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I am in the planning phase for a new PM 136 and have pretty much decided on the Isotemp Spa water heater. The installation manual says that the heat exchanger should be located below the engine header tank. I imagine that means where the heater hose tubes come out of the engine, which would limit the installation to horizontal.

I don't understand the reasoning since the van heater is above the engine. It also says to install with as short of hose as possible and I am thinking an idea location might be vertically in a cabinet behind the drivers seat (or somewhere else). Have any of you installed this unit vertically where the connections are above the engine?

What, where, and how did you install your water heater?
 

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4 gallon Isotemp Spa mounted horizontally on floor over rear axle.

3/8 inch Silicone heater hoses under the floor connected to the van heater hoses with two 3/4 x 3/8 x 3/4 tees from Napa and ball valves to allow isolating the Isotemp.

Topped up coolant to replace small amount lost when cutting heater hoses to insert tees.

Topped up again after a couple engine starts and air had worked itself out.
 

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4 gallon Isotemp Spa mounted horizontally on floor over rear axle.
Do you understand why the heat exchanger in water heater is suggested to be below engine connections? Do you imagine a problem if it was installed vertically with heat exchanger on top?
 

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Do you understand why the heat exchanger in water heater is suggested to be below engine connections? Do you imagine a problem if it was installed vertically with heat exchanger on top?
I'm not sure what the problem would be but if you mount it on the floor (mine is behind the rear axle, driver side, below twin bunk)the tank will be lower than the heater connection tubes. The only issue with mounting the tank a distance from the engine is heat loss from the tube and some flow resistance. It's about fifteen feet to my tank and plenty of hot water gets through the 3/8" hose. The link below is to a pic of the tank in position. The blue silicone hose contains engine coolant and the unit to the left of the tank is a heat exchanger which allows use of the tank heat for space heat in rear of van.

https://www.promasterforum.com/forum/attachment.php?attachmentid=36218&d=1496841723
 

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mounting below the connection to the heater hoses makes purging air from the lines easier.

the manual says you can mount it vertically but the connections have to be on the bottom not the top.

After you heat the water with the engine if you try to use the 120vac heating element to heat the water, it won't work unless you reset the high limit thermostat which is under the cover on the front so this has to be easy to access.

I have a small hole drilled in the cover so I can reset the thermostat with a pencil.

I read that somebody removed the high limit from the tank so it would never trip. I may try that.

you could contact Isotemp and ask why you shouldn't mount it with connections on top.
 

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You can replace the high limit thermostat with a resettable thermostat that will reset itself after tripping. The Rialta group has done this as the heat exchanger/water heater was very hard to reset after driving. The engine coolant would get to +195*F and trip the thermostat and then have to be reset by hand. You can obtain this automatic resettable at any RV supply store. The resettable thermostat just replaces the manual thermostat.

MLogan
Formerly 04' Rialta
Smyrna, TN
 

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You can obtain this automatic resettable at any RV supply store. The resettable thermostat just replaces the manual thermostat.
Is the HWH in your Rialta an IsoTemp? Auto-reset would be nice. Thankfully, our IsoTemp is accessible-ish under one corner of the bed.
 

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I hope the PDF file transfers here about the procedure for changing the high limit thermostat.
It did! Fun reading by the way. Rialta's have an Atwood system with a thermostat that looks a lot different from the one in an IsoTemp. Definitely worth looking into further. Thanks!
 

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4 gallon Isotemp Spa mounted horizontally on floor over rear axle.
Do you understand why the heat exchanger in water heater is suggested to be below engine connections? Do you imagine a problem if it was installed vertically with heat exchanger on top?
Any new input on this question.... My isotemp is going to be mounted on top of my wheel well box which seems to be just above the vans header tank.

The manual says if you install above the engine header tank a bleeder must be installed....

This valve looks interesting.... Has a bleeder in the side. And is female npt... So I should be able to thead it right to the tank.


https://www.lowes.com/pd/AMERICAN-VALVE-Brass-1-2-in-FNPT-Ball-Valve/1000242255
 

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I installed our IsoTemp at about wheel well height. I inserted one of these flush-tee fittings at the high point in one of the hoses next to the IsoTemp:
[ame]https://www.amazon.com/Dorman-47126A-Radiator-Flush-Tee/dp/B0042OTDSA[/ame]
It doubled as a bleeder and a place for adding coolant from that end. It worked really well.
 

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I installed our IsoTemp at about wheel well height. I inserted one of these flush-tee fittings at the high point in one of the hoses next to the IsoTemp:
[ame]https://www.amazon.com/Dorman-47126A-Radiator-Flush-Tee/dp/B0042OTDSA[/ame]
It doubled as a bleeder and a place for adding coolant from that end. It worked really well.
Thanks for the reply....

Did you have any issues with the factory expansion tank overfilling? From my measurements my isotemp could become the highest point in the cooling system.

Do you have a picture of your install?
 

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Any new input on this question.... My isotemp is going to be mounted on top of my wheel well box which seems to be just above the vans header tank.

The manual says if you install above the engine header tank a bleeder must be installed....

This valve looks interesting.... Has a bleeder in the side. And is female npt... So I should be able to thead it right to the tank.


https://www.lowes.com/pd/AMERICAN-VALVE-Brass-1-2-in-FNPT-Ball-Valve/1000242255
Wankel7
I would imagine their only concern is that there may be air in the lines. With the positive flow from the engine coolant pump you won't have to worry about air as long as your plumbing design permits you to direct full flow through all line segments. The Isotemp is designed for marine usage so they probably figure on the boat staying level whereas a van will tilt a lot in all directions. I put a number of ball valves in the system to permit isolation in case of leakage in a component and even added an air hose fitting near the tank in case I needed to purge the lines at some time in the future. A ball valve with a drain tap is fine if you don't have other provisions in your design.
 

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Did you have any issues with the factory expansion tank overfilling? From my measurements my isotemp could become the highest point in the cooling system. Do you have a picture of your install?
No overfill issues that I've noticed so far. Coolant level stays within range. The heat exchange loop is roughly 21" above the factory floor, so maybe not quite as high as yours will be. Recent photos on Shiny's build thread show the mounting location. Let me know if you want others.
 

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Did you have any issues with the factory expansion tank overfilling? From my measurements my isotemp could become the highest point in the cooling system. Do you have a picture of your install?
No overfill issues that I've noticed so far. Coolant level stays within range. The heat exchange loop is roughly 21" above the factory floor, so maybe not quite as high as yours will be. Recent photos on Shiny's build thread show the mounting location. Let me know if you want others.
Mine would be about two inches higher than that....

I am going to just proceed and see what happens. If it becomes an issue.... I will install an expansion tank in the van.

It seems like a T fitting into the outlet of the isotemp with the expansion tank above it would do.
 

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Another thing -- the hose run takes a long low dip under the floor between the engine and IsoTemp. This creates a big high air pocket at the IsoTemp end that is difficult to fill with coolant working only from the engine end. Some kind of fill access at the IsoTemp end really helps. That was the main (only) benefit of the flush-tee I installed. It let me fill the big dip from both ends. At the engine end, I filled through a long funnel stuck in one detached hose. Slow and careful, almost didn't spill a drop. After closing up the system, I ran the engine then bled air out the factory bleeder a couple times. What little air remained worked it's way out through the expansion tank over time. It was actually easier than I expected.
 

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About to tee into the coolant system....My plan is to over fill the stock expansion tank with distilled water, get my splices into the heater core installed but leave the outlet from the Isotemp hose unplugged at the heater core outlet. Start the van...and wait until I have coolant coming out of unattached hose and then quickly hook it up. I have ball valves at the heater core

The only thing I wonder is if I will have to wait until the thermostat opens to get full flow?

I got this expansion tank just in case I need it.
https://www.summitracing.com/parts/mor-63773

If I do have to install it....

Do I need to change out the stock cap for a no pressure relief cap?

I'm assuming I would use a 1.4 bar....20 psi cap on the new expansion tank?
 

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Whatever caps you get must provide the pressure in the radiator system to the limit of the system before you began, probably 20 psi???
 

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...cut...

The only thing I wonder is if I will have to wait until the thermostat opens to get full flow?

...cut...
Heater core loop is tied into the engine block, doesn't require the thermostat to provide flow.
 
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