With my coolant overdue for its 2-year change, and with a very slightly leaking heater valve to also replace, it seemed a convenient time to undertake both these jobs and also complete my pet project – to install a coolant heater element on my AJ16 XJS.

The reason for the project was 2-fold. Primarily, it was to try and reduce the wear on the engine occasioned by cold starting. I’m a believer in the principle that 90% of engine wear happens in the first 30 seconds of a cold start. Secondly, it was because the parts suddenly became reduced in price by Jaguar. The T-piece, heater and wiring plug were bought for £30. The coolant heater was standard on Canadian 4 litre XJSs but I’ve never seen one fitted on a UK car.

I’d bought the parts 2 years ago – the 400 watt heater element, alloy T-pipe, hose clips and the wiring plug. As the only available heater is the 110v unit for use in North America, I’d also bought an additional wiring plug to which I’d wired a site transformer plug as I’d decided that the use of a110v site transformer is was my preferred way to power the heater.



Some of you may remember my requests a while ago for a photo of one of these heaters on an AJ16 XJS. Despite some very helpful responses, I’d been unable to get a photo of the exact installation on an AJ16 XJS (which has a complex multi-branch lower hose arrangement). Therefore, I decided to fit the T-pipe in an orientation which would not obstruct the alternator, enable me to bleed the T-joint and also to visually see if there were any leaks.



I commenced by removing the air filter housing and trunking to allow better access to the lower hose area. I then drained the coolant via the lower rad hose connection. After that, I reconnected the hose, took a deep breath and made the first cut of the hose with a small hacksaw. I then removed the cut section from the rad, measured (three times!), marked and cut out a 3” section of the pipe. In hindsight, I’d probably have cut 1/2” less as it might have eased the installation process.

I then installed the T-piece, heater element and connected it all back together. (I’d also replaced the leaking heater valve and hoses at the same time). I then filled the system with fresh coolant. It took 10 litres to refill which indicates that without a cylinder block drain and heater matrix drain, only just over 50% of the coolant is removed if draining the system only from the lower rad hose connection.



I ensured there was no air trapped in the vertical section of the T-piece by backing out the element a few threads until coolant escaped. Again, in hindsight, I would use more pipe sealing compound or PTFE tape initially as I did struggle a little to get a coolant seal on the element.



With everything back together and the wiring plug in place, I then went through the heating procedure. I took readings with my IR thermometer at the lower hose, thermostat housing, water pump housing and cylinder head. I then turned on the power. After 30 minutes I took another set of readings, and after 60 minutes I took another set. (On the following day, I also took readings at 2 hours and 3 hours to see if there was much incremental change.) The readings were:




After 60 minutes, I unplugged the heater from the transformer. When not in use, the 110v transformer plug can sit neatly between the air filter and the inner wing.





I then started the car. Like most owners, my car has a very different sound emanating from the engine, exhaust and fan when started from cold, compared to the sound when it’s fully warm. The car started easily, sounding much more like it does when hot compared to its usual cold start sounds. It then very quickly came up to temperature.

As you can see from the readings, the car can’t really be fully warmed by the heating element. After all, it’s only heating static coolant and relying on the transfer of that heat up through the coolant thus transferring to the engine block, cylinder head and radiator. It would need a pump and heater to really be effective in fully warming the engine. However, it’s undoubtedly making a positive contribution.

It would be even easier for an owner to fit this to a V12 or AJ6 XJS as they have simpler lower hoses which could be more easily removed, cut on a bench, the heater installed and the whole lot put back as a single unit. The complexity of the AJ16 hose made it a bit more awkward but well within the capability of most owners.

Overall, I’m pleased with the installation. At the cost of a bit of electricity, my car starts easier, presumably has reduced engine wear on startup and comes up to working temperature much quicker, which will be both more convenient on cold days and also improve fuel consumption. £30 well spent, I would suggest.

Paul