Which VW T25 engine?

Whether you’re an air-cooled purist, like the idea of a fuel-sipping diesel or prefer the smoothness of a later ‘wasserboxer’ there’s a VW T25 engine in the line up to suit all tastes and driving styles. But the million dollar question, and something we’re being asked all the time by prospective T25 buyers is – which one is best? Here’s our warts ‘n’ all guide…

Air-cooled – simply the best?
The first T25s from 1980 were available with either a 1.6 (50bhp) or 2.0-litre (70bhp) air-cooled engine and you can instantly identify these by the absence of a second grille just above the front bumper. Air made way for water and was eventually dropped altogether in 1982.

air cooled bus

The early 50bhp air-cooled units (carrying a CT code) were derived from the Beetle engine but had hydraulic tappets, conventional oil filter and a cooling fan on the end of the crank. These engines are robust but painfully slow and worryingly thirsty – when buying it’s mainly a case of looking for cracked cylinder heads and evidence of overheating due to stuck thermostats.

air cooled 2.0

Despite being even more thirsty the 2.0-litre 70bhp CU engine (above) was the better of the two air-cooled offerings. It was based on the Type 4 unit and first saw VW bus duties in the later Bay Window. Its twin Solex carbs, however, are troublesome; they are prone to air leaks and tricky to balance and often replacement is the best remedy. Oil leaks from the pushrod tubes is also common (but relatively easy to sort) while rusty heat exchangers should be viewed with caution because they are pricey to replace. Meanwhile, blue smoke on the overrun points to worn valve guides or general bore/ring wear. Nasty knocks from the crank bearings aren’t a good sign either. It’s not as easy to check for end float because there’s a mesh guard over the fan. We sell remanufactured CU units here for £2,494.95.

Diesel do the trick…
The water-cooled 50bhp 1.6 diesel unit (below) was fitted to the T25 from early 1981. An altogether much better 70bhp turbodiesel was introduced from 1985.

1.6 diesel engine
People like the diesels because they suit the nature of the T25 and most were derived from the Golf, tilted over to fit the lower engine bay. A word of warning, though, the early 50bhp CS 1.6 is dangerously slow and many diesels will have endured a hard life as it was the obvious choice for commercial use. The 1.7-litre KY engine (57bhp) was slightly better, but parts are scarce, which makes the JX codenamed 70bhp 1.6 turbodiesel (below) the one to go for. Performance is about on par with the air-cooled petrol unit but with far better economy.

1600 JX turbodiesel

Some owners have managed to eek out 40mpg on a run but between 30-36mpg is probably more realistic. However, cylinder heads crack and turbos can fail, so beware misfires and worryingly sluggish performance. We sell JX cylinder heads here for £549.95 while replacement turbos are £508.96.

Water way to go?
By the end of 1981 there was a switch from air to water-cooling for the petrol units with a 60bhp and 78bhp version being offered (below). The 60bhp DF 1.9 feels a little underpowered, making the 78bhp DG unit a much better option – although beware any with leaky exhausts as it’s a complex system and tricky to fit. Economy from these engines is likely to be in the region of 25mpg.

water cooled 1.9

Unfortunately, all ‘wasserboxers’ suffer from a design fault by virtue of the fact that the cylinder head bolts pass through a water jacket and can corrode if the anti-freeze (containing rust inhibitors) hasn’t been changed regularly. Some owners swear by the use of pink phosphorous free antifreeze (G12), but basically it’s a case of ensuring it’s been changed every two years on the dot. If the bolts go and the gasket starts leaking coolant (you might see a feint crystalised trace initially), then a full rebuild or replacement engine is the only option. Our full range of T25 water-cooled petrol engines are listed here.

The fuel injected 2.1 from 1985-on (with 87-95bhp) is brilliant and can be made to produce a bit more poke if you (legally in the UK) remove the catalytic converter. The pick of the bunch, if you can find one, is the 2.1 carrying the DJ engine code which produces an eye-watering 112bhp and has a surprising amount of usable torque. Being fuel injected any running problems are likely to be a result of faulty sensors, so make sure it idles nicely and doesn’t cut out when warm.

