Great explanation, Rick.
FYI, the reverse coolant flow that you refer to did, in fact, see
production. The LT-1 engine series that came out on Corvettes in 1992
through 1996 and was also used in the Impala SS, Camaro Z28, and Caprice
police package of the same era has reversed flow. Much improved efficiency.
They also moved the distributor to the front of the timing cover, behind the
water pump. I haven't had to work on mine, but hope that isn't asking for
trouble. The newer design, the LS-1,replaces the distributor with individual
coils; don't know if it is reverse coolant flow, but since GM was bragging
about the benefits, I wouldn't be surpised.
Travis
- -----Original Message-----
From: RickStapls
To: gmcmotorhome
Date: Friday, April 02, 1999 9:36 PM
Subject: Re: GMC: Ready to explode another myth about the GMC motorhome
thatreally wo...
>
>> If the pump runs backwards the radiator will run at greatly reduced
>> efficiency ie;reversed flow thru the thermostat, reverse water flow thru
>the
>> radiator etc.
>
>Sorry Tom, but that's not the way it works. All automotive cooling water
>pumps that I've ever seen, seen pictures of, or heard of, including that on
>our GMCs, are CENTRIFUGAL pumps. That is to say, the water enters the pump
>chamber near the center, and is flung outward by centrifugal force as it is
>whipped around by the whirling impeller. Doesn't matter which direction
the
>impeller rotates, the flow is still from center outward.
>
> Now some water pumps, especially those with cast impellers, may have
>curved or angled blades (analogous to the angled blades on the centrifugal
>cooling fan of our alternators) which help them pump more efficiently in
one
>direction than the other. But just as our alternator fans will ALWAYS suck
>air in from the back of the alternator and fling it outward at the fan, so
>too will our water pumps ALWAYS draw water from the lower radiator hose
>(whose passage leads to the center of the pump as you can see by looking at
>your pump) and discharge that water into the annular passage around the
>impeller, which leads to the cylinder block's two banks.
>
> It is fortunate that this is so, as the thermostat would be very slow to
>open with reversed flow, if it ever opened at all! (It would have to be
>relocated to the lower (newly hot) hose to function.)) Water flow in the
>radiator might also be complicated, as the system now uses the natural
>thermo-syphon action: cooled water in the radiator sinks toward the lower
>(return) hose, while water being heated in the engine tends to rise to the
>thermostat. In a Model T that thermo-syphon flow provided all the
>circulation it needed: no water pump was necessary. Even today it helps to
>circulate the coolant, sometimes allowing us to limp gently to the next
exit
>when we lose a water pump belt.
>
> Incidentally, there has been some experimentation with a reverse-flow
>cooling system, with the coolant going first to the heads, thence to the
>block. The object is/was to keep the engine at a more uniform and higher
>temperature, to improve efficiency. Usually the cylinder walls run far
>colder than we would like, especially with modern oils that can take the
>heat. Keeping the cylinders hotter would reduce flame quench (for more
>complete combustion) and reduce the heat lost to the cooling system. The
>famous race car driver/mechanic Smokey Yunick was working on this IIRC, and
>was written up in Popular Science a few years back. Since I've heard
nothing
>further, I can only assume that the difficulties in controlling and
balancing
>reverse coolant flow, and the tendency to trap air and/or steam bubbles in
>the engine still outweigh the benefits.
>
> Finally, I have heard of overheating caused when the coolant flows TOO
>fast through the radiator to lose enough heat. Almost invariably this is a
>result of someone removing the thermostat, usually in a misguided attempt
to
>REDUCE operating temperature. In a race car there may be some slight
>justification for replacing the thermostat with a flow restrictor to
>eliminate one potential mechanical failure on the track. But in the real
>world, we ALL need a proper thermostat, to get our engines up to operating
>temp and keep them there. This is especially crucial on fuel-injected
>engines.
>
> HTH.
