[wbullivant]

Gurgle into the expansion tank?

The cooling system pressure cap is designed to let vapor escape when the pressure in the system exceeds something like 15psi. That is how air is removed from your cooling system as you run the engine. Just keep adding more coolant to the reservoir as necessary when the engine is cool. On the Promaster the tank is pressurized where on older cars it was not and new fluid was added through a suction hose when the system cooled down. In either system it is going to take a number of warm/cool cycles to get all the air out.

BTW, one great feature is that the pressure cap regulates maximum pressure on the entire new loop we have added. I remember one poster theorized adding a heat exchanger in the loop so that only non-toxic coolant would flow through the Isotemp. While that would be a theoretical advantage it would also require adding a coolant pump and pressure relief on the secondary loop, a complication and expense I didn't want to deal with. I think the Isotemp heat exchange tubing is very sturdy and each time you winterize your domestic water system and drain the Isotemp tank you are effectively testing that transfer loop for leaks (you would see pink liquid draining from your HWT if there was a leak). The engine coolant system is at about 15psi and your hot water system around 40psi so if there is ever a leak water will quickly be added to the engine coolant system and overflow. With any system like this your need to keep an eye on things.
Bill

 

[RonFrank]

I'm also putting in an Isotemp Spa in the very rear of a 136, and am about ready to run the heater hoses. Is everyone that is using 3/8" heater hose satisfied with heating, or has anyone experienced a difference from 5/8"? Is there any issue with significant difference in heating ability running the hose under the van floor rather than inside the van? I also don't quite understand the reason for silicone over standard hose material?

 

[Wankel7]

I'm also putting in an Isotemp Spa in the very rear of a 136, and am about ready to run the heater hoses. Is everyone that is using 3/8" heater hose satisfied with heating, or has anyone experienced a difference from 5/8"? Is there any issue with significant difference in heating ability running the hose under the van floor rather than inside the van? I also don't quite understand the reason for silicone over standard hose material?

3/8ths is what ram choose for their uses.

 

[ThomD]

I went with silicone because it should be more flexible and easier for me to deal with in tight spaces. I have the factory "kit" so 3/8" for me.

 

[SteveSS]

I'm using 5/8 only because that's what Isotemp claims as the minimum, but 3/8 seems to work for other folk too. Not sure how we'll ever know which is better unless someone tries both. I got good quality (Gates Green Stripe) rubber hose for the long outside runs. But I'm using silicone for the short runs inside the van, mainly to avoid any chance of hot rubber smell.

 

[eric1514]

I'm also putting in an Isotemp Spa in the very rear of a 136, and am about ready to run the heater hoses. Is everyone that is using 3/8" heater hose satisfied with heating, or has anyone experienced a difference from 5/8"? Is there any issue with significant difference in heating ability running the hose under the van floor rather than inside the van? I also don't quite understand the reason for silicone over standard hose material?

I'm using 5/8" because that's what the inlet on my WH is and I'm using a good quality Gates rubber heater hose.

 

[RonFrank]

I'm thinking the primary difference that could be determined (without trying both) is in comparing with each other the time it takes to heat the water or how how hot the water gets, depending on whether using 3/8 or 5/8 hose (and the length of run). Does anyone have input on that? I like the idea of 3/8 for flexibility and space if it provides sufficient hot water.

 

[SteveSS]

I'm thinking the primary difference that could be determined (without trying both) is in comparing with each other the time it takes to heat the water or how how hot the water gets, depending on whether using 3/8 or 5/8 hose (and the length of run). Does anyone have input on that? I like the idea of 3/8 for flexibility and space if it provides sufficient hot water.

The retired scientist in me thinks there are likely too many variables to make a meaningful comparison. Including the size of the HWH, the initial water temp, the length of heater hose, and the time it takes to warm up the engine and coolant. Technically speaking, 3/8 has to be a bit slower than 5/8, but the difference is likely not big enough to matter most of the time. I decided to go with the manufacturer's recommended 5/8 because I have a big 25-ltr Isotemp Spa, plus the cost and logistical differences seemed minimal to me.

 

[Zoomyn]

5/8" ID x 24' = 0.3825 gallons volume held in hose.. .

3/8" ID x 24' = 0.1377 gallons volume held in hose.. .

Flow rate is along the same lines, about 4x the flow from larger hose size.. .

Next episode we'll look at that favorite doomsday scenario of how long it takes to empty ALL engine coolant onto roadway or flood storage areas, insulated floor and carpets...

:crying::nerd:

 

[Wankel7]

5/8" ID x 24' = 0.3825 gallons volume held in hose.. .

3/8" ID x 24' = 0.1377 gallons volume held in hose.. .

Flow rate is along the same lines, about 4x the flow from larger hose size.. .

Next episode we'll look at that favorite doomsday scenario of how long it takes to empty ALL engine coolant onto roadway or flood storage areas, insulated floor and carpets...

:crying::nerd:

Interesting...thank you for doing the calculation.

I wonder how much coolant is lost splicing into the van's system?

I was thinking about skipping out on buying coolant and just refill with distilled water.

 

[ThomD]

For total volume, don't forget it is a round trip. And you need to fill the water heater. Ask me next week how much it took.

 

[Wankel7]

For total volume, don't forget it is a round trip. And you need to fill the water heater. Ask me next week how much it took.

What size Isotemp did you get? I wonder if the heat exchangers are different sizes for the different sized tanks.

 

[SteveSS]

I wonder if the heat exchangers are different sizes for the different sized tanks.

Yes, a factory rep confirmed that when we bought our Isotemp Spa 25. The longer tanks have longer heat exchangers.

 

[wbullivant]

The retired scientist in me thinks there are likely too many variables to make a meaningful comparison. Including the size of the HWH, the initial water temp, the length of heater hose, and the time it takes to warm up the engine and coolant. Technically speaking, 3/8 has to be a bit slower than 5/8, but the difference is likely not big enough to matter most of the time. I decided to go with the manufacturer's recommended 5/8 because I have a big 25-ltr Isotemp Spa, plus the cost and logistical differences seemed minimal to me.

Steve
I can tell you that my system has a 40 liter tank and 3/8" hoses. The tank will exceed 150F in about an hour of driving. I've installed an wireless oven thermometer. That way I have a temp readout and alarm up front. I usually set the alarm for 180F and then turn a ball valve to stop the circulation. I have no regrets about using 3/8 vs 5/8 hose.
Bill

 

[SteveSS]

Steve, I can tell you that my system has a 40 liter tank and 3/8" hoses. The tank will exceed 150F in about an hour of driving. I've installed an wireless oven thermometer. That way I have a temp readout and alarm up front. I usually set the alarm for 180F and then turn a ball valve to stop the circulation. I have no regrets about using 3/8 vs 5/8 hose. Bill

Thanks, Bill. Good to know. Why not just let the HW temp come to equilibrium with the coolant temp? Does it trip the pressure relief valve and drip too much?

Is the ball valve under the hood? A generic heater control valve with a cable control would let you adjust circulation from inside the cab while driving.

 

[wbullivant]

Thanks, Bill. Good to know. Why not just let the HW temp come to equilibrium with the coolant temp? Does it trip the pressure relief valve and drip too much?

Is the ball valve under the hood? A generic heater control valve with a cable control would let you adjust circulation from inside the cab while driving.

Although I have ball valves on each line at the firewall, I normally close a valve near the tank which is accessible by lifting a cushion (can be done while driving). I guess I could just let it cycle all the time but I really don't want it up to 210F or so which is what my coolant gets to. The ideal would be an adjustable thermostatic valve with the thermocouple at the tank. Just haven't found one at a price I want to pay. When we stay at a campground for a while I let it cycle and the short drives during the day keep the tank temp up enough for use. Not the perfect system but good enough for the time being.

 

[eric1514]

After I get my system up and reliably running, I will change one of the ball valves (I have 2) under the hood with one of these.

Solenoid Operated Valve

I'll control it with a switch near the dash with electric only available when the van is running so that it won't suck juice when I'm parked.

 

[wbullivant]

After I get my system up and reliably running, I will change one of the ball valves (I have 2) under the hood with one of these.

Solenoid Operated Valve

I'll control it with a switch near the dash with electric only available when the van is running so that it won't suck juice when I'm parked.

That valve looks interesting except that the specs indicate it is not designed to stay open for more than eight hours (overheats) and it consumes 20 watts whenever it is open. On the same Amazon page they had motorized ball valves that only take power when changing position. Their weak spot is that they are designed for fluids up to 190F. A higher temp version would seem to be ideal then use a micro-controller with a thermocouple sensor at the HWH.

[ame]https://www.amazon.com/dp/B06X99PHJJ/ref=sspa_dk_detail_3?psc=1[/ame]

 

[eric1514]

That valve looks interesting except that the specs indicate it is not designed to stay open for more than eight hours (overheats) and it consumes 20 watts whenever it is open. On the same Amazon page they had motorized ball valves that only take power when changing position. Their weak spot is that they are designed for fluids up to 190F. A higher temp version would seem to be ideal then use a micro-controller with a thermocouple sensor at the HWH.

https://www.amazon.com/dp/B06X99PHJJ/ref=sspa_dk_detail_3?psc=1

I figured, like you have observed, that it wouldn't take more than a couple of hours to heat a tank of water. My plan was to turn it on 1 or 2 hours before reaching camp. The problem with that scenario is remembering to do so.

Yes, the solenoid consumes some electricity, but it would be wired to the starting battery in such a way that it could only come on if the engine was running and I think the alternator could stay ahead of the load.

Something as nice as the micro-controlled thermocouple you describe would be ideal, but way above my paygrade to implement.

 

[ThomD]

What is the downside to just letting the tank get to max temperature? That is what it is designed for. The mixer value on the output should keep the tap water at the right temperature.