@Jackspratt2 Actually the stock style thermostat has as much or more variation temps due the location. My Black OEM will run 177 to 188 in winter depending on load, mostly settling around 183. In the summer at mid 80's F 188 to 215. So 10 to almost 30 degrees F. The grey soft spring was more stable at 188 to 197 under load but easily reached 201-203 at idle, the black maybe 194 in the summer.

In the stock design the thermostat is at the coolest point, at the exit of the rad, which means it will open less often keeping the engine warmer overall. The inline puts the thermostat back where it was for most of the engine's life, it was only changed for the D2. On the top the thermostat is open more often which should lead to a more stable engine temp.

Either way air in the system is a problem, I would note this is not unique to Discovery's many modern vehicle suffer from it due to complicated cooling system hose runs.

As to at TBH at -15c driving at about 20-30 mph in high winds and heavy snow with it bypass and I had no issues. I am not actually certain how much it actually does, it gets plenty warm under the hood.

 

I also recently installed @Extinct ’s inline kit and saw the same fluctuations. It’s air in the system. Do you hear water gurgling behind the dash when accelerating? I was thinking it might be a good idea to put a bleed screw at the top of the thermostat housing to help bled the air out easier. I have done a few drive cycles and got most of the air out but some is still in there.

 

Interesting. I do not hear the water gurgling behind the dash. Just got back in from letting it heat up in the driveway. Warms up normally(gradually until low 180s) then quickly rises above 200 then just as quickly drops into the 160s. I have followed the bleed procedure as recommended by Extinct and also the one Richard Gallant suggested. Anything else I should try?

 

At initial startup I had some fluctuations as above, so I took a different approach. After taking the coolant back out, I realized that it would be wise to vacuum fill the system, as all of my hoses and tank are less than a year old. After the vacuum fill, I did the recommended bleed procedure and the fluctuations were minimal, and completely gone after the first drive/refill. Now I am 177-182 on the highway, very pleased with that result!

Rhys L.

 

1) The T-stat closes when the temperature drops.

2) The Inline doesn't close.

 

I'm not familiar with with the vacuum fill method. Would you mind walking me through it?

 

It stops the TB from freezing and could save someones life in extreme cold weather. Engineers put it there for a reason. It should never be removed. Cold air hits the intake. At some point if the cold air wins the temp drops. It's simple to understand and not worth risking someones life because you... and other members don't want to replace TBH's and hoses when they leak.

When you sell the car you don't know where it will go.

It''s crazy people here saying you never need a TBH because the engine is plenty warm. That's just obtuse.

 

@Jackspratt2 I know what the TBH does I also know the conditions required for freezing of a throttle body to occur. They are extremely difficult to obtain/encounter, it requires moist freezing air to reach the throttle body in enough quantity and cause an ice build up to lock the throttle plate in place, the amount of extra heat from that tiny set of pipes is literally tiny. It can only happen in very specific atmospheric conditions.

It was actually a bigger problem in old carbureted cars than a modern fuel injected cars and not much of an issue in them either.

And the inline mod simply moves the thermostat, it does not removes it.

 

I would remove the thermostat out of its housing and drive it normally. If temperature variations stop, that did it. If temperature variations continue, should be air in the system. When diagnosed/solved; reinstall the thermostat.
Is the thermostat 'spring' towards the block or towards the radiator ?

 

The spring is towards the block