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Jaguar S-Type Aux Heater / Webasto Thermo Top V Part 1 – Teardown & Cleaning

Jag Label
Jag Label

Here’s another Diesel-fired heater related project – these Webasto heaters are fitted to Jaguar S-Type cars as auxiliary heaters, since (according to the Jag manual), the modern fuel-efficient diesels produce so little waste heat that extra help is required to run the car’s climate control system. (Although this seems to nullify any fuel efficiency boost, as the fuel saved by not producing so much waste heat in the engine itself is burned in an aux heater to provide heat anyway). The unfortunate part is these units don’t respond to applying +12v to Pin 1 of the ECU to get them to start – they are programmed to respond to CAN Bus & K-Line Bus only, so they require a bit more effort to get going. They also don’t have a built-in water circulation pump unlike the Webasto Thermo Top C heaters – they expect the water flow to be taken care of by the engine’s coolant pump.

Webasto Label
Webasto Label
Water Side
Water Side

The water ports are on the side of this heater instead of the end, the heat exhanger is on the left. These hearers are fitted to the car under the left front wing, behind a splash guard. Pretty easy to get to but they get exposed to all the road dirt, water & salt so corrosion is a little problem. The fuel dosing pump is in a much more difficult spot to get at – it’s under the car next to the fuel tank on the right hand side. Access to the underside with stands is required to get at this.

ECU Side
ECU Side

The ECU side has all the other connections – Combustion air, exhaust, fuel, power & control.

External Connectors
External Connectors

Only two of the external connectors are used on these heaters, the large two pin one is for main power – heavy cable required here as the current draw can climb to ~30A on startup while the glow plug fires. The 8-pin connector on the left is the control connector, where the CAN / K-Line / W-Bus buses live. The fuel dosing pump is also supplied from a pin on this connector. The small 3-pin under that is a blank for a circulation pump where fitted. Pinouts are here:

PinSignal
1Battery Positive
2Battery Negative
Pin NumberSignalNotes
1Telestart / Heater EnableWould usually start the heater with a simple +12v ON signal, but is disabled in these heaters.
2W-Bus / K-LineDiagnostic Serial Bus Or Webasto Type 1533 Programmer / Clock
3External Temp Sensor
4CAN-CAN Bus Low
5Fuel Dosing PumpFuel Pump output. Connect pump to this pin & ground. Polarity unimportant.
6Solenoid ValveFuel cutoff solenoid optionally fitted here.
7CAN+CAN Bus High
8Cabin Heater Fan ControlThis output switches on when heater reaches +50°C to control car heater blower
PinSignalNotes
1??
2Circulation Pump +
3Circulation Pump -
ECU Cover Removed
ECU Cover Removed

Removing the clipped-on plastic cover reveals the other ECU connectors. The large white one feeds the glow plug, & the large multi-pin below brings in the temp & overheat sensor signals.

MC9S12DT128B Microcontroller
MC9S12DT128B Microcontroller

The heart of the ECU is a massive microcontroller, a Freescale MC9S12DT128B, attached to a daughterboard hooked into the ECU power board.

Power Section
Power Section

The high power section is on the board just under the connectors, here all the large semiconductors live for switching the fan motor, glow plug, external loads, etc.

LIN & CAN Bus Transceivers
LIN & CAN Bus Transceivers

The bus transceivers are separate ICs on the control board, a TJA1041 takes care of the CAN bus. There’s also a TJA1020 LIN bus transceiver here, which is confusing since none of the Webasto documentation mentions LIN bus control.

Combustion Fan Motor
Combustion Fan Motor

The combustion fan motor is in the ECU compartment, nicely sealed away from the elements. There is no speed sensor on these blowers, unlike the Eberspacher ones.

Motor Details
Motor Details

The motor is a Buhler, rated at 10.5v.

Water Ports & Combustion Fan Cover
Water Ports & Combustion Fan Cover

Unclipping the cover from the other end reveals the combustion fan, it’s under the black cover. (These are side-channel blowers, to provide the relatively high static pressure required to run the burner).

Sensor Clip
Sensor Clip

The overheat & temperature sensors are on the end of the heat exchanger, retained by a stainless clip.

Temp & Overheat Sensors
Temp & Overheat Sensors

With the clip removed, the sensors can be seen better. There’s some pretty bad corrosion of the aluminium alloy on the end sensor, it’s seized in place.

Burner
Burner

The heater splits in half to reveal the evaporative burner itself. I’ve already cleaned the black crud off with a wire brush here, doesn’t look like this heater has seen much use as it’s pretty clean inside.

Burner Chamber
Burner Chamber

Inside the burner the fuel evaporates & is ignited. There is a brass mesh behind the backplate of the burner to assist with vaporisation.

Glow Plug
Glow Plug

The glow plug is fitted into the side of the burner ceramic here. This is probably a Silicon Carbide device. It also acts as a flame sensor when the heater has fired up. The fuel inlet line is to the left under the clamp.

Heat Exhanger
Heat Exhanger

The hot gases from the burner flow into the heat exchanger here, with many fins to increase the surface area. There’s only a couple of mm coating of carbon here, after 10 years on the car I would have expected it to be much more clogged.

I’m currently waiting on some components to build an interface so I can get the Webasto Thermo Test software to talk to the heater. Once this is done I can see if there are any faults logged that need sorting before I can get this heater running, but from the current state it seems to be pretty good visually. More to come once parts arrive!

