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300TDi into 2.5TD with LT77, snorkle 7 airbox

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Guest otchie1

Putting an ex-Discovery 300Tdi in a Defender 110 2.5TD

When the timing belt finally snapped on my 2.5TD I discovered 4 cracked pistons - explains the smoking I suppose. With the price of diesel in teh UK only going one way (thanks Mr Brown) I thought it cheaper in the long run to change the engine for something designed within my lifetime. The traditional route here is to slap in a 200TDi but they are getting a bit long in the tooth now and the good ones left seem to want silly amounts of money so I decided on a 300TDi. It turns out to be rather easy.

Choice of Donor

All 300TDi engines are not equal. All those fitted with automatic gearboxes and everything after 1996 for the UK market used a 'fly-by-wire' throttle and had electronic control. All manual gearbox versions pre 1995/6 have a manual throttle and no electronics.

The changeover seems to be the usual ragged Land Rover affair with no fixed date so it's best to look before you buy. There is nothing wrong with the electronic version, it's just more complex than I wanted to be.

300TDi engines were always mated to R380 gearboxes which have reverse next to fifth rather than next to first as with the LT77. It is possible to fit the R380 in place of the LT77 but you will have to move the gearbox mounts, replace the gearbox tunnel and you may have to mix & match drive shafts. I kept the original LT77 gearbox as it's a lot easier.

Tools & Equipment

I use a manual throttle version from a 1995 (P) Discovery 2 door eBlagged with no tax or MoT for £425. Bargain.

I had access to an engine hoist, a full set of professional tools including air tools, grinders and a welder. All welding was done with a Cebora/SnapOn/TaskMaster 130T MIG running 0.8mm wire and argoshield.

Parts you will need

A 300TDi Disco (obviously)

Suitable electric radiator fan, Spal, Ford, whatever

Thermo-switch housing for fan switch - LR A/C thermostat housing or an inline housing

Hydraulic male-male adapter for PAS pump (Pirtek P/10/10)

extensions for fuel/oil lines - copper pipe & hose joiners & clips

(2 x 90deg) & (2 x 135deg) 2" intercooler hoses

(1 x 90deg elbow) & (1x 100mm joiner) 2" aluminium intercooler pipes

Aftermarket engine temperature gauge with matched sender (VDO for preference but TIM works)

(12V regulator if using a TIM)

New 300TDi thermostat (original or OEM waxstat)

Parts you might want to replace

300TDi timing belt kit - AFAIK the BritPart kits are identical to the Bearmach ones YMMV

2.5TD clutch friction/pressure plates

2.5TD release bearing, clutch slave, release arm.

300TDi glow plugs (even though you may never use them)

300TDi engine rubbers

200TDi intercooler in place of the 300TDi one

300TDi serpentine hose - you can re-use the existing but you must re-fit it to run the same way as when you take it off

300TDi EGR blanking plate

Strip the 2.5TD

You don't need to jack the vehicle but you do need to chock the wheels and remember to disconnect the battery. Get the existing 2.5TD out including radiator. This is best done with the bonnet off and the floor and tunnel removed so you can get at the bellhousing nuts. Also pull out the air filter box as it makes life easier. I reuse mine as I already had a snorkle plumbed in. I also think it looks better and is more robust that the Disco version. There is probably an element of performance loss in doing it this way but on a 15 year old engine it hardly matters. Clean the years of filth off the chassis and bulkhead. You'll thank yourself for spending the time doing this now. If you're feeling energetic then paint anything that's showing its age.

Keep the existing steering box in situ with pipes attached. Just remove the pipes from the PAS pump and leave it all connected down from the resevoir.

Salvage all the old radiator pipes and the blue turbo pipe from the engine.

There is only one electric connector on the 2.5TD engine. It lives near the rear injector and feeds the oil pressure sender, fuel shutoff solenoid and temperature sender - label these unless you have a good memory.

There are also the wires that run down to the alternator, starter motor and glow plugs - disconnect these and tuck them up out of the way.

Most of the nest of fuel pipes run from the filter to and from the lift pump and injector pump but the only ones you need are the return/feed to/from the tank. Again label them, plug them if you can and tuck them out of the way.

Unscrew the oil cooler pipes from the oil cooler and engine keep them for use later.

Disconnect the exhaust pipe all the way back to the join aft of the gearbox crossmember. Keep the pipes as you'll need to cut and join the two systems later.

Don't forget to disconnect the throttle cable ;-) and keep all the bits as you can re-use the existing one for the new engine.

Leave both driveshafts alone - non eof that needs to be touched.

