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Underheating
MikeCapon - 9/2/12 at 01:07 PM

Just bear with me if you would. I may just be a rambling old loon but would be happy to know if anyone else follows this logic.

Cars not being able to get up to temperature in cold (its -10 here) conditions seem to be a recurring problem.

Cold engine = poor fuel consumption and increased engine wear.

To the point that some manufacturers (like VW) have added diesel burners to their cars to artificially create heat and speed the warming up process.

Which costs money and ruins fuel consumption.

Back in the mists of time we used to blank off the grill to speed warm up and (although we didn't realise at the time) improve Cd.

So why, instead of burning extra fuel to warm up, don't the manufacturers use a variable grill to do the same job without burning extra fuel and make the car slippier in the process.


Mike

wylliezx9r - 9/2/12 at 01:14 PM

quote:
Originally posted by MikeCapon
Just bear with me if you would. I may just be a rambling old loon but would be happy to know if anyone else follows this logic.

Cars not being able to get up to temperature in cold (its -10 here) conditions seem to be a recurring problem.

Cold engine = poor fuel consumption and increased engine wear.

To the point that some manufacturers (like VW) have added diesel burners to their cars to artificially create heat and speed the warming up process.

Which costs money and ruins fuel consumption.

Back in the mists of time we used to blank off the grill to speed warm up and (although we didn't realise at the time) improve Cd.

So why, instead of burning extra fuel to warm up, don't the manufacturers use a variable grill to do the same job without burning extra fuel and make the car slippier in the process.


Mike


I think you'll find that the new Ford Focus does.

MakeEverything - 9/2/12 at 01:14 PM

I seem to remember that there's a new car out that does have an automatic grille for exactly these reasons.

I forget which one though. Peugeot?

Dingz - 9/2/12 at 01:16 PM

You mean just like the air cooled citroens where you got a plastic gumshield to put in the grill?

loggyboy - 9/2/12 at 01:22 PM

But the thermostat does that job. A radiator with no flowing water wont cool an engine. Pass Air cooling the engine bay has a minimal effect.

balidey - 9/2/12 at 01:24 PM

Remember when you used to swap the summer thermostat for the winter 'stat?

MikeCapon - 9/2/12 at 01:25 PM

quote:
Originally posted by Dingz
You mean just like the air cooled citroens where you got a plastic gumshield to put in the grill?


My Ami 8, now the property of Dave Ashurst on here, had one. But what I'd be imagining for a modern car is some sort of variable aperture, controlled by the ECU...

I'm tempted to block off the grill on my VW and the Audi (same 1.9TDI motor) but I don't want to have to stop on the motorway for example to unblock it in the case of overheating. Or to be honest I'm probably more worried about SWMBO driving the car and noticing nothing until the engine melts.....

jossey - 9/2/12 at 01:26 PM

My BMW does that. Closes off when it's Cold and opens if it's too hot or the air con is on.

MakeEverything - 9/2/12 at 01:48 PM

quote:
Originally posted by loggyboy
But the thermostat does that job. A radiator with no flowing water wont cool an engine. Pass Air cooling the engine bay has a minimal effect.


But the cold ambient -15 (wind chill factor) into the engine bay will,have a similar effect.

cliftyhanger - 9/2/12 at 01:55 PM

I have experimented with my older cars, and blocking th eradiator (tinfoil) does raise the temp. I am not sure exactly why, as the thermostats work as they should, but maybe enough water gets by to keep the engine cold? I know blanking shouldn't make a difference, but it just does! Never tried it on a modern car though, it may be different?

Confused but excited. - 9/2/12 at 01:57 PM

Rollers have had thermostatically operated radiator grills for donkey's years.

MikeCapon - 9/2/12 at 02:05 PM

quote:
Originally posted by Confused but excited.
Rollers have had thermostatically operated radiator grills for donkey's years.


I seem to remember that someone (Kenlowe?) sold radiator blinds you could control from inside the car?

Which would be good right now but my original point still stands. Why burn extra fuel when you could get the same similar) result from a presumably cheaper and more ecological means.....

coyoteboy - 9/2/12 at 02:11 PM

You can't. That's why they use heaters - they're not stupid and do generally have a team of engineers doing the calcs on these things. The effect of wind chill into the engine bay will be negligible (a few hundred watts lost at most when at full temp, especially on a car with full under-trays). Rad curtains make no sense at all.

Most of the cars that use variable rad blinds these days do so for aerodynamics, not for warm-up - they only open when the static rad can't deal with the heat it needs to shed.

[Edited on 9/2/12 by coyoteboy]

nick205 - 9/2/12 at 02:25 PM

Fuel economy on my Passat has dropped badly in these low temps which is annoying. It doesn't half warm up quick though 2-3 miles and it's bang on 90 degrees with hot air aplenty! The pre-heater on SWMBOs Alhambra doesn't work and it takes an age to warm up.

Concurring with the OP it seems a poor design approach to burn extra fuel when passive measures could overcome the issue.

