Can someone tell what this does? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**ScottH** · 08-25-2005, 09:09 PM

The part in question is the piece that is mounted on top of the thermostat housing. Two vacume lines hook to it. The one on my 76 454 is broken and I'd like to know if I can eliminate it or if it should be replaced. BTW the air pump on mine has been removed, not sure if it is related but thought I would mention it.

Thanks for any info.

*iceman7329* · 08-25-2005, 09:35 PM

Never seen one of those. Kinda strange.

ureckme · 08-25-2005, 09:41 PM

Its a themostat housing w/ a thermo vacume switch. It might go to your EGR? not enough info. Matt

bodydropped · 08-25-2005, 10:52 PM

not sure but my 78 doesnt have it or it did and broke off but i dont think u need it

82c10 · 08-25-2005, 11:04 PM

eliminate it

bagged74 · 08-25-2005, 11:37 PM

EGR parts, just scrap it.

jermasaurus · 08-26-2005, 12:13 AM

Does it go to the thermostatic air cleaner or heat riser? I think it might.
-Jeremy

79gmcc15 · 08-26-2005, 12:21 AM

my 79 has one like that just has more ports. if you scrap it how do you re-rout the vacume likes? I actualy have two ports like that. the other is on the manafold and is kinda purple.

hotrodhomi · 08-26-2005, 02:29 AM

mine has 4 ports on my '81.

86 GMG · 08-26-2005, 09:35 AM

i believe it is in relationship with the ???/heatriser???? something or nother to work a smog control unit of some sort basically scrap it and plug the lines that connect to it as well these truck had a lot of vacuum lines originally and they run like crap with them all there imo.

60-66 Nut · 08-26-2005, 10:31 AM

On the 454's that we used to have in our fleet(about 60 at one time) that switch was used to regulate the distributor vacuum advance. As I recall, it would switch the advance from ported vacuum to manifold vacuum or vise versa when the engine warmed up. Like everyone else said, it's not necessary. Just make sure the vacuum advance is hooked up.

60-66 Nut

PHOENIX · 08-26-2005, 11:25 AM

Thermal vacuum switch.
It regulates vacuum to components based on coolant temperature (engine warm up).
It could be used for a few things.
If the vacuum lines are all hooked up and everything is working fine I wouldn't remove it.
If you do have to keep your EGR you need to keep atleast one of the TVS's with two ports, one in, one out.
My a.i.r. pump vacuum line was not (and is not) routed through a TVS.
My TVS is only used for the egr (i believe there is a line to the canister also).
I used to have a TVS with more ports. One went to the heat riser.
The heat riser is located on the bottom of passenger side exhuast manifold.
It help the engine to warm up faster.

08-25-2005, 09:09 PM	#1
ScottH Senior Member Join Date: Sep 2002 Location: Hampstead, NC Posts: 8,190	Can someone tell what this does? The part in question is the piece that is mounted on top of the thermostat housing. Two vacume lines hook to it. The one on my 76 454 is broken and I'd like to know if I can eliminate it or if it should be replaced. BTW the air pump on mine has been removed, not sure if it is related but thought I would mention it. Thanks for any info. Attached Images

08-25-2005, 09:41 PM	#3
ureckme ureckmefixit2@cox.net Join Date: Dec 2004 Location: Mesa AZ. (Phoenix) Posts: 1,284	Its a themostat housing w/ a thermo vacume switch. It might go to your EGR? not enough info. Matt __________________ That's U RECK ME FIX it 2 74 Chevy Short Bed 355ci Sportsman II 64cc Angle Plug Crower Custom Grind .462in .486ex Dyno Test 422hp @ 5600 And it's got a Holley 3.73 Gears 12 Bolt 3.73 w/Posi 700R4 Going In I'm a Body Man So There! That's why it's not painted

08-25-2005, 10:52 PM	#4
bodydropped Registered User Join Date: Jan 2005 Location: beaumont,tx Posts: 757	not sure but my 78 doesnt have it or it did and broke off but i dont think u need it __________________ http://img.photobucket.com/albums/v5...ropped/sig.jpg