With the engine lifted out it'll look like this.



I had replaced my clutch only a few thousand miles ago so I kept it for re-use. Wise to replace the release bearing though and clean out the bellhousing while it's all apart. Check your release arm and either strengthen it with a welded on brace or buy one pre-done. Also make very sure that the clutch slave cylinder is in good condition and that the pushrod is secure in its little clip - a cable tie helps it stay put.



Dump the old 2.5 in the back of the Disco as it'll weigh in for more than it's worth to anybody as an engine.

Strip the 300TDi

Again you don't need to jack the vehicle but chock the wheels anyway. You will need a hoist and as the 300TDi doesn't have lifting eyes you will also need some straps secured around the engine - the seatbelts out of the Disco are ideal if you're confident you know how to secure them properly.

Remove the radiator cowling, viscous fan, air box, radiator (with intercooler and oil cooler) and disconnect as much of the wiring as you can get at. You will re-use precisely none of the 300TDi wiring so don't worry about cutting or labelling.

Unbolt the diesel filter assembly complete from the bulkhead keeping as much of the feed/return pipes as you can. Label them before you forget which is which.

As with the 2.5TD, keep as many of the pipes and hose as you can especially the lower radiator hose.

Fetch out your angle grinder and cut away the front slam plate. You can now actually get at stuff.

Undo/remove the front and rear driveshafts. Undo as many of the bellhousing bolts as you can reach while you're under the vehicle. You will not be able to reach the top ones so don't bother struggling. Undo the two engine rubbers (NS & OS) and lift the engine with the hoist. Now unbolt the 4 bolts that hold the engine mounts on each side of the engine and put them to one side as you'll re-use them in the Defender. You should now be able to lower the engine enough to get at the top bellhousing nuts. If you still can't reach them just unbolt the gearbox mounts and swing the entire engine/gearbox/transfer box assembly forward and rest it on the front chassis cross member. Secure the gearbox so it can't fall and then lift the engine away.

You will want to clean the engine as it is much easier to do it now. Make sure you block up any orifices - a glove and cable tie does the job. Do not be tempted to do the timing belt now. Not only is that easier with the engine bolted down but at least you know that your engine runs as it is right now.

Take the clutch off and if you're feeling wise take the flywheel off and replace the ladder gasket and rear main seal will you're here. They are cheap enough and it is unbelieveable de-moralising to have to take this all out again to do it later. On that note DO NOT use 3rd party seals here - original parts only unless you like oil leaks.

Don't bother re-assembling with the 2.5TD clutch assembly yet as it makes life harder, just refit the flywheel. Make sure you use threadlock and torque the bolts up properly.

You can change the glow plugs now or do them later when it's all fitted. Even though they cost more only ever use Beru or original plugs. They are the OEM and their plugs will not break off whilst your engine is running as can happen with cheaper alternatives, scoring your cylinder, wreaking your turbo and generally ruining your day.

300TDi into 2.5TD Engine Bay

With the 200TDi conversion you can re-use the 2.5TD engine mounts. Although the 200 & 300 share the same block casting and the 200 engine mount holes are there on the 300 you can't use them as the exhaust and oil filter get in the way.









Thus you have to use the 300TDi engine mounts and as they sit further back than the 2.5TD mount you need to cut yours off.





Carefully cut the engine mounts out of the Disco chassis, dress them to fit the Defender chassis and clean up both ready for welding. Then bolt them on to the 300TDi

The 300TDi does fit up to the LT77 but you need to pull the lower dowels out and you will lose a couple of mounting bolts. Feel free to counterbore the LT77 to accept the dowels and/or tap the redundant holes in the 300TDi if you want to.



Now swing the 300TDi into the engine bay, mount it up to the gearbox and secure with a couple of nuts. Set the level of the engine with the hoist so that it's all square and so that the engine mounts are central against the chassis. Fix the engine mounts on with a few tack welds, undo the engine rubbers/gearbox nuts and the swing the engine out again leaving the mounts behind.

Weld it all up properly and paint. It should look remarkably like this.





Swing the engine back in and bolt it all up properly. If you're doing the timing belt then it is easiest to do it now before you fit the radiator but you'll still probably need to use the starter motor method to undo the bottom pully bolt.




Re-fit the original 2.5TD electrial engine connector and run the cables down to the oil sender and fuel solenoid. Replace the existing coolant temperature sender with your new one and crimp on a suitable connector.

