OK guys, I now have an engine that behaves.
I've been out for a short run (well, a long run based on past experience!) about 12 miles yesterday and 20 miles today.
Engine temp is just fine and was a bit lower today (rock steady at mid-scale) compared with yesterday - a. it was cooler today and b. I fitted a couple of vents in the bonnet sides last night.

However, there's still excessive heat under the bonnet. There are two more things to do immediately: I'm going to cut further vents towards the trailing edge of the bonnet, probably about 15 inches by 2 1/2 and going to wrap the headers to where they emerge into fresh air.

The auto box is getting rather warm too. I'm a bit between a rock and a hard place on this... Having holed the sump pan of my first box I have now fitted a skid under the engine and gearbox sumps. It's about 3' 6" long, 12" wide and necessarily hugs their undersides, so there's going to be no cooling of the ATF via the sump pan surface (best part of a square foot). Moreover, there's no oil cooler ...yet So I'm wondering about trying to duct air through (more!) holes in the side panels to go past the box; although I'm not sure whether the pressure distribution will allow this to work. And I'm on the lookout for a suitable cooler for ATF - would a regular engine oil cooler be up to it?...there's 8 1/2 litres of the stuff!
What do you think on all this? Apart from 'Idiot for not fitting an ATF cooler'
John.

glad to hear that you are getting out and about more, you'll be up to 25 miles next (i've done about 90 in mine today)

i have put three vents in the top of my bonnet, 10",8" & 6" in a triangle shape, my under bonnet temp has dropped by 10 degrees, remember that heat rises so putting vents in the side won't be as efficient as vents in the top.

as for the oil cooler i would fit a 13 row minimum, works on mine!

You need a cooler on the box, that could explain your issues as it will go slushy when very hot.

You do not need a huge thing, just a little oil cooler will surfice.

Regards Mark

make some air scoops from the bottom of the space frame i have made 1 out of a bit of ally its only small but it must make a dirence,i was going to use it to fire cool air into my turbo air filter,
it hangs down about 1.5in il get a pic if you want

have you got a shorted sump???


[Edited on 24/6/09 by jpindy3]

Good answers again, guys!

@Alex: Sounds like your new rad is working - is it getting warm enough?

@Mark: You seem to know a bit about autos - do you happen to know what the flow rate is around the cooler loop for an A4LD?

@jp: Yes please, a pic would be useful! My sump is chopped about 1" to 1.5" and extended forward to recover some volume. The autobox sump pan is actually the lowest point, currently about 4 1/8" ground clearance unladen.

Cheers,
John.