Why head gasket restrict coolant flow?

Manco
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Manco
Edited Date/Time 11/6/2015 10:41pm
What up with cylinders that have head gaskets designed to restrict coolant flow? Case in point, 2001 Honda CR125r: The cylinder to head faces could potentially flow more coolant then the head gasket. Why does the head gasket restrict flow? To keep the head warm? Assist pressure for pump? or Does pump only move less then "x" volume at "y" rpms which is less then max rpms where "x" volume can easily pass through the restricted gasket? Check pics below. Thanks for any info you have on this.

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Manco
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Manco 11/3/2015 10:04pm
11/3/2015 10:04pm
head



head gasket



cylinder



colintrax
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colintrax 11/3/2015 11:07pm
11/3/2015 11:07pm
Looks like it's trying to concentrate the flow around the exhaust side. Coulda been a cheap fix to a poor cooling design.
Could also be to keep the stock engine warm, but make it easy for modded engines to cool better.
Slosh 112
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Slosh 112 11/4/2015 12:08am
11/4/2015 12:08am
Not being familiar with Hondas but does it have a bridged exhaust port? if so could be like what Colin said, to focus the cool charge around the ex port?...
Manco
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Manco 11/4/2015 11:17am
11/4/2015 11:17am
I think you guy nailed it on the exhaust port area cooling. The large coolant hole in the head gasket is above the exhaust port. Thanks for the insight.

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mxtech1
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mxtech1 11/4/2015 2:30pm
11/4/2015 2:30pm Edited Date/Time 11/4/2015 2:30pm
The large port allows more coolant to be concentrated in the exhaust port area. More coolant means more surface area contacting the coolant and the cylinder. Since more heat is concentrated in that area, the cooling system is engineered so that most of the coolant flows through the path of the large opening, drawing out heat, and then pushing it to the top of the radiator for cooling before being returned to the pump.

It's not a cheap fix to fix solve engineering issues, it's actually an incredibly ingenious solution by engineers who really understood fluid and thermal dynamics.
sandman768
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sandman768 11/4/2015 3:10pm
11/4/2015 3:10pm
mxtech1 wrote:
The large port allows more coolant to be concentrated in the exhaust port area. More coolant means more surface area contacting the coolant and the cylinder...
The large port allows more coolant to be concentrated in the exhaust port area. More coolant means more surface area contacting the coolant and the cylinder. Since more heat is concentrated in that area, the cooling system is engineered so that most of the coolant flows through the path of the large opening, drawing out heat, and then pushing it to the top of the radiator for cooling before being returned to the pump.

It's not a cheap fix to fix solve engineering issues, it's actually an incredibly ingenious solution by engineers who really understood fluid and thermal dynamics.
I"ve often wondered about this same scenario on alot of my builds, Iearn something new everyday! Thanks
colintrax
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colintrax 11/4/2015 3:42pm
11/4/2015 3:42pm
mxtech1 wrote:
The large port allows more coolant to be concentrated in the exhaust port area. More coolant means more surface area contacting the coolant and the cylinder...
The large port allows more coolant to be concentrated in the exhaust port area. More coolant means more surface area contacting the coolant and the cylinder. Since more heat is concentrated in that area, the cooling system is engineered so that most of the coolant flows through the path of the large opening, drawing out heat, and then pushing it to the top of the radiator for cooling before being returned to the pump.

It's not a cheap fix to fix solve engineering issues, it's actually an incredibly ingenious solution by engineers who really understood fluid and thermal dynamics.
It'd be a cheap fix... because if they did it right to begin with they wouldn't need a gasket to close off ports.
Cancerman
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Cancerman 11/4/2015 3:48pm
11/4/2015 3:48pm
Another reason to slow the coolant is to allow more heat transfer to the coolant itself. This is very common in cars as well.
Matt Fisher 11/5/2015 8:54am
11/5/2015 8:54am
Cancerman wrote:
Another reason to slow the coolant is to allow more heat transfer to the coolant itself. This is very common in cars as well.
Not really. If slower fluid movement helped cooling, then flow would be reduced to almost nothing.

The flow restrictions on the outlet side of a cooling system are to build additional pressure in that area. Higher pressure makes it harder for cavitation or boiling to occur; both of which are bad since air doesn't transfer heat nearly as well as water does.
Slosh 112
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Slosh 112 11/5/2015 5:29pm
11/5/2015 5:29pm
Restricted coolant flow won't build pressure in that area, water will take the path of least resistance, the entire cooling system is already pressurised so you're not going to get high and low pressure areas in one connected system. The head gasket is restricted on the cool side of the head and open on the exhaust port area to encourage the cooler water at the back of the head to follow through the hot area on its way out before it goes to the radiator.

