FORD 460 Overheating Mystery

goprolocal wrote:
All the rubber in the engine compartment is intact and directing air through the radiator directly.

Here again is a list of items that have been replaced to diagnose this hot issue.

SYMPTOM:
Rig: 1996-1997 Fleetwood Southwind 35P
Ford 460 engine
I bought it from auction at 23K miles about 5 years ago. I noticed right away that it ran on the hotter side of normal when traveling down the highway at speed over time. This seems to have progressively gotten to be worse over the last 10K miles (rig now has 33K miles on it).

Now, when driving down the freeway with the overdrive off to simulate towing rpm, after about 10-15 minutes at 65mph, the temperature suddenly jumps from 210 to 255 degrees....like within 15 seconds. It will then stay at 255 until we either slow down to city street speeds. If I turn the overdrive on, it will cool to 245 degrees or so.

Driving around town, the rig runs at 210 no problem...even with it being 115 degrees outside here in Arizona. But get on the highway for a bit and she gets hot. The rig has never boiled completely over. It runs excellent, no transmission slipping, engine missing, hard starting, nothing...runs great!

Here is what we've done and tried:

Check for exhaust gases in coolant (nope, not a blown head gasket)
Checked clutch fan blades to be sure they are oriented properly (sucking air from the front to back of the radiator)
Flush block and radiator (some **** came out)
Vacuum filled block and radiator (in case some air pocket?)
Replaced clutch fan (it's oriented correctly and working..I can hear it come on)
Replaced radiator (yes, it's the proper radiator)
Replaced thermostat (3x)
Replaced fuel filter and fuel pump (in case it was running lean)
Replaced spark plugs and wires
Replaced oil and tranny fluid (very small amount of metal shavings in tranny fluid)
Replaced water pump
Replaced radiator hoses (in case it was kinking at high rpm)

It was suggested that possible hot O2 sensors may be causing the rig to run lean under load. Anyone have any insight into this possibility. It has done something like a vapor lock when it was super hot after we pulled off the highway into a gas station...the rig sputtered and died at the pump. I could hear the fuel boiling so I'm pretty sure that was why. After letting it cool for 3 hours, it ran fine again. Just in case, I also opened the fuel cap to rule out a vacuum holding fuel back.

At this point, I don't even know what else to replace or try...maybe an auxiliary electric fan? The other test I think we need to try is a flow test to see that water is circulating properly.

It remains a mystery!
Thank you to everyone for your ideas and input. I don't want to sell this rig but it's looking like that may be the final answer...either that or drive it until it's dead.

Anyone have any input on the long term damage of running it at 255 degrees for 4-6 hour legs?

Goprolocal, you're in too deep to give up on it now. Sounds like a great unit otherwise. You are in Arizona correct? I have a 1997 Winnebago Adventurer 34RQ that I just went through this with. A 460 is a hot runner, but running any V8 big block at a sustained 255 degrees is never ideal and will shorten engine/trans life. I have a few questions:

-What brand radiator was used? The factory one has been discontinued for sometime, and there are more than a few incorrect radiators advertised as correct radiators.
-Do you have a trans temp gauge? If so, what does it read?
-What brand fan clutch was used (model number if possible?)

If your engine is nearing 230F and the fan clutch is not fully engaged, it is not operating properly. The fan (once running) should be able to pull engine temp down fairly quickly (within 60 seconds). The fans on these chassis are quite aggressive, and when they are singing, capable of cooling the rig down quite well. As with radiators for this chassis, there are more wrong fan clutches than right ones.

If you are not boiling over running it hard in the desert at 110+ degrees you are doing pretty good, just not quite good enough.