GM Factory Installed Hydronic Heater Information Wanted.

TheRealPapaK

Active member
Hello everyone,

My GMC 4500 cutaway has a factory installed hydronic heater to heat the coolant for a heat exchanger and to help warm up the engine faster etc. I can't seem to find any information online for how it works. Is it just thermostat regulated? It is installed by the drivers side frame rail. I am wondering if I can high jack it and have some manual control over it.

Thanks!
 

Mwilliamshs

Explorer
You're saying there's a GM installed appliance that burns engine fuel to heat the coolant without the engine running?
 

Recommended books for Overlanding

Vehicle-dependent Expedition Guide
by Tom Sheppard
From $144.97
Don't Go There. It's Not Safe. You'll Die.: And other mor...
by Jared McCaffree, Jessica Mans, Kobus Mans
From $19.99
Long Way Down: An Epic Journey by Motorcycle from Scotlan...
by Ewan McGregor, Charley Boorman
From $40

TheRealPapaK

Active member
You're saying there's a GM installed appliance that burns engine fuel to heat the coolant without the engine running?
Right now it only works when the engine is running and is completely hands off but I’m wondering if I could control it manual. If anyone had info on that


“A fuel-operated heater (FOH) is available for vans equipped with the Duramax 6.6L to quickly provide heat to the vehicle interior in cold weather. This seamlessly integrated system is designed into the Savana chassis, saving customers the time and labor of upfitting an aftermarket system. The electronically controlled, fuel-operated heater operates automatically, turning on and off within parameters that include outside air temperature, fuel level, coolant temperature and engine use. It features a self-contained, pressurized auxiliary coolant heater (with a surge tank) that uses diesel fuel to generate up to 17,200 Btu/h (5 kW) of heating energy”
 

luthj

Engineer In Residence
Can you post a photo of the unit? There are only a couple major manufacturers. Some versions can be wired up to a manual switch. I use the Espar hydronic model in my camper for hot water, engine preheat, and water tank antifreeze.
 

TheRealPapaK

Active member
I'll climb under in the next day or so. I found it but I for got to check the manufacturer. I would have to add some check valves etc so I could bypass the engine if I wanted to so this probably won't happen until spring now. I figure there is probably a wire on it somewhere that I can trick into thinking the engine is on by a switch. Do these things typically have their own pump on them?
 

whith

Active member
Mine has this as well and I’ve been curious about doing the same thing. I’m not exactly sure what temp causes it to fire but it’s pretty cold. Seems to be low 30s. I’ll see if I can get a photo also or some other info.
 

luthj

Engineer In Residence
Typically these heaters will not activate if the temps are above a certain threshold. Some configurations require the engine to be running, or have a runtime limit (battery preservation). Typically this is all controlled by an external module programed by the OEM. The heater itself will usually have a control wire which is supplied 12v to command operation.

In some cases the coolant pump is external to the heater and controlled by the OEM module instead of the heater. In those cases it may be necessary to do some extra wiring to allow the pump to run with a manual switch.

Webasto makes a thermostatic Tee, which can be used to drive coolant one direction until the loop is warm. There are other options though, including a second coolant pump and loop for heating camper items. This can be setup to avoid needing to waste heat on the engine when not necessary.
 

TheRealPapaK

Active member
Mine has this as well and I’ve been curious about doing the same thing. I’m not exactly sure what temp causes it to fire but it’s pretty cold. Seems to be low 30s. I’ll see if I can get a photo also or some other info.
I found out it kicks on at 4C when the engine is started. Mine is. 2014 Savanna so we should have the exact same set up. I'll let you know you know what I find out.

Thanks everyone for your input so far. I haven't jumped under yet just because it's been snowing and cold and apparently I haven't been in the mood to do it yet lol.
 

luthj

Engineer In Residence
The sprinters also use the D5WZ. Some of the information in this thread will be applicable.


You will have a wire (typically yellow) which when connected to 12V will start the heater. The heater will run at high power (5kw) until the coolant reaches ~150F. At which point it will drop to low power (800w). If the coolant temp drops it will cycle to high. If it exceeds ~175F, the heater will stop heating, but the coolant pump (if controlled by the D5, which isn't always the case) will continue to run.
 

Recommended books for Overlanding

whith

Active member
Very helpful, thanks all! PapaK, love to see how you go about it if you do wire it to a switch.
 

TheRealPapaK

Active member
The sprinters also use the D5WZ. Some of the information in this thread will be applicable.
thanks for pointing me in this direction.

Very helpful, thanks all! PapaK, love to see how you go about it if you do wire it to a switch.
I might not get to it until spring but I’ll let you know what I come up with. First glance, there is is no auxiliary coolant pump so I would have to get that as well as a solenoid to close the flow to the engine until the ignition opens it etc
 
Top