I have done all the searches and read all the threads concerning this issue. all I find is argument on removing or gutting the thermostat, only brief attention to drilling holes in the thermostat. what can I expect from this. lower coolant pressure? increased warm up? any negative effects is what I am concerned with. let me know if anybody knows about this. I am right in the middle of putting in a new one. thanx

 

Some people drill thermostats for road racing applications. I don't recommend it for street use. drilling will make your car warm up slower.

Always ues an oem Mazda unit. Aftermarket t-stats are of lower quality, and are less dependable.

 

i think most of the people that do this mod are either doing it for road racing or because theyre switching to Evans coolant

 

so f-it is what you are saying? what about mounting my defi temp. sensor in the thermostat housing. I don't want to have to remove the water pump and tap that bitch. what do you think.

 

For road racing, people drill thermostats for a couple of reasons:
1) eliminate trapped air or steam at the thermostat
2) prevent debris in the cooling system from blocking coolant flow thru the thermostat bleed hole (blockage here can cause overheating if there is no recirculating bypass built in)
3) minimize thermal cycling and thermal shock that occurs when cold water from the radiator(s) hits a hot block or cylinder head

On the street, thermostat drilling may prevent the engine from ever warming completely, especially in cold weather. In addition (I think) the FD has a bypass built in to equalize engine temperatures even when the thermostat is closed.

 

My engine builder Don @ Marvel Speed actually suggested cutting the jiggle pin out and drilling two extra holes the same size. One on each side of the original hole. He said that it would help the air bubbles in the cooling system escape. 500 miles so far no problems.

 

When I bought my car the t-stat was drilled out with 6 holes, I did not have any issues with it up until I changed to a v-mount setup, my temps would always be a 74c which was not good for the motor, could not go WOT since temps was too cold, I then replaced it with the OEM one without the extra holes and fixed my problem.

Dont do it unless you plan to track the car only..

 

What exactly are you guys talking about "drilling" of the thermostat?

I am going to be installing an aftermarket water temp gauge soon and was intending to tap into the thermostat housing, like I'd been reading on these forums.

I'm thinking you guys must be talking about drilling extra holes in the thermostat housing, a seperate thing to tapping in a water temp sensor? Just want to check before I go ahead and start putting in the temp gauge.

Sorry for being a dumbass

 

Ok, I've gotta ask. What exactly is the theory behind drilling the thermostat, and how does it really help the car? I read DaveW's points above, but I cannot see that those would be sufficient for the miracle cure that many claim from drilling the thermostat.

While I was feeling somewhat ignorant asking this question, I actually got into a pretty good debate about it with some fairly knowledgable engineers today, and I suppose we'd all like to know.

I assume that once the car is up to temp the thermostat is open all of the time anyway, right? So what do a few small holes do really when running it hard on the track? Behavior as the car warms up is really moot for a track car.

Is it really just to let air bubbles escape? Is it to improve flow on a thermostat that is open anyway?

I can understand how removing it completely would facilitate constant, unimpeded circulation... isn't that really the incentive at the track?

Thanks, and sorry if this is elementary stuff...

 

Never mind I sorted it out.

Drilling thermostat versus drilling thermostat cover.

Just ignore me and I might go away.

(goes away)

 

Here's a good thread on it (instead of me repeating the other guys ):
https://www.rx7club.com/3rd-generation-specific-1993-2002-16/gutting-thermostat-146501/

 

Thanks Mahjik, great discussion in that thread. It's good to see I'm not the only one who is confused!

What I extract from the debate is basically that the thermostat serves a critical function in regulating coolant flow through a motor that is generating less heat than the radiator can disperse, i.e. it ensures that your engine comes up to operating temp and stays there in cold weather or under light load. Bad things can happen to an engine that runs cold all the time. So never remove the thermostat on a street car.

This doesn't present a problem for a track car since heat generated by the motor typically maxes out the cooling capacity of the radiator, in which case the thermostat is not required for coolant flow regulation; the thermostat remains wide open.

Perhaps removing or gutting the thermostat could speed up coolant circulation. But as several very knowledgeable-sounding debaters attempted to clarify in that thread, no more or less net heat gets transferred by faster circulating coolant!!!

