We believe the cooling system that we have developed, documented on this site and which we manufacture the products for, is by far the simplest, neatest way to plumb a Subaru engine in a rear engined VW. Our kits use reinforced OEM spec hoses designed by us for the application, not hoses from another application which ‘sort of’ fit, or multiple generic hoses with joiners everywhere.  Considerable effort went into designing a cooling system which is as simple and neat as possible while also being as simple to fill, bleed and understand as possible – a lot of other circuits out there have clearly been ‘designed’ by people with little to no understanding of how cooling systems work.

  • Designed for climates which do not regularly go below around -10 oC (14 oF), but can be modified for colder climates where required.
  • Requires the use of a coolant manifold which we have modified for fitting reversed. This is not included in the kits because a cooling plumbing kit is a product, and reversal of a coolant manifold is (usually) a service – i.e. we modify the customers own manifold. Unfortunately we do not have an infinite supply of sensibly priced Subaru coolant manifolds, so any we do have are only available to customers abroad, when sending their manifold to us to reverse could cost more than a used manifold is worth. If you have EJ series coolant manifolds which you don’t need, we’re always after certain types. Manifolds modified to reverse by others may not be suitable – if they are, they’re copying our products, as nothing like this system was available when we developed it
  • EPDM hoses manufactured to our design specifically for Subaru – VW engine conversions, to SAE J40 R4 by an OEM. The same material and one of the same standards that most OEM coolant hoses are made to. No silicone rubbish.
  • Exclusively uses exactly the same materials that Subaru and VW used  throughout – aluminium, EPDM hoses, polypropylene and nylon. No materials unsuitable in the cooling system of an aluminium engine such as copper and stainless steel.
  • Hoses manufactured to the same specifications as OEM’s use (the relevant SAE automotive coolant hose standards)
  • Up to 41% less coolant hoses and hose clips than in some rear engined water cooled VW models. No wonder VW added a low coolant warning system after the first couple of years of water cooled model production! (the wasserboxer’s cooling system is a total mess, and there is clear evidence that adding the low coolant level warning system was an afterthought)
    *manual T25 / T3 / Vanagon without rear heater or Webasto coolant heater
  • Retains the low coolant level warning system in the 1984 onwards models which had it – some competitors cooling systems do not
  • Includes all hose clips (stainless steel)
  • Designed for EJ series engined VW conversions, originally for normally aspirated applications, but there are also advantages to using this plumbing system on the turbo engines too, althouigh doing so is no as straight forward as normally aspirated
  • Designed for T25 / T3 / Vanagon applications, but also quite widely used in other rear engined VW conversions where the radiator is positioned forwards of the engine (except the late Bay / T2b, which they are not suitable for because reversed coolant manifolds do not fit).
  • Requires modification in automatic T25 / T3 / Vanagon models which have the oil to water transmission fluid cooler – you’ll need to add two tee pieces yourself for the heat exchanger feed and return to use these kits in such models

Coolant plumbing kit – 32mm

Price: £116.67 GBP +VAT (£140.00)

From the introduction of water cooled models in 1981 to 1983, the T25 / T3 / Vanagon used steel coolant pipes with an outer diameter of 32mm. Includes all parts needed except the reversed coolant manifold and parts which many customers already have in their VW (header tank 025 121 403 B, Blau or genuine VW pressure regulating cap 025 121 321 B, expansion bottle 025 121 403 and cap 025 121 482):


Coolant plumbing kit – 38mm

Price: £104.17 GBP +VAT (£125.00)

From 1984 onwards, the T25 / T3 / Vanagon models used plastic coolant pipes with an outer diameter of 38mm. Mny models which originally had the 32mm pipes (much) later had them swapped for 38mm too, as the 38mm pipes superseded the 32mm ones at some point. Includes all parts needed except the reversed coolant manifold and parts which many customers already have in their VW (header tank 025 121 403 B, Blau or genuine VW pressure regulating cap 025 121 321 B, expansion bottle 025 121 403 and cap 025 121 482):

