Trying to reduce under bonnet temp

Competition engines and ancillaries - general discussion
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Slim
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Trying to reduce under bonnet temp

Post by Slim » Thu May 22, 2014 8:51 pm

Hello all

I run my Uno turbo Mk2 on the road and at sprints and hillclimb.

I would like advice on the two following possible modifications.

1) Reducing the running coolant temp by way of a alloy racing radiator and thermostat controlled fan. Standard thermostat begins to open 80-84degC - Fully open 96degC - Fan cut-in 90-94degC - Fan cut-out 84-89degC

The reduced under bonnet temp would aid more efficient combustion by reducing inlet manifold temp, another benefit of this reduced temp would be that more boost could be applied. This is just my very simplistic logical mind making these assumptions hence my putting this to all you boffins...

2) Running the fan to suck air out of the engine compartment rather than in.

As the standard fan only runs when at a stand still, in very slow traffic or when queuing at the sprints and hillclimbs, having the hot air sucked out would keep the under bonnet temps down. Again, I stand to be corrected!

Thanks

Slim
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Nobby
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Re: Trying to reduce under bonnet temp

Post by Nobby » Fri May 23, 2014 1:30 pm

There's a few things you should be concerned about

- what is the optimum temperature for everything to be at (coolant/oil/air/fuel/heatsoak scenarios)
- how to keep it at that temperature

Guy would be able to help on what the optimum should be, but for coolant and oil I believe it is between 70-85 for both. Have you thought about a different thermostat which opens at a lower temp?

Remember underbonnet temperatures are not only about getting nice cool fresh air in, but also about getting the air out otherwise you will have choke points. A great big alloy rad is going to be useless unless it has ducts to funnel air through the fins and away from the car too.
Chris Burgess
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Slim
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Location: Pembrokeshire, Wales, Uk
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Re: Trying to reduce under bonnet temp

Post by Slim » Fri May 23, 2014 2:55 pm

Yes I understand that I need to keep it within the optimum operating temperature of all fluids etc. I guess I need to know what that temperature is? When driving at normal road speeds with ambient temperature of say 15 DegC the gauge reads between say 75/85 DegC. The coolant temperature only goes up to 90/94 DegC when driven hard or when stationary. It is only at this point that I want to stop the temperature raising.

I have thought about a different thermostat but the car runs at a good temperature at normal speeds so think the standard thermostat is OK?

Could I just set my rad fan to cut-in at a lower temp?

What do you think about sucking air out through the rad instead of in?
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LeoM
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Re: Trying to reduce under bonnet temp

Post by LeoM » Tue May 27, 2014 9:30 pm

Hi
Do you mean blowing through from the engine side out through the radiator ? I don't think that would would because of the air flow when on the move.
I have a Fiat 600D Abarth Replica which always overheated so tried all sorts things to redirect the air flow but none of it worked. I have to give a lot of respect to the engineers because the original system was the best. In the end I used all the original ducts and shields and fitted an uprated electric fan blowing in the same direction as the original. I also had the exhaust manifold ceramic coated and together these have resolved all my under bonnet temperature issues - and to think I also ran with the engine cover open.
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