Other options
If you’ve got this far and still don’t feel particularly impressed by the factory T25 offerings, there’s always the option of upgrading to newer technology. With a different bellhousing a Mk3 Golf diesel engine can be made to fit (below left), although its extra height means you would lose a bit of space in the back unless you angle it right over. You can even fit a later PD diesel unit – anything is possible if you have deep enough pockets. The flat-four EJ22 Subaru Impreza engine gets round the height issue and while you’ll appreciate the extra kick in the back from the turbo version, economy would be similar (or perhaps a little worse) than the original VW water-cooled unit – and it would still involve a fair amount of work. That said, you could always fit Subaru’s turbodiesel…

Golf engine in T25 3382.2 Subaru EJ22 338

To be honest, none of the T25 engines were particularly strong so a vehicle that’s just had a freshly reconditioned unit fitted is likely to be the safest bet. Arguably, the non-turbo diesels and early air-cooled units are possibly more reliable than the later water-cooled lumps, but they’re not nearly as smooth to drive and a fully kitted out camper with elevating roof will struggle to keep up with  modern traffic.

Of course every T25 owner has their favourite engine, so expect to hear lots of different views on this matter. In our humble opinion though, the two best options are the 1.6 turbodiesel and the later 2.1-litre water-cooled unit. The best advice, though, is to try one of each before you buy and make your own mind up…


The opinions expressed here are the personal opinions of the author and do not necessarily represent the views and opinions of VW Heritage


52 responses to: Which VW T25 engine?

  1. We have just bought a 1983 T25 with a 2.0l aircooled engine. However we are really confused as to why the van has a radiator?! Can anyone help? Assumption is it was originally a water cooled engine and has been swapped out.

    1. Hi Andrea, if the van was originally watercooled it would have a second grille below the headlamp grille for the radiator to be fed cold air. We’re presuming the radiator you have found it located right at the front, and it’s not an oil cooler instead?
      Please feel free to send us some photographs, and one of our team could advise a little more – esales@vwheritage.com

  2. Hi,

    our T25 from 1980 is an aircooled 2.0L one. It’s giving us some headaches now, and were considering replacing the engine with a golf gti one. There’s people who do it, but apparently it’s waaaay more difficult and expensive do to it in a aircooled engine than in a watercooled one. Is that the case?

    great post by the way! 🙂

    1. I am sure it can be done but the obvious issue will be where to put the radiator. You could always buy a bigger capacity, reconditioned air-cooled lump to go in there…

      1. There was no ‘bigger air-cooled lump’ than the 2-litre. Unless you’re thinking of sticking a Porsche motor in there. Which, believe me, would really not be worth the hassle – not to mention the expense.

    2. The big problem for you with a conversion is the lack of water cooling on your van. A radiator will need fitting somewhere and the pipework running to and from it back to the engine at the rear.
      This could be retrofitted of course, but will be more work than if you had started with wbx or diesel van.
      An alternative to the GTI engine would be a Subaru engine conversion; and there is arguably more information about this online now, than for the GTI conversion.

    1. Hi Paul, The main issues will be tinware, engine mounts and the support bar. These all differ between the Type 25 and the Bay.

  3. I have a 1989 1.7 D DOKA, After having a top end rebuild and now finding I need to plan for a bottom end build on an engine that really is not up to the job. I’m confused to be confidently able to choose my next option. 2.1 2.3, turbo VW or go for a Subaru???? Many thanks. Pete.

    1. Hi Pete, it’s all down to personal taste to be honest. Another option, if you like the idea of a diesel, is to source one of the more powerful turbodiesels that were fitted in the T25…

    2. Or look at fitting an AAZ Diesel from the Mk3 Golf, or better (although far more complicated) the PD from Mk4 Golf/ Passat etc.

  4. We’ve just got our first t25 it’s a1.6 diesel. It’s had a recon engine put in buy the owner but is now not running. Was told injector pump failed and possible loss of compression. I’ve been told That I can just change the engine and I’m to look for ahu engine code that would just drop straight in. Or I can have it blown out and check for blockages.which means nothing to me to be truthful. But I want to learn. So my questions are as follows if I need a new engine why do I need to find an engine with that code? Is there anything I can do to fix the engine I have already, and what do I do to blow it out and check for blockages. Lol any help please

    1. Hi Clair, the AHU engine code is a TDI unit from some slightly newer VWmodels (Golf, Caddy, Passat etc 96-00), it produces 90bhp so is a nice upgrade from your original engine. Fitting should be fairly simple, but your mechanic will offer the best advice, as they can see exactly what they have in front of them.

