We just got a late 2010 G3500 Duramax Ambulance where I work. It is an LML with DEF. I was looking it over on its first service and noticed it had what looks to be a diesel fired coolant heater mounted on the drivers side frame rail under the cab, looks to be oem. Anyone know why they have this? Anyone know any other differences on these? I have always been around LB7, LLY, and LBZ trucks, so this is new for me. Thanks

We just got a late 2010 G3500 Duramax Ambulance where I work. It is an LML with DEF. I was looking it over on its first service and noticed it had what looks to be a diesel fired coolant heater mounted on the drivers side frame rail under the cab, looks to be oem. Anyone know why they have this? Anyone know any other differences on these? I have always been around LB7, LLY, and LBZ trucks, so this is new for me. Thanks
That's the RPO K08 Fuel Operated Heater, which is an oem version of the Espar Hydronic D5W:
http://www.dieselplace.com/forum/attachment.php?attachmentid=93475&d=1257564687
I have one on my van. It provides additional heat to warm up faster.

The GM oem version of the D5W has a unique internal control module:
http://www.dieselplace.com/forum/attachment.php?attachmentid=122670&d=1318533963
that is activated by a digital signal from the Body Control Module. Nobody seems to know what this signal is, and it will be difficult to figure it out.
This control scheme will only allow it to run if these conditions are met:
* Outside air temperature is below or equal to 39°F (4°C).
* Fuel level is greater or equal to 12.5 percent of the total fuel tank volume.
* The engine is running.
* Coolant temperature is less than 167°F (75°C).

Most people want to use the Espar heater to pre-heat the engine in cold weather before starting, but due to the way it is controlled, the GM version will not work that way, and so far there seems to be no cost-effective way to make it work as a pre-heater. The internal GM-spec. controller can be replaced with a standard Espar controller (Espar part # 22 5201 01 90 02) to allow on-off control via a regular switch, but that module costs about $450.

After coming up with a way to make the heater turn on when the engine is off, an electric water pump like this:
http://www.suremarineservice.com/images/products/detail/906089Kit.jpg
http://www.suremarineservice.com/906-089KIT.aspx
must be added in order to work as a pre-heater, since the oem GM version of the D5W does not have a built-in or external electric water pump.


Search on "K08" and you'll find these threads:
http://www.dieselplace.com/forum/showthread.php?t=337962
http://www.dieselplace.com/forum/showthread.php?t=333347

Search on "Espar D5W" and you'll find this thread:
http://www.dieselplace.com/forum/showthread.php?t=435917

Hmmm... did I leave anything out? ;)

It could be the factory option diesel fired heater, and it's purpose is to provide extra coolant heat when the engine is not producing it.

If you are at an accident scene, engine idling and have the back doors open for a while, the idling diesel may not provide enough heat to keep the interior warm, the extra heater will provide the extra heat.

Nice option to have, try and make sure it runs once a month to keep it in working order.

It could be the factory option diesel fired heater, and it's purpose is to provide extra coolant heat when the engine is not producing it.

If you are at an accident scene, engine idling and have the back doors open for a while, the idling diesel may not provide enough heat to keep the interior warm, the extra heater will provide the extra heat.

Nice option to have, try and make sure it runs once a month to keep it in working order.

Nomad is correct it is the OEM coolant heater. It can be had on "any" d-max equipped van. I believe it started as a option in 07. Would be nice if they put a timer on it or a remote start system so you could fire it up 20 mins before you got ready to roll, that is.... for those of you that do not LIVE in your van:D

Piper you get you espar bunk heater yet or are ya gonna fool with a propane heater or just idle that beast. @ 1.21 a liter it would get expensive quick!!

New Webasto AirTop 2000 sitting in the shop waiting for me to put it in along with a Webasto coolant heater....the 06 may get the coolant heater as it does short trips.

I just can't idle, drives me nuts and I damn near froze last week so the install has gotten a lot higher on the list.

i got that heater on my van. it is oem.
a couple years after i got my van, my heater decided not to turn on when winter came. dealer ended up replacing it under warranty. when it was cold out, my van would always kick to high idle when in park. when the heater works, the high idle only kicks on when the engine is cold.
it would be nice to be able to manualy trigger it on.

New Webasto AirTop 2000 sitting in the shop waiting for me to put it in along with a Webasto coolant heater....the 06 may get the coolant heater as it does short trips.

I just can't idle, drives me nuts and I damn near froze last week so the install has gotten a lot higher on the list.

I know what you mean about idling, Also the way the ecm works in this thing makes it annoying to try to sleep when its below 25 degrees outside, raising and lowering the rpms all night long. I got use to it in a tractor where it stayed steady all night, but after 2 nights of idling in this thing I had Ray install the Espar asap!!

i got that heater on my van. it is oem.
a couple years after i got my van, my heater decided not to turn on when winter came. dealer ended up replacing it under warranty. when it was cold out, my van would always kick to high idle when in park. when the heater works, the high idle only kicks on when the engine is cold.
it would be nice to be able to manualy trigger it on.
Yes, it sure would be. Most everyone who has one of these oem Espar heaters wants to be able to turn them on manually for pre-heating, or if they are sleeping overnight in the van.

But GM's control scheme ensures that manual control is not possible.

I am working on finding a way to do it, but I'm not too optimistic at this point. In order to make that happen, I will have to find someone willing to tackle this project, who has the right type of oscilloscope to try to pick up the signal going across the CANBUS when the heater turns on & off. That signal is a series of voltage changes (representing the data bits) that probably only lasts a fraction of a second, and there are other signals present at the same time on the CANBUS, so picking out that specific signal would require a recording oscilloscope, and careful analysis.

It might also be as simple as applying the correct voltage to line "J" (BCM Comm Enable), which is there on the chassis side of the connector, but does not connect to the heater. http://www.dieselplace.com/forum/attachment.php?attachmentid=122678&d=1318537586
Line "J" is located next to the ground, and is a similar color to the wire that sends 12v power to turn on the fuel metering pump.
Who knows? Maybe Line "J" is a manual control trigger wire that sends a signal to the Body Control Module, telling it to turn on the heater.

Since there are people at GM who know what the signal is, the other approach is to try to find someone who knows someone who knows someone who will tell what it is.

The other approach is to come up with a good reason why the heater needs to be turned on, such as to do the annual service Espar recommends.
I assume that the extent of a dealer's service on this unit is to replace it, which is what your experience was. But a service manager *might* be able to get someone at GM to provide the information needed, to provide a way to turn the heater on to perform the annual service. As it stands now, these heaters aren't particularly useful in most cases, and as your experience showed, bound to fail prematurely since there is no way for the owner or even a GM dealer to perform the recommended annual maintenance, all because GM made no provision to manually turn it on.

But since the factory setup does not include an electric water pump (which would have to be added to run the heater without the engine running), it is also entirely possible that GM made no provision to activate the heater even for testing purposes.

Update: after a lengthy conversation today with a GM tech, it appears that *probably* the oem fuel operated heater can be commanded to turn on using a Tech II. If so, that should make it easier to isolate the on-off signal.

http://www.dieselplace.com/forum/showpost.php?p=4424870&postcount=6

Thanks for the info guys. Our medics are inside if they are not running so they are at least 50 degrees.