I was thinking about this as I was contemplating buying a 180* t-stat while driving to work along the interstate the other day.

When the thermostat hits its temperature it opens up to allow coolant to flow through the engine & radiator, correct? If so I'm confused how a lower temp t-stat improves operating temperatures? I understand one would open sooner, but once they are both open would they not be running at the same temperature at either an idle or a fixed speed cruising on the interstate?

 

A thermostat has three ports. When under its acting temperature, coolant flows from the engine outlet to the engine pump inlet, recirculating.
When temperature rises over its acting point, the engine outlet is directed to the radiator inlet, and the radiator outlet feeds the coolant pump inlet into the block.
Different thermostat operating temperatures do the same at different temperatures.

I do not understand the 'both' sentence. There is only one thermostat, blocking one recirculating port to open another 'circulating' port when rated temperature is reached.

In other words, the coolant pump inlet changes its feed from engine outlet to radiator outlet at rated temperature.

 

it doesn't stay open.....180 opens and closes at a lower temp to regulate a desired temp....180...it works with partial open close as well.


for example. 180 = full open at 180 full close at 170
vs 190= full open at 190 full close at 180.... (I made those numbers up, but you get the idea.

 

I just meant that all things the same, the only difference being the t-stat temperature (2 rover clones making the same drive, except one has 180, one has 195).

So the coolant isn't always flowing through the radiator, only at acting temperature. Side question, are there any other items in the circuit through which coolant flows (besides the throttle body heater, I've already seen that one).

I think dusty1 cleared up my confusion, that they don't stay open. I guess I was underestimating the effectiveness of the coolant system. I assumed once it hit a certain temp in the engine the system would stay circulating through the radiator.

 

correct, think of it as a regulator as opposed to on/off valve. i took my stat out, doing an experiment, i couldn't get to 150.....
in the stock set up, the heater core also always has coolant flowing through it...

 

As dusty mentioned, your thermostat temperature just implies the general point at which it's fully opened. Altering this temperature will impact other things though as you might suspect, such as the on/off points of the ECU's on/off points for the aux fan (although with a lower temp I guess the idea is you'd never get to those points anyways.)

Also the clutch fan is loosely-based on the OE tstat temperatures and lowering the tstat temp may reduce engine temps while moving, but in traffic or in a parking lot etc.. it'll simply heat up till the clutch fan engages anyways which kinda makes the mod pointless, as it induces 10-20 deg temp fluctuations.

I think everyone has been secretly lying to you in this thread - avoiding the fact that your DII has a cooling system design which is almost exclusively limited to a few short years with land rover and a couple other vehicles, known as a pressure relief bypass system.

Since you asked if there were other loops besides the throttle body heater plate.. I felt I should finally spill the beans.

Yeah, there is another loop.. it's the basis for the entire system. When the thermostat is closed, and at idle.. the ONLY water flowing through the system is through the heater matrix. This causes rapid engine warm-up and cabin heat.

With a closed thermostat and NON-idle condition, a bypass spring opens reducing pressure on the heater matrix.

When thermostat opens, it allows an EXIT point for radiator coolant, thus entrance for hot engine coolant (kinda backwards, and confusing at first glance of diagrams) through radiator.

The weak point of the design and why it saw limited use was that in the closed / bypassed state the thermostat had limited contact with actual engine coolant temperature. Since it was closed/isolated, the only path of "current" water temp was 4 sensing holes in the tstat which allowed SOME of the radiator loop to bleed through, letting engine-temp water through radiator and over the thermostat. One problem was that in cold temps, this reduced sensing-flow would be so cold after passing through a cold radiator that it would CLOSE the thermostat even more, regardless of actual engine temp (this can even cause the "emergency" aux fan to turn on!) The other problem is that any of the 4 sensing holes getting clogged reduced the flow enough to slow the sensing-flow and reduce the flow temps to the point of inaccurate thermostat temps at idle, hence famous DII high-idle-temp problems (due to one of these two issues). The solution is to use the motorrad-thermostat unit which has 2 large holes vs. 4 smaller holes.

 

All the questions and rationale answered.

 

Or just redesign the system to take a thermostat online and call it a day. Most do the online mod where it's hanging a good 2 feet from the block. I'm working to put a small thermostat in the lower intake itself. Yea, it'll be a pain to get to, but temperature fluctuations will be a thing of the past.

 

you just need a spare lower intake and have the coolant inlet milled to accept a reg thermostat, ive thought about it many times but I havent had any problem with a stock 190 when everything is working correctly. YET

 

Of which I have both. Looking for a smaller sized thermo to fit and a machine shop in NJ willing to do the work.