      ‘Blowing out an injector’ sounds like they will remove it from the engine and blow hi pressure air though it, to try and clear any blockage. We would suggest this as the best course of action first. It will be a lot cheaper if this fixes the problem!
      Hope that helps a bit. Andy

  5. hi I have a 1987 1.6d t25 and I have a 1998 golf 1.9 tdi I would like to put the 1.9tdi engine in the t25 first thing will this fit on the t25 bell housing. second thing can I get away with not changing the gear ratios in the box straight way(if I drive it nicely)

  6. Hi Just change engine on my 1988 camper with a 1915cc recon , new water pump new thermostat. bleed system when running the temperature gauge rise very fast to 3/4 and stays there . replaced sender its still the same . Have notice at the back of the temperature a bolted brass plate running from the voltage stabilizer fix to edge of the fuel/water gauge Can anyone tell me what this does. also would the wrong fitted thermostat be the trouble. New to this type of vehicle.
    But learning fast. Tony

    1. Hi Anthony, We would always recommend replacing the thermostat when fitting a new engine. Also, it is not uncommnon for radiators to clog up with sludge and increase running temperature. It would be sensible to flow test this and clean it out. We hope this helps. Andy

  7. Hi Andyvwh Have changed thermostat flushed radiator and pipe all clear bleed system and replaced temperature sender. i still trying to figure out what this bridge plate is doing at the back of fuel/ temperature gauge . its attached from the voltage stabilizer to the top corner off the gauge. is this action as as earth . i am going to disconnect it and fit a new voltage stabilizer to see what happens. Any one got any ideas as all fuel / temperature gauges work even if temp is high .

  8. Hi I have a 1.9 water cooled engine reconditioned, can I put a Porsche engine in to give more power. I need to tow a caravan can you help please. My van is a 1984 t25 cravelle.
    Many Thanks

    1. Hi Nichola, the short answer is yes, anything is possible.
      In reality, a Subaru conversion is probably your best ‘bang for buck’ engine swap. Porsche engines aren’t cheap to buy!
      Another option could be a later VW TDI engine.
      Depending on whether you are doing it yourself, or needing a specialist to do it, maybe check out the facebook groups for owners of Subaru VW swaps; and see if you think that would fulfill your criteria.

  9. Hey, I’ve bought a t25 87 1.9 water cooled. Having carb issues at idle speed and can’t find the idle adjustment. It’s a Pierburg 2E carb if that helps. Is this a standard carb? All tutorial videos I have found all have different carbs.

  10. My 1980 T25 has an air cooled 2 litre engine. Tickover was a problem only solved by a VW specialist who started his apprenticeship with VW in 1980. The carbs were loose with leaking gaskets and pipes, a cross shaft with a piece missing, and the distributor base was loose too. Rerivetting that solved it. After carefully balancing tbe carbs and adjusting the timing it now runs sweet as a nut. I am wondering if there are alternative carburettors and exhausts available for these air cooled engines to improve breathing and enhance performance and economy?

    1. Hi Alan, we can offer a twin carburettor kit for these engines. See here.
      We can also offer a number of ‘sports exhaust’ options too. See here.
      Performance and economy don’t typically go hand in hand sadly, coupled with the brick-like aerodynamics of the Type 25, it will
      always be a little bit thirsty! Andy

  11. Hi, has anyone ever fitted a turbo to a ADG 1.9 industrial unit and put it in a t25. The engine is rated at 64 he without a turbo, the engine block is stamped T/TD…. Thanx in anticipation.

  12. I would like to do somthing to give my 1.6 aircooled CT brick some more poke on the hills but not make the fuel economy any worse 😉, is the first place to start a better/bigger/twin carb set up or should I go up to an 17-1800 piston and head swap!.

    Thanks guys

  13. Hi, I might be slightly off topic, but can a type 4 cu engine be installed in a Karmann Ghia? I know that 1700’s can, but didn’t find anything on this particular type. Do you have conversion kits?

  14. Hi
    I’ve owned a few VWs but unfortunately had to get rid of my last T25 more than 10 years ago..so I’m now a bit rusty..

    This was a really good article for someone like me..!

