Dr.Jeff
True Classic
I just went out and looked at the '79 block. The small hole for the EGR valve is at the same level as the block drain petcock. Which is a little below the freeze plugs. On the picture it would be about here (red arrow):
I remember when I had the freeze plugs out there wasn't too much distance below them to the bottom of the water jackets. So the EGR feed would have to be at the lowest point of the jacket. Which makes sense because the drain valve also is. That might concern me. All of the SOHC blocks I've stripped had a lot of sediment sitting on the bottom of the water jackets. It looks like sand or gravel. I think that would not be good for the turbo's smallish water passages.
Looking back at the UT diagram that @mkmini posted, the turbo feed appears to also be low in the water jackets (assuming the jackets are the same, which I have no idea). But much more rearward than the EGR spot on the '79 X block. So it obviously works.
This all raises a couple questions regarding the after-run cooling "thermosiphon" effect that @rachaeljf described. How significant are the relative heights of all the water connections (on the engine, turbo, and coolant tank) in terms of functional difference? Also how significant of a functional difference does the temperature differential for various locations of water feed (i.e. block vs head) make? And is one of those factors of greater importance than the other in terms of the overall functional outcome? Basically, what's most important?
Completely non-scientific. Purely ameture armchair guesses. But I imagine the ideal arrangement in terms of thermosiphon would be a cold water supply feed location that is below the the height of the turbos' water inlet. And a hot water return location that is above the turbo's outlet. Because physics tells me hot water (less dense) will rise above cold water (more dense). However I also imagine the ideal arrangement for regular cooling (with the pressurized cooling system) while everything is running is sort of the opposite; a cold feed from above and a hot return below? But that last part may not necessarily be true because radiators flow from top to bottom, which is hot to cold. However their purpose is the opposite, remove heat from the water opposed to absorb heat into the water.
Engineers please help.
I remember when I had the freeze plugs out there wasn't too much distance below them to the bottom of the water jackets. So the EGR feed would have to be at the lowest point of the jacket. Which makes sense because the drain valve also is. That might concern me. All of the SOHC blocks I've stripped had a lot of sediment sitting on the bottom of the water jackets. It looks like sand or gravel. I think that would not be good for the turbo's smallish water passages.
Looking back at the UT diagram that @mkmini posted, the turbo feed appears to also be low in the water jackets (assuming the jackets are the same, which I have no idea). But much more rearward than the EGR spot on the '79 X block. So it obviously works.
This all raises a couple questions regarding the after-run cooling "thermosiphon" effect that @rachaeljf described. How significant are the relative heights of all the water connections (on the engine, turbo, and coolant tank) in terms of functional difference? Also how significant of a functional difference does the temperature differential for various locations of water feed (i.e. block vs head) make? And is one of those factors of greater importance than the other in terms of the overall functional outcome? Basically, what's most important?
Completely non-scientific. Purely ameture armchair guesses. But I imagine the ideal arrangement in terms of thermosiphon would be a cold water supply feed location that is below the the height of the turbos' water inlet. And a hot water return location that is above the turbo's outlet. Because physics tells me hot water (less dense) will rise above cold water (more dense). However I also imagine the ideal arrangement for regular cooling (with the pressurized cooling system) while everything is running is sort of the opposite; a cold feed from above and a hot return below? But that last part may not necessarily be true because radiators flow from top to bottom, which is hot to cold. However their purpose is the opposite, remove heat from the water opposed to absorb heat into the water.
Engineers please help.
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