Heater core shutoff causing overheating
Thread Starter
Burning Brakes
Joined: Oct 2008
Posts: 955
Likes: 50
From: Jersey Shore
My gauge sender is in the passenger side head.
When I had the valve closed, the temp would drop back down to 180 or so after a few minutes, but it would never settle at a temp like it does with the valve open. (just like couperdecar's "valve closed" scenario)
Just out of curiosity, what is the point of replacing the heater lines with a loop from the manifold to the pump? You will get the same result as leaving it as it is with the valve open. Sure there is heat exchanged when it goes through the heater core, but we know that it has no measurable engine cooling capability, therefore, no effect on the problem at hand.
When I had the valve closed, the temp would drop back down to 180 or so after a few minutes, but it would never settle at a temp like it does with the valve open. (just like couperdecar's "valve closed" scenario)
Just out of curiosity, what is the point of replacing the heater lines with a loop from the manifold to the pump? You will get the same result as leaving it as it is with the valve open. Sure there is heat exchanged when it goes through the heater core, but we know that it has no measurable engine cooling capability, therefore, no effect on the problem at hand.
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
My gauge sender is in the passenger side head.
When I had the valve closed, the temp would drop back down to 180 or so after a few minutes, but it would never settle at a temp like it does with the valve open. (just like couperdecar's "valve closed" scenario)
Just out of curiosity, what is the point of replacing the heater lines with a loop from the manifold to the pump? You will get the same result as leaving it as it is with the valve open. Sure there is heat exchanged when it goes through the heater core, but we know that it has no measurable engine cooling capability, therefore, no effect on the problem at hand.
When I had the valve closed, the temp would drop back down to 180 or so after a few minutes, but it would never settle at a temp like it does with the valve open. (just like couperdecar's "valve closed" scenario)
Just out of curiosity, what is the point of replacing the heater lines with a loop from the manifold to the pump? You will get the same result as leaving it as it is with the valve open. Sure there is heat exchanged when it goes through the heater core, but we know that it has no measurable engine cooling capability, therefore, no effect on the problem at hand.
The original Mini Minor manual stated that when the engine temp got too high, to turn on the heat to add cooling. It can help, the amount is questionable in a c3.
Drifting
Joined: May 2005
Posts: 1,629
Likes: 4
From: Somers CT
My gauge sender is in the passenger side head.
When I had the valve closed, the temp would drop back down to 180 or so after a few minutes, but it would never settle at a temp like it does with the valve open. (just like couperdecar's "valve closed" scenario)
Just out of curiosity, what is the point of replacing the heater lines with a loop from the manifold to the pump? You will get the same result as leaving it as it is with the valve open. Sure there is heat exchanged when it goes through the heater core, but we know that it has no measurable engine cooling capability, therefore, no effect on the problem at hand.
When I had the valve closed, the temp would drop back down to 180 or so after a few minutes, but it would never settle at a temp like it does with the valve open. (just like couperdecar's "valve closed" scenario)
Just out of curiosity, what is the point of replacing the heater lines with a loop from the manifold to the pump? You will get the same result as leaving it as it is with the valve open. Sure there is heat exchanged when it goes through the heater core, but we know that it has no measurable engine cooling capability, therefore, no effect on the problem at hand.
Interesting on your sender being in the head though, I would have bet it was in the intake where an air pocket could form.
Maybe there's some turbulence being created by having the line blocked allowing an air pocket to form. All just a guess............but there is something going on by blocking that line with a shutoff. I've had an air pocket before after having drained the coolant for another reason and this heater shutoff problem acts EXACTLY the same way.
Instructor
Joined: Jun 2011
Posts: 183
Likes: 1
From: Litchfield CT
circulation
My gauge sender is in the passenger side head.
