Maybe this has been done by many, but I haven't found anything on LS1tech or this forum about it, so I thought I'd share my modest success...

I've wanted to change my thermostat to a cooler 160 for some time, but the $50 price tag is just a little high when you're used to paying $5 for any older engine, so I thought I'd take a hint from the little roadraing experience I have and modify my thermostat housing. Typically, one would drill 3 to 5 holes in the perimeter of the thermostat, but since ours are one piece, it had to be a little different.

I know the lower temps may not be ideal for performance, but a few here have mentioned a full 20 degree drop in trans temperatures with the 160 thermostat, and so that alone is worth it for me.

Here's the thermostat with three .203" (13/64") holes drilled exactly in between the o-ring groove and the open center. One is through where the check valve is stock, so after drilling that hole half way through, you stop to let the check ball fall out, and then finish the hole. I went back through that check valve hole with a 1/4" drill halfway through to clean out the steel ring that secures the check ball in place.

Should you decide to do this with standard steel drill bits, I'd suggest starting with a smaller 1/8" bit and then stepping them up to the 3/16"-13/64". I've got a nice stash of reamers, so my holes get stepped up within 2/1000"



If the hash marks on the gauge are accurate, I'm seeing about 185 for the last few days, with the highest being 190, as pictured. My truck previously ran a firm 210 at all times. My seat of the pants dyno says it's more powerful as well, but it's not terribly reliable.

the gauge, however, doesn't lie

 

Looks like a great (free) mod! Good write-up, too. Thanks for posting this.

I thought lower temps were ideal for performance?

 

You can also take it apart and put a spacer in it.

 

How does drilling the holes affect the thermostat, can you explain that?

 

intake are temps are more ideal, denser cooler air, less detonation, but engines have temperature ranges where they are more efficient at burning fuel/moving oil around. An extreme example, if the engine is too cold (aka winter startup) it will run rough till it warms up. Things like cam specs and port size/shape depend on the factory set temperature opperating range to have the best combustion event.

 

it's too bad no one has ever done a write up on that. I've seen a dozen thermostat threads every week since I've been a member and never once heard of anyone putting a spacer in.

It allows the coolant to flow before it has opportunity to reach the full open temperature of the thermostat.

 

i think on those you can also do the bb mod which i geuss is the same as the spacer.

 

Within .002" of what? Each other? What made you decide on 13/64"?

 

within .002" of the drill size used, by hand. My job involves some precicion drilling and you'd be suprised at just how sloppy a hole can get with standard steel drill bits... like +.020"

13/64 is equal to .203" which is the largest reamer I felt I could fit in between the o-ring groove and the thermostat opening while keeping some wall thickness.

 

Please explain the BB mod.... If nothing else, at least this thread could serve as a resource for all of the thermostat mod choices.

For that matter, explain the spacer mod too, because I don't see an easy way of taking it apart and then reassembling it.