Those 4 holes are not to let air pass but to let coolant flow at a reduced rate when the t/stat is closed.

 

When all your changes are made, I bet you will not realize any more cooling efficiency then just using a 180 degree soft spring for $40.

 

Meh.
Lets just pretend that I am building this thing for the end of the world.
In the event that the poo hits the fan, I am in survival mode and I suddenly need a thermostat It will be a lot easier to find a plain old small block chevy thermostat than it will a disco T-stat.

And hey, now I have a "trick cool mod" on my rover.

 

Well, there might be some differences, but the performance of both thermostats beats oem. But another point may be that you want to keep the engine in a narrow band of temperatures. Under the oem stat, you might run 195-205, and bump up to 212 when the extra fan comes on.

With the new system you run 180 - 190, but that electric fan won't come on until 212. Unless you have AC on. Wonder if long term having lower temp, wih larger swings to where the booster fan comes on, will be an issue?

D1 has the boost fans on all the time with AC on. Wonder if that would be better for a D2, or a mod to add a radiator thernmostat that you set to turn on the fan sooner.

Don't get me wrong, I think the lower temps are great. Just wondering if the electric fan setpoint should be slid down to match.

Spare thermostats are a good travel stock item, along with belt, hoses, crank position sensor, etc..

 

I've been thinking the same thing Buzz.

That said, I'm pretty sure mine hasn't gotten above 195 yet. It rarely gets above 190 at all. I'm curious to see how cool it stays this summer.

 

As for the holes in the disk, those have a major job to bring hot coolant into the chamber, mix with radiator water, and warm up the thermostat to where it open and closes, and perhaps even stays open partially. On cold mornings, the rpm is elevated to warm up, and above idle the water pressure makes the disk with holes descend, on that "soft spring", allowing more warm water to reach the heater core. When the main stat opens, it forces the disk back closed, returning the holes to "metering" function.

Bypass thermostats are nothing new, you'll find them in Mercedes and Fords and others.

 

Ok I wrapped up my version of this mod.
I did have to buy a hose that had the necessary bend in it to complete the upper hose section.

It is Dayco Part numer 71577
Oddly enough I cannot find what vehicle this hose is for.
It just seems to be some generic hose.
It cost me about $14 at advanced auto parts.
Any way I cut this hose as well as the factory upper hose and put it all together like so.



I put it all together and took it for a spin.
So far so good.
I guess only time will tell.

 

So far, mine has been rock solid. My ext thermo said 98° last week during my 30 mile commute to work. The coolant temp never broke 190°, even during the last 5 minutes where I'm in stop and go traffic with a max speed of 35 mph.

 

91 - 2002 Saturn lower hose = Dayco 71577

 

it doesn't really get cold where I am, should I try the in line Tsat?