When I had the valve closed, the temp would drop back down to 180 or so after a few minutes, but it would never settle at a temp like it does with the valve open. (just like couperdecar's "valve closed" scenario)
Just out of curiosity, what is the point of replacing the heater lines with a loop from the manifold to the pump? You will get the same result as leaving it as it is with the valve open. Sure there is heat exchanged when it goes through the heater core, but we know that it has no measurable engine cooling capability, therefore, no effect on the problem at hand.
When I had the valve closed, the temp would drop back down to 180 or so after a few minutes, but it would never settle at a temp like it does with the valve open. (just like couperdecar's "valve closed" scenario)
Just out of curiosity, what is the point of replacing the heater lines with a loop from the manifold to the pump? You will get the same result as leaving it as it is with the valve open. Sure there is heat exchanged when it goes through the heater core, but we know that it has no measurable engine cooling capability, therefore, no effect on the problem at hand.
Don't forget the second part of the suggestion; run the car with the rad cap off (not driving, parked).
Thread Starter
Burning Brakes
Joined: Oct 2008
Posts: 955
Likes: 50
From: Jersey Shore
I suggested the short hose loop so that circulation is allowed. If, as many suggested, there is cavitation from the loss of circulation, it will be eliminated. Also, if there is an airlock somewhere, this will help to flush it out.
Don't forget the second part of the suggestion; run the car with the rad cap off (not driving, parked).
Don't forget the second part of the suggestion; run the car with the rad cap off (not driving, parked).
If there was an air pocket in my system, it would be evident all the time. There are no problems (ie: no air pockets) with my cooling system when the valve is open.
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
When the valve is open, there is circulation. It doesnt matter if it has to go through the heater core or not. Its just more hose to travel through.
If there was an air pocket in my system, it would be evident all the time. There are no problems (ie: no air pockets) with my cooling system when the valve is open.
If there was an air pocket in my system, it would be evident all the time. There are no problems (ie: no air pockets) with my cooling system when the valve is open.
My vote is your pump bypass is blocked or restricted or your pump is overly sensitive to back pressure. When you have time pull the pump off and remove the back cover and see if there is anything visible about the impeller that might cause this.
Drifting
Joined: Jul 2002
Posts: 1,944
Likes: 20
From: The only Corvettes in Highett Victoria
Back to basics
G'day,
Did you notice the OP's avatar? 427-sbc. Presumably he has a 400 ci block with a stoker crank to give him 427 ci. These blocks have a bore of 4.125" and siamesed cylinder bores. i.e., no water passage between the cylinders. The water in these blocks had less "space" than 350 blocks and more cubic inches to cool and naturally ran hotter. These blocks had extra holes drilled in them to let the hot water ("steam") into the 400 heads. He says he is not running 400 ci heads.
Have the steam holes been drilled in the heads to match the block? If not, this could be the root cause. In any case, he's running an engine block that was never designed to go in a Corvette, therefore it needs special attention in the cooling department.
If the OP is not sure about the steam holes, he should contact the engine builder to ascertain if this was done.
Just my $0.02 worth.
Regards from Down Under.
aussiejohn
Did you notice the OP's avatar? 427-sbc. Presumably he has a 400 ci block with a stoker crank to give him 427 ci. These blocks have a bore of 4.125" and siamesed cylinder bores. i.e., no water passage between the cylinders. The water in these blocks had less "space" than 350 blocks and more cubic inches to cool and naturally ran hotter. These blocks had extra holes drilled in them to let the hot water ("steam") into the 400 heads. He says he is not running 400 ci heads.
Have the steam holes been drilled in the heads to match the block? If not, this could be the root cause. In any case, he's running an engine block that was never designed to go in a Corvette, therefore it needs special attention in the cooling department.
If the OP is not sure about the steam holes, he should contact the engine builder to ascertain if this was done.
Just my $0.02 worth.
Regards from Down Under.
aussiejohn
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Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
The only difference I can see in your case between just opening the valve and running through the core and looping a hose is the tiny bit of cooling the core will provide. I doubt there would be any difference BUT what if you would loop with a piece of hose and it still overheated ? That might be one for the books.
