Inline Thermostat

Less Spaghetti, More Cooling

I made the mistake of performing a coolant flush on the Discovery last year, which in it’s life had never experienced problems with the cooling system. It was long overdue, but instead of being a simple matter of replacing old coolant with new it turned into a nightmare of unstable running temperatures, genuine “repair” failures, and frustrations with the original Land Rover design. I decided it was time to toss out the complexity, hard to find parts, and acid-based coolant and build something better.

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The Modification

The original 3-way thermostat is prone to failure, relatively expensive, and not a commonly stocked part. Fortunately, conversion to a more common and more reliable inline thermostat is easy to do during a routine coolant flush. A good write-up, complete with a shopping list of part numbers, can be found on the Land Rover Club V.I. site. The one part number not included is the thermostat itself, and I recommend going with the Land Rover specified 195°F Stant model 45359—the modified cooling system does not need the extra cooling of a 180°F thermostat.

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If you’ve ever done a coolant change on a Discovery, then you know how much of a pain bleeding the system can be. One way to make it easier is to park the truck nose-up on a steep incline while bleeding. Another way is to use an air bleeder with a coolant sight glass so you can actually see what’s going on, such as this one from Jags That Run (you’ll need the 1 1/4″ version).

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Coolant & Additives

Dex-cool is evil. Prince of Darkness evil. It’s corrosive, harmful to both gaskets and metal, and the slightest bit of air exposure causes it to gunk up and aggravates it’s other harmful tendencies. This stuff is so bad, it’s directly responsible for causing the polymer expansion tank on my Discovery to become brittle and break (a $400+ repair in parts alone). Fortunately Dex-cool is not the only option: despite being the only “approved” coolant, conventional “green” coolant works just as good.

Water Wetter was suggested as a coolant additive by a reputable independent Rover technician after switching to green. I’ve noticed this stuff in the auto parts store before, but ignored it due to the gimmick-esque claims on the label. In reality, it does significantly improve the cooling performance over 50/50 anti-freeze alone. The Discovery’s average running temperatures are listed below, as measured during an Arizona summer:

  • Dex-Cool: 206°F average temperature, 210°F under load
  • Conventional Green: 197°F average temperature, 202°F under load
  • Green + Water Wetter: 186°F average temperature, 193°F under load