Step by Step How To Bleed Espar Hydronic

2003 3500 RV with diesel D5WSC Espar Hydronic that circulates engine coolant to preheat engine, circulates to the rear cabin heater box, and circulates to a water-water heat exchanger for shower water. There is no storage tank-style hot water heater.

The Espar is mounted behind the driver side underneath. Its elevation is below the top of the engine radiator. When mounted there is zero access to the bleed screw. I suppose I could remove the mounting bolt and rotate the unit out just far enough to get access to the bleed screw.

I repaired the combustion blower to solve a F31 and then reinstalled it.

Now, I need to bleed it to solve a consistent F14 overheat, most likely caused by insufficient coolant flow due to air pockets. Yeegads! Now I gotta bleed the sucker.

Has anybody here done this? Espar documentation is woefully short on this issue. To my knowledge there are no other bleed ports in the system.

Exactly what is the step by step procedure to bleed it? HELP!!

Thanks in advance.

Rick M

Bleed??

Most likely your auxiliary coolant pump is shot. Test by hitting the REST button on the automatic temp. Control unit and put your hand on the aux pump. If it’s not vibrating (not working) that’s most likely your problem. Replace. Bosch unit.

vanski said:

Most likely your auxiliary coolant pump is shot. Test by hitting the REST button on the automatic temp. Control unit and put your hand on the aux pump. If it’s not vibrating (not working) that’s most likely your problem. Replace. Bosch unit.

Click to expand...

That was my first thought. The electric circulating pump should flush the air from the system. I have disconnected/reconnected plumbing attached to the D5 without problem.


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Oh man, you guys, thanks. I did not think about that aspect.

Glad to hear that I might not need to access the Espar bleed screw.

OK, more help needed. Where, most likely, is the auxiliary REST pump located?

Is it the Electric Coolant Pump shown on page PLUMBING 24-57 of the 2003 service manual? On the front of the engine next to the battery?

Thanks in advance.

It’s on the firewall behind the egr.. behind the fuel filter... just below the intake manifold.. it’ll have two hoses coming into it. The rest button, just in case you’re not sure where that is, is the bottom button on the same ‘dial’ as your AC.

Anyone ever DIY a system like this using the cheap-Chinese units off eBay at 1/8th the price?

I’ve put on a Dorman for a couple people who didn’t want to pay for a Bosch. The price was still like $80 I think from Rock Auto. So far so good but they haven’t been in service that long so not sure how they will compare.

I think aquaputana researched some brushless replacements which are more expensive than Bosch but theoretically should last 10x a Bosch..

Well, I drove the Sprinter until fully warm. Parked. Ignition off, key out. REST button on. You can hear the heater blower motor running at lowest setting, as designed. Touching the pump there is nothing.

I disconnected the harness and checked voltage with REST. 12 VDC. All good.

Jumpered some alligator pigtails from the battery to the pump--with correct polarity. Big nothing.

I have a Bosch pump on order.

It is easy to access, and will be easy to replace.

Thanks, guys, for your guidance on this.

OK, I am still getting the F14 overheat error in the Espar Hydronic.

I did replace the electric coolant pump since the old one had stopped working. It was an easy replacement. The new one works fine. I have tested it several times with REST.

This 2003 3500 Sprinter is a van conversion with both front and rear heat and front and rear AC. The rear heat is a heater core in a box under the sofa bed. There is also a plate water-water heat exchanger to heat on-demand shower water.

The engine coolant system is plumbed all the way back there to heat the cabin heater core and the water-water heat exchanger. All of this works when the engine is running.

Also plumbed into this system is the Espar Hydronic D5W SC unit that has its own coolant pump. This Espar is located under the chassis some 5 feet behind the driver seat. It is NOT up front near the engine like most of them are.

I recently had to remove this Espar Hydronic (putting 3/4" plugs into the coolant lines) to replace a blown combustion blower motor. All of that went fine. Combustion now works fine.

So, I re-assembled the system and made sure the coolant level was correct with several trips to monitor coolant level (cold) and replace any that is lost. All per the service manual.

I have driven the van 400 miles now, heat on, heat off, rear heat on, rear heat off. Engine-driven heat works in all rear cabin systems just fine. REST works just fine.

However, when I start the Espar I ALWAYS get a F14 overheat error. Per Espar troubleshooting documentation, this happens when there is an excessive temperature delta between the temperature probe and the overheat sensor.

