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Drilling Hole In Thermostat

08-04-2008, 09:59 AM
I read somewhere about drilling a small hole in the thermostat to help it bypass. I can't remember where I saw it. Does anybody have any information about such a procedure?

08-04-2008, 12:16 PM
nothing too difficult, you drill a small hole in the plate that is the outer area of the valve

It is usually to help bleed the system when you don't have the right equipment to fill/bleed the system or it is used as a very poor bandaid when an engine is overheating for other reasons, such as a blown head gasket.

As a bandaid, it doesn't really "fix" anything

08-04-2008, 01:20 PM
If the thermostat mounts in the block on its side, then place the thermostat with the hole (should you decide to drill one) up. That will help bleed the system of air.


08-04-2008, 05:49 PM
Some thermostats actually are made with a tiny hole in place as specified by the manufacturer, for certain engines (I forget the model) which are prone to have air pockets when filling.

08-05-2008, 11:39 AM
Here's a real old timer trick. The old Zerex antifreeze cans were metal and under the cap was this punch-out cap. If you carefully removed the cap, it would fit into any thermostat housing. We would drill holes in them and that regulated how hot or cool the car ran. We did it mainly on stock cars.


08-05-2008, 03:16 PM
Doesn't every thermostat have a tiny hole?

08-06-2008, 05:00 AM
Doesn't every thermostat have a tiny hole?

The ones in my vehicles all do. Must be some that don't though.

08-06-2008, 10:09 AM
The ones in my vehicles all do. Must be some that don't though.
All the new stats I have installed in my vehicles I have owned over the years (more than 20 cars and trucks) have not had this hole.

Mind you, this has been almost entirely older American cars. I have not changed a stat in a car newer than '91, so things may be different these days.

08-06-2008, 01:57 PM
Some stats have holes, others don't. The only time a hole helps bleed air is when you're filling the engine. All other times, the thermostat opens which lets air through.

Drilling a hole can affect how quickly the engine warms up, but if you block the bypass, no hole you can drill will be big enough to replace a bypass.

So, drilling a hole is mostly pointless. It won't prevent overheating, it doesn't improve flow, and other than when you're filling the engine from empty it has no real reason for being there.

08-18-2008, 10:47 PM
The reason I asked the question was the fact that I put an Edelbrock high flow water pump in and they have a tendency to hold a regular thermostat closed due to this added water volume. You need to put a high flow thermostat in to help alleviate this problem. All of the high flow thermostats were 160 degrees and this keeps a 460 to cool for optimum performance, so I was trying to find a way to put a stock 190 thermostat in. I had read about drilling a hole in a stock thermostat to help it bypass so the added water volume would not hold it closed, but couldn't remember where I read it. Thanks for all of the responses.

08-30-2008, 11:04 PM
Why not try to use a fail-safe stat in it? These are designed to stay open and never stick shut. You can get them in any temperature and since you are afraid of the pressure keeping the stat shut try one of these fail-safe stats. They cost about 12 bucks or so.....

08-31-2008, 11:39 AM
I had never heard of the fail safe thermostat until you responded to this post. I googled it and came up with the MotoRad website. They have a video demo that you can download. I downloaded and watched it. It is a very interesting concept, but I believe that you would have the same problem with the high water volume holding it closed. It functions the same as a regular thermostat in that it opens against the direction of flow of the water and the pressure and volume from the water holds the darn thing shut. The high flow units have a v-notch that allows a small amount of coolant to flow even when cold and the spring is 50 percent stronger and allows for proper opening and closing of the thermostat even under high pressure and volume applications. You couldn't get a high flow over 160 degrees until recently and that was the problem. Now it seems like every body is making the in several temps, so the question is now mute. Thanks for the response, Gary

03-24-2011, 04:03 PM
In my case, using a remote thermostat housing, There needs to be some leakage through the thermostat in order for the hot water to get there and caus the thermostat to open. Without a hole in the thermostat, no fluid flow so that the cold water near the thermostat does not circulate and stays cold. An alternative would be a bypass in the thermostat housing.

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