Figured out my oveheating problem.
Thread Starter
Racer
Joined: Oct 2005
Posts: 273
Likes: 1
From: Fabens TX
Figured out my oveheating problem.
I was seeing temp of about 230 and the inside cab felt like an inferno. I couldn't drive my vette anywhere. I changed out a real nice looking aluminum waterpump for the az variety. I also changed to a aluminum rad and installed 2 electric puller fans . Still my temps would eventually reach 230 . Checked timing , changed my vacuum advance to manifold vacuum and nothing changed. Eventually came across a thread not related to oveheating but a heat riser being mentioned . I go look at mine and it's stuck in the closed position 
. I should have noticed the exhaust sounded louder on one side but didn't . I guess I figured the stock manifolds were quite restrictive. Anyways I opened up the valve and my exhaust gets louder and I can hear a different sound to the engine. Watch my temps go down! 
. I should have noticed the exhaust sounded louder on one side but didn't . I guess I figured the stock manifolds were quite restrictive. Anyways I opened up the valve and my exhaust gets louder and I can hear a different sound to the engine. Watch my temps go down!
Drifting
Joined: May 2002
Posts: 1,546
Likes: 282
From: Back in Nebraska
I was seeing temp of about 230 and the inside cab felt like an inferno. I couldn't drive my vette anywhere. I changed out a real nice looking aluminum waterpump for the az variety. I also changed to a aluminum rad and installed 2 electric puller fans . Still my temps would eventually reach 230 . Checked timing , changed my vacuum advance to manifold vacuum and nothing changed. Eventually came across a thread not related to oveheating but a heat riser being mentioned . I go look at mine and it's stuck in the closed position . I should have noticed the exhaust sounded louder on one side but didn't . I guess I figured the stock manifolds were quite restrictive. Anyways I opened up the valve and my exhaust gets louder and I can hear a different sound to the engine. Watch my temps go down!
. I should have noticed the exhaust sounded louder on one side but didn't . I guess I figured the stock manifolds were quite restrictive. Anyways I opened up the valve and my exhaust gets louder and I can hear a different sound to the engine. Watch my temps go down! 
Intermediate
Joined: May 2010
Posts: 31
Likes: 0
From: Emerald Coast Florida
It's on the passenger side exhaust manifold right between the ram's horn and exhaust pipe. It should have a vac hose connected to an EFE TVS Switch located on the thermostat housing. The heat riser opens as the temp gets hot enough, but if the hose is not connected it stays shut. (increases back pressure/makes engine sluggish) you can get a spacer to take out the HR or just wire it open. There are some good pics of all that stuff here:
http://forums.corvetteforum.com/c3-t...oes-it-go.html
i wired mine open since I live in FL and do not drive in extreme cold weather, runs 100 times better now. Good Luck.
-Nick
http://forums.corvetteforum.com/c3-t...oes-it-go.html
i wired mine open since I live in FL and do not drive in extreme cold weather, runs 100 times better now. Good Luck.
-Nick
Safety Car
Joined: Apr 2000
Posts: 3,802
Likes: 61
From: Wichita KS
They make heat riser eliminators that replace them with a piece shaped the same with a big hole through them instead of the valve for about $25.00.
I have one even though I live in Kansas because I rarely drive the car in winter.
cc
I have one even though I live in Kansas because I rarely drive the car in winter.
cc
Thread Starter
Racer
Joined: Oct 2005
Posts: 273
Likes: 1
From: Fabens TX
I was so spoiled with my big block on my camaro(powerwise) that I contributed the lack of power to driving a stockish 350 egine on the vette. But yes the engine feels much healthier now. It's hard to gauge the difference since I also fixed the throttle cable at the same time I discovered the valve shut. The cable was not opening the throttle blades completely at wot.
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Pro
Joined: Dec 2006
Posts: 695
Likes: 5
From: tx
Yeah, for those who didn't drive their car in cold weather, they either removed or hollowed out the heat riser. If it is stuck closed usually you'll notice the loss in power, but since you dropped in a different motor .....?
Watch to be sure it doesn't shut again and stay closed. By blocking the exhaust too long, you could burn a valve.
Watch to be sure it doesn't shut again and stay closed. By blocking the exhaust too long, you could burn a valve.
Drifting
Joined: Jul 2002
Posts: 1,944
Likes: 20
From: The only Corvettes in Highett Victoria
Weld it!
