04 Disco. Is there a way to test if your thermostat is opening?

 

Put it in a pot of water with a themometer and turn up the heat, see if & when it opens

 

The D2 is a three port thermostat. The cold water from rad enters the bottom, and exits the side toward water pump when stat opens. If you pour in hot water from the top port, it will also fill the "chamber" and make main stat open. So if you pop it in a pan of heated water, you'll have to look in the bottom opening to see the change.

 

This may be a crazy question but can you just bypass the t stat? I had another vehicle years ago that was overheating and we just removed the t stat and never had another problem.

 

Please don't. Here is a pix of the stat, and plumbing diagram. You can buy a 180F soft spring stat and swap out. Most likely, the stat is not the cause of overheating. You can also re-plumb the system and use a regular truck thermostat (like a Chevy, etc.).

But the normal cheap things to fix for over heat are:

Low coolant due to external leak around a clamp
Radiator, tranny cooler, and/or AC condenser plugged up with mud and leaves/
Fan clutch continues to freewheel when engine off, warmed up, and spun by hand and released. Clutch is like $60, one for Chevy 2000 van, 4.3 engine, without AC, is a swap.

Head gaskets, cracked block, cracked heads - those are expensive to solve.

Pix of rad fuzz, rad that was clogged with Dexcool coolant sludge, D2 rads are cheap to replace (compared to D1). Pix of stat cut open, and what is inside. The hot water sample comes thru the holes in the top disc, and flows out the chamber. It mixes with cold water from the rad in the chamber, when it gets warm enough the main stat opens. That top disc can also descend when the main stat is closed, so the passenger compartment can get heat sooner in the cold morning. When main stat opens it forces that sampling disc back closed. I guess a hot water test would involve take stat out of truck, pour in water at known temperature to top opening, wait for main stat to open and it come out the bottom.

Note that the gauge can't be trusted. If you "think" you are having an overheat problem, the gauge may have moved up above the 50% range and is in the "frying" zone. Even when at 50% you can still be too hot for most people. Use a scanner or Ultra Gauge to know what is going on.

 

and the plumbing routes
I ran my D1 without a stat, and the engine temp would get up to maybe 150ish. Too cold for best oil flow (increased wear), and mpg will suffer (ECU thinks it is so cold it needs more gas). I do visit the junkyard, and frequently see vehicles with stat removed. It is something people do when headed to the auto auction.