[Lattimer]

Originally Posted by mechanicalman

Before the thermostat opens, if no coolant is flowing (just sitting still and creating hot pocket) across the top of the heads, multiple steam pockets form, enough air will remain in the system to allow the thermostat to sit in open air, then it will not open and the engine will overheat and head cracking is common from just the steam pockets, let alone the ensuing overheating.

Let me break it down simple: You need coolant flowing from the upper part of the engine below the thermostat when the thermostat is closed to keep steam pockets from developing from stagnant coolant sitting still on top of the hot heads. ANY hose coming off the top of the intake going to the suction side of the water pump will keep the coolant moving and prevent steam pockets from developing. The heater circuit will do this, if you don't shut it off with a water valve.

With no heater valve and coolant flowing all the time from the top of the intake through the heater core to the water pump (like you said it does )you do not need a bypass hose.

I said that if you by-passed your heater core you could damage your engine, but now that I think about it that would be only if you plugged the hoses. If you looped the 3/4" outlet hose from the top of the intake (heater supply) and adapted it down to 5/8" and connected it directly to the water pump heater intake, that would be a good bypass system.

So, consider not having a bypass hose but if you do carry a 3/4" to 5/8" heater hose adaptor in your glove box for emergency IF YOUR HEATER CORE BLOWS A LEAK.

But if you ever add a/c, and install a heater valve (aftermarket systems do that), again you will need a bypass hose.

The instructions HAVE to say you need a bypass hose and they cannot get into the complexities of a/c or no a/c. But the fact of the matter is, a heater running off the intake manifold to the suction side of the water pump IS YOUR BYPASS HOSE if flow is allow un-interrupted.

I've always just popped a hole in the t-stat to do the same thing. Truck warms up a little slower like was mentioned earlier, but its not a daily driver so no issues for me.