    Have a quick question am about to look at another T25 (diesel). I’m told the original lump (1.6) which j remember being painfully slow was replaced a few years ago with a VW 1.9 LY engine..

    Is anyone familiar with this 1.9 LY engine which car it would originally fitted to and what performance and economy might be of shoehorned into a T25..?


  15. Hello, i have a 1.9 tdi skoda fabia (HV plate) and before it goes for scrap thght id try amd find out how difficult it would be to the Engine from it into sat a 1981 air cooled T25? And i suppose the gearbox from the skoda would all have to be switched. If anyone would tell me if its even possible and if so how hard it would eventually become, thanks

  16. My 1987 RHD T 25 has a 1.9 petrol engine.
    In the original VW Transporter Instruction manual which I still have, it advises to use G11 Coolant,
    in your article above it advises to use G12 coolant.
    The mechanic who is working on my bus, advised using G12 coolant.

    I am confused as to which one I should be using, can you help?
    Chris W.

  17. Hi Ian
    I have t25 pick up 1.6 td jx which has gone!!! I’m looking at a 1999 Audi 1.9 tdi ahu code which I can get.Would this do or would I be better waiting on a mk3 golf. Is the golf an easier fit?

  18. I have a DF 1900 watercooled engine in my T25, and feel at 60bhp it’s a bit underpowered. Can anyone tell me what causes the power differences between the 5 1900 watercooled engines, and can the increases in power be retro fitted? Eg carbs etc
    Many thanks.

  19. Hi you said in your rundown of engines that the cu pushrod tubes are easy to replace. My friend has one with the all but common leak. She has asked me to look at it (do the job) for her. Trying to find parts it looks as if the only way to go is removing the cyl heads as I can’t find any collapsible tubes for this model. I also would need to know the valve clearance so I can adjust after rebuild any advice would be great thanks Gerry

    1. I know this is way too late but in response to Gerry’s question

      Hi Gerry,

      If I’m correct, at least I know I am for my camper, a 2.0 air-cooled VW Transporter, dating from 1982, the tubes are removable from the sides, you do not have to remove the cylinder heads. You carefully grab each tube with a suitable pair of pliers (ones that will fit around a tube with enough space between pliers and next tube, without crushing anything, and twist gradually getting them loose and working them outwards.
      1) Remove the cover behind which the rockers are housed, have something clean to lay each rocker out on, so you can remember/keep track of how they fit together.

      There are two nuts for each rocker piece. Using a torque wrench is best, at least… don’t overtighten the nuts when putting the rockers back in place. However, I had a damaged thread and nut, and found out that the threaded rocker arms can be purchased. In the end I did not use a torque wrench and just kept in mind that ”tight is tight” and so don’t force anything. My first attempt had been unsuccessful, I suspect because of the damaged rocker arm/stud. Second time not a drop of oil in sight, a relief, as that oil on the hot heat exchangers and what not, stinks.

      It took me ages to work out what that particular problem was.

  20. Hi there HP,
    thanks for this excellent article on engines. This and other info by you really helping me whittle down my options and I think I’m (nearly!) there. My (3-part) question is I’m on the precipice of buying a T25 with a 1584 cc petrol engine….so
    (1) is it possible to upgrade this to a 2 litre petrol?
    (2) if so I imagine that perhaps the Subaru or a Golf would be the preferred option and if so which of these 2 the better option?
    (3) Any idea (ball park figure at worst) of the cost of getting this done? (1.6 removed, 2 litre installed)
    (4) (ok, so I lied about 3 questions..!) Do you do this? If not any recommended people that do? (ok, that’s 5 questions, sorry!)

    My finger hovering on the “buy” button and all and any answers greatly appreciated! I envisage visits to you (online and in-store) pending!