We developed this system back in around 2004 / 2005, and published it shortly afterwards. You’ll find numerous copies online now (other people’s diagrams showing our cooling schematic), but ours was the first to show this system. We developed it from scratch after seeing how terrible some of the most commonly used schematics around at that time were. There still are a lot of other circuits out there which have clearly been ‘designed’ by people with little to no understanding of how cooling systems work. No wonder the engine conversion forums at the time were full of people having problems filling and bleeding their cooling system – the schematics they were using had seemingly been designed with no consideration to filling and bleeding.

Other variants of this system can work, with the usual corner cut being not being bothering fitting a reversed coolant manifold. Our coolant plumbing kits and reversed coolant manifolds are not particularly expensive. If you’re plumbing a conversion without a reversed manifold yourself, using many ‘off the shelf’, new hose bends straight joiners and hose clips, you could probably spend more attempting to plumb that system than reversing your coolant manifold costs.

Designed for the models which had two short front to rear coolant pipes (mainly Syncros), which terminate above the RH rear drive shaft, as they need the longest hoses. Most 2wd models have one short and one longer pipe, and the longer pipe can be one of a few different designs. Many of the longer pipes are too long for the hoses in this kit, but can always be shortened by sawing the end off leaving more pipe / hose overlap than usual, and using two hose clips on the resulting pipe end with no bead.

See Coolant Plumbing Schematic – Subaru EJ Series Engine in a Rear Engined VW

See Coolant Filling and Bleeding Procedure for details of how to fill this system with coolant

If you’re interested in these kits, you may also be interested in the following associated parts:

125-00001 Reversal or your own coolant manifold
800-00048 Reversed coolant manifold outright purchase (sorry, customers outside the UK only)
100-00078 VW coolant header tank – the right one for out coolant plumbing kits
100-00079 Coolant header tank cap
100-00077 Low coolant level sensor – early
100-00083 Low coolant level sensor – late

Coolant plumbing kit FAQ:

Reversing the coolant manifold on a Subaru engine where possible is the best approach for a few reasons:

  • done right, a reversed coolant manifold can make filling and bleeding the system easier
  • a reversed coolant manifold can make the cooling system very much neater than is possible with a standard manifold – messy coolant plumbing is one of the main things which makes many aftermarket engine conversions look amateurish. This combined with the OEM VW cooling system being a total mess on a lot of the engines which are being replaced (i.e. the wasserboxers) means that done right, the coolant plumbing for a Subaru engine conversion can be very much neater than in either the Subaru or the VW

Don’t jump to the ‘diagnose by randomly swapping parts until the problem goes away’ conclusion, and change the thermostat, especially if you know it is a genuine Subaru part, and don’t have any reason to believe it may be faulty. It almost certainly isn’t. Definitely don’t replace it without first testing it. Follow our filling procedure exactly, and if it is an aftermarket thermostat, throw it I the bin and replace it with a genuine one. For a lot more information on both, see Cooling a Subaru Engine in a VW.

Not very. They’re specifically designed for conversions which do use a reversed manifold, and only one of the moulded hoses will fit in its intended location without.

Not unless you are also using the dash instruments (or at least the coolant temp gauge) from a model with the low coolant level sensing system. VW used a bizarre design, where the low coolant level signal is multiplexed onto the same wire as the coolant temperature signal by a ‘relay’ in the fuse box (it’s not actually a relay at all – it just looks like one , ‘42’, or 191 919 376A), and de-multiplexed by another circuit inside the temperature gauge. Interestingly, the only sensible explanation can be that the low coolant warning system was added as an afterthought, after the instrument cluster design was finished – hardly a surprise given that some models have 22 hoses / 44 hose clips thanks to the awful wasserboxer external coolant plumbing. You would have to destroy a temperature gauge to get at it’s de-multiplexing circuit, as they’re not dismantleable.
Making a stand-alone low coolant warning system for customers with VW models which did not originally have one has been on out ‘to do’ list for many years, but it never gets near the top.

