I think i may know the answer.

[Bumpa]

My 1850HL still has only the engine driven fan which is fixed, not on a viscous coupling. The temp gauge is so steady in the middle of the dial at all times that I sometimes wonder if it is like a modern car where the gauge is controlled to show NORMAL all the time until a catastrophe occurs.

You're absolutely right about the MGB V8 Steve. The engine bay is very crowded and that 4 litre V8 makes an excessive amount of heat. I do have a type of air spoiler on the front valance and the valance does have apertures in it to allow air to get to the bottom of the rad. I also have the exhausts headers exiting through the front inner wings, so there are holes there for air to escape. I refuse to punch louvres in the bonnet - that's a step too far!

[Carledo]

My 1850HL still has only the engine driven fan which is fixed, not on a viscous coupling. The temp gauge is so steady in the middle of the dial at all times that I sometimes wonder if it is like a modern car where the gauge is controlled to show NORMAL all the time until a catastrophe occurs.

You're absolutely right about the MGB V8 Steve. The engine bay is very crowded and that 4 litre V8 makes an excessive amount of heat. I do have a type of air spoiler on the front valance and the valance does have apertures in it to allow air to get to the bottom of the rad. I also have the exhausts headers exiting through the front inner wings, so there are holes there for air to escape. I refuse to punch louvres in the bonnet - that's a step too far!

I'd forgotten that some lower spec models have fixed fans, but it makes no significant difference to cooling. The viscous fan is just an early attempt to relieve the power drain from driving a fixed fan (typically 6-9bhp) when it's not actually doing anything useful, ie over 5 mph or MOST of the time!

I've not louvred the bonnet on the Dolomega, mainly, as you so rightly stated, because I have EFI and it runs perfectly whatever the underbonnet temperature and secondly because I knew from experience with the Carledo that the Saab rad was well up to the task of keeping it cool. I DO love louvres though and sometimes regret not doing them, just because they look cooler than a Polar bear's dangly bits.

However, in your case, i'd consider it for practical reasons. You can, to a point, open as many holes in the front to let air in as you can fit, but if the airflow is constrained by a big, hot lump of alloy in it's way (is the Alloy construction to blame for the hot running?) combined with poor engine bay design and consequently hot air can't get back out easily, you're wasting the effort!

Its been a hobby horse of mine for a long time, that underbonnet airflow is a neglected field and no effort has been put into it, even by manufacturers, who build an underbonnet like a box with only a small hole going in, a vertical brick wall of bulkhead at the back, a bonnet on top and flitches to the sides so air can only escape DOWNWARDS and EVERYBODY knows hot air RISES. Fitting louvres lets more air out in exactly the right place to do the most good. Yes, when the car is in motion, the area ahead of the screen is a high pressure area, it's still nowhere NEAR as high as that under the bonnet! As I've proven beyond doubt on a number of cars including Vitesse, Dolomite, Stag, T2000 and TR6 (note all have rear opening bonnets to aid the experiment!)

Steve

[cliftyhanger]

Its been a hobby horse of mine for a long time, that underbonnet airflow is a neglected field and no effort has been put into it, even by manufacturers, who build an underbonnet like a box with only a small hole going in, a vertical brick wall of bulkhead at the back, a bonnet on top and flitches to the sides so air can only escape DOWNWARDS and EVERYBODY knows hot air RISES. Fitting louvres lets more air out in exactly the right place to do the most good. Yes, when the car is in motion, the area ahead of the screen is a high pressure area, it's still nowhere NEAR as high as that under the bonnet! As I've proven beyond doubt on a number of cars including Vitesse, Dolomite, Stag, T2000 and TR6 (note all have rear opening bonnets to aid the experiment!)

Steve

So there is high pressure under the bonnet? That is interesting, I have always thought that when moving at any speed (ie 10mph ish) that air would be sucked out the engine bay and under the car. It just made sense in my head.
How did you measure the pressure? was it leaving the bonnet unlatched and seeing it lift? if so that may (just may, we need wool and tape) be down to low pressure over the bonnet. This airflow stuff is difficult to get your head around.

[series111]

A catch up about the fan.had a look today and removed the radiator and electric fan and reinstalled the viscous fan,put it all back together and took car for a drive and the gauge did not go above half way even at idle at the traffic lights and parked up on idle,seems my car does not like the electric fan, as the saying goes if it ain't broke and all that, so if anyone requires an electric fan for a dolomite please contact me.