Route the existing fat, red starter cable up to the starter and the four brown starter-to-alternator wires round the back of the engine, along past the injectors and round the front to the alternator. Do not be tempted to go the short way as the exhaust and intercooler pipes need to go there. Crimp all three together in one big yellow crimp and fit it to the alternator. Don't forget to fit the solenoid wire to the starter. I cut all the old, rotten flexi conduit off and used spiral wrap to keep it all in place.



For reasons of emissions control and convenience the 300TDi uses a temperature sensitive variable timer to control the glow plugs. The 2.5TD uses a manual system controlled by the ignition key. The 300TDi is MUCH easier to start from cold than the the 2.5TD so just screw the single glow-plug cable that hangs out of the bulkhead on to the rearmost glow plug. So far I haven't had to use any heat at all to start the engine although that doesn't yet include cold Winter mornings.

Plumbing in the Ancillaries

The PAS pipes left in situ will nearly bolt up to the 300TDi PAS pump but you need the male-male adapter to make it fit.

The 300TDi fuel filter housing bolts on in place of the 2.5TD one. You need to cut your 2.5TD fuel pipes and make or buy joins to the 300TDi pipes. I used 10mm copper pipe with high pressure fuel hose joints. Make sure the overlap is at least 2", use quality clips and if in doubt get your local hydraulics place to make up proper pipes for you.

The Defender heater is good enough for me and the original Defender heater hoses easily reach the heater outlets on the back and top of the Discovery head. The Defender heater is a lot higher than the Discovery one so you will need to modify the coolant system bleed procedure a bit (see below).

Radiator/Oil Cooler/Intercooler Frame & Air Filter Housing

The entire assembly is too tall and too wide to fit in the Defender. The frame has side mounting lugs that are used in the Discovery but just get in the way in a Defender so cut them off. You must either shorten the frame by hacking away the standoffs or lower the mounts welded to the front cross member. Failure to do one or the other will mean that your bonnet won't close properly. I think lowering the mounts is a better solution so I did that. Chop out 30mm and try to keep it all square - the white paint just makes it easier for you to see and I over painted in black later.





The Defender radiator has two top spiggots in place of the Disco side brackets and these can be replaced with two M10 bolts fed up from and welded under the top bar of the frame.



The 2.5TD air filter assembly is fouled by the 300TDi top intercooler hose. I wanted to keep the 2.5TD air filter so I turned the 300TDi intercooler upside down. This moved the intercooler pipes a few inches inboard, giving the space I needed.



This involves some butchery of the frame and is not pretty. A better solution would be to either fit an aftermarket full-width intercooler or use a 200TDi intercooler as they have their hose mounts more centrally biased.

If you invert the 300TDi one you need to hack the bottom bracket and lose the top 2 frame bolts on that side. As the top of the frame is bolted to the old radiator top brackets by the 2 M10 bolts it is secure enough, just a bit ugly.





However it does work whereas the 200TDi solution is untested - I'll do it when I get one as I think it will be neater.

The air filter housing need slight modification to one of the legs in order to clear the alternator pulley. Just wave your grinder at it until it looks like the one below and bolt it back down to the original mounts.



The Discovery comes with a 50mm insulated aluminium pipe in the bottom intercooler circuit and you can re-use it here. Feed it through the legs of the air cleaner tripod and use 2 off 90deg hoses and one joiner to connect it to the turbo outlet.

The top intercooler connection is made up from 2 off 135 deg hoses cut down to suit and joined by a 90deg aluminium elbow. The gentle kink neatly keeps it all clear of the water pump pulley and serpentine hose.

Re-use the Discovery bottom radiator hose and don't forget to fit the two vent hoses; one from the thermostat housing and one from the radiator. They both run back to a valve that then feed the expansion tank. I toyed with the idea of using the Defender brass expansion tank but in the end fitted the Discovery plastic one as it holds about 3 times the volume of coolant.

Use a combination of Discovery and Defender radiator hoses for the top hose - you can even see my old radiator switch housing now doing duty as a pipe joiner.



The short 1" hose with the brass stop end that you can see is just a convenient way to block off the old engine breather vent on the original snorkle-to-air-filter hose.

The original 2.5TD snorkle-to-air-filter hose fits back on just as you would expect. The 300TDi air-filter-to-turbo hose fits neatly on the turbo but needed a bit of extension to reach the air filter. I had already replaced my 2.5TD hose on the Defender with some bling blue and alloy pipe but it should be as simple to do with the original LR hose. This section of the inlet tract is low pressure but high flow so it needs to be as wide as you can make it and smooth as possible. Probably best to not get too carried away though as it is a 15 year old Land Rover engine :-).



