Eberspacher parking heater trouble


Heating problems in Germany 50° 21' 30.9996" N, 7° 18' 7.9992" E
berspacher parking heater trouble

Eberspächer is a well known and popular brand of independent parking heating system in the transportation market. It’s compact diesel fuel heaters are found in many trucks, boats, RV’s and mobile homes. Regular maintenance is key for dependable operation, though there’s one part which can drive Eberspächer owners to the brink of insanity – the fuel metering pump. From experience for those who travel far outside the European region a few details about the mysterious Eberspächer fuel suction pump - key to warm feet when it gets real cold.


In this article you find the following info;

Eberspacher fuel metering pump

Classic parking heater problem

Eberspacher pump problem

Parking heater fuel line

Eberspacher pump design issues

Parking heater fuel diagnostics

Eberspacher versus Webasto

Alternative fuel metering pumps



Eberspächer fuel metering pump

It’s a small and quite expensive part, the electrical suction fuel pump from Eberspächer driving fuel from a fuel tank to the heating system.

Eberspacher fuel metering pump dosierpumpe brandstofpomp
Eberspächer fuel metering pump / dosierpumpe / brandstofpomp - 24 volt version

Webasto, a fierce competitor,  uses a similar solution to supply fuel to the fossil fuel heater. On the surface it seems like a fairly simple suction pump, but there’s a lot to know, specially when there’s a problem with fuel supply and your feet get real cold.

There are many variants of this fuel metering pump with different suction action and voltage supply (12 / 24 volt). The 24 volt pump (partnumber 25.1831.45.00.00) in the picture is used in the Eberspacher D3LC (3 Kw Compact Standheizung)

Classic parking heater fuel problem

Without doubt the most striking problem is no fuel arriving at the heater with a tank full of fuel. Those with experience know about this hair-raising situation which already surfaces during heater installation and can occur later-on in it’s operational life.

A long and very thin fuel line combined with a long heater start sequence makes an average fuel suction run a lengthy procedure averaging up to 5 minutes each. This is specially the case with installations in large trucks / lorries where the parking heater usually has a long and separate hose connected to the diesel fuel tank.

Eberspacher D3L-C Compact parking heater Eberspacher D3L-C Compact heating housing core
Eberspächer D3L Compact - with heating housing core on the right

With an empty fuel line it can easily take 20-30 minutes and 5-6 restarts before the heater switches on and stays on. Not to mention the waiting frustration when there’s a problem in fuel supply – of course when it’s getting real cold!

Workshops usually have a fuel dosing pump pulse box to fill long fuel lines - avoiding going through several parking heater startup / shutdown sequences. The box is nothing more than a relay creating a 12/24V pulse.

Specially for those traveling far outside the European regions, diesel fuel can be outside purity specification and here's what can happen.

Eberspacher fuel pump – 2 key problem areas

The Eberspacher fuel metering pump has 2 key problem areas at each ends of the pump.
Both can surface at the same time either during installation or later-on when fuel has run out or when using (contaminated) diesel fuel outside (western) specifications. More about diesel fuel quality at the end of this article.

Eberspächer filter for fuel metering pump dosierpumpe brandstofpomp
2 samples of internal fuel filters from a Eberspächer fuel metering pump / dosierpumpe / brandstofpomp

At the supply side there’s a tiny filter (partnumber 20.1312.00.00.06) sometimes hampering fuel supply. Even in new pumps! Removing the tiny filter can make a big difference. The fine filter mesh can be contaminated with tiny fuel impurities invisible to the eye. When temperature drops and fuel gets thicker the fine mesh can become an obstruction hampering already weak suction action. While removing the tiny filter - add an extra seal to prevent (air & diesel) leaks and make sure to install an external fuel filter. Please note that Eberspacher doesn't recommend doing this - but in rough conditions without access to support this can be difference between cold and warm feet.

On the other side sits a brass tube with a spring and metal ball inside. Sometimes the ball is stuck blocking fuel supply - specially after it's not been used for quite some time. Before opening this end of the pump - make sure to mark the exact position of the nut since it's the fuel supply adjustment. (usually its sealed with stuff similar to nail polish)

Eberspächer ball bearing and spring for fuel metering pump dosierpumpe brandstofpomp
Ball bearing and spring (not shown) in Eberspächer fuel metering pump 

The brass tube with rubber ring on the left is the diesel fuel supply adjustment nut for the Eberspacher heater. Turn this one outwards for more fuel and inward for less. In normal cases it's not necessary to adjust the fuel supply. For long term heater operation it's recommended to re-adjust the fuel supply by an Eberspacher dealer if the original adjustment is changed or lost after opening.

Be careful when opening this end of the fuel metering pump, the spring is very small and can easily jump away to be never found again. Same for the tiny metal ball. Note that these parts can NOT be ordered separately and a tiny replacement spring is not easily found.

