[Sburn]

Originally Posted by JackandJanet

I monitor the CHT, and, on hot days under normal driving it tends to stay in the 206-208 degree range. If I put the truck under heavy load, climbing a long hill pulling the trailer at higher RPM, I've seen it get to 216. Never higher. The coolant temperature gauge on my dash doesn't change at all, and, it really should be in the 195 degree range. That's what your thermostat is rated at

A CHT of 258 puts the engine into failsafe mode and 310 causes the engine to shut down.

The above sounds very correct. I see pretty much the same temps. Also, assuming a normal 50/50 coolant/water maix and 15 lbs cap, that means stuff starts to boil around 265 degrees. So Ford's failsafe mode at 258 makes sense.

Oil temperature can really bounce around. I've seen it jump to 245 or so under heavy load conditions. Usually, though, it's close to the CHT. The only thing I can find on Ford's recommended oil is that its flash point is 365 degrees. The owner's manual says to change it every 3000 miles or 3 months if used in severe service..

I can't say about this one because 4.6s don't have the oil temp sensor. But from my mecahnical gauge days, oil temp pretty much follows water temp.

According to the New Jersey Forest Fire Service, using f350 and f450 trucks, if transmission fluid is operated at no higher than 175 degrees, it should last about 100,000 miles. Prolonged operation at 195 degrees, it's good for only 50,000 miles. At 240 degrees, it breaks down rapidly, ruining it for further use. Now, our f150's don't use the same transmission, but I'd bet the fluid has similar properties. I've seen the TFT climb to the 210 degree range too, while pulling a trailer up a long hill (torque converter unlocked, in a lower gear and at 3000-4000 RPM).

This also sounds very correct and seems to match Ford's maintenance schedules. "Normal" driving, no load, no tow, my TFT runs no higher than 175. Stop-and-go, or some light towing bumps it up another 20 degrees. So going by Ford's maintenance, I can go 150K miles before changing trans fluid. Add in that towing or stop-and-go, with those extra 20 degrees, puts me into the maint. schedule that says to change fluid at 30K miles.

I've never even thought of looking at intake temps, and have no idea what they should be.

Agreed. No point in watching IAT. Moving at speed, it's close to the ambient. At a stop light, it sucks up the warmer air from under the hood (even drawing from the cooler fender area) and goes up 30+ degrees. So, there's really nothing to be done about it other than as an "FYI".

There, no flames, no snide remarks, just the answers as I know them. And, I'm not an authority! If anyone thinks these numbers are wrong - PLEASE, chime in!

- Jack

It's nice participating in a civil forum...:tiphat: