Intake manifold water tube leaking

[LeonV]

Here's a pdf, some sketches to help me understand coolant flow with various setups, based on the hybrid Z thread John posted.

That thread is about coolant flow, not heating the carbs, but it answered my question about John's setup. A lot of that thread is about high horsepower Z cars that are tracked - I left those setups out since they're over my head. Also I left out conditions where there's heater with a closed valve and a carb heating tube with a closed thermostat (in the tube) since not much happens.

Fig. 1:Stock setup, heater on. Improves circulation at cold start (see that 24p thread for why it's important, esp for racing) and helps cool rear cylinders.

Fig. 2. Stock, heater closed. Same as plugging outlet D and branch of tee F.

Fig. 3. Heater hose looped, carb heater tube remains. What I've got now. This setup gets bad press because it sends hot coolant from the head back to the intake, but it helps cold start circulation and helps equalize engine temps.

Fig. 4. Heater hose looped, carb heater tube gone. Helps equalize temp and improves cold start circulation. Proven to raise coolant temp, but maybe because more is circulated at rear of engine.

Fig 5. John Coffey's setup if I'm correct. This is what I want to do with mine. Improves circulation at cold start and helps equalize engine temp.

Good effort.

Your arrows are a little funky in Figure 1-3, the carb water loop should flow the opposite direction since the lower thermostat housing is a high pressure area and the water pump inlet is low pressure.

Figure 3-4 aid in quicker warmup but to the detriment of out-of-control coolant temps at the back of the head. It absolutely does not equalize temperatures! It's a huge short-circuit for hot coolant to take right back to the water pump inlet, bypassing the radiator. This is hard to notice because our temp gauge is at the thermostat housing.

Figure 5 does nothing to improve cold-start (closed thermostat) circulation. It may slightly aid in equalizing temps at the back of the head. Routing to the top of the thermo housing (bypassing thermostat) would be more beneficial. However, this would also have to be spec'd as to not completely shunt the thermostat (maintain some restriction in the line).

[Stanley]

Thank you, I was pretty sure it wasn't 100 percent correct. All I know is from reading that thread and there are some varying opinions there. As I understand it, coolant stagnates at the back of the engine (compared to the front 3 or 4 cylinders) so anything that gets coolant from the back to the front helps.

Regarding the arrows in the carb loop, I see how they would run the other way if the thermostat is closed, but what if it's open? Seems like the larger flow from the engine to the radiator would create a suction that would pull coolant from the smaller carb tube. But maybe not. Could there be a situation where the flow would slow down, stop, or even reverse? I also wasn't sure about the direction of flow in certain setups and conditions between the head and the water pump inlet.

[John Coffey]

Remember, the water pump is pushing the water through the system from the block up through the head and out the thermostat. There are internal bypasses for when the thermostat it closed but water is always entering the pump through the two inlets and always trying to exit via the thermostat. Solution number 5 (what I've implemented a few times) is an alternative route to the thermostat when pressure builds up at the back of the head. Its also a good air bleed for when you're filling the cooling system.

[Captain Obvious]

I also believe you have the flow direction through the carbs going the wrong way in Figs 1, 2, and 3. Not sure about the direction in Fig 5... I don't know what would happen there.

Figure 3-4 aid in quicker warmup but to the detriment of out-of-control coolant temps at the back of the head. It's a huge short-circuit for hot coolant to take right back to the water pump inlet, bypassing the radiator.

So about looping that heater hose as shown in Fig 4. I understand the concept about it short-circuiting the radiator and sending hot coolant back to the water pump inlet, but here's my question...

With a completely stock setup, how is that any different than driving around with the heat selector control slid all the way to HOT and putting the air selector lever to OFF so there isn't any air flow through the heater core? You're doing the exact same thing, right?

[LeonV]

Thank you, I was pretty sure it wasn't 100 percent correct. All I know is from reading that thread and there are some varying opinions there. As I understand it, coolant stagnates at the back of the engine (compared to the front 3 or 4 cylinders) so anything that gets coolant from the back to the front helps.

Regarding the arrows in the carb loop, I see how they would run the other way if the thermostat is closed, but what if it's open? Seems like the larger flow from the engine to the radiator would create a suction that would pull coolant from the smaller carb tube. But maybe not. Could there be a situation where the flow would slow down, stop, or even reverse? I also wasn't sure about the direction of flow in certain setups and conditions between the head and the water pump inlet.

It doesn't matter whether the thermostat is open or closed, it is at higher pressure that the water-pump inlet which is the lowest pressure point in the system. This means that everything "wants" to flow back to the water pump inlet. Pressure at the water pump inlet will be less than at the thermo housing, thus flow goes towards the WP inlet.

I also believe you have the flow direction through the carbs going the wrong way in Figs 1, 2, and 3. Not sure about the direction in Fig 5... I don't know what would happen there.

Good point, and I don't know either. This is why I suggested that routing that line from the back of the head to the top of the thermo housing (or beyond) would be a better idea, if even head cooling is the goal.

