As the guy who started this tread I wanted to say thanks to Malcolm in Kent and also to tell you how I solved the problem. New expansion tank cap was good advice (the rubber had split and was looking old) got a new cap and that increased the pressure in the water system result it blew holes in the radiator!!!
So searched for a new LS400 rad, found what I wanted online from ADVANCED RADIATORS LTD in Newcastle-upon-Tyne the cost of £61.86 inc VAT and delivery to me I thought was good value. (I ordered Monday received early Weds) you can pay more for 24 hr delivery.
I found various forum folks saying changing the rad is easy which it was (40mins to take out) 15 mins to transfer pipe to expansion tank from old rad and also to transfer the temp sensor, all simple stuff. Then 20mins to refit. All now seems well on the engine water side temp guage dead level never moves above this, and no leaks.
The long job was flushing out the water in the engine, 2 heat up sessions (with holts rad flush) , 2 draining sessions, and 3 refills, the time consumming part was letting things cool down so not to cause me any danger when draining off
The surprising item was where the rad was made!!!
Made by a company called DOLPHINheattransfer.com who are based in the United Arab Emirates, their website is massive,and they make rads for just every car I have ever heard of, makes you think what does it really cost to make a Rad?
Ian Lord
1990 LS 400
Bournemouth