And, removing the thermostat could potentially cause your water pump to operate less efficiently due to altering the head pressure to the pump...

Now, all of this addresses removing or gutting the thermostat. Don't do it. No good will come from it according to the physics.

But what about drilling small holes? I am going to assume that practice is done for an entirely different purpose, or purposes. There very well may be some need for, or some benefit derived from, having some small holes to allow steam / air to bubble through the thermostat. And given that one hole can get clogged, more is better? But would that dramatically affect the efficiency of your cooling system??? I dunno

Sorry for the long post and sorry to get off-topic, sonix7 - I know you are curious about drilling specifically. But I posted the question and did some research, so the least I could do is share my personal, hopefully valid, conclusions. My thermostat is staying in the car, exactly as it came from the factory.

 

Basically, the extra holes is the general practice of the road racers (I'll be doing it when I assemble the motor). Allows for more flow but still keeps the thermostat there for the needed restriction that our cooling system apparently requires.

 

I know this is an old thread but i recently drilled four holes on my t-stat and the car for some reason runs a little hotter and the coolant boils over when the car is left idling too long. I recently put in a koyo radiator and with the stock tstat and the car ran fine. But once i replaced it with a new unit that i drilled four hole, the coolant boils over. The warm up times was about the same but at idle the cooling system is not pressurized, but if you rev the car then the pressure builds up. I dont know why the car does this but i will be replacing it with another new mazda tstat. What a waste of $20.

 

HMMMMMMMM....

Sounds to me like you have a bad AST pressure cap, and the coolant is boiling because of that. The fact that the system doesn't pressurize at idle seems related to the boiling, but that doesn't have anything to do with the thermostat, since you say the warm-up time is the same. I'd look for other problems, since I don't think the drilled thermostat is the cause.

 

I just put back the old mazda tstat and everything seems to be fine. I thought the car was running hotter but i changed the location of my greddy temp sensor and it now reads about 10 degrees hotter than before. I tested the pressure cap and its good.

 

I just found out that its not the holes on the tstat thats causing my car to run hot. I was thinking and it was just impossible. It was a combination of a bad fc fan switch(brand new from the dealer) and a bad metal ast. The neck for the cap was not true so it would only hold 7psi. I tested the cap off the car but i decided to test it on the car and after 7psi all i would hear is air bubbles in the overflow tank.

 

Well i just drilled 6 1/4inch holes in a Napa 180F Thermostat.

Background: Koyo Racing Rad, Custom Rad surround, New Water Pump, 16psi cap.

Just wanted to see if i could drop my temps from 190 to somewhere around 175-180 and after i drilled the holes, my temp doesnt get above 150F.

I did a good run about 10 miles at 85 and my temp never got above 150F, then i got back to my house and let it idle for about 10mins to see if it would over heat and it stayed around 135-140.

After that i killed it and let it sit for about 10min and started it back up, the temp was at 185F when i turned the key on and after it started it went right to 145F and stayed righted there.

Well i like the temps how they are but i think i am going to pull that thermostat and get another one and only drill 4 1/4inch holes in it.

This should lead to about 160F temps most of the time.

Forgot to say that i live in the Texas Heat and dont really have a need for a heater.

 

190F is not too hot; it's perfect! On the other hand 150F is much, much too cold to be driving the car hard!!! There's a reason the stock thermostat opens at 180F and it's not because Mazda is stupid. The stock ECU won't even let you have full boost until 160F and that's for good reason. You're trying to fix a problem you don't even have! Too cold is just as bad as too hot!

The real question is always what problem are you trying to fix by drilling the thermostat? There's no need for it on a road car and if you think there is you're overlooking something else.

-DamonB
stock motor, stock turbos, stock radiator and stock thermostat. Drives and races his Texas car everyday (even in July and August) and has yet to have his car overheat even though the conventional wisdom around here says I should be on fire before I get to the end of my driveway

 

In my Formula Continental racecar (~150 HP) I use two 3/16 holes for racetrack use. In cold weather (below 50F), even on the track, I have trouble getting the water up to 180F. I would think that for the street, one single 3/16 hole would be about all you could effectively use. Six 1/4" holes are, as everyone has said, vast overkill.