I have a 1987 XJ-SC that has been in our family since new and I am trying to fix a few issues. Overall the car is in fantastic shape however the coolant appears to leak. I figured I would start the season by flushing the rad and toping up with new coolant. I have disassemble all of the skirting underneath the car and am embarassed to say I cannot locate the drain plug.....any advice?? Any other suggestions on what I should do?

Also....late last year, the car died as soon as I pulled into my garage....I watched the battery charge go down as I was driving home. I figured it was the alternator, but a neighbour of mine showed a quick test with a voltmeter on the battery and said it looked fine. I recharged the battery and the car starts right up but I'm somewhat scared to just go for a drive in case it leaves me on the side of the road. Is there a better way to test if it is the alternator? I here it is a real pain to change.

Any advice would be greatly appreciated

 

You can drain the rad by unplugging the bottom hose/s and flushing and back flushing. Is it a 3.6 or V12??

If your not sure about the battery, best thing is to take it to your local battery shop and they should be able to do a load test for free.

The alternator can be checked by observing the voltage at the battery with the car running and not running. Not running it should be about 12.7v and running it should reach about 14.4 or 14.7 volts with all electrical things switched off.

The other thing worth checking if you have an ammeter and someone who knows how to use one, is the battery drain when the engine is switched off, to see if theres any excessive drainage.

 

Thank you very much. It is a V12. The car has not been used very much over the last 7-10 years as my Dad was getting older. I took it over last year and am now just trying to do a few things I think would help....overall the car doesn't really need much work......it appears mostly to be small leaks.

I will take your advoce on using the bottom hose and see if that helps.

Thanks again for the advice

 

I disagree on battery voltage. The stock Lucas alternator usually reads just barely over 13v and is woefully inadequate for our cars. In addition if the battery tests good, voltage readout while running is acceptable and no significant battery drain is found, the likely culprit would be the diodes in the alternator. Ask me how I know!! I switched to a GM 1 wire alternator with a mount by John's Cars and never looked back!

 

Let you know when I get my XJC running, probably about 5 years from now!!
I will look into an alternator upgrade as well.

 

I agree. Well, mostly

I'd describe them as "barely adequate" versus "woefully inadequate".

Both my Ser III XJ6 and my '88 XJS had the 65(?) amp alternators. I never had any battery run-down problems or such but the output wouldn't keep up with demand IF multiple high-load systems were in use simultaneously....such as full blower, wipers, rear defog, etc.

No problem while driving but at idle you can watch the voltmeter drop-drop-drop. Not very reassuring!

Jaguar really should've specified higher output alternators. Eventually....they did.

As far as runnng voltages go, the standard I grew up with was 13.8 to 14.7 <shrug>. However, I was recently replacing an alternator (non-Jaguar car in this case) and was a bit surprised when the data sheet said to expect as high as 15.2 !

Cheers
DD

 

Thank you for all the updates.....I'll start with trying to flush the rad and will look into the alternator......you mentioned Johns Cars for the updgraded alternator. Is that a website??
I'm not by far a car expert, but can handle the DIY as long as I have something showing me what to do.....these engines are very overwhelming and the last thing I want to do is mess something up. Do you recommend a specific shop manual or website that has good pointers? Surely I can't trouble everyone in this forum every time I have a problem

 

Is there some one here at 4 am.

 

I believe Haynes made a manual for your car and they are a great starting point tool for DIYers.

If you are flushing the radiator then why not do the engine at the same time.
You don't want that bad boy over heating in the future. A replacement thermostat would also be advisable.

On the electrical side, though the alternator may be "barely adequate" it was good enough when the car was new. Over time, the ground point straps will degrade and corrode causing high resistances and all sorts of gremlins. Make yourself a check list of all ground points, electrical connectors in the engine bay and trunk, light clusters and fuse box locations. Then one by one go around and disconnect, clean, preserve and then reconnect. These simple steps will help keep electrical problems at bay.

These are all things that you will be able to and as a by product you will learn more about your car.

Hope this helps,

 

Battery voltage must be several volts higher when the engine is running, slightly above idle, 1500rpm to be sure. The amount is also temperature dependent. The colder it is the higher the voltage. In any case it should be greater than 13.5V.