So, why the F14? Either the coolant to and/or from the Espar is blocked or there is an air bubble that does not get pumped away.

I have double-checked all the coolant lines. No kinks. All joints look good. All valves work. This is confirmed since the engine-driven hot coolant successfully heats the rear cabin systems.

This leaves air. I think the internal coolant pump is trying to pump air instead of coolant. There is an air bubble in there that no amount of driving or using the electric coolant pump can remove.

The Espar is located at an elevation below the top of the engine radiator. However, the coolant lines to the Espar have an uphill run of about 12" vertical from the front-to-rear coolant lines to the rear cabin systems. I am thinking that that 12" vertical is holding an air bubble.

You still with me?

The top of the Espar has a bleed screw. I can see how this bleed screw would bleed air from both the input and output coolant lines to the pump. However, from the way the Espar is mounted, I cannot access this screw without partially removing the Espar from its mount. Ugh! Despite the hassle, this is probably worth doing.

So, has anybody performed this bleed? Do you bleed while running the Espar (before it trips out with the F14, of course), or can you just bleed it statically? Espar documentation says nothing about any of this.

Or does anybody have Espar Hydronic documentation that includes instructions for bleeding?

Thanks in advance.

RM

I received a reply from Espar USA. He included documentation about bleeding the air out of the Hydronic.

I have no access to the bleed screw, but easy access to the inlet and outlet hoses. I asked about just removing the outlet hose, holding my thumb over the hose and letting it bleed past my thumb.

He said, sure, I can do it that way.

I did it that way. Problem is that you are supposed to get a continuous gravity flow of coolant if you release your thumb, AND get a continuous bleed of coolant out the open pipe from air that bleeds from the inlet pipe through the pump. This did not happen.

All I got were a few drops, then nothing. Huh? This has to mean that there is a blockage in one or both lines. There are no kinks. Nothing in the plumbing has been changed from when it ran just fine three months ago.

So, maybe there is a malfunctioning valve that is not opening.

This is now beyond my abilities to find and fix. I will take it in to a local Thermo King. They do these systems for big trucks.

I’ve had my espar unit apart several times and there was no bleed screw. Unless your unit is totally different, I would test the temperature sensors. If you’ve driven the van with all the heaters operating then you have bled the air.

With units that have experienced excessive overheating, the sheathing on the sensor cables crumbles and shorts

This Espar is a D5W SC Hydronic. There is a bleed screw on the very top of the built-in pump. It is shown, and fully labeled, on the Espar documentation and diagrams. Espars without the built-in pump, like what you find as a default OEM up near the engine on Sprinters, do not have this bleed screw. You bleed those in other ways. Somebody here said the electric coolant pump for the REST will vent all air pockets, but that is for the much simpler-plumbed OEM system.

Back to my problem with current status.

Because this is a RV conversion with the Espar underneath the chassis behind the driver, about halfway back to the rear axle, there is a LOT of plumbing back there. This means SEVERAL FEET of 3/4" heater hose, connections, valves, rear heater core box, plate water-water heat exchanger, turns and twists, lions, tigers, and bears, on and on.

My local Thermo King shop installs these system in big trucks and has a lot of experience with multi-feet plumbing and the Espar Hydronic units to preheat engines and heat cabins through cabin heater cores. I gave up trying to bleed it myself and took it to them.

Due to the plumbing complexity, they plan to bleed it with a Airlift Vacuum bleed and refill system, which they use on big trucks. Trying to push-bleed individual air pockets in this system will not get it all. Gotta suck it out with vacuum.

I will report back on final results.

Final results.

My local Thermo King shop bled the coolant system by running the engine and Espar with all heat turned on, front and back, and then opened the bleed screw on top of the Espar to get the air out while coolant was circulating. They must have timed this since the Espar would normally get the F14 overheat error within a minute of starting.

They did what I was trying to avoid: partially dismount the D5 and rotate it out to get access to the screw. Ugh.

It now runs nicely without any errors. I have driven the van 300 miles in 95F heat, towing a boat, up and down hills, without getting any engine overheats caused by air in the system.

They said they were going to use a vacuum lift system to perform this bleed, but they ended up just using the Espar bleed screw. I suspect they did not want to deal with the hassle of draining the coolant from the radiator and engine block.

The results seem to be good.

Congrats on getting sorted.. what did TK charge for this service?