G'day,
I have one on my Holden 308 V8, on the driver's side (Right Hand Drive) so it's just like the Corvette. Several years ago, it closed due to a split rubber vacuum hose and I melted the right side of my aluminum inlet manifold, but only at the bottom. The exhaust gas pushed through the head, just like a Chevy, and through the manifold to the left side, where it exited through the left exhaust manifold.
The bottom of the inlet manifold where it joins the inlet ports in the head "shrunk" inwards, allowing some of the exhaust gases to fill the valley of the engine and I guess were then sucked up through the PCV valve and into the air cleaner, through the Qjet and into the engine again. Some must have been getting out through the breather in the other rocker cover.
When I finally found the problem I pulled the heat riser off, (it's probably the same part as on a Corvette or any Chevy - it IS a Holden after all - so you can do the same), and put a dab of weld on the arm, locking it open. But it is a restriction, and if I don't fit headers to the car, I'll pull the whole thing out.
Hope this helps.
Regards from Down Under
aussiejohn
I have one on my Holden 308 V8, on the driver's side (Right Hand Drive) so it's just like the Corvette. Several years ago, it closed due to a split rubber vacuum hose and I melted the right side of my aluminum inlet manifold, but only at the bottom. The exhaust gas pushed through the head, just like a Chevy, and through the manifold to the left side, where it exited through the left exhaust manifold.
The bottom of the inlet manifold where it joins the inlet ports in the head "shrunk" inwards, allowing some of the exhaust gases to fill the valley of the engine and I guess were then sucked up through the PCV valve and into the air cleaner, through the Qjet and into the engine again. Some must have been getting out through the breather in the other rocker cover.
When I finally found the problem I pulled the heat riser off, (it's probably the same part as on a Corvette or any Chevy - it IS a Holden after all - so you can do the same), and put a dab of weld on the arm, locking it open. But it is a restriction, and if I don't fit headers to the car, I'll pull the whole thing out.
Hope this helps.
Regards from Down Under
aussiejohn
Thread Starter
Racer
Joined: Oct 2005
Posts: 273
Likes: 1
From: Fabens TX
G'day,
I have one on my Holden 308 V8, on the driver's side (Right Hand Drive) so it's just like the Corvette. Several years ago, it closed due to a split rubber vacuum hose and I melted the right side of my aluminum inlet manifold, but only at the bottom. The exhaust gas pushed through the head, just like a Chevy, and through the manifold to the left side, where it exited through the left exhaust manifold.
The bottom of the inlet manifold where it joins the inlet ports in the head "shrunk" inwards, allowing some of the exhaust gases to fill the valley of the engine and I guess were then sucked up through the PCV valve and into the air cleaner, through the Qjet and into the engine again. Some must have been getting out through the breather in the other rocker cover.
When I finally found the problem I pulled the heat riser off, (it's probably the same part as on a Corvette or any Chevy - it IS a Holden after all - so you can do the same), and put a dab of weld on the arm, locking it open. But it is a restriction, and if I don't fit headers to the car, I'll pull the whole thing out.
Hope this helps.
Regards from Down Under
aussiejohn
I have one on my Holden 308 V8, on the driver's side (Right Hand Drive) so it's just like the Corvette. Several years ago, it closed due to a split rubber vacuum hose and I melted the right side of my aluminum inlet manifold, but only at the bottom. The exhaust gas pushed through the head, just like a Chevy, and through the manifold to the left side, where it exited through the left exhaust manifold.
The bottom of the inlet manifold where it joins the inlet ports in the head "shrunk" inwards, allowing some of the exhaust gases to fill the valley of the engine and I guess were then sucked up through the PCV valve and into the air cleaner, through the Qjet and into the engine again. Some must have been getting out through the breather in the other rocker cover.
When I finally found the problem I pulled the heat riser off, (it's probably the same part as on a Corvette or any Chevy - it IS a Holden after all - so you can do the same), and put a dab of weld on the arm, locking it open. But it is a restriction, and if I don't fit headers to the car, I'll pull the whole thing out.
Hope this helps.
Regards from Down Under
aussiejohn
. I was worried about heat issues with the big block. I mean if I was getting to 230 with the stockish 350 imagine with a healthier motor. But now I can kind of relax about the cooling issue 