Drilling hole in T-stat
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Senior Member
Joined: Feb 2005
Posts: 195
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From: Sturgis, MI
Drilling hole in T-stat
Hello everyone,
I have a 1999 GTP that is pretty heavily modified. The people who drive these cars say to drill a .125 hole in the center of the t-stat to have coolant flow thru it to help keep it cool when racing or whatever. Now to the question. I'm going to be purchasing (in the next month or so) the Troyer E-fans and underdrive pulleys for my 1999 F-150 5.4 litre.
The truck currently has a 160° t-stat since I had a hypertech reprogrammer. I know that if I'm going to be using the E-fans I need to go back to the stock t-stat, I think it's 192°. Should I drill that same hole in this t-stat? Any help is greatly appreciated. Thank you.
I have a 1999 GTP that is pretty heavily modified. The people who drive these cars say to drill a .125 hole in the center of the t-stat to have coolant flow thru it to help keep it cool when racing or whatever. Now to the question. I'm going to be purchasing (in the next month or so) the Troyer E-fans and underdrive pulleys for my 1999 F-150 5.4 litre.
The truck currently has a 160° t-stat since I had a hypertech reprogrammer. I know that if I'm going to be using the E-fans I need to go back to the stock t-stat, I think it's 192°. Should I drill that same hole in this t-stat? Any help is greatly appreciated. Thank you.
Senior Member
Joined: Jul 2004
Posts: 6,200
Likes: 39
From: Easton, Pa.
.125 is only 1/8" and not very big in the scheme of things.
The small hole helps air exit the block areas to the radiator tank area.
This indirectly help cooling but is only a one shot deal meaning after the air finds it's way to the tank there is no more benifit.
The hole is fine when refilling the system but has no ongoing benifit as it's to small.
As the hole is made larger , it would cause the thermostat to take longer to fully open if it bypasses coolant around the thermostat in enough volume. Making a significent hole in relation to the thermostat will sort of fight with each other and could actually cause a temporary heating condition until the thermostat opens.
You want the coolant and engine temp to be controlled by regulation.
Related subject for compairson is a radiator of higher cooling capacity replacing a stock sized unit in a non-faulty system tends to make the thermostat open and close more often do to the radiator cooling at a faster rate.
The small hole helps air exit the block areas to the radiator tank area.
This indirectly help cooling but is only a one shot deal meaning after the air finds it's way to the tank there is no more benifit.
The hole is fine when refilling the system but has no ongoing benifit as it's to small.
As the hole is made larger , it would cause the thermostat to take longer to fully open if it bypasses coolant around the thermostat in enough volume. Making a significent hole in relation to the thermostat will sort of fight with each other and could actually cause a temporary heating condition until the thermostat opens.
You want the coolant and engine temp to be controlled by regulation.
Related subject for compairson is a radiator of higher cooling capacity replacing a stock sized unit in a non-faulty system tends to make the thermostat open and close more often do to the radiator cooling at a faster rate.
Senior Member
Joined: May 2000
Posts: 1,961
Likes: 1
After I changed a thermostat I had a problem with coolant blowing out of my fill tank. Whenever the thermostat would open for the first time on a cold start, the built up air would rush out, build pressure that exceeded the rating of the coolant cap and coolant would be forced out.
Just by accident I found an obscure line in a service manual noting the vent hole in the thermostat must be placed in the 3 oclock position. I could not ascertain if they meant from the front or from the back of the vehicle so I drilled a 1/8 inch hole opposite the vent hole already there and placed the holes at the 3 and 9 position. It fixed my problem.
When I spoke with a mechanic friend of mine he said it was common practice to drill 3 additional small holes in the thermostat just for this reason.
Air builds up on every cold start so this benefit is continuous. I don't see any other benefit and I don't think it would significantly change the operation of the thermostat.
Just by accident I found an obscure line in a service manual noting the vent hole in the thermostat must be placed in the 3 oclock position. I could not ascertain if they meant from the front or from the back of the vehicle so I drilled a 1/8 inch hole opposite the vent hole already there and placed the holes at the 3 and 9 position. It fixed my problem.
When I spoke with a mechanic friend of mine he said it was common practice to drill 3 additional small holes in the thermostat just for this reason.
Air builds up on every cold start so this benefit is continuous. I don't see any other benefit and I don't think it would significantly change the operation of the thermostat.
Senior Member
Joined: Jul 2004
Posts: 6,200
Likes: 39
From: Easton, Pa.
As simple as a cooling system seems to be, there are a number of things that can cause problems with both air and coolant flow that shows it'self in many different ways.
One is the sudden heating the cool down, pushing coolant out the overflow, running to cold among the many.
A radiator that has flow restriction in the lower areas that feeds the coolant to the pump intake can indeed cause sudden actions when the thermostat opens, due to starvation of 'coolant flow' before that time.
This will cause sudden flows that can end up filling the overflow bottle or tank and result in any number of reactions.
In a normal cooling system, once the air is purged from the system very little goes back into the engine except what is in natural suspension in the coolant.
Normal operation is the cap pressure rating raises the boiling point.
The cap has two way pressure controls. One for blowoff of system pressure if above the cap rating and the second that allows 'coolant in' from the reserve bottle upon cool down. These normal actions should never take in extra outside air as long as the reserve bottle is kept at it's specified hot level.
One is the sudden heating the cool down, pushing coolant out the overflow, running to cold among the many.
A radiator that has flow restriction in the lower areas that feeds the coolant to the pump intake can indeed cause sudden actions when the thermostat opens, due to starvation of 'coolant flow' before that time.
This will cause sudden flows that can end up filling the overflow bottle or tank and result in any number of reactions.
In a normal cooling system, once the air is purged from the system very little goes back into the engine except what is in natural suspension in the coolant.
Normal operation is the cap pressure rating raises the boiling point.
The cap has two way pressure controls. One for blowoff of system pressure if above the cap rating and the second that allows 'coolant in' from the reserve bottle upon cool down. These normal actions should never take in extra outside air as long as the reserve bottle is kept at it's specified hot level.
