New Disco owner/forum member and a question about thermostat

Knightspirit

Well-known member
Sep 22, 2019
213
62
Mount Shasta, CA
Silly me to believe the 180 degF/ 82 degC labeling - just wondering if anybody else had noticed this "discrepancy" is all. My jeep w/4.0l cast iron block & head seems to run comfortably at 195 degF (what the t-stat is labeled as) and everybody says not to run it colder.
I put a 180 degree thermostat in my D1 and it actually runs at about 180 degrees consistently. The gauge on the dash won't even move until you get well past 200 so good to monitor it with something else. Mine rarely ever goes past 200...
 

Harv

Well-known member
I'm not an expert on the system, but it seems that as most engines have the t-stat at the coolant outlet at the top of the engine, the engine temp should be roughly the t-stat temp. On this generation of Rovers, the t-stat is on the engine inlet end, so the engine temp will always be higher than the t-stat temp. Please enlighten me if I'm not correct about this.
 

rovercanus

Well-known member
Apr 24, 2004
9,485
158
The D2 water flow comes out hot at the intake plenum into the top of the radiator and thermostat (by-pass hose).
The direction of flow is from the top (hot) of the radiator to the bottom where it flows into the thermostat and then to the engine.
Here is a link for several easy to follow coolant flow schematics.
 

discostew

Well-known member
Sep 14, 2010
6,503
525
Northern Illinois
My mechanic (former Land Rover Master Tech and now has an independent shop) told me this morning that a D2 running in the 220s is really not all that hot. He's concerned when he see (or hears) about 230 or 240. I think 220 is way too hot. My D2 is in for an oil change and he's also installing a genuine parts 180-degree thermostat. We'll see if that helps. I think my engine is toast though and my Disco days will sadly be coming to an end soon.

The old rule of thumb is if it didn't boil over, it didn't overheat.
 

discostew

Well-known member
Sep 14, 2010
6,503
525
Northern Illinois
The D2 water flow comes out hot at the intake plenum into the top of the radiator and thermostat (by-pass hose).
The direction of flow is from the top (hot) of the radiator to the bottom where it flows into the thermostat and then to the engine.
Here is a link for several easy to follow coolant flow schematics.

I got so excited and then.....no link
 

rovercanus

Well-known member
Apr 24, 2004
9,485
158
I got so excited and then.....no link
Der!
This is a P38 but same coolant path. I see what Harv is saying now but I'm not sure why it would matter. I think the Thor system was designed for heating up quickly. With the thermostat closed the coolant would go through the by-pass line to the top of the thermostat circulating warm coolant until the thermostat opens allowing the majority of the coolant from the bottom of the radiator to pass through.P38_THOR_COOLING.jpg.211b51ddcb0c9a56f459ef495dc953f4.jpg
 
Last edited:

Harv

Well-known member
The reason I think it matters is that the coolant will be at the t-stat temp before it enters the engine, then gathers heat. The other way, all the heat has been transferred to the coolant before the t-stat controls it.
 

discostew

Well-known member
Sep 14, 2010
6,503
525
Northern Illinois
Coolant will not be at the thermostat's rated temp when it enters the engine. Not sure why so many people believe that. The 185 degree rating means that it will begin to open at 185 degrees.
 

Harv

Well-known member
Even if that's the case, it still seems to me that the way the coolant flows through the Rover engine, it picks up the heat after the t-stat regulates it, so it will be hotter by the time it returns to the radiator, than an engine with the t-stat at the engine outlet.
 

discostew

Well-known member
Sep 14, 2010
6,503
525
Northern Illinois
I think I understand what your saying. I think that BMW put a cooling system on an engine that was designed to run like your describing. The t stat was in the intake manifold and hot coolant in the engine was let out when it opened. Like it's supposed to. So doing the modification that makes it more like that is what I would want to do. From the very beginning of the Disco2 the cooling system has been it's biggest problem. You have that goofy cooling system flow thru a t stat and the radiator is half the size of the Disco1 radiator. The best way to fix it is to get rid of it and park Disco1 in it's spot.
 

WaltNYC

Well-known member
Mar 3, 2010
591
68
NYC
Even if that's the case, it still seems to me that the way the coolant flows through the Rover engine, it picks up the heat after the t-stat regulates it, so it will be hotter by the time it returns to the radiator, than an engine with the t-stat at the engine outlet.
Does the red (in the diagram) hose to the top of the thermostat not contain “engine temp” coolant? Is that not where the temp sensitive bit of the thermostat is positioned?
 

discostew

Well-known member
Sep 14, 2010
6,503
525
Northern Illinois
Does the red (in the diagram) hose to the top of the thermostat not contain “engine temp” coolant? Is that not where the temp sensitive bit of the thermostat is positioned?
.yes thats correct. One of the problems with these stats is a crack forms or the closed t stat allows some coolant to pass thru. This allows cool side coolant to leak into the sensing bulb area and causes it to stay closed. I think even in a perfect t stat the sensing bulb is so close to the cooled coolant that it tends not to open.
 

WaltNYC

Well-known member
Mar 3, 2010
591
68
NYC
... I think even in a perfect t stat the sensing bulb is so close to the cooled coolant that it tends not to open.

Thus the frequent recommendation to use a 180F thermostat which sorta compensates for that lower temp coolant mix.