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Thermostat Drilling

C

Cherokeekid88

NAXJA Forum User
Location
North Carolina
I think i might have a little bit of air in my cooling system, so im looking to burp the system. Ive searched but couldn't find a write up. Now i understand that you are to drill a small hole (1/16") into the T stat housing at the 12 o clock position? I'm sure that is the Jist of it but would like a little more info.
 
Two holes, one at 12 and one at 6. Make sure the holes are straight up and down when you place the thermostat in.

That's how I understand it.
 
Apparently, more than one someone does!!


23211108.jpg



:D
 
Ok, I’m going to shoot my mouth off without looking in my manuals…

Where did the concept of drilling a hole in a thermostat that is literally a controlled aperture come from? Are we worrying over the small area between the top of the hole in the thermostat and the top (inside) portion of the housing?

Once the engine gets to operating temperatures it seems that the air would get sucked with the coolant through the system and end up in the holding tank.

Just my .02

------------
xjcruiser90
http://xjcruiser.com/
 
xjcruiser90 said:
Ok, I’m going to shoot my mouth off without looking in my manuals…

Where did the concept of drilling a hole in a thermostat that is literally a controlled aperture come from? Are we worrying over the small area between the top of the hole in the thermostat and the top (inside) portion of the housing?

Once the engine gets to operating temperatures it seems that the air would get sucked with the coolant through the system and end up in the holding tank.

Just my .02

------------
xjcruiser90
http://xjcruiser.com/
Click to expand...

You can get air trapped in the top of the housing on the engine side, this results in the temp sensor reading the wrong temperature. Kind of like holding a thermometer above boiling water, it won't read the boilingwater temp it will read lower.
 
add a 1/8th" NPT bleeder to top of thermostat housing and burp your cooling system when ever. Bleeders are found on alot of GM vechicles, Plus the Europeans ,Saab, Volvo, etc.
 
I drilled the holes at the 12 and 6 o'clock position on my T-stat. Solved my overheating problems. Just make sure you dont drill the hole where the flange (lip) is touching the brace that helps hold it in place otherwise the holes will do no good. You have to make sure the holes are going to be in the open of the opening and not on the inner lip if that makes sense.

tstat.jpg


A quick pic to show what im talking about...
Red dots = 12 and 6 o'clock holes
Purple line = the lip on the hole that the tstat housing attaches to.
The tstat lip sits on the lip of that hole since there is a little ledge/lip persay. That's where you DONT want the holes as it will just be blocked and not work how you wanted it to. So you'd need to drill more or less in the middle of the tstat between the edge and the middle of the tstat itself. Like where the dots are... hope this helped.
 
tigerShark said:
is it safe to say that this mod is not necessary on an open system?
Click to expand...

OEM/Stealership thermostats have a hole with a chack ball/ one way valve in it. this hole I position at the top 12 O,clock position. This allows air to pass from the the engine into the radiator and the holding tank. I find this useful when filling the system after it had been empitied. I have also seen some thermostats with a slit wher the popper valve rest on the outer ring. this essentially do the same thing as the OEM bypass valve.
When I use a thermostat that do not have a slit or hole already in it, I always drill one hole and position this at the 12 O'clock position. In theory, this should work since air is lighter than water which causes it to rise to the top.
 
OK, I am going to go out on a limb here and buck the conventional wisdom on thermostat hole drilling, at least for the closed system renix jeeps!

I just happen to be replacing my heater hoses, and while I am at it I am chaning my working 165 F thermostat for a 180 F thermostat to run fuel efficiency tests on my 87, and to get a wee bit more heat on cold mornings this winter.

Two things have occured to me during the heater hose replacement, one is that it is easy to criss cross the two heater hose connections at the engine which will kill the normal degassing process of the plastic closed system renix bottle, and will allow the water pump to suck air from the side connection of the plastic bottle instead of coolant out of the plastic surge bottles bottom, thus reintroducing air into the engine block!!!!

:doh:

Second is that on the closed Renix system if air gets past the thermostat, via added holes in the thermostat, into the upper radiator hose it is forever trapped with no way back out. The best way to refill this system is to make the last conection at the upper radiator hose to the thermostat housing, and to elevate the upper radiator hose and top of the coolant in that hose, then quickly reconnect it to the thermostat housing.
 
Ecomike said:
Second is that on the closed Renix system if air gets past the thermostat, via added holes in the thermostat, into the upper radiator hose it is forever trapped with no way back out. The best way to refill this system is to make the last conection at the upper radiator hose to the thermostat housing, and to elevate the upper radiator hose and top of the coolant in that hose, then quickly reconnect it to the thermostat housing.
Click to expand...

That's why for you drill two holes. The upper one will pass air out, and the lower one will pass water in to displace the air. I've been doing it for years, and I've not had any trouble.
 
5-90 said:
That's why for you drill two holes. The upper one will pass air out, and the lower one will pass water in to displace the air. I've been doing it for years, and I've not had any trouble.
Click to expand...

Did this to mine last week when I replaced the rad. Filling was easy and it took no time to "burp" the system. I would do it again next time. Thanks for the help. Again.
:patriot:
 
5-90 said:
That's why for you drill two holes. The upper one will pass air out, and the lower one will pass water in to displace the air. I've been doing it for years, and I've not had any trouble.
Click to expand...

I too have had no problems with mine since I serviced it 3 years ago and installed a new thermostat that had no holes and no bleeders in the thermostat at all. :scared: I just verified the no holes and bleeders today. Mine is a closed renix OEM set up.

