Rear By-Pass Water Tube In Back Of Engine ?

[timsz]

I have triple Mikunis with a Mikuni manifold. Do I need the coolant tube that runs around the back of the engine? I have a metal tube. Didn't it connect to the manifold? If I need it, where does it connect? 71Z with a F-54 block. What does it do? Thank you.

[Captain Obvious]

Yes, that tube around the back of the block carried water that passed through the original manifold back to the water pump inlet. With your new manifold, I'm assuming there are no provisions for water heat?

 

I'm no cooling system expert, but I think it's important to have a small amount of flow through the thermostat housing, even when the engine is cold. If that area is completely stagnant, then you run the risk of overheating because the thermostat won't be subjected to the hot water and could instead be sitting in a stagnant cold pool.

I believe most thermostats have a small bypass hole built into them to allow for just this kind of issue, but I wouldn't completely block off all those path(s) without first confirming that is the case.

Eventually heat will make it's way into that area through conduction and eddy currents, but if you don't ensure some flow somewhere prior to the thermostat getting hot enough to open, it may be too late by the time it does.          

 

[John Coffey]

Coolant flow out of the back head is important.  Here's an in-depth discussion of the L6 cooling system including cutaways of the head:  http://forums.hybridz.org/topic/59029-head-cooling-on-cylinder-5-solutions/

[Stanley]

Bypass originally provided heat to intake during warm-up and bypass when thermostat closed, with cold=open thermostat connected to back of stock intake manifold. I figured flow in that bypass when from lower thermostat housing but after reading post #155 on p. 8, looks like it might flow the other way.

 

That discussion on Hybrid Z goes 24 pages, didn't finish yet but here's an excerpt from #155.

 

A comment about the port above #6. When the t-stat is closed, water will probably be routed from the lower t-stat housing into #6. The pressure in the t-stat housing will most likely be higher than #6. Remember, the water in #6 is most likely stagnating due to the pressure differential between #6 and #1.

When the t-stat opens, water will then reverse flow, as the t-stat opening is now the lower pressure zone. The pressure through the t-stat and into the hose will most likely be lower than the pressure at #6, thereby allowing water to flow from #6 to the t-stat.          

 

Seems like it would be easy to run a hose from the heater outlet on the back of the head over to the lower thermostat (without a restrictor or the cold=open thermostat in line).  Could put a tee at the heater outlet if you want the heater, otherwise block off the heater return to the lower radiator hose water inlet.

 

I bought the hoses and fittings to do that last year, about $50, haven't got around to it though.