My vote is your pump bypass is blocked or restricted or your pump is overly sensitive to back pressure. When you have time pull the pump off and remove the back cover and see if there is anything visible about the impeller that might cause this.
My vote is your pump bypass is blocked or restricted or your pump is overly sensitive to back pressure. When you have time pull the pump off and remove the back cover and see if there is anything visible about the impeller that might cause this.
No telling what the pump is. Even a lot of new and rebuilt replacement pumps don't have the flow capability of the oem pumps. The temp gauge in the head shows the added heat and the only change with the pex valves is the flow/pressure.
You may be giving an easier route to disperse the vapor pockets thru the heater lines away from the tstat. It would be interesting to gut an old tstat, use the housing and test with the heater valves closed.
G'day,
Did you notice the OP's avatar? 427-sbc. Presumably he has a 400 ci block with a stoker crank to give him 427 ci. These blocks have a bore of 4.125" and siamesed cylinder bores. i.e., no water passage between the cylinders. The water in these blocks had less "space" than 350 blocks and more cubic inches to cool and naturally ran hotter. These blocks had extra holes drilled in them to let the hot water ("steam") into the 400 heads. He says he is not running 400 ci heads.
Have the steam holes been drilled in the heads to match the block? If not, this could be the root cause. In any case, he's running an engine block that was never designed to go in a Corvette, therefore it needs special attention in the cooling department.
If the OP is not sure about the steam holes, he should contact the engine builder to ascertain if this was done.
Just my $0.02 worth.
Regards from Down Under.
aussiejohn
Did you notice the OP's avatar? 427-sbc. Presumably he has a 400 ci block with a stoker crank to give him 427 ci. These blocks have a bore of 4.125" and siamesed cylinder bores. i.e., no water passage between the cylinders. The water in these blocks had less "space" than 350 blocks and more cubic inches to cool and naturally ran hotter. These blocks had extra holes drilled in them to let the hot water ("steam") into the 400 heads. He says he is not running 400 ci heads.
Have the steam holes been drilled in the heads to match the block? If not, this could be the root cause. In any case, he's running an engine block that was never designed to go in a Corvette, therefore it needs special attention in the cooling department.
If the OP is not sure about the steam holes, he should contact the engine builder to ascertain if this was done.
Just my $0.02 worth.
Regards from Down Under.
aussiejohn
Race Director
Joined: May 2006
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From: Dayton, Ohio
Le Mans Master
Joined: Jan 2006
Posts: 6,504
Likes: 139
From: Butler Pa
The built in bypass must be plugged. The purpose of the bypass is to circulate water in the block, bypassing the radiator until water temp is hot enough to open the thermostat. When the water to the heater core is shut off, water is no longer circulating in the block and it takes too long for the water at the thermostat to heat up and open the thermostat.
Drifting
Joined: May 2005
Posts: 1,629
Likes: 4
From: Somers CT
The built in bypass must be plugged. The purpose of the bypass is to circulate water in the block, bypassing the radiator until water temp is hot enough to open the thermostat. When the water to the heater core is shut off, water is no longer circulating in the block and it takes too long for the water at the thermostat to heat up and open the thermostat.
Le Mans Master
Joined: Jan 2006
Posts: 6,504
Likes: 139
From: Butler Pa
Race Director
Joined: May 2006
Posts: 16,528
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From: Dayton, Ohio
Race Director
Joined: Mar 2006
Posts: 14,112
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From: Florida
I use a Stewarts Stage 2 that has no pump bypass port AND I also have both the heater hose ports in the manifold and water pump plugged off with brass plugs. The engine runs rock solid at tstat temps under all conditions.
The tstat has been modified to allow minimum circulation during warm up.
I suggested trying a modified tstat to test because
1-serves the same purpose as the bypass port when cold
2-any vapor pockets rise to the highest point possibly affecting tstat operation
3-it's easier than removing the pump
I'm leaning ultimately towards #2 since the heater hose port is also at the top relieving any vapor pockets formed.
