|
These days, cars seem to have the same effective frontal intake size regardless of the size/power of engine fitted whereas I can remember Vauxhall Cavalier mk2's having plastic blanking plates in the lower grill on petrol engines, even the SRI 130, but no blanking on the diesels.
In my days on Astra forums, owners of 1.6 8v versions were always advised to block the upper grill as the intake was designed for diesels and the 2.0 turbo - but it's important not to restrict airflow to any cold air intake for the engine.
|
|
Many manufacturers include testing in Death Valley, California before they go into production - it can routinely get to 50 C there. Now a car thermostat is fully open at around 90 C so such testing will show that a temperature differential of just 40 C is sufficient to dissipate all the heat.
In the UK, at this time of year, you'll have a temperature differential of 80-90 C, in other words twice as much cooling as you need, possibly more.
|
|
15miles
Being an A series the HG is tough as old boots so no damge done if you did.
|
|
I gave up after 30 miles which I thought was enough to heatsoak the engine and radiator. It is a megane, not a Minor, so no A-series engine.
I was surprised. Granted, cooling systems are generally overkill for most of the UK, but where was the heat being dissipiated? There's no undertray, so the sump is exposed to the stream of air running underneath. Can't believe it is enough to cool an entire engine though.
|
|
Exactly how bored were you prior to undertaking this investigation?
|
|
I did this many years ago in winter in an effort to save fuel. No problems at all, until one day I got stuck in a bit of a traffic jam, and it boiled over very quickly.
Edited by Pete Mansell on 29/01/2013 at 19:42
|
|
There's probably enough air moving around the engine compartment to get some flow through the radiator and also, would you have noticed if the cooling fans cut in?
Perhaps they're not called radiators for nothing and it was, erm, radiating a lot of heat?
|
|
The next test is to drain all the coolant out and repeat the procedure. I've heard that an old Saab 9000 could happily run without coolant provided the engine wasn't pushed too hard.
|
I've heard that an old Saab 9000 could happily run without coolant provided the engine wasn't pushed too hard.
I can vouch from bitter experience with a Saab 99 2.0L that this is definitely not true.
Edited by brum on 29/01/2013 at 23:20
|
I can vouch from bitter experience with a Saab 99 2.0L that this is definitely not true.
Let me guess, water pump? The Triumph engineer who designed that should never have been allowed anywhere near a cooling system component ever again.
|
Perhaps they're not called radiators for nothing and it was, erm, radiating a lot of heat?
My physics teacher made us call them 'convectors'-and the habit has stuck. Still, at ~100C radiation isn't entirely negligible (although half of it is straight back into the engine bay. Also the exhaust manifold is at the front of the engine, so that will be radiating out a fair bit of heat into the radiator.
I'm stumped.
|
My physics teacher made us call them 'convectors'-and the habit has stuck. Still, at ~100C radiation isn't entirely negligible (although half of it is straight back into the engine bay. Also the exhaust manifold is at the front of the engine, so that will be radiating out a fair bit of heat into the radiator.
I'm stumped.
So they should! Comparatively little radiating goes on from a 'radiatior'; it's mostly convection for ones in rooms, anyway.
You haven't got a double pass radiator have you?
|
I'm stumped.
Why am I not surprised?
Firstly, if its a diesel engine, these often barely produce enough heat to dump into the engine radiator if you are just tootling about on a light throttle. My Alhambra 1.9Tdi , for instance, can travel for many many miles in winter months and the top hose is barely lukewarm and radiator stone cold.
Secondly, theres the entire surface area of the engine, lots of pipework and the cars heater system acting as radiators.
Thirdly, even you did manage to seal all radiator grille aperatures (upper/lower sections etc) perfectly (which I doubt), there are plenty of other air leak areas, around the bonnet, around headlights, front/side of undertray, around driveshafts etc etc. With forward movement of the car, the aerodynamics draws air into the engine bay under pressure through these "holes", and the exit of all the "hot air" in the engine bay, (by design) is sucked out at the bottom rear of the engine bulkhead. i.e. there is still plenty of ventilation of the engine bay.
Forthly....mmmm.....I've got bored writing this......
Edited by brum on 29/01/2013 at 23:21
|
Firstly, if its a diesel engine, these often barely produce enough heat to dump into the engine radiator if you are just tootling about on a light throttle
This is not really true. Diesels dump a much higher proportion of their fuel energy into the coolant system than petrols. There's a widespread misconception that diesels are so efficient that they don't warm up. They appear to take longer to warm up because the engine is heavier.
Secondly, theres the entire surface area of the engine, lots of pipework and the cars heater system acting as radiators.
This is very true. But if you choke off the supply of air into the bay, it only buys you a little more time until the engine bay is heat soaked.
aerodynamics draws air into the engine bay under pressure through these "holes", and the exit of all the "hot air" in the engine bay, (by design) is sucked out at the bottom rear of the engine bulkhead. i.e. there is still plenty of ventilation of the engine bay.
You've hit the nail on the head. But I don't see why. In the absence of external air currents, warm air is bouyant and won't tend to be vented underneath the engine. Ah the mysteries of fluid dynamics!
|
But I don't see why. In the absence of external air currents, warm air is bouyant and won't tend to be vented underneath the engine. Ah the mysteries of fluid dynamics!
I tried to say, when a modern car moves, it acts a bit like a wing, pressure builds up over and around the frontal area. Air enters under pressure through all the leaky bits, (, bonnet edges, wheel arches, headlights, maybe the under windscreen bit, front bumper area etc etc)
Hot air is sucked out under the car at the rear of the engine by the ground effect ( Bernoulli's principle) as when the vehicle is moving air pressure under the car is lower than ambient. The front lower skirt assists in acheiving this lowered pressure.
I imagine that taping over the grilles, will both increase the upper body air pressure (due to higher air flow forced over and around the car) and lower the under car pressure (due to lower air flow from the engine bay), somewhat compensating for what you did with the gaffer tape.
Edited by brum on 30/01/2013 at 00:40
|
|
Given the irregular shape of the underbody (especially around the engine bay), I am slightly skeptical that long distance ordered airflow would be possible. Clearly there are high pressure and low pressure areas, but I thought that the pressure differential would merely result in eddies and vortices.
You must be right though! Btw, there is a lot of space around the engine (unlike a lot of modern cars) so plenty of room for air currents.
|
|
Was airflow through the heater matrix sufficient with the ambient temperature being so low?
|
|
Turned the heater to 'off' after a few miles.
|
|
If there's no undertray then you'll get all sorts of currents in front and behind the block once you're moving at anything above 30mph, I'd reckon.
When I had my old BGT V8 I used to block the grille entirely in winter, the coolant temp reached 'normal' much quicker than when the grille was exposed, but it didn't seem to affect the actual running temperature (not from the analogue water / oil temp gauges, anyway)
|
|
|