08-25-2005, 11:04 PM	#5
82c10 needin' money Join Date: May 2005 Location: Chickasha, Oklahoma Posts: 1,106	eliminate it __________________ *SWB Stands for Short Wide Bed*

08-26-2005, 12:21 AM	#8
79gmcc15 Gettin It One Pice At A Time Join Date: Oct 2004 Location: everett, washington Posts: 2,688	my 79 has one like that just has more ports. if you scrap it how do you re-rout the vacume likes? I actualy have two ports like that. the other is on the manafold and is kinda purple. __________________ RIP ELJAY Work In Progress 1979 GMC C1500 Trailering Special. Getting the truck done, one piece at a time. “You can tell a lot about a fellow’s character by his way of eating jellybeans.”Ronald Reagan “I don’t know the key to success but I know the key to failure is trying to please everybody.” Bill Cosby

08-25-2005, 09:35 PM	#2
iceman7329 Account Suspended Join Date: Mar 2005 Posts: 453	Never seen one of those. Kinda strange.

08-25-2005, 11:37 PM	#6
bagged74 its just $$$$$ Join Date: Jul 2003 Location: OK Posts: 2,078	EGR parts, just scrap it.

08-26-2005, 12:13 AM	#7
jermasaurus Registered User Join Date: Dec 2004 Location: New Lenox, IL Posts: 442	Does it go to the thermostatic air cleaner or heat riser? I think it might. -Jeremy

08-26-2005, 02:29 AM	#9
hotrodhomi Registered User Join Date: Apr 2004 Location: Sacramento Posts: 3,737	mine has 4 ports on my '81.

08-26-2005, 09:35 AM	#10
86 GMG Registered User Join Date: Apr 2005 Location: Tulsa Oklahoma Posts: 943	i believe it is in relationship with the ???/heatriser???? something or nother to work a smog control unit of some sort basically scrap it and plug the lines that connect to it as well these truck had a lot of vacuum lines originally and they run like crap with them all there imo. __________________ square body trucks an addiction or an investment either way they consume all my extra time and money

08-26-2005, 10:31 AM	#11
60-66 Nut Professional Beer Tester Join Date: Aug 2004 Location: Louisiana Posts: 453	On the 454's that we used to have in our fleet(about 60 at one time) that switch was used to regulate the distributor vacuum advance. As I recall, it would switch the advance from ported vacuum to manifold vacuum or vise versa when the engine warmed up. Like everyone else said, it's not necessary. Just make sure the vacuum advance is hooked up. 60-66 Nut __________________ 60 Ford F100 Custom Cab 61 Apache Short Fleetside 64 C10 Short Stepside 65 C80 409 V8 5spd(X-Firetruck) 83 GMC 350 Olds Diesel 85 GMC Short Bed 86 GMC Short Bed 90 GMC R3500 Crew Cab 92 GMC 1500

08-26-2005, 11:25 AM	#12
PHOENIX Registered User Join Date: Oct 2002 Location: Phoenix, Arizona Posts: 4,703	Thermal vacuum switch. It regulates vacuum to components based on coolant temperature (engine warm up). It could be used for a few things. If the vacuum lines are all hooked up and everything is working fine I wouldn't remove it. If you do have to keep your EGR you need to keep atleast one of the TVS's with two ports, one in, one out. My a.i.r. pump vacuum line was not (and is not) routed through a TVS. My TVS is only used for the egr (i believe there is a line to the canister also). I used to have a TVS with more ports. One went to the heat riser. The heat riser is located on the bottom of passenger side exhuast manifold. It help the engine to warm up faster. __________________ * AVOID: LOPER'S PERMORANCE / LOPERSPEED.COM OF PHOENIX, AZ & COTTMAN TRANSMISSION * Last edited by PHOENIX; 08-26-2005 at 12:02 PM.

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