[Lear35A]

In another thread the concept of "drilling the thermostat" is mentioned. I have never heard of doing that. How does one drill a thermostat? (Where? How many holes? What diameter?) What are the advantages/disadvantages for a street car? Here's a picture of my thermostat which as far as I know is factory original. FWIW, it is stamped 82 deg C. Thanks for any insight!

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[flash]

   

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[Lear35A]

A picture is worth a thousand words. Thanks. That covers the how perfectly, but what about the why>

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[flash]

it allows a small amount of coolant to pass all the time, which helps maintain a more even temp, which is the key to a good running system

the downside is that it takes a bit longer for the engine to warm up

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[jfrahm]

I only do it to make coolant bleeding slightly easier, though my bleeding method is dead easy. I drill one hole maybe 2mm in diameter and put it on the highest point in the t-stat housing, if applicable. IMO drilling more holes is not going to help anything. The t-stat will not cycle, it will open slowly to whatever point the temperature warrants.

-Joel.

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[flash]

it continually opens and closes as the temps go up and down - it's not like a switch, and it does move slowly, but it moves nonetheless - drilling allows a smoother transition, particularly under sudden increased load conditions, because it doesn't have to wait for the thermostat to react - it's an old race trick, and time tested

there is a fairly good explanation of the continual actions of a thermostat here:

http://en.wikipedia.org/wiki/Thermostat

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[jfrahm]

Well I disagree that the thermostat reacts significantly more slowly to the delta T than the gallons of water around it. I would be surprised if the effect were measurable. I think there is more of a downside to slowing proper warmup of the motor.
Whatever. Up to you.

One tiny hole to prevent an air pocket is all I do. For some cars you can buy a thermostat with a jiggle valve that allows air to escape but closes to prevent coolant from bypassing the thermo.

-Joel.

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[flash]

no worries - many people think the thermostat and cooling system operate differently than they really do, but when you see it in action, it's really rather amazing that something so simple is as reactive to changing conditions as it is - i got a chance to see a clear tube "system" many years ago - simply amazing

you can quickly see the difference on the track, where a few seconds of full throttle causes the needle to rise on a "normal" thermostat, but is significantly delayed on a drilled one

"proper" warmup is not what it used to be - no longer are you supposed to let the car idle before driving it - instead they actually tell you not to do that - granted, it does take a bit longer to get to temp with a drilled thermostat, but it also doesn't suffer from the sudden rush of much lower temp coolant the first time the thermostat opens, which can lead to gasket failure, and metal fatigue - instead it gets a more gradual introduction to the reduced temp coolant

there are many things that contribute to the heat being generated, and managing those can be specific to the conditions, so no single solution is universal

the key to the best operation is for the slowest and most limited change in temperature during operation

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[raydog]

I would rather have the engine warm up as fast and as efficiently as possible. I just don't see where drilling holes add any benefit. If that was the case, then why wouldn't they (the manufacturers) just pre-drill hole or have a metered bypass to accomplish the same thing? Maybe in racing it would work but for street use I just don't get it.

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[flash]

it would have been more expensive, and could create emissions problems in colder climates, as the coolant needs to be at a certain temp to atomize the fuel enough to run cleanly

it does actually benefit any of us who have summer weather and drive our cars hard, street or not

as i said, this is a VERY old technique, and one that is time tested

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[raydog]

"could create emissions problems in colder climates"

That's what I thought. My wife's BMW broke a tstat at the spot weld point, effectively leaving it slightly open. And wouldn't you know, it threw an engine code that it wasn't warming up fast enough in the given amount of time that the computer allows. It is also OBDII so I am not sure if it would throw a code on our cars.

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[flash]

maybe not, as OBDII is much more sophisticated than our system, but i wouldn't want to find out the hard way at inspection time

like i said, for those of us who live in warm climates, it's not an issue, and really does work well, but for those in cold climates, it might be a problem that would be a pain in the butt to correct if you guessed wrong

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