Thermostat, different design w/o 2nd spring work?

[IsaacHayes]

I picked up a 180F thermostat, but it's different than my 195 one. It doesn't have this protruding 2nd spring on the back... I see how it goes down into the 3x00 LIM where that part might get more coolant flow directed on it from the water pump...

The new one doesn't have this.

1) Is it ok to use?
2) What is the purpose of the 2nd spring thing?

[IsaacHayes]

Anyone have a clue on this? What in the world is that 2nd spring thing sticking out the back for?? Looks like the coolant would hit it hard from the water pump and it kind of restricts the flow there where it shoots out from the hole... ???

[IsaacHayes]

Ok from what I've figured out, when the thermostat opens, this rear piece seals up the passage that gets coolant from the water pump....

Can someone tell me why it does this and what the function of this is? And do I need a thermostat that operates like the stock one???

[IsaacHayes]

Argh anyone have a clue? I'm running out of time.

[IsaacHayes]

Ok from what I can tell with the stock thermostat:

Stat Closed: Coolant goes through the heater core and by-pass only.
Stat Opened: Coolant goes through heater core and radiator only.

So it appears to me that when it opens it will cool the coolant a lot faster this way because it's not circulating hot coolant, instead it's forcing it all through the radiator (& heater)....

So without this bypass blocker, it may slow the movement of the coolant through the radiator, resulting in less responsive cooling. Meaning the temp gauge will fluctuate instead of hold steady, as it can't re-act as fast once the thermostat does pop open...


So with the 180F shown, it will allow flow through the bypass, heater core, and radiator when open..

So should I worry about it though? It's a PITA to change these thermostats so I'd like to get it right the first time...

[CNCguy]

The second spring acts as a bypass valve for when there is too much coolant flow to the heater core. Without the second spring you will have minimal flow through the heater core at low RPMs.

[3100 MPFI]

The only thing I was able to learn is that the double spring one is called a reverse poppet, and I am not 100% sure, but the people at the summit store (when I was buying a 160* for my 3100 MPFI) said that the normal one will not work right. Not sure, but I think it has to do with the coolant flow.

[IsaacHayes]

Hmm, not sure if I understand that all correctly.

The way I see it as when it opens, it pushes that plunger on the back to seal up the bypass... So when it's open you get maximum cooling because no hot coolant is going back to the water pump... I can see when th e stat open sup with the version without it, you will loose some flow to the heater core since it will go through the bypass.

I don't see the plunger version as much of a restriction when the stat is closed from looking into the manifold with it installed. Looks like it keeps the bypass open so that the coolant warms quickly.

[IsaacHayes]

To clarify how it's constructed, the copper part with the 2nd spring is solid. It moves backwards as the stat opens, with the spring and plunger seat moving together with it. The 2nd spring is only for when the plunger seats into the LIM, so that it puts pressure to seal it off and doesn't stop the stat from opening all the way and bottoming out.

[IsaacHayes]

CNCguy: I'm a bit confused by what you said. Bypass for when too much coolant flow to heatercore? I don't understand that... It only closes off the bypass that sends coolant back to the pump directly when it opens. When the stat is closed it lets coolant go through the bypass to heat up the engine quicker...

Why wold there be minimal flow to the heater core at low RPMs? If the stat is closed, either design wouldn't change the amount of coolant going to the heater core..