The full service manual for these heaters can be grabbed from here, along with the wiring details for the Jaguar implementation & the Thermo Test software for talking to them:

[download id=”5618″]

[download id=”5620″]

[download id=”5622″]

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nb Tanya Louise Heating System – Oxide Sludge

I wrote a few weeks ago about replacing the hot water circulating pump on the boat with a new one, and mentioned that we’d been through several pumps over the years. After every replacement, autopsy of the pump has revealed the failure mode: the first pump failed due to old age & limited life of carbon brushes. The second failed due to thermal shock from an airlock in the system causing the boiler to go a bit nuts through lack of water flow. The ceramic rotor in this one just cracked.
The last pump though, was mechanically worn, the pump bearings nicely polished down just enough to cause the rotor to stick. This is caused by sediment in the system, which comes from corrosion in the various components of the system. Radiators & skin tanks are steel, engine block cast iron, back boiler stainless steel, Webasto heat exchanger aluminium, along with various bits of copper pipe & hose tying the system together.
The use of dissimilar metals in a system is not particularly advisable, but in the case of the boat, it’s unavoidable. The antifreeze in the water does have anti-corrosive additives, but we were still left with the problem of all the various oxides of iron floating around the system acting like an abrasive. To solve this problem without having to go to the trouble of doing a full system flush, we fitted a magnetic filter:

Mag Filter
Mag Filter

This is just an empty container, with a powerful NdFeB magnet inserted into the centre. As the water flows in a spiral around the magnetic core, aided by the offset pipe connections, the magnet pulls all the magnetic oxides out of the water. it’s fitted into the circuit at the last radiator, where it’s accessible for the mandatory maintenance.

Sludge
Sludge

Now the filter has been in about a month, I decided it would be a good time to see how much muck had been pulled out of the circuit. I was rather surprised to see a 1/2″ thick layer of sludge coating the magnetic core! The disgusting water in the bowl below was what drained out of the filter before the top was pulled. (The general colour of the water in the circuit isn’t this colour, I knocked some loose from the core of the filter while isolating it).

If all goes well, the level of sludge in the system will over time be reduced to a very low level, with the corrosion inhibitor helping things along. This should result in much fewer expensive pump replacements!

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nb Tanya Louise Heating Upgrades – The Pumps

 

Pierburg WUP1
Pierburg WUP1

With some recent upgrades to the boat’s heating system, the hot water circulation pumps we’ve been using are becoming far too small for the job. After the original Johnson Marine circulation pump died of old age (the brushes wore down so far the springs ate the commutator) some time ago, it was replaced with a Pierburg WUP1 circulation pump from a BMW. (As we’re moored next to a BMW garage, these are easily obtainable & much cheaper than the marine pumps).

WUP1 Cutaway
WUP1 Cutaway

These are also brushless, where as the standard Johnson ones are brushed PM motors – the result here is a much longer working life, due to fewer moving parts.

The rated flow & pressure on these pumps is pretty pathetic, at 13L/min at 0.1bar head pressure. As the boat’s heating system is plumbed in 15mm pipe instead of 22mm this low pressure doesn’t translate to a decent flow rate. Turns out it’s pretty difficult to shove lots of water through ~110ft of 15mm pipe ;). Oddly enough, the very low flow rate of the system was never a problem for the “high output” back boiler on the stove – I suspect the “high output” specification is a bit optimistic.
This issue was recently made worse with the addition of a Webasto Thermo Top C 5kW diesel-fired water heater, which does have it’s own circulation pump but the system flow rate was still far too low to allow the heater to operate properly. The result was a rapidly cycling heater as it couldn’t dump the generated hot water into the rest of the system fast enough.

The easiest solution to the problem here is a larger pump with a higher head pressure capability. (The more difficult route would be completely re-piping the system in 22mm to lower the flow resistance). Luckily Pierburg produce a few pumps in the range that would fit the job.

Pierburg CWA-50
Pierburg CWA-50

Here’s the next size up from the original WUP1 pump, the CWA50. These are rated at a much more sensible 25L/min at 0.6bar head pressure. It’s physically a bit larger, but the connector sizes are the same, which makes the install onto the existing hoses easier. (For those that are interested, the hose connectors used on BMW vehicles for the cooling system components are NormaQuick PS3 type. These snap into place with an O-Ring & are retained by a spring clip).
The CWA50 draws considerably more power than the WUP1 (4.5A vs 1.5A), and are controllable with a PWM signal on the connector, but I haven’t used this feature. The PWM pin is simply tied to the positive supply to keep the pump running at maximum speed.

Once this pump was installed the head pressure immediately increased on the gauge from the 1 bar static pressure to 1.5 bar, indicating the pump is running at about it’s highest efficiency point. The higher water flow has so far kept the Webasto happy, there will be more to come with further improvements!

CWA-50 Pump Teardown

CWA50 Cutaway
CWA50 Cutaway

Above is a cutaway drawing of the new pump. These have a drilling through the shaft allows water to pass from the high pressure outlet fitting, through the internals of the pump & returns through the shaft to the inlet. This keeps the bearings cool & lubricated. The control & power drive circuitry for the 3-phase brushless motor is attached to the back & uses the water flowing through the rotor chamber as a heatsink. Overall these are very well made pumps.

Impeller
Impeller

Here’s the impeller of the pump, which is very small considering the amount of power this unit has. The return port for the lubricating water can be seen in the centre of the impeller face.

3-Phase Driver
3-Phase Driver

Inside the back of the pump is the control module. The main microcontroller is hiding under the plastic frame which holds the large power chokes & the main filter electrolytic.