what is the behavior of a bad thermostat? How hot would a 4.6 get at idle with a bad TStat?

Would the fan system keep it under 230 (at idle after stop and go city driving) for instance in a 65 degree ambient environment?

I realize temps in the 220 range are high but everything (including tstat) being new or recently working correctly would the themo being bad out of the box alone cause temps to this point but no higher with no movement of analog gauge in cockpit, no sign of overheating, no waterfall noise.

I've tried the usual bleed methods, cold raising reservoir and opening bleed screw then re inserting bleed screw when steady stream is flowing out. Heater on full lowers temp to 208 at idle. repeated bleeding leads to no further gain in lowering temps. and again no waterfall.

Would you say bad new stat out of box or more bleeding required?

 

Have you ever replaced your viscus clutch, do you know how to test it and has the radiator ever been replaced. Both of these can cause that higher temp along with a possible bad, new, t/stat.

 

230 is too hot no matter which stat (oem or 180) that you run. Would expect healthy cooling system to maintain within 5-10 degrees of open point of stat while on level ground at highway speed.

When you slow down, air flow thru rad drops from 5280 feet per minute to maybe 800 from your fan. So temps will rise. At idle temps are impacted as stated by the viscous clutch and radiator clogged outside and inside.

The factory gauge is a worthless pointer, says 50% from about 130-240F.

Note attached photos with 2 trucks, 2 temps, same gauge reading.

Another impact after cooling system work is trash caught in the metering holes of the thermsotat. Will make stat open later.

Viscous clutch test is spin and release when warmed up, should coast to a stop in under 1 full turn. Freewheels as fluid is lost.

Rad test is review temps top to bottom when warmed up, engine off, on fins, in a vertical line. Expect some spread, but lower rows should not be more than 10F cooler. Sludge and gunk block them off first, making them cooler, eventually you have half a radiator.

At 212 the elctric fan should come on, unless motor siezed, fuse blown, relay cooked.

A paper towel should be sucked to grille by proper air flow, not blown away. I had blown fan clutch and power reveresed to electric fan by PO, at idle the main fan would almost stop, and overheating was rampant.

 

"UG volt" !!!

Thanks for that pic Buzz. I'd been trying to figure out why there's no way to display voltage on the Ultra Gauge. Apparently I wasn't looking for the right thing.

Hijack over.

 

It won't show voltage.

 

It shows the supply voltage from the OBDII connector to the UG, which is technically a little off from the main battery, but still shows when volts are dropping below where you want them. But I believe that the OBDII live data does not have volts as a displayed data. My D1 certainly does not, but my Kia does.

Eventually there will be so much info in/out of the system in vehicles that service departments will have Information Technology specialists and the IT fee for bandwidth used by your truck while being diagnosed ($1 per byte at some dealers).

 

Update, I know all about the viscous clutch and the radiator. I knew going in those were not the problem. but thanks anyways for other viewers of these forums.

I specifically asked whether the mentioned conditions were indicative of a failed out of the box thermostat.

I found the problem to be not a failed Tstat but the Tstat installed was actually rated to open at 97 degrees C.

That totally explains the readings on my ultragauge.

 

You asked multiple questions, not just one.

So was the suspect thermostat rated to be fully open at 97C, and starts to open earlier? The D2 oem stat is supposed to open about 179 and be fully open at 205. There is some delta from the thermsostat being remote from the engine block. Thermostats in the US are usually marked for start to open temp, so my 180 (D1) cracks open at 178-180. Some Euro stats are fully open at the stamped temperature.

There have been members who posted about aftermarket stats not opening at correct temp. Testing on the stove is always possible.

 

I noticed a 6 to 8 degree up swing in my engine temps this week compared to last week. Of course, this was in hard stop and go and the ext temp was a balmy 98 as opposed to unseasonably cool weather prior. Should I be concerned?