on the trip and it never came close to overheating. Did one 3 mile steep climb up a pass during that time but honestly wasnt watching the gauge. Did look at it later on the drive (after the climb and the road had flattened out) and it was normal. It seems coolant is circulating per readings on infrared gun.

One note on mechanics reciept said there was some gunk in the pump and hoses so they changed them. This got me thinking perhaps the radiator is clogged. I will likely pull it tomorrow and try to flush it with a garden hose and see if water/air can pass through the fins.

Anything else to check that I'm missing? It only overheats on the climbs. Flat ground it was not over heating.

 

I would suspect bad fan clutch, water pump and radiator. The downside to these is the genuine parts are the best parts with the minor exception being the radiator. The clutch fan most likely isn't pulling, I know you said it's hard to turn but does it pull air? Also the water pump if it's an aftermarket with the non oem shaped impeller you aren't going to move water correctly.

 

Thank you for the reply. I'm curious as to what symptoms led you to suspect all 3? I'm not trying to argue or disagree just trying to learn what led you to that conusion.

The fan moves lots of air. I recall even when it was pulled over from overheating feeling a lot of air blowing on the engine. I couldn't tell if it was pulling air through the radiator.

There is a large difference in water pumps? I hadn't heard that before. I'd suspect it was not an OEM pump as the work was not done at a dealer.

 

 

The fan seems to always be on. And yes it is loud.

The condenser is pretty full of bugs. A lot of the fins are not straight. When I pull the radiator I'll try my best to clean it out and check for air flow through it.

 

 

Those combs are for plate fin coils only. If your condenser coil is that bad, best to replace it as it's probably blocking too much air flow to the radiator.

 

Mine was doing the same thing. My fan was moving what I thought was lots of air and it was also hard to turn but I never heard it actually cycle in a hard pull. I bought a cheap replacement...don't do that...that never unlocks but it completely solved the cooling issues. In a hard pull, turning 3000 or more rpm, that fan should be obnoxiously loud when it cycles on. If you aren't hearing that, it's not working correctly. My engine temp was hitting 230°+ and my transmission 215° pulling my 10k camper up Fort Mountain in Chatsworth, Ga. After changing out the clutch, I topped the same mountain at 206° engine temp and 190° transmission temp. A better quality fan clutch is on its way here now.

 

 

Thanks. It may be my issue.

Should the fan always spin? I believe mine is.

I'm going to try and eliminate all other options first. If the air flow and coolant flow checks out for the radiator and condenser I dont have much left as an option causing the overheating.

 

Typically a clutch fan will spin by hand when cold and will lock up when hot, it will spin with the engine all the time but when cold/warm it will spin in a semi-freewheel mode at lower RPMs than the engine. That freewheeling when not needed for max cooling draws a lot less power to be supplied by the engine.
Damaged, flattened, mud/dirt caked or bug fouled fins can seriously reduce the ability of an otherwise healthy cooling system to keep the engine temps under control.

 

Check out this Youtube video for an explanation, if somewhat over simplified, of how a viscous fan clutch operates.

 

I ordered this one on Amazon. Should be here by tonight.

 

Thanks for the fan explanations and video. It seems mine is not operating properly. I'm still going to clean the radiator and condenser first.

 

I drained the coolant and pulled the radiator. I also straightened lots of fins on the condenser. The condenser was in better shape than I first thought. It was just covered in insects from the long trip.

I flushed the radiator. There was some brown film in the top and bottom black part. But water flowed freely through it. It is definitely not the original radiator.

I also cleaned out the fins with a hose spray from the back on both the radiator and the condenser. Nothing too bad.

I guess it's time to change the fan clutch. I'm about to order a Motorcraft unit from Rock Auto unless someone steers me different?