If you use a evo 9 thermostat housing will it work on an evo 8 hard pipe?

 

Good read on this.

 

I believe that it will fit, but there are 2 different part numbers and designs. evo 8 and evo 9 thermostats are different. I have a post on evomn.net, but it is speculation that it is only a lower temperature? No one on evomn.net, calling Mishimoto, and evolutionm could not confirm if they are interchangeable?

http://www.evomn.net/forums/showthre...824#post135824

I bought a evo 9 Beck/Arnley from Amazon for this reason, good luck!

 

It looks like the Evo 9 thermostat is similar to the ones I see at work at Honda.
The extra plate opens and closes a bypass route, that lets the coolant flow straight back into the engine through the connect pipe when the thermostat flow to the radiator is closed.

There are two whys behind the bypass

The first is cavitation toughness. The extra opening reduces the head generated by the pump, since its easier to pump the fluid through the system with the bypass open compared to no bypass and all flow having to go through the heater core during warm up.

Second is it increases flow through the block during warm up, which helps with uniformly warming up the engine. You'd expect the outlet side of the engine (where thermostat is) to get warm before the side where the pump is pushing in cold water.

The Evo 8 has no bypass circuit other then the heater core. My guess is they got rid of the bypass for cost savings then decided to go back for part commonality or performance improvements.

moral of the story, not interchangeable.

 

Sounds like you know what your talking about! ☺

You can't put a evo 9 thermostat in an 8 cause it is a larger thermostat, but you could put the cheaper $30 evo 8 oem thermostat in an 9.

What in your opinion would this do to the performance and bypass functionality that you are talking about?

 

Water pipes are different between 8 and 9. I am doing a MIVEC swap and finding out these differences the hard way. It seems the Evo 7/9 design is superior. I only knew about this because I have my old Evo 8 thermo housing and the MIVEC one that was attached to the Evo 9 head I got.

 

Eric, can you post pictures of the differences?

 

Yeah, I'll do that tonight.

There's a pressure relief valve (I think that's what it is) or at least a bypass on the bottom of the Evo 9 thermo housing. And a few other minor differences. I am assuming the water pipes are a little difference, because I know the Evo 9 lower radiator hose won't work on an Evo 8.

Ah, the joys of adding parts to your build list

I think you could use the Evo 8 housing on the 9, but A) I have the 9 unit already and B) I'd like to buy a new water pipe anyway.

Plus, someone mentioned that the Evo 9/7 housing is a little better than the 8.

 

Ok, here are 3 side-by-side pics of the Evo 8 and 9 thermos housings and thermostats.

Side view. You can see the 8 housing (on right) has an extra bolt hole for something. And the Evo 9 (on left) has the relief valve and/or spring on the bottom of the thermostat. The bottom of the 8 housing is smooth.



Bottom view. Here you can see the relief port on the Evo 9 housing. Evo 8 has no port.



Back view. The Evo 9 thermo has a smaller spring attached to the relief valve (which I am assuming goes to the water pipe). The Evo 8 thermo (on right) only has the larger spring and the water pipe attaches to the back of the housing. Back of Evo 9 housing has no accommodation for water hard pipe.

 

Close up of Evo 9 thermo, where you can barely see the smaller secondary spring on the bottom. Evo 8 thermo does not have this.