Yes, if your VW is one of the models which they suit. Doing so is not as straight forward as it is with the normally aspirated models, but there can be some advantaged to doing so too. The turbo models do not use the radiator as the header tank, as the normally aspirated Subaru models do. They have a header tank (somewhat unusually) mounted on the engine itself. It also acts as a manifold for coolant flow for features unique to the turbo application, and as a bleed point at the top of the engine (which has considerably more coolant plumbing) – both features which are useful with the engine in a VW too. However, it has a big disadvantage when used as the header tank in a VW conversion too.

The volume of cooling in the VW will be far higher than in the Subaru, and the header tanks on the turbo engines are very small, with a very small filler neck diameter. This makes using them to fill a VW very difficult. Turbo engines in VW conversions are much easier to fill via a VW header tank mounted higher up, with its far larger volume and filler neck diameter. However, you then have two header tank caps capable of controlling the system pressure. You should only use one, and it should be the one which is highest up – i.e. the VW one. The cap on the Subaru header tank on the engine can still be used as a bleed point during filling if required, but it’s vent pipe (from directly below the cap, on the neck that it fits too) must be blocked off.

Also, there is less space around the coolant manifold on the turbo engines, mainly due to additional coolant pipes closely following their route, and being attached with the same bolts. This can make reversing the coolant manifold on a turbo engine more difficult, as the brazed steel coolant assemblies need modifying to fit, and this is not easy. On turbo models from MY90 – MY97, the original manifold can be fitted in reverse once modified for this. The manifolds used on turbo models from MY98 onwards cannot be reversed. However, the reversed manifold from an MY02-03 normally aspirated model can fit them very nicely, with few or no modifications to the steel coolant pipe assembly needed.

If you’re having us reverse a coolant manifold for your turbo engine, be sure to mention if your model has tumbler valves, and / or two vertical breather pipes from the crank case (as opposed to one), as both of those require the work to reverse the manifold to be done differently, otherwise they won’t fit.

The header ranks have a large hole in to top which needs sealing. We could machine blanking plugs for this hole, but they would cost more then the early sensors do, so just using the sensor to seal the hole, but not plugging it in to anything makes sense.

Please get in touch with whoever designed the system that you are using for help troubleshooting before us! They know 100% more about their system than we do. We have detailed knowledge of how our cooling system behaves, but have no time to experiment with others. It’s clear just from looking at how they’re plumbed that some of the other circuits out there will be very difficult to use at best. Clearly designed by folk with more time to promote their efforts than they have to spend learning about and understanding what they are doing.

If you’re plumbing a Subaru engine into a T25 / T3 / Vanagon which is already water cooled, leave the radiator, heater(s) and their plumbing as VW intended. You’ll need these VW parts in the engine compartment, which you may or may not already have depending on the model year and original engine type that your VW had:

We stock all of these except the expansion bottle (top left) and its cap (white). Which low coolant level sensor you need depends on the wiring in your VW. All water cooled models from around 1982 – 1986 used the early type (which connector in a rubber boot). After about 1986 some models continued using the early sensor type, and others used the later type (plastic connector held on with a stainless steel spring clip). if shopping elsewhere for these parts, make sure you understand that there are two very similar variants of the header tank, and than many aftermarket header tanks caps do not work properly, and can cause a lot of expensive damage. See

See here for an awful lot more detailed information on cooling Subaru engines in VW conversions .

Those in the US, don’t be taken in by the company in your country attempting to charge $300 USD ($475 USD – $175 core charge)* for a reversed coolant manifold. That’s 424%* of what we charge to reverse your own coolant manifold or 458%* of what we charge for a reversed coolant manifold outright (when we have them in stock – only available to overseas customers), and we make a profit on them. They are either attempting to rip you off, or being ripped off themselves by someone they subcontract the work to, and are passing that on to you.
* April 2022 prices