Your questions answered: Cruise control and TDi conversion


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Ed Evans thinks a 300Tdi conversion is an improvement : credit: © Ed Evans
This month, we look at Defender cruise control compatibility and a Ninety 300Tdi conversion

Making Defender cruise control compatible with overdrive

I was amazed and pleased to see a query I had written to Trevor Cuthbert
regarding a cheap cruise control solution for a Td5 Defender, was published in the April 2023 magazine, along with the original article.

I queried as to whether having a Roamerdrive overdrive unit installed would affect the working of the cruise control. We both assumed that, because the Roamerdrive is purely mechanical it would work just fine. Well, I can confirm that it works in all gears but not in fifth overdrive. I researched online and found a chap who had done the same installation and also had this problem. So, just in case there is anybody out there who would like to do this very worthwhile cruise installation with the overdrive, there is a solution, but it will cost another £80. I still reckon that is a bargain.

It seems the ECU will only allow the speedo to register speeds in fifth gear that fall within parameters provided by the standard ratios. So the ECU and speedo have to be fooled into thinking that the actual speed is less than it is. A company called Healtech make a gadget called a Speedohealer, and they can supply the correct harness for a Defender. This just plugs into the speed sensor in the transfer ’box and can be set to adjust the signal to the ECU. It is fully customisable and was originally designed to correct motorcycle speedos due to the great variety of gear ratios and sprockets being fitted. Set-up is easy, and I have put mine under the bonnet. It is about the size of a matchbox with its own mini-screen and set-up buttons.

The only issue I then had was that my speedo displays the speed it is being told which, of course, is now wrong. This is solved by a great app for my iPhone which cost £3.50 and is called Speedometer. This sounds long-winded, but the app is full of extra bits and gives a nice big digital display and loads of other info [obviously when used hands-free in an appropriate mount – Ed]. I have tested it in my BMW and it reads the same as the car speedo, so I think the accuracy is well proven. All this might be a good shortcut for someone wishing to do this upgrade.
Phillip Knechtel


TD to Tdi conversion

I’ve been told of someone who is scrapping a 300Tdi Discovery because the bottom’s fallen out of the body and it’s beyond economical repair. He’s breaking it to sell off the individual parts and there’s a good engine to be had. I have 1988 Land Rover Ninety and I’m thinking of fitting the 300Tdi in place of its original turbo-diesel engine. Do you think this would be a worthwhile swap and, will the Tdi engine fit without too much modification? I want to keep my Ninety looking original.
Colin Barnes

​​​​​​Ed Evans replies: It’s a good idea and a bad idea. The 300Tdi is a far better engine than your existing 2.5TD, smoother, with increased performance, quieter, better fuel consumption, and it will fit. On the other hand, a Land Rover Ninety TD with its original 2.5-litre turbo-diesel engine is a rarity. You have something special here, but if you swap the engines you have just another old Land Rover with a later non original engine fitted.

In the pre-Tdi engine era, a ‘turbo’ badge was seen as a performance statement, so it became a bit of a joke when Land Rover applied it to the new TD. A genuine turbo is a rare sight today, though

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The Tdi engines used to be a popular no-brainer swap a few years ago, especially when these early turbo-diesels were failing on a regular basis because the bottom end was weak. The turbo engine used the same big-end bearings and bolts as the earlier naturally aspirated 2.5-litre engine, and the additional load from the turbo caused the bolts to stretch, resulting in major failure. Probably all engines have since been upgraded and, in any case, if they haven’t failed by now, they’re good. The scene is different now, with originality becoming progressively more important.

The original Turbo Diesel engine was fitted from 1986 to 1991. Few survived, but those that have, should stay reliable

​​​​​​If you want to fit the 300Tdi engine, it preferably needs to come from a manual transmission Discovery, not an automatic which has Electronic Diesel Control (EDC) and makes the conversion far more complex. You’ll need new engine mountings to weld to your chassis (though bolt-on mounts are available, see later), the front section of exhaust, the intercooler and associated piping, and the radiator and oil cooler, plus many other connecting parts such as fuel pipes and filter and the ingenuity to plumb all of this in. There will be some juggling with the air intake, too, but none of this is difficult, just time-consuming.

The 300Tdi is a vast improvement over the turbo diesel, but swapping engines means a loss of originality value

The bellhousing will need its bolting arrangement altered to suit the Tdi engine. It’s a long while since I’ve done this, but I recall the bellhousing will need to be drilled to accept a couple of studs on the rear of the engine, and a stud or two may need to be removed. It’s simple enough, and will be obvious when you set the bellhousing up to the rear of the engine before installation (alternatively, swap the engine backplates).

The 300 Tdi will sit further away from the radiator and so the cooling fan will be less effective. So it’s worth fitting an electric fan which can be positioned closer to the
radiator. Also confirm the running gear including transmission, brakes, steering and suspension are in good condition to handle the increased performance.

You can buy many dedicated parts for this job, including a complete conversion kit and the bolt-on engine mounting conversions (which avoids welding and fabrication) from


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