Drilling thermostat?

[Aslet]

I am in the process of troubleshooting an overheating issue on my 944 track car. While talking to some 944 spec racers, I heard about drilling holes in the thermostat to improve coolant flow. Apparently they drill two 2mm holes. I have also heard of a smaller size hole being drilled to aid bleeding the coolant system (to allow air to pass through before the thermostat is fully open).

If I didn't hear it from multiple people I would say it is crazy, but maybe it helps on a track car? Can anyone on here add confirmation that this is done? If anyone has done it, where do you drill the holes?

Thanks!

[kdjones2000]

Also have some SPEC racers who drill the thermostat, but only for aid in bleeding.

I put in a LR bleeding kit on my race car, which involves drilling a hole into the back of your head.

Again this only for aid in bleeding the engine, not to prevent overheating.

[cockerpunk]

drilling the thermostat wont stop you from overheating. the thermostat controls the lower end of the coolant temp. drilling it would only help if the thermostat is malfunctioning (ie not opening)

[flash968]

i've been drilling thermostats for decades with nothing but improvement in the system. the only potential downside i have ever found is that the heater will take longer to generate heat in the cabin. it makes bleeding a snap, evens out the temp swings, and helps prevent superheating due to flow restriction.

it won't cure an undersized or blocked system.

the holes sizes and quantities vary from thermostat to thermostat, based on the flow needs and the thermostat size. on the 968, i drilled 6 .06" holes.

[onZedge]

Flash:

"...i drilled 6 .06" holes."

Is that 6 holes equally spaced around the thermostat, or concentrated on one side (up), or does it even matter?

I'm about to do my third quadrennial front "seal/race/o-ring/belt/water pump/hose" thing.

[flash968]

it was a concentric pattern

[dgcantrell]

I've noticed on some thermostats for newer vehicles, there is a small hole in the plate separating the two sides. I put a new thermostat in a Dodge Intrepid for a fellow that had a waterpump let go and puke the coolant into the oil. The installation instructions were to install the thermostat with the hole in the 12o'clock position. This made bleeding the coolant much easier on that car.

[Jfrahm]

Some thermostats have a "jiggle valve" for easier bleeding, which is a hole plugged with a small loose rivet that seals the hole under coolant flow. It allows air or coolant to pass through unless the coolant is moving, which forces the valve shut. I've bled 944 cooling systems with and without a hole drilled in the thermostat, it's pretty easy either way and I would not bother.

On the street I do not think you want to slow warmup or lower the lower setpoint in cold weather. If drilling the t-stat "fixes" something, you should instead fix the real problem. Cool running on the street can lead to major carbon buildup, stuck rings, etc.

On the track, I dunno, maybe there is a cooling gain (or reduced parasitic loss) from drilling it or you have a softer landing if the thermostat fails closed.

[dgcantrell]

I agree with you about drilling the 944 stats. I can bleed them. If it's running hot, there's something else causing it.

[Rasta Monsta]

I've raced my 2.5 in 90+ degree weather without issue, factory t-stat installed. I agree that there is another problem with the cooling system.

Condition/age of radiator? Belly pan installed? AC condenser removed?

[Aslet]

Thanks for the input.

I know that drilling the thermostat is not a fix, but I figured if it helps with the track usage, I can also do it.

My car had started having issues awhile back. At that time I had a brand new 951 radiator installed (mine had many flattened fins, etc). At the track last week it was a 75F day and the stock coolant temp gauge was at the bottom of the red zone. As the issue is that same as before the new rad was installed (and bleed) I am thinking it may be the thermostat itself.

As the water pump and belts are due soon, I may just replace everything now (pump and thermostat). Any other thoughts?

[cockerpunk]

Originally Posted by flash968

i've been drilling thermostats for decades with nothing but improvement in the system. the only potential downside i have ever found is that the heater will take longer to generate heat in the cabin. it makes bleeding a snap, evens out the temp swings, and helps prevent superheating due to flow restriction.

it won't cure an undersized or blocked system.

the holes sizes and quantities vary from thermostat to thermostat, based on the flow needs and the thermostat size. on the 968, i drilled 6 .06" holes.

and premature engine wear, carbon buildup, and ring seal issues, from not coming up to temp as quickly (thats after-all the entire point of the thermostat).

you could run the engine without a thermostat if you dont believe it does anything, i wouldnt recommend it

[Rasta Monsta]

Originally Posted by Aslet

At the track last week it was a 75F day and the stock coolant temp gauge was at the bottom of the red zone.

Early temp gauges are notoriously inaccurate (due to bad grounds, not the gauges themselves). Before you make yourself crazy, get a laser pyrometer and shoot the head and water flanges.

[flash968]

the system needs a "fix". the temp swings way too much. a proper cooling system does not fluctuate much. take a look at any modern car.

drilling the thermostat helps stabilize that.

it is important though to be sure that all of the components are in top order. it is also equally important to make sure the belly pans are in place. they are integral in maintaining negative pressure behind the radiator.

[cockerpunk]

Originally Posted by flash968

the system needs a "fix". the temp swings way too much. a proper cooling system does not fluctuate much. take a look at any modern car.

drilling the thermostat helps stabilize that.

it is important though to be sure that all of the components are in top order. it is also equally important to make sure the belly pans are in place. they are integral in maintaining negative pressure behind the radiator.

most modern cars don't even actually have a temp gauge. its digital, and is really just an overheat gauge, that the computer pins when it senses an overheat. otherwise the computer puts in the middle and no one is the wiser.

even modern cars coolant temp fluctuated the same 5-10 degrees that our cars do. it is perfectly normal, and will not hurt the engine.


drilling the thermostat does not stabilize it.

[djnolan]

I think it would be easier to drill or remove the front bumper than remove that thermostat again

[Staubsauger!]

Haha ja! ^
Why drill it?

[flash968]

drilling allows a small amount of coolant to pass at all times. this minimizes fluctuation in temperature. the system SHOULD NOT run significantly hotter at one time versus another, regardless of how hard you are driving the car. if it does, it is because it is too small or inefficient. it should never vary more than about a needle width.

many new cars come with thermostats that are already drilled, for this very reason. they didn't do it for reasons of performance though. they did it for reasons of emissions. it is the same reason that all cars now run over 200 degrees, unlike cars of yesterday.

[djnolan]

So the temp gauge reading should match the thermostat rating, e.g. 80C, year round w/ or w/o AC running?

I am not getting this.

[flash968]

not exactly.

in a properly designed system, the temp should be about 100 degrees F over ambient, or 10-15 degrees above the thermostat point, whichever is greater.

it should do this regardless of AC, load, or anything else, with very little variation.

it took me a few mods to get the 968 to run like that, but i did. every one i have set up since runs the same way.