    Barney 🙂

  21. And of course a 6th question (last I promise!).
    (6) I’m buying a vintage vehicle so tax and mot exempt but more importantly ULEZ exempt (I live outside the current area which the same as congestion charge zone but will still be living in London inside the North & South Circular come October 25th 2021 when it expands to this area…). Does changing the engine (from 1.6 to 2 litre petrol) count as a change so substantial as to render my vehicle NOT exempt? (this will in fact be a crucial question for many many people in the next 2 years I believe) . Thoughts appreciated 🙂

    1. Hi Barnaby
      1) yes, you could upgrade – the 1600cc petrol isn’t great if we are being honest.
      2) The Golf is probably cheaper from a sourcing point of view, and simpler to connect – although you are going to need to sort the plumbing regardless.
      3) Costs, you’ll need to speak to a specialist. If you are local try Dougs VW Werks (Angmering) or Combe Valley Campers (Bexhill) both are great with T25 models.
      4)See above!
      6) Currently none of the T25 models will be tax or MOT exempt – you’ll need to wait until 2020 or 2021 for the very earliest models to fall into that territory. The engine swap to 2litre shouldn’t be an issue – the Subaru could cause more complications as that motor was never offered in that vehicle.
      Hope that helps and good luck!

  22. Hi Andy,

    I’ve had a kamper with 1.9 DG wbx for 22 years, engine now v tired.
    I have an old but lovely, rusting Golf GTi turbo, petrol 1.8, have you heard of anyone changing this [only 70,000 miles genuine] for the DG?

    1. Hi James,
      The 1.8Turbo swap has been done into the T25, however, it typically uses the longitudinal mounted Passat or Audi A4 lump, rather than the transverse Golf engine.

  23. Exchange my DG engine for a 1997 Subaru Impreza 2L none turbo did wiring exchange my self all on internet . What a lovely engine not like the DG with all it problems
    Very very happy

  24. Hi, we need a new engine for our 1.6 diesel C-reg T25 and would like to upgrade to something with a little more oopmh (ie not another T25 engine, but maybe a golf one?). Can anyone provide me with details of engines that would be suitable as a replacement please – I’ve spent so much on the bl@**#y van already (hence the need now for a new engine!) that I don’t want to risk sourcing an engine that then turns out to be unsuitable.
    Any info much appreciated, thanks! 🤞🏻🙏🏻

    1. Hi Sophie, it sounds like you could do with a local VW Specialist to help you through this.
      The Mk3 Golf TDI engine (AAZ) is a popular swap, although donor vehicles are becoming harder to find now.
      Other Diesel VW engines of the early nineties should also work. Alternatively, you can fit a Golf GTI engine, but that would be petrol.
      Best of luck. Andy

  25. Can anyone please tell me where I can buy a complete air filter and box for a t25 1.9gd water cooled engine? Pierburg 90mm!
    Please I need it ASAP.
    Thank u.

  26. Ive had now for 22years a vw t25 (1989) caravelle with the best engine Ive ever had. The 2.1dj watercooled. It was imported from America to Belgium where I was living where an lpg system was fitted (2 x 50ltr tanks under the van). It also has air condition so quite a rare model. Ive just spent £200 on gear linkage throughout and also £1550 on a gearnox rebuild by Bears motorsport, recomended as Aiden Talbert has ceast to take orders for a while. I am at a total loss as how to set up the linkage. I have followed the instructions Haynes manual and foot notes from Aiden Talbert which I git online but are at a loss as ti what is wrong. When driving I can go through all the gears but from standstill and pulling away there is a spinning loud rattle from the box. Even at stand still with clutch in all the gears rattle. My intention was next to buy a new engine or have my old one rebuilt but dont know where to turn. Im 70 and love my bus but have been ripped off so often, ie, two heads fitted in Southend and got it back with quite a lot of power loss. Also buying a second hand gearbox online for £420 which never turned up and the bank could do nothing about it as Acc & telephone contacts were shut down. My wife now keeps telling to get rid of it as its costing me a small fortune so Im frightened it going to end up a white Elephant. I love my van coz it does everything for me from sitting by the beach with the awning out or lunchtimes at work in th winter with the heater on (Truma that I fitted £750) playing my guitar and mouth organ) where Im in my element. So please is there anybody out there that I could speak to or meet that can answer my distress call. I still want to invest in it but need help. My wife says get a nice car, I dont want to. I have so many memories in my van and yes when its all done someone will buy it .when Im unable to drive anymore . I will miss the waving from other campers though. Thats me and my plea/plight done. Regards, Mick.

  27. Hi Andyvwh,

    This has caught my eyes as this is the time I’m about to do a t3 conversion with a 1.8 t golf engine , you mentioned about the longitudinal , is the a4 and Passat not same engine? How do they differ? Kindly advice the components required for a successful swap.

    Kindly reply.

    Daniel M.

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