Highway vs. City Eng Temps question
 

Hey folks!
Long time reader, first time poster - so cut me some slack :)

I need everyone's opinion on my Hwy vs Stop-n-Go temperatures. Currently, I'm getting 186f - 194f in the city, including long idles, hot days, stop and go, etc etc. Never budges above 197, ever. The confusing part is that on the Highway I'll sit in the 199f - 207f range, usually around 207f at ~70 mph, or around 2,500 rpm's. I'm wondering why my temperatures are increasing over the highway here? Especially considering how I usually sit in the upper 80's / low 90's driving around town, in the summer. Any ideas I can look into?

I've pretty much re-built the cooling system here at 142k miles:

-New hoses throughout
-New Nissans radiator
-New 180deg thermostat
-New water pump
-Completely flushed old coolant, running roughly 60 / 40 ratio water / coolant + water wetter
-New expansion tank
-OEM fan, but viscous clutch seems to be fine, works like it should
-No obvious air way blockages across the grill

Disco 2 is a 2004, around 143k miles. Any ideas on why my temps are going up so much over the highway? Seems like every thread people mention their hwy temps being lower than city / stop and go, so I'm confused here. Not sure if this matters, but my throttle body heater plate is bypassed. Thanks and much appreciated!

Yup - forgot to mention this is reading from an UltraGauge - Plan is to install a water temp sensor - line to a dashboard mount at some point, but still - it's weird.

Ran the UG in a E-350, and temp readings are on point. City driving the van sits around 198f~, on the Hwy is stays at 192f, and doesn't ever budge. On a 450 mile trip it sat at 192f, around 78mph the whole way. I'm jealous that my Rover can't sit at that temp on the hwy.... XD

When the outside temp is above 80 degrees, I run around the same temps with all the same new parts you mentioned. If I drive 30-50mph, 194-195 steady, never higher. 70 mph, 197-206 degrees, 203-206 is uphill highway or higher rpms. Idle at stop lights, temps jump to 203-206, sometimes 210 very briefly. As soon as I drive 1/4 mile, they are down to 194-195 degrees. Pretty normal I think. Engine creates more heat at 70mph+ and heatsoak at idle. Your temps are fine.

I have almost the exact same situation. Same new parts. Same new coolant. Same temps. Seems to me this is very normal for these trucks.

Check temperature along different areas of the radiator. Making sure it's working properly, no blockage internally or externally (coolant or air flow). Only appears to be a problem at higher sustained rpms. Water pump pushing coolant through faster at higher rpms. Not in radiator long enough to cool, suggesting loss of cooling area that coolant is not reaching. An undersized radiator will be overwhelmed by faster flow. Your presumed proper sized radiator may have a factory defect (it's new) or external blockage like mud or grass clippings, etc. blocking air flow (or bent fins from stones).

Edit: Another thought, check for loose panels around radiator. At higher speed, some panel may be bulging, allowing airflow around radiator, rather than through it.

What ambient temps are we talking about here? What brand of t-stat and did you test it before putting it in? Did you pull the rad out and flush the fins out?

A lot of t-stats are failed in the box, they are either stuck open or open late.

The amount of crud I got out of my fins after I pulled it was pretty gross. That will hinder cooling by a large margin.

At 30C (82f) and my AC cranked, I never get above 185f coolant temps.

Hmm.. as far as radiator size goes, it's an exact fit from OEM. Something mentioned was loose panels... Might be on to something because the fan shroud is "loose" and not screwed in via the two top screws that plug into the top of the radiator. Maybe I can try tightening it down, I'm guessing at 50+ and high rpm it's allowing airflow around the radiator and not through the fins. Will do this and report back!

Also, someone mentioned the thermostat being crap out of the box - that did happen to me! Don't recall the brand right now but had a white 180 stat that put my idle temp at 204 - 210, I tried a different brand (same part #) and I'm down to 186 - 194, so big difference.

Also - has anyone tried a full aluminum frame radiator and reported back on any difference between that and stock?

Sorry but running a higher temp on the highway is not normal. Just because a lot of people are having the same issue does not make it normal.