So if the dual hole bleeder thermostat is bleeding air from the thermostat housing into the upper radiator hose, how prey tell :)worship::laugh3:) is the air getting from the top of the radiator to the bottom of the radiator and back to the plastic air bottle expansion tank? I suspect, from what I noticed under the hood today, that most of the air in coolant problems experienced by others with the Renix closed set up, had their two heater hoses at the engine, near the upper radiator connection, swapped, and that they were drawing air directly into the water pump from the coolant expansion bottle top fitting, instead of drawing liquid from the bottom plastic bottle fitting.

The only thing special I ever did to fill my system was to slowly fill it using an elevated upper radiator hose as the fill point until coolant, and not air came out of the thermostat housing hose conection. Then I topped it off at the plastic coolant bottle.

My point is there are dozens and dozens of posts here where people have added holes to the thermostat, burbed it here and there and then finally blamed the closed system as worthless and replumbed the system as an open system when there real problem was probably crossed over heater hoses at the front of the engine.

I nearly hooked my new heater hoses up backwards today, before I looked for a reason to attach the hose in a specific place, and then it snapped and dawned on me! One is a return to the pump inlet (Passenger side) while the other (drivers side) is a bypass of the thermostat to BLEED AIR to the plastic bottle and supply hot water to the heater core during warm up. Also if they are connected backwards solids plug the top of the heater core, and coolant flow is next to nill as the flow is easier through the plastic bottle if the hoses are backwards.
 
Ecomike said:
I too have had no problems with mine since I serviced it 3 years ago and installed a new thermostat that had no holes and no bleeders in the thermostat at all. :scared: I just verified the no holes and bleeders today. Mine is a closed renix OEM set up.

So if the dual hole bleeder thermostat is bleeding air from the thermostat housing into the upper radiator hose, how prey tell :)worship::laugh3:) is the air getting from the top of the radiator to the bottom of the radiator and back to the plastic air bottle expansion tank? I suspect, from what I noticed under the hood today, that most of the air in coolant problems experienced by others with the Renix closed set up, had their two heater hoses at the engine, near the upper radiator connection, swapped, and that they were drawing air directly into the water pump from the coolant expansion bottle top fitting, instead of drawing liquid from the bottom plastic bottle fitting.

The only thing special I ever did to fill my system was to slowly fill it using an elevated upper radiator hose as the fill point until coolant, and not air came out of the thermostat housing hose conection. Then I topped it off at the plastic coolant bottle.

My point is there are dozens and dozens of posts here where people have added holes to the thermostat, burbed it here and there and then finally blamed the closed system as worthless and replumbed the system as an open system when there real problem was probably crossed over heater hoses at the front of the engine.

I nearly hooked my new heater hoses up backwards today, before I looked for a reason to attach the hose in a specific place, and then it snapped and dawned on me! One is a return to the pump inlet (Passenger side) while the other (drivers side) is a bypass of the thermostat to BLEED AIR to the plastic bottle and supply hot water to the heater core during warm up. Also if they are connected backwards solids plug the top of the heater core, and coolant flow is next to nill as the flow is easier through the plastic bottle if the hoses are backwards.
Click to expand...

Is there not a heater hose connected to the thermostat housing? I'd think that air bubbles would trickle along that to the volume tank, rather than going through the radiator (and ending up back in the block. Oops.)

At least, that's my first spin on it.
 
Well I don't think drilling a hole in the T-stat housing is going to be a good idea either. The metal is pretty thin in the upper-most housing and thats where a bleed would serve the best. Using the sending unit on the head makes the most sense to me.
As for drilling the two holes in the T-stat itself, well I've tried it with and without the holes and I see little or no difference. I know that both of you two(Mike & Jon) are the Renix experts on here and I respect the opinions of both of you guys, but I can't see any difference as to the holes in the T-stat.
Just MHO.
 
mikeforte said:
Well I don't think drilling a hole in the T-stat housing is going to be a good idea either. The metal is pretty thin in the upper-most housing and thats where a bleed would serve the best. Using the sending unit on the head makes the most sense to me.
As for drilling the two holes in the T-stat itself, well I've tried it with and without the holes and I see little or no difference. I know that both of you two(Mike & Jon) are the Renix experts on here and I respect the opinions of both of you guys, but I can't see any difference as to the holes in the T-stat.
Just MHO.
Click to expand...

If you take the time to bleed the system properly, there's really no difference. What drilling does is allow you to not have to bleed the system manually - and it provides a small safety net if, say, you should get a compression leak into the cooling jacket (I've seen it happen on industrial equipment, and most of us use our rigs about the same way.)

Since you're supposed to leave some air space in the volume tank anyhow, you can just set the system up to bleed itself into that airspace. But, if you bleed properly (sounds like you do,) it's really not necessary - especially if you don't lose your head gasket! Once the system has purged itself of air, it shifts from "a useful two minutes" to "cheap insurance" for the 'just in case' eventuality.

You don't need to add an actual bleeder valve to complement it. If I were going to modify the engine casting proper, I'd probably look into doing a bypass around the thermostat at 12:00 that would remain sealed - and do much the same thing. I just find it easier to drill out the flange, instead.

Neither idea is "right" or "wrong" - it's just what some people find easier to deal with than others. You probably automatically bleed the system after service, and have the time (even if it's only five to ten minutes) to do so. With my situation, I need to get jobs resolved as quickly as possible so I can move on to the next crisis...
 
once the thermostat opens it pulls water from radiator and through motor then back to radiator if your system was low and needed to burp then it will have done so. your vehicle comes with a bleeder valve its called a radiator cap.and if your getting a false reading then your temp sender is bad. it is also not located at the thermostat housing.
 
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