Does anyone know why there is a 5/8 water hose from the stock merc. water block pump that feeds into the intake manifold just below the thermostat. Is it needed and does it make a difference on a Gen 4 as compared to a Gen 5? Could this hose add or reduce water pressure in the block?or does it just help regulate water temp.?

Thanks Nordic95

Hey Anthony, been wondering the same myself. From my understanding it's a bypass for when the t-stat hasn't opened yet. Lets water circulate (warm up) until t-stat opens and probably helps regulate psi a little until t-stat opens.

I want to put water psi gauges in my manifolds so I'll be curious to see what others have done. My t-stats are drilled so not so worried about psi build up. A little longer for warm up shouldn't hurt.

My t-stats are drilled also. But my motor guy says I only need this hose on the Gen 4 block, not sure why. It came stock on both motors. Everything seems to be working OK but I would just like to know for my own mental stability.
Anthony

I was told it primes the pump.

I have the 1-1/2" hose from the t stat to the pump,wouldn't that prime the pump?

I would guess that the hose from the t stat is above the waterline in the block. And unless the water in the hose leak down it could prime the pump. Just what someone told me. I'm running a crossover on my mark IV so i have never thought about it.

Anyone else have any answers?

Nordic95