Looks like there are a couple options out there. I wonder which one would be best for the 4.6?

 

After pricing the housing for the thermostat to do an inline conversion(not including the bleeder valve housing), I am gonna go with the oe-style,lower temp stat.

 

here is the Land Rover factory number for the thermo...

PEL 500110 it is a grey colored body. this is the 180 degree with the softer spring there is a Black colored body one as well. It to is a 180 degree but with a stiffer spring. from what I have read and talked to people with the grey softer spring is the one for us series II owners.
good luck and Keep us posted. When my schedule finally calms down next week I will be putting one in along with a new radiator and viscous fan.. looking for cool temps and easier flow. as well as a new oil pump gears as I have a small coolant leak from the front cover... whew.. going to be a long weekend under the truck.

 

So roughly how much cooler could we be running with PEL 500110? 5-6 Degrees? Maybe 10 with water wetter?

 

Water wetter style products won't reduce below the operating range of the stat. Will help from going higher.

 

I will be installing the stat with the stiffer spring today, will post back on how much temp drop if any.

 

Before you install the new stiff spring version, go test your temps, while driving around town, with a scanner so you can see just how much of a change you can make.
Make sure to test at long idle, in town stop and go as well as highway driving and get back to us.

 

98-2004 Disco II

From the beginning they used PEM100990K up until they replaced it with the PEM10090 (these were both used on VIN's up to 5A476242). Then when the last 8 of the VIN changed to 5A476243+ it was PEL500110. That might help you guys track down where you are and where you're going with some of the knowledge. Let me know if you guys need to know anything else!

 

It is now installed and put about 20 miles on it. Cruising at 55-60mph on rural 2 lanes with it around 80 deg. out side. Temp stays the majority of the time at 199 deg. on uphill grades it rises to 201deg and the down hill grades drops it to 197deg. The lowest I saw on the rural roads was 194deg and the highest was 204 deg. The biggest climbs in temperature where always when climbing a grade at about 50mph and it is right at the threshold right before the transmission downshifts so its almost bogging but not quite and its spinning about 1500rpm. I guess its related to water pump speed,fan speed to engine load ratio. Did a short blast down the interstate between exits and the temps stayed between 195-199deg. The interstate was with a/c running. I live too far from the city to get into any traffic situations today so, I slowly drove stop and go offroading around the farm. The highest I hit was 206 deg. and that was at idle right after pulling up a steep hill. As soon a I began driving again it dropped right back down to 201deg, which is where it was most of the time off road.
Basically, I have a consistent 4-5deg drop from what I was seeing on the ultra-guage before this swap. One variable, I bled the system just once before taking it on this drive so, its possible there is still some air in the system being that I lost about a gallon of anti-freeze during the thermostat swap.

 

Sounds like a worthy investment. And for comparison sake what are the general temperature differences in an inline thermostat(180) versus stock? I think some guys run a consistent 195 degrees.