The oil cooler is remarkably simpler. If you've kept the original oil cooler hoses I suspect that they will be long enough to fit straight on. However my Defender hoses went to the scrappy so I had to cut and join the Discovery ones with some 15mm copper pipe in a similar manner to the fuel hoses. I forget how many bar the copper pipe and hose joints are rated to but it's several times the expected pressure in these oil hoses. If in doubt, get new hoses made up for you.



You will need to fit an electric fan as the viscous hub fan would sit too far back from the radiator to be effective. Using a thermostat housing from an engine with air conditioning gives you 2 mounting holes for fan switches.


The Discovery turbo flange has a different design from the Defender exhaust downpipe and you will probably find that your Defender downpipe is cracked where the bracket once bolted to the block. The Discovery design uses a flexi sock to overcome this which also makes it more forgiving when it comes to routing.

You could use a complete 300TDI Defender exhaust with all new brackets or make a complete big bore straight through system yourself if it's important to you but that all cost money and you can get moving with what you have laying around. The 300TDi exhaust bore is slightly wider than the 2.5TD which means that the old 2.5TD pipe will slide inside the new 300TDi down pipe. Bonus.





You will need to cut the horizontal section of the downpipe and the leading flange off the 2.5TD pipe that routes over the gearbox cross member. The two need something more that a couple of inches overlap, some exhaust paste and a clamp to hold it all together. Leaving it too long will make it hard to fit and put extra strain on the pipe and joints so don't be stingy with the cutting.

Temperature Gauge

The 300TDi temperature sensor and the 2.5TD gauge are a mismatch and the gauge will always over read, frequently going deep into the red which is disconcerting. I replaced the whole system with a TIM electric gauge I had laying around but there is probably a way to either modify the resistance of the 300TDi sensor with a shunt or fit the 2.5TD sensor. As you would still only have a gauge that reads in bananas then I think it is better to fit something else.

The TIM gauge turned out to be very sensitive to supply voltage, with the reading varying by 10deg C or so from being high with the engine running (14V) to being low with the lights on but the engine off (12V). A simple 12V filter made from a suitably rated low-loss regulator sorted it out for about £3. Still cheaper than a VDO but not as bling bling.

Coolant Bleeding

It's well worth running a hose through the coolant system to give it a good flush and then use a rad flush for a while. It's also sensible to replace the thermostat (bleed toggle upper-most). Use a 50/50 mix to re-fill the system and use an antifreeze with a corrosion inhibitor suitable for mixed metal engines as the 300TDi has an aluminium head.

Open both bleed valves (radiator top & thermostat housing) and remove one of the heater hoses from the head. Point the hose straight up so that it's the highest point of the system. Pour coolant into the expansion bottle until it comes gushing out of the radiator vent. Wind that one back in and keep pouring until coolant come out of the thermostat hole. Wind that plug back in and then, with your thumb over the open heater spigot on the head, pour more coolant into the vertical heater hose. This last bit fills the heater circuit which othewise runs the risk of being one big airlock. When you're sure you've filled the matrix refit the hose. There is no need to be too fussy about this as the heater circuit will probably burp itself but that could take a while and cause a sudden drop in the expansion tank.

Final Checks

I wouldn't change the oil until it's at least started once so just make sure there is oil in there and that it isn't contaminated. Make sure everything is clear of the serpentine belt and that you've wired it all up properly.

Re-connect the battery. If there isn't an odd burning smell then it's probably safe to start.

Mine started first turn with no need to bleed the diesel lines so if you've got problems make sure the fuel lines are the right way round and the cut off solenoid is connected properly.



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Temperature Gauge

The 300TDi temperature sensor and the 2.5TD gauge are a mismatch and the gauge will always over read, frequently going deep into the red which is disconcerting. I replaced the whole system with a TIM electric gauge I had laying around but there is probably a way to either modify the resistance of the 300TDi sensor with a shunt or fit the 2.5TD sensor. As you would still only have a gauge that reads in bananas then I think it is better to fit something else.

The TIM gauge turned out to be very sensitive to supply voltage, with the reading varying by 10deg C or so from being high with the engine running (14V) to being low with the lights on but the engine off (12V). A simple 12V filter made from a suitably rated low-loss regulator sorted it out for about £3. Still cheaper than a VDO but not as bling bling.

even easier use a temp gauge from a 300Tdi Defender & the matching temp sender unit.

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  • 8 years later...

Photo bucket have made a lot of old posts redundant. Unless the op still has the photos and can be bothered to reinstate them direct to the forum (As several have for build threads myself included) I'm afraid they maybe lost forever.


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