Its common in heavy machinery and older cars that have cast iron cylinder heads and engine blocks to have low flow coolant systems and massive radiators. Not to give the water time to absorb the heat but to give the engine block time to dissipate its heat to the water. Aluminium is a lot better at dissipating heat so cooling systems can be more efficient.
BAMX
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BAMX 11/5/2015 9:11pm
11/5/2015 9:11pm
The small holes help build pressure. The pressure helps with cooling. The way it was explained to me, a system with too low a pressure system can build steam pocket at the cooling surface. This keeps the heat from transferring.
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Cancerman 11/5/2015 10:53pm
11/5/2015 10:53pm
Cancerman wrote:
Another reason to slow the coolant is to allow more heat transfer to the coolant itself. This is very common in cars as well.
Matt Fisher wrote:
Not really. If slower fluid movement helped cooling, then flow would be reduced to almost nothing. The flow restrictions on the outlet side of a cooling...
Not really. If slower fluid movement helped cooling, then flow would be reduced to almost nothing.

The flow restrictions on the outlet side of a cooling system are to build additional pressure in that area. Higher pressure makes it harder for cavitation or boiling to occur; both of which are bad since air doesn't transfer heat nearly as well as water does.
Then why is it that if you remove a thermostat in a car motor, you can see it run hotter. I've tested this theory in small block chevys, and in my mazda miata. Different temp thermos, and it starts running hotter, unless you are at serious speeds. Just my observations, that's all. The Hot rod mags all tested this as well, back in the 70's and 80's, before everything went computer controlled.
Matt Fisher 11/6/2015 9:03am
11/6/2015 9:03am
Cancerman wrote:
Another reason to slow the coolant is to allow more heat transfer to the coolant itself. This is very common in cars as well.
Matt Fisher wrote:
Not really. If slower fluid movement helped cooling, then flow would be reduced to almost nothing. The flow restrictions on the outlet side of a cooling...
Not really. If slower fluid movement helped cooling, then flow would be reduced to almost nothing.

The flow restrictions on the outlet side of a cooling system are to build additional pressure in that area. Higher pressure makes it harder for cavitation or boiling to occur; both of which are bad since air doesn't transfer heat nearly as well as water does.
Cancerman wrote:
Then why is it that if you remove a thermostat in a car motor, you can see it run hotter. I've tested this theory in small...
Then why is it that if you remove a thermostat in a car motor, you can see it run hotter. I've tested this theory in small block chevys, and in my mazda miata. Different temp thermos, and it starts running hotter, unless you are at serious speeds. Just my observations, that's all. The Hot rod mags all tested this as well, back in the 70's and 80's, before everything went computer controlled.
In some cooling systems the thermostat is the restriction that increases the pressure inside the motor. In that instance, removing it reduces the psi and when air pockets form, the overall temp goes up. In other motors the restriction might be on the feed side of the radiator, or any number of other places.

My parents had 79 E350 with a 460 in it. Coming home from Colorado the thermostat stuck and the shop we stopped at didn't have a replacement, so they removed it. The engine never fully warmed up the entire way home to CA! Different designed cooling systems will have different results if the thermostat is removed.
motox331
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motox331 11/6/2015 1:58pm
11/6/2015 1:58pm
Theres a ton of reasons why the gasket restricts flow. The main one I believe is to try and maintain the entire cylinder at the same temp. the exhaust side will be hotter needing more cooling than the intake side. if your cylinder has a temperature distribution it will be no bueno
Manco
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Manco 11/6/2015 2:03pm
11/6/2015 2:03pm
This turned into a really cool thread. It has lots of great info that will be food for thought when engine building. Thanks for delivering the goods folks.
Cancerman
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Cancerman 11/6/2015 10:41pm
11/6/2015 10:41pm
Matt Fisher wrote:
Not really. If slower fluid movement helped cooling, then flow would be reduced to almost nothing. The flow restrictions on the outlet side of a cooling...
Not really. If slower fluid movement helped cooling, then flow would be reduced to almost nothing.

The flow restrictions on the outlet side of a cooling system are to build additional pressure in that area. Higher pressure makes it harder for cavitation or boiling to occur; both of which are bad since air doesn't transfer heat nearly as well as water does.
Cancerman wrote:
Then why is it that if you remove a thermostat in a car motor, you can see it run hotter. I've tested this theory in small...
Then why is it that if you remove a thermostat in a car motor, you can see it run hotter. I've tested this theory in small block chevys, and in my mazda miata. Different temp thermos, and it starts running hotter, unless you are at serious speeds. Just my observations, that's all. The Hot rod mags all tested this as well, back in the 70's and 80's, before everything went computer controlled.
Matt Fisher wrote:
In some cooling systems the thermostat is the restriction that increases the pressure inside the motor. In that instance, removing it reduces the psi and when...
In some cooling systems the thermostat is the restriction that increases the pressure inside the motor. In that instance, removing it reduces the psi and when air pockets form, the overall temp goes up. In other motors the restriction might be on the feed side of the radiator, or any number of other places.

My parents had 79 E350 with a 460 in it. Coming home from Colorado the thermostat stuck and the shop we stopped at didn't have a replacement, so they removed it. The engine never fully warmed up the entire way home to CA! Different designed cooling systems will have different results if the thermostat is removed.
I've experienced this as well, mostly when you have an oversized radiator core and a cool day at highway speeds......

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