Thermostat air relief hole
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Joined: Jan 2007
Posts: 62
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From: LaGrange Georgia
Thermostat air relief hole
I am putting new heads on my 81, and have heard of people drilling a small hole in the thermostat to prevent air from building up in the engine block. Anyone have details and opinions on this procedure?
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Joined: Oct 2004
Posts: 64
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From: MI
The tiniest hole will allow the air to pass. I put about an 1/8 hole in a grand am thermostat and the stupid thing wouldn't even stay warm when it got cold out. It happened again in my truck, you dont need a very big hole if you want the engine it to warm up and run at a constant temp especially when it gets cooler outside. I always put a small hole in somewhere in a flat unobstructed location but now I use a #40 drill to minimize the water flow just to allow for quick airbleed only. The last thermostat I bought actually had a small leakhole in it so I didnt even bother.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,851
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
I’ve never had to drill a hole in a thermostat! When installing a thermostat simply place two aspirins under it to hold it open.
When you fill the engine and radiator with water, it will fill with no air and dissolve the aspirin.
Saves you from drilling a hole and keeps the thermostat honest.
Willcox Inc.
When you fill the engine and radiator with water, it will fill with no air and dissolve the aspirin.
Saves you from drilling a hole and keeps the thermostat honest.
Willcox Inc.
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
Most of this style of thermostat already has the hole, though hard to see and it does take some time for the air to bleed out naturally.
The better type are full flow and prssure balanced, but do npt have the bleed holes.
It is better to put a less the 1/8" one in to solve fill up and air pocket problems. It realistically is not be noticeable at all and the good tstats are calibrated to run at +/- 2° from advertised. They are around 10 bucks, a good deal.
The better type are full flow and prssure balanced, but do npt have the bleed holes.
It is better to put a less the 1/8" one in to solve fill up and air pocket problems. It realistically is not be noticeable at all and the good tstats are calibrated to run at +/- 2° from advertised. They are around 10 bucks, a good deal.