Parking heater fuel line specifics

The thin transparent plastic fuel line is connected with rubber hoses and clamps. Each system has several of such connections. The see through transparency of the fuel line is key to diagnosing a fuel supply problem. It can show air bubbles, fuel being transported or the absence of fuel.

Rubber fuel line joints in parking heater system
Rubber fuel line joints in parking heater system

Aged rubber hoses can grow tiny cracks or when not clamped properly causing suction to be weakened by airleaks. Specially in transition from very hot to very cold regions can surface this condition. The heater stays on for a while and then shutsdown. Each restart takes ages and fails often - quite frustrating when it's real cold.

A fuel line with oversized diameter doesn’t work either – suction is too weak to carry the extra fuel weight. Also rubber connection hoses with a diameter too wide can cause tiny airleaks even when clamped to the max.

Fuel filter before fuel metering pump dosierpumpe brandstofpomp
Fuel filter just before Eberspächer fuel metering pump - with airpocket

External fuel line filters are practical alternatives
in stead of the tiny internal mesh filter. When mounted under a slight angle, airbubbles gather in the filter and create an airpocket as shown in the picture. Fuel transport is still ok under these conditions – it’s sucked through the filter material into the output tube.

Eberspacher fuel metering pump design issues

Now when opening the supply side of the pump, turning the aluminum tube with a wrench, it’s possible the face plate suddenly turns inside the housing.

Eberspächer faceplate and aluminium tube in fuel metering
Faceplate and aluminum tube in Eberspächer fuel metering pump

Behind the plate sits the coil connected to the pins on the other side. Normally the plate is clamped firmly into the coil housing and shouldn’t move. If it does, the aluminum tube has been overtightened in the past.

On the same end the aluminum tube – partnumber 20.1621.45.00.02 – can have hair shaped cracks when tightened too firmly. Such cracks can cause tiny airleaks - but the condition is quite rare.

Simple fuel metering pump diagnostics

The ticking / clicking sound of the fuel suction pump in Eberspacher and Webasto heaters is a familiar noise to those who depend on mobile heaters. The sound of the “tick” says quite a bit about what’s going on.

Hard ticking noise indicates an air pocket inside the fuel pump. A soft ticking noise is re-assuring – because fuel is transported to the heater. Intermittent soft and hard ticking can signal airleaks in the fuel supply line or even (too) thick diesel fuel blobbing through the fine mesh filter.

Eberspacher fuel metering pump disassembled
Eberspächer fuel metering pump / dosierpumpe / brandstofpomp disassembled

The angle of the fuel metering pump can be the difference between continued operation or (1)  occasional flame-outs or (2) auto-shutdown due to the heater temperature being too low. The maximum fuel supply is reached with a vertical mount, causing all possible air is pumped out of the fuel metering pump. This way the "click" or "tick" produces the maximum stroke of fuel.

When the heater shuts down with a vertical mounted fuel metering pump while the heater doesn't get really hot, try adjusting the fuel metering pump. (Note: This is not recommended by Eberspacher) Turn the bigger brass nut outwards for 1 turn and try again. When combustion at the exhaust sounds quite a bit louder, there's more fuel being burned. The Eberspacher should blow hot air now. When it sharts smoking a lot during operation - there's too much fuel coming from the metering pump. In this case the adjustment nut should be turned inwards.


Fuel metering pump Filter comparison - Eberspächer versus Webasto

During frantic testing with the Eberspächer fuel metering pump a Webasto pump was used under the same cold conditions using the same fuel. While the Eberspächer fuel metering pump refused to pump diesel, the Webasto fuel metering pump worked perfectly.

See the difference between both internal fuel filters.

Eberspacher Webasto fuel metering pump filter comparison
Webasto 12556A fuel metering pump filter comparison with Eberspächers version

The picture shows a Webasto 12556A fuel metering pump for a the Webasto HL 18 D Airtop
 parking heater. For the Eberspächer D3LC the Webasto pump supplies way too much fuel resulting in excessive smoke.

Alternatives for Eberspacher and Webasto fuel metering pumps

The firm Thomas Magnete in Herdorf - Germany manufactures fuel metering pumps compatible with Webasto and Eberspacher fuel metering pumps.

Here's an example of a 24 volt Thomas Magnete fuel metering pump used in a Webasto Coolant heater Thermo 90 ST (diesel). It worked off the shelf without further pump adjustments.

Webasto 90 ST alternative: Thomas Magnete 24 volt fuel metering pump 89373A
Eberspacher - Webasto alternative: Thomas Magnete fuel metering pump dosierpumpe brandstofpomp

The partnumber for the Thomas Magnete pump seems to correspond with Websato partnumbers. The Thomas Magnete fuel metering pump has a price advantage compared to the expensive Webasto fuel metering pump for the Coolant heater 90 ST.

Detailed parking heater information

Diesel Fuel Quality details

More details about the Eberspacher fuel metering pump

Thomas Magnete fuel metering pump

Manuals for parking heaters (dutch language)

For manufacturer information have a look at:

Eberspacher website
Webasto website


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