Discovery 3.9 Auto to 200 Tdi 5 speed manual conversion

The page you have been waiting for!

This is a step by step guide on how to get a 3.9 engine out and replace it with a more economical 200 Tdi

These photos were taken 8/Feb/05 and I will do a brief description of what we are up to followed by an in-depth description when the job is over - there are a lot of photos to please allow time to load 

So work along with Mike and I while we get the job done (come on! get your overalls on and put that tea down!)

Standard 3.9 V8 as fitted in the 1995 Discovery - runs nice but uses too much petrol! 

Mike worked out how to get the bonnet open! 

It is preferred to mark round the hinges before undoing them - be careful there are packing washers on top of the hinge - don't lose them!

Next the battery comes off - we made a note of the radio code first, but you should supply a small current to keep the SRS (airbag) alive - we do this through the cigarette lighter socket

How come I get the dirty jobs eh? The oil has to come out but the plug was rounded - a pipe wrench was the only way to get it off.


Bull bars are very nice but it needs to come off as we can't get the hoist in properly (guess who got that job)


The Discovery does not have a drain on the radiator, so you need to pull off the bottom hose - be careful to release the rad cap first as the pressure can be a bit of a surprise! The coolant never drops right into the bowl so be prepared for a lot of spillage.

Now we can start to remove all the engine pipes and connections. With the cover removed from the radiator shroud we can get to the fan. Using the correct spanner, a light tap anti clockwise will unscrew it.

This is the only Snap on tool we have! (No Jim, Not the hammer!)

However sometimes the nut can be tight and the pulley turns. By using a pipe wrench you can lock the pulley as shown - be careful not to damage the pulley!

The fan can be now lifted out

The oil cooler pipes can now be removed - you must hold the fitting attached to the radiator while undoing the fitting - they are not too tight, but if you plan using the rad again, the less damage the better.


Remove the two top pipes to the expansion tank and breather.


The rad assembly can now be removed - looks a bit ratty but it is fine.

The pipes from the power steering can be remover easy now - only some joker put the hose clip on the return on backwards - no way to get a screwdriver in so we cut off the clip - the must have fastened it before working on the pump - the pressure hose is a 5/8 nut and can be tight - it is advisable to use a spanner for pipe fittings as it is easy rounded off!

Next the wiring can be removed - this white plug at the back is one of the oxygen sensors - squeeze to undo.

Note we have removed the heater hoses on the bulkhead

The linkages to the kick down can be removed along with the accelerator cable


We had the A/C discharged at  a local garage - now we can disconnect the pipes and plug the holes to prevent humidity getting in.


This is where the fun starts!

Removing the wiring

Remove the wires from the coil and pass them through the engine - for some reason there is no quick detach plug for the engine - so just follow everything and disconnect it - you don't need any of it at this stage 


The alternator wire is connected here - in the fuse box inside the car.


Now working in the passenger compartment unplug the main harness to the engine - this is the part at the front but there are plugs behind the heater - so that must be removed too. The blue box contains our lunch!


Take out the glove box with 4 x 7mm screws holding the hinges on and pull it free to find a lot more wiring!

Remove the plate holding the relays on and there are are 3 more bolts behind on a triangular bracket holding the heater. In the picture you can see 2 x 7mm screws on the bottom right corner of the dash - remove them and the opposite side - on the inside are 4 x more 7 mm screws - get 'em out! 

On the under side are 4 10 mm screws - remover them, then the metal support bar will come out.

There are 2 x 10 mm nuts holding the heater on at the bottom - remove these too.

By now you should have 1,000 screws and nuts on the floor! Un plug the blower harness and it will drop out. In my right hand is the lower dash support plate.


This is what you have been looking for! The white plug contains most of the wires we need to tap into for the diesel - we only need 5, so the rest are junk. The brown plug has the starter wire only.

Mike holds aloft the harness out of the body - now we can get on with the underside.

Click here for day 2

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Copyright 2004 [Britannica Restorations]. All rights reserved.
Revised: February 18, 2014 .