I was recently weighing the same and put some information into a thread. Decision is yours.
https://landroverforums.com/forum/ge...ion-why-77300/
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So, I did the inline mod before I'd heard about the 180 TD5 thermo. If I had it to do over, I might just go for the TD5.

That said, one thing that really bugs me is there's a blurb in the RAVE (26-2-6) that says:

"In cold ambient temperatures, the engine temperature is raised by approximately 10°C (50°F) to compensate for the heat loss of 10% exposure to the cold coolant returning from the bottom hose."

With the stock thermo, +50°F is way too hot IMO. Even with the TD5 thermo, +50°F makes me uncomfortable. Also, I personally think temp swings like that contribute to head gasket failure, especially if you are running the stock TTY head bolts.

 

10C = 18F differential on most converters.

Referring to coolant temp not outside air temp.

That blurb is just part of descriptive rubbish about the thermostat. A short term increase of 10C when coolant is cold will disappear when normal operating temp is reached.
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That's a nutso amount of temp increase, but wouldn't the heat loss in that hose translate to the coolant running into the engine also being cooler so you probably wouldn't lose that much cooling power. Not that I've seen with my aftermarket temp sensor, atleast. I run steady temps pretty much no matter the outside temp.

 

Ah yes, I made the same mistake as france until you pointed that out. The mistake I made was googling 10C in F, which is 50 F. That does not mean there is a 50 degree difference between F and C, but that 10C is equal to 50F and there is indeed only an 18F difference between the two.

 

The °C to °F conversion in that RAVE paragraph is incorrect. A 10°C increase equates to 18°F, not 50°F.

 

I see what y'all are saying, and agree, the RAVE temp conv is wrong. I also feel silly for not seeing that. So, if I were to do it now, I'd very likely run the TD5 stat.

However, I have no complaints at all with inline, and at least thermostats are now dirt cheap and easily attainable. Also, I have gotten the very non-scientific feeling that people who run the TD5 stat do see wider swings than us inliners. Mine is rock steady when ambient temps are

 

Again a stupid question: do people with inline stats report more frequent water pump issues? I'm thinking the pump will be pushing against a smaller volume of water with the stat on the top hose when the stat is closed. Would that tend to put stress on the impeller?

I'm leaning toward the Td5 stat at the moment – I also have been reading that sometimes the ECU doesn't like the temp differential with the inline mod. And the debate about drilling the hole or not doesn't seem to be fully settled.

 

Volume will remain the same. The by-pass valve bleeds some of the top hose coolant to initially open the thermostat. Above idle it may slightly reduce water pressure until thermostat opening but shouldn't have any significant affect on pump life. D1s aren't known to go through pumps any faster than D2s are they?

Prior to thermostat opening both types are circulating the coolant through engine and heater. By-pass valve shouldn't affect heater performance during warm-up as some are lead to believe.

D2 WM:
D1 WM:
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We do.....on average, im seeing a 18-20 degree swing. low point being 188. High point being 207.

That being said, my inline setup is on the way.