>
>Rick Staples
>'75 Eleganza
>Louisville, CO
FYI, the reverse coolant flow that you refer to did, in fact, see
production. The LT-1 engine series that came out on Corvettes in 1992
through 1996 and was also used in the Impala SS, Camaro Z28, and Caprice
police package of the same era has reversed flow. Much improved efficiency.
They also moved the distributor to the front of the timing cover, behind the
water pump. I haven't had to work on mine, but hope that isn't asking for
trouble. The newer design, the LS-1,replaces the distributor with individual
coils; don't know if it is reverse coolant flow, but since GM was bragging
about the benefits, I wouldn't be surpised.
Travis
- -----Original Message-----
From: RickStapls
To: gmcmotorhome
Date: Friday, April 02, 1999 9:36 PM
Subject: Re: GMC: Ready to explode another myth about the GMC motorhome
thatreally wo...
>
>> If the pump runs backwards the radiator will run at greatly reduced
>> efficiency ie;reversed flow thru the thermostat, reverse water flow thru
>the
>> radiator etc.
>
>Sorry Tom, but that's not the way it works. All automotive cooling water
>pumps that I've ever seen, seen pictures of, or heard of, including that on
>our GMCs, are CENTRIFUGAL pumps. That is to say, the water enters the pump
>chamber near the center, and is flung outward by centrifugal force as it is
>whipped around by the whirling impeller. Doesn't matter which direction
the
>impeller rotates, the flow is still from center outward.
>
> Now some water pumps, especially those with cast impellers, may have
>curved or angled blades (analogous to the angled blades on the centrifugal
>cooling fan of our alternators) which help them pump more efficiently in
one
>direction than the other. But just as our alternator fans will ALWAYS suck
>air in from the back of the alternator and fling it outward at the fan, so
>too will our water pumps ALWAYS draw water from the lower radiator hose
>(whose passage leads to the center of the pump as you can see by looking at
>your pump) and discharge that water into the annular passage around the
>impeller, which leads to the cylinder block's two banks.
>
> It is fortunate that this is so, as the thermostat would be very slow to
>open with reversed flow, if it ever opened at all! (It would have to be
>relocated to the lower (newly hot) hose to function.)) Water flow in the
>radiator might also be complicated, as the system now uses the natural
>thermo-syphon action: cooled water in the radiator sinks toward the lower
>(return) hose, while water being heated in the engine tends to rise to the
>thermostat. In a Model T that thermo-syphon flow provided all the
>circulation it needed: no water pump was necessary. Even today it helps to
>circulate the coolant, sometimes allowing us to limp gently to the next
exit
>when we lose a water pump belt.
>
> Incidentally, there has been some experimentation with a reverse-flow
>cooling system, with the coolant going first to the heads, thence to the
>block. The object is/was to keep the engine at a more uniform and higher
>temperature, to improve efficiency. Usually the cylinder walls run far
>colder than we would like, especially with modern oils that can take the
>heat. Keeping the cylinders hotter would reduce flame quench (for more
>complete combustion) and reduce the heat lost to the cooling system. The
>famous race car driver/mechanic Smokey Yunick was working on this IIRC, and
>was written up in Popular Science a few years back. Since I've heard
nothing
>further, I can only assume that the difficulties in controlling and
balancing
>reverse coolant flow, and the tendency to trap air and/or steam bubbles in
>the engine still outweigh the benefits.
>
> Finally, I have heard of overheating caused when the coolant flows TOO
>fast through the radiator to lose enough heat. Almost invariably this is a
>result of someone removing the thermostat, usually in a misguided attempt
to
>REDUCE operating temperature. In a race car there may be some slight
>justification for replacing the thermostat with a flow restrictor to
>eliminate one potential mechanical failure on the track. But in the real
>world, we ALL need a proper thermostat, to get our engines up to operating
>temp and keep them there. This is especially crucial on fuel-injected
>engines.
>
> HTH.
>
>Rick Staples
>'75 Eleganza
>Louisville, CO