So about looping that heater hose as shown in Fig 4. I understand the concept about it short-circuiting the radiator and sending hot coolant back to the water pump inlet, but here's my question...

With a completely stock setup, how is that any different than driving around with the heat selector control slid all the way to HOT and putting the air selector lever to OFF so there isn't any air flow through the heater core? You're doing the exact same thing, right?

Good question. There are two things going on here: (1) even with the heater valve fully open, there is still some added restriction in the valve and core which makes it a little harder for coolant to bypass the radiator and (2) the heater core itself is a radiator. When set to fully hot, the coolant will slough heat through the core, which drops coolant temps before going back to the WP inlet.

I remember going on family trips in a Chevy Lumina that we had for a little while. The cooling system in that car was a joke (heads sat above the top of radiator) and my dad did both head gaskets at one point. When taking grades in the summer heat on the way to Yosemite, he'd turn the heater to full hot and blast the interior fan... in 100deg weather.

Oh the good ol' days!

[John Coffey]

IIRC, even with the heater valve closed it still allows some flow through the heater core.

[Stanley]

S30 coolant plumbing v2.pdfThe wrong way arrows were bugging me so I fixed them. Would have got it right first time if I'd looked at the engine manual. There's a small mistake in the manual where it says the carb heater provides consistent fuel temps at all times, but there's that hot-closed thermostat in the stock line. Also put small arrows in the heater in fig. 2, and removed the arrows for now in fig 5. My CAD looks like Custer's last stand with all those arrows scattered around.

Is the coolant forced out (stock) of the head outlet by pressure in the engine from the water pump, or is it sucked out by negative pressure at the inlet? I'm guessing both. In the fig 5 setup it seems more likely that it flows from the T housing to the head "inlet" (reversing the stock flow) esp. when the thermostat is closed, but I don't know enough about the internal flow. I want it to flow to the radiator per Leon's suggested mod, but without doing the mod.

I did a variation of fig 4 a few years back to my truck, after a July trip to Tucson: took a new heater core and mounted it in the loop, in the engine bay. It worked to reduce overheating - takes a slightly longer to warm up.

One more thing, in that hybrid z thread it was stated that the external bypass helps the internal bypass to prevent water pump cavitation during high rev events during warmup. This could happen for a race car leaving the pits (or if your neighbor's waiting to street race as soon as you start up the car). I'm guessing this is a non-issue otherwise.

Edited March 27, 2013 by Stanley
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[LeonV]

Your attachment doesn't work on my end.

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The wrong way arrows were bugging me so I fixed them. Would have got it right first time if I'd looked at the engine manual. There's a small mistake in the manual where it says the carb heater provides consistent fuel temps at all times, but there's that hot-closed thermostat in the stock line.

The manual has it right. That thermostat ensures that coolant over 180deg does not flow through the manifold.

Is the coolant forced out (stock) of the head outlet by pressure in the engine from the water pump, or is it sucked out by negative pressure at the inlet? I'm guessing both.

That's saying the same thing, really.

[Stanley]

Fixed it, thank you. I was wrong about FSM. On my car, there's no thermostat in the heater tube, maybe the PO's mechanic removed it. Was going to get one someday, guess I won't now.

[John Coffey]

This could happen for a race car leaving the pits (or if your neighbor's waiting to street race as soon as you start up the car). I'm guessing this is a non-issue otherwise.

Generally a non-issue but if I was the crew chief and my race driver redlined the car on a cold engine leaving the pits he would get his butt kicked when he got back.

[Captain Obvious]

When taking grades in the summer heat on the way to Yosemite, he'd turn the heater to full hot and blast the interior fan... in 100deg weather.

Haha! Yeah, I remember those times as well. Don't remember which family car it was, but I remember Dad turning the heater on full blast in the middle of summer and then trying to explain to me why.

As for the looped heater tube, I really don't think there will be much heat rejected by the core in completely stagnant air, but granted, it will be non-zero. Same situation for the resistance to flow... I suspect there's not much, but, non-zero.

Oh well, just curious if I was missing something simple and there really was some big reason why those two situations were different.

Edited March 28, 2013 by Captain Obvious

[LeonV]

Fixed it, thank you. I was wrong about FSM. On my car, there's no thermostat in the heater tube, maybe the PO's mechanic removed it. Was going to get one someday, guess I won't now.

Looks good!

Haha! Yeah, I remember those times as well. Don't remember which family car it was, but I remember Dad turning the heater on full blast in the middle of summer and then trying to explain to me why.

As for the looped heater tube, I really don't think there will be much heat rejected by the core in completely stagnant air, but granted, it will be non-zero. Same situation for the resistance to flow... I suspect there's not much, but, non-zero.

Oh well, just curious if I was missing something simple and there really was some big reason why those two situations were different.

Good times!

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

Also, I think there's a lot more resistance to flow when the coolant has to snake through the heater core as well as past the control valve, than just a short hose loop. It's definitely not negligible.

In the bigger picture, whether you have a heater or a loop, the engine will be OK in normal street driving. I haven't run through the calculations, but 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).