Intake manifold water tube leaking

[Stanley]

"It's a lot easier to reject heat through a radiator than it is a rubber hose."

Good point. The thick heater hose insulates. The loop wouldn't be as bad if it were a metal pipe instead, the longer the better. The carb heater also takes hot water and runs it back to the intake (when the hot-off valve is missing) but it's metal so it sheds some heat.

Running a hose from the head outlet to a fitting on the thermostat outlet, just in back of the radiator hose connection, doesn't sound too hard. If the outlet is too thin to tap in a fitting just braze or aluminum weld one on at an angle. A valve at the head outlet would take care of the warm-up problem - open for summer, closed for winter.

More food for thought.

[LeonV]

"It's a lot easier to reject heat through a radiator than it is a rubber hose."

Good point. The thick heater hose insulates. The loop wouldn't be as bad if it were a metal pipe instead, the longer the better. The carb heater also takes hot water and runs it back to the intake (when the hot-off valve is missing) but it's metal so it sheds some heat.

Running a hose from the head outlet to a fitting on the thermostat outlet, just in back of the radiator hose connection, doesn't sound too hard. If the outlet is too thin to tap in a fitting just braze or aluminum weld one on at an angle. A valve at the head outlet would take care of the warm-up problem - open for summer, closed for winter.

More food for thought.

If you're thinking of bypassing the thermostat, that hose from the back of the head is in no way required to go to the top of the thermo housing! For example, you can have it go straight into the upper rad hose, using a hose coupler with a radially-located fitting for the smaller hose. Basically, slice the upper rad hose in half and figure out a way to incorporate that hose from the back of the head.

Or, just tap right into the top of the radiator...

[Captain Obvious]

There won't be as much heat rejected with the control lever on HOT and the fan off, but there is still air going through the core (it's not stagnant). The fan being off doesn't mean zero airflow.

Actually it is stagnant. There is an air intake control flapper door on the input to the blower motor that selects either outside fresh air, or recirculated. You get that air intake door into the recirc position with the fan off, and it's dead stagnant (or at least as stanant as your sealing foam on the door will allow). I don't know about the 240s, but it's easy on the 260 and 280.

Without A/C, if you move the top lever (the "AIR" lever) to "OFF" this will put the air intake door in the recirc position. No fan, and you're stagnant. (260 FSM BE-46) (260 FSM BE-48) And if you do have A/C, you're running in recirc any time you have the lever on "A/C" or "REC HEAT". Put the lever into either of those two positions with no fan, and you're stagnant. (260 FSM AC-6) (280 FSM AC-6)

Good point about the coolant flow valve. I have to remember that my modified flow valve provides pretty much no resistance when wide open. Something I should probably keep in mind... When wide open, I bet I'm sending a lot more hot water back to the water pump than stock. I'm going to consider adding a restriction to that line. It's not like I need more heat in the interior. I get plenty.

Between that and the fact that my PO took off the heating pad under my AAR, I'm thinking I should install some sort of small thermostat bypass just to make sure I get some flow into the thermostat housing to keep the thermostat up to date with the rest of the engine.

Thanks for the help!

[LeonV]

Ok, I meant if it's on HOT with the FLOOR/DEFROST still selected, i.e. flapper open.

Sounds good.

[Captain Obvious]

Yeah, that's why it seemed like the same thing to me as looping the heater hose. Sure, you'll get some convection currents in the air in the box where the core is, but that's gotta be negligible. Makes me hope you were right about this:

I'd like to think that the engineers sized things correctly, or as best as they could. It's when engine demands are increased that a loop from the head to the WP inlet will have a detrimental effect (dangerously unstable temps at back of head).

I agree, and based on the empirical data of "we don't hear from lots of stock owners with overheating problems" I would guess they did OK with the margin of safety. Still makes me wonder if I may have complicated matters with my fancy schmancy heater flow valve...

[LeonV]

I agree, and based on the empirical data of "we don't hear from lots of stock owners with overheating problems" I would guess they did OK with the margin of safety. Still makes me wonder if I may have complicated matters with my fancy schmancy heater flow valve...

The thing is, and I mentioned it earlier, the temperature gauge reports to the sensor in the thermostat housing. We have no idea what's going on at the back of the head. Temp can be OK in the front, but tens of degrees higher in the back. Tony D and Jeff P did some engine dyno testing, monitoring temps front and back among other things, and posted results in that HybridZ thread.

This is also why most stress-related head gasket failures seem to be at cylinder 5.

[Captain Obvious]

The thing is, and I mentioned it earlier, the temperature gauge reports to the sensor in the thermostat housing. We have no idea what's going on at the back of the head.

Gotcha. That's a good point.

[Stanley]

Googled "branched radiator hose" and this came up:branched coolant hose - Google Search

[Stanley]

Radiator hose Tee fitting:V8 Chevrolet TPI & TBI, Radiator Hose Tees, Stealth Conversions

[LeonV]

Precisely.

[Stanley]

Looks like the tee connection might not work in the stock upper radiator hose - there's no straight section long enough to fit the tee. You could try it (on an old hose first) but it might tend to leak since you'd be clamping a curved section to the tee. The new silicon hoses have tighter radius curves - looks like a workable setup could be made from 2- 45 deg. angle hoses with the tee in the diagonal section. The 45 deg. silicon hoses are available online. I would go for black rather than the usual blue silicon. I've read both good and bad things about silicon radiator hoses.

It will be a bit pricey: about $15 each for the angle hoses, $25 for the tee, $15 for a nice EPDM heater hose, plus clamps (special clamps recommended for silicon) and shipping. More with a valve or restrictor.

As a possible alternative, there are hundreds of branched radiator hoses available for the newer cars - someone knowledgeable at the (independent store) parts counter might be able to find one that fits.