Hi Nick,
I have been following the discussion of your overheating problem and cannot offer any more techinical information than the post from Cool-Cat but I can relate my experience and post a question to the group:
I bought a 1967 E-type last year and it always ran hot when in city driving. The prior owner had installed a manual switch to turn on the fan which would usually keep the temp from getting above 100 C if the fan was turned on immediately. In highway driving it ran about 90 C.

I did change out to a Cool Cat radiator and the Cool Cat multiblade fan with a stock shroud(my car also did not have a shroud). My mechanic thought that a shroud would have a major influence on cooling. I can say that the Cool Cat fan moves alot of air through that radiator so my suggeation would be to change your fan to a Cool Cat fan and put in a stock shroud since you already have an aluminum radiator.

This past weekend I drove over 300 miles with the new radiator and fan. The weather was in the low 80's and sunny. The temp gauge with highway driving was never >70 C and with slow/stop/go driving in town it remained So I am very impressed and pleased with the Cool Cat set up that I have now.
As an aside the person who referred me to Cool Cat lives in Florida and drives a 1967 series I and she states "I never need to look at or be concerned with the water temp. I never have overheating since changing to an aluminun radiator and Cool Cat fan."

After my story a question:
Is there any problem with running at 70 C? Is that too low of an engine temperature for the engine to run efficienctly?

Matt Sell
1967 XKE Roadster

Submitted by mfrank@westnet.com on Mon, 06/27/2005 - 23:03

70C is the lowest temperature at which you would want to operate your engine. Below this temperature, you would have problems with deposit build up. In general, the hotter the engine runs the more efficient it is, and modern cars are often designed to run at 90C. But the problem is controlling boiling in the water passages. Even a pressurized glycol system can have enough localized boiling by around 90C to cause a decrease efficiency. Modern cooling systems compensate by running at higher pressures than our old Jaguar engines.

That said, it's worthwhile to verify the accuracy of your gauge with a digital thermometer before you make any judgements.