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Cooling System
The cooling system is only just adequate for the stock
engine, but the turbo produces even more power, and the super-hot turbocharger
in front of the bay doesn't help at all. To make matters worse, the radiator is
partially covered, so that the stock intercooler could fit up front (kinda). As
the icing on the cake, the super-hot turbo bearing dumps most of its heatload on
the coolant, which is then promptly emptied into the (plastic!) expansion tank.
A tuned turbo will produce 50-100% more power under load, and all the heat
that goes with it. No wonder people get desperate in the summer, with coolant
temps hovering over 100C. Switch the engine off and it can easily exceed 110C
for a short while. Nothing good can happen at these temps.
Is there an ideal coolant temperature?
It depends on how the car is used.
On a track day, you'd like the coolant temp to be around 90C all long
(whether it stays there is another matter!)
On normal start/stop driving where part-throttle response is more important,
mid-nineties is better.
Emissions are lowest around 100C, that's why manufacturers try to keep temps
around there.
If you find yourself 'needing' a cooler thermostat, then you need to clean up
the whole cooling system. A thermostat cooler than 92/102 should only be needed
in tropical climates. Otherwise it is a botch, masking the inadequacy of the
radiator, expired coolant, neglected cooling passages (full of scale) or even
water pump. Don't fall for the "easy fix" of a cooler thermostat, far from being
a cure --- it's not even an aspirin.
Coolant flow
Liquids flow in strange ways, sometimes counterintuitive.
You think it may be better if you run the water pump a bit faster, and sometimes
this is indeed a good idea, as it circulates the coolant quicker. Other times
this is counterbalanced by eddies in the wrong places, *reducing* flow and
losing pistons
Ah, but then you think it may be better to run the pump a bit slower, giving
more time for the coolant to do its stuff, and sometimes this is indeed a smart
move. In other cases you get localized boiling and hot spots - not good at all.
You then have a stroke of genius and decide to increase the diameter of the
waterways to promote flow -- and you end up actually decreasing pressure,
depriving remote spots of their cooling. This is a common issue with aftermarket
'performance' cylinder head gaskets, where the coolant holes have been enlarged
to promote flow. It's like the manufacturer was negligent or absent-minded and
made the gasket passages smaller than the block/head waterways. The aftermarket
'guru' fixes this oversight, pressure in the head goes down, and remote chambers
in the head lose their coolant circulation altogether. The head goes west, and
something else takes the blame (usually the turbo!)
The motto is THINK before forcing an 'improvement' in the coolant circuit - it
may have far-reaching repercussions you never thought of.
Radiator
When a FMIC is fitted, the radiator should be repositioned. The rad mounts can
be extended by small brackets, allowing the rad to be positioned a bit more
centrally and leaving some space for extra cooling air to get into the bay.
An even better move would be to replace the radiator with a bigger one, that
would use up this extra space for a good cause. The coolant hoses might need to
be extended in this case.
An intermediate solution is to use an aftermarket rad, direct replacement of the
existing one, but with a thicker core. It wouldn't cost much, and it would bring
the following benefits:
- Totally clean outside, the fins are straight and the paint is intact
- Totally clean inside, all the muck, scale and electrolytic garbage are
thrown away. No cleaning can ever achieve that.
- Core can hold another 0.5 liter of coolant. More coolant in the system
means less chances for it to hit critical temperatures.
Can I run the turbocharger without the coolant?
Funnily enough, yes.
It's not recommended of course, and the extra heat load will be dumped on the
oil. The turbo obviously doesn't live as long (around half the lifespan, which
is not too bad really) and the oil changes have to be frequent and only use
fully synthetic (which is a good idea anyway!)
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