MikeRJ - 9/2/12 at 02:39 PM

quote:
Originally posted by cliftyhanger
I have experimented with my older cars, and blocking th eradiator (tinfoil) does raise the temp. I am not sure exactly why, as the thermostats work as they should, but maybe enough water gets by to keep the engine cold?


A wax thermostat is a very crude control system. The movement of the thermostat is only proportional to temperature e.g. if the engine is running too hot the thermostat will open a little in response. A simple proportional control system like this is not capable of removing all error, i.e. the amount the stat opens won't perfectly correct the error (if it did it would simply close back down again). This is why a radiator blind can make a significant difference to the engines running temperature in extreme cold conditions. Some modern cars have the thermostats controlled by the ECU which can implement a much more sophisticated control scheme and hence regulate temperature more accurately, so radiator blinds would be less useful.

The diesel burners mentioned by the OP are usually for heating the cabin space, not the engine. Because diesel engines are quite efficient these days, they have less waste heat so they naturally warm up more slowly. A diesel engine is typically more robustly built than a petrol as well, so there is a greater thermal mass to heat.

MakeEverything - 9/2/12 at 02:50 PM

quote:
Originally posted by coyoteboy
The effect of wind chill into the engine bay will be negligible (a few hundred watts lost at most when at full temp,

[Edited on 9/2/12 by coyoteboy]


The original point was that the cars couldn't get up to temperature though. If the wind chill effects through the grille and a cold radiator (closed stat) are negligible, then where does the cold air go once passed through the rad? It might not be too windy in there (negative pressure though), but it will still be chilled by the colder (positive pressure) air in front of the car.

designer - 9/2/12 at 02:54 PM

Of it's really cold and I am poodling about locally, I put a sheet of cardboard in front of the radiator which had holes in it so that it is just reducing the exposed area of the radiator..

MakeEverything - 9/2/12 at 03:01 PM

quote:
Originally posted by designer
Of it's really cold and I am poodling about locally, I put a sheet of cardboard in front of the radiator which had holes in it so that it is just reducing the exposed area of the radiator..


That's what the black cabbies do, and it seems to work well. They have a sheet of laminated A3 paper in the front.

fesycresy - 9/2/12 at 03:32 PM

quote:
Originally posted by balidey
Remember when you used to swap the summer thermostat for the winter 'stat?


No?

Did you have crank handles to start the car

coyoteboy - 9/2/12 at 04:12 PM

quote:

The original point was that the cars couldn't get up to temperature though. If the wind chill effects through the grille and a cold radiator (closed stat) are negligible, then where does the cold air go once passed through the rad? It might not be too windy in there (negative pressure though), but it will still be chilled by the colder (positive pressure) air in front of the car.



Just seems unlikely that your engine is so over-cooled that it effectively needs wrapping up to let it get warm. With a stat in place there's sweet FA flow through the rad, so the only cooling it's getting is to ambient and through the heater matrix. Often people run the heaters on full and it takes ages to get up to temp, naturally. The other point is the stat may be partially stuck open. But if the engine puts out so little heat that stopping the airflow over its surface means it gets up to operating temp I'd suggest they've created one of the most thermally efficient engines known to man.

Warmup just takes longer in winter due to the colder block starting temp and the fact that people put heaters on full chat, airflow and ambient air will have a much lower effect in the pecking order.

steve m - 9/2/12 at 05:18 PM

To add to this "winter problem"

we used to have airfilters that could move from winter to summer, to aid in the running
and presumabley stop carb icing

Steve

coyoteboy - 9/2/12 at 05:25 PM

Do you mean the old settings that used to suck air from over the exhaust manifold? Died out in the early 80-90s about when injection became a norm IIRC?

steve m - 9/2/12 at 05:31 PM

Thats the one m8, i certainly had it fitted on one of my earlier cars, cant remember which though!

PSpirine - 9/2/12 at 05:47 PM

quote:
Originally posted by coyoteboy
You can't. That's why they use heaters - they're not stupid and do generally have a team of engineers doing the calcs on these things. The effect of wind chill into the engine bay will be negligible (a few hundred watts lost at most when at full temp, especially on a car with full under-trays). Rad curtains make no sense at all.

Most of the cars that use variable rad blinds these days do so for aerodynamics, not for warm-up - they only open when the static rad can't deal with the heat it needs to shed.

[Edited on 9/2/12 by coyoteboy]



That's spot on. Active vanes as they're called are done for aero reasons, and nothing to do with increasing engine temps - they close on motorways and open in traffic.


The reason for fuel-fired heaters is twofold. Firstly it's to heat up the cabin, and secondly it's so the engine warms up QUICKLY to reduce consumption and emissions, and let the catalyst work (they don't work when they're cold). The effect of blanking out the grille would do very little to speed up warm up in most people's conditions (first couple of miles tend not to be motorway miles anyway), and after that point you're sitting at thermostat level anyway.

If you're struggling to get up to temperature at our sort of "cold" of -10, I'd suggest your thermostat is knackered, as even my 90hp TDi Passat (which is a silly efficient engine) gets to 90 degrees eventually with an open grille and a missing undertray.

Ninehigh - 9/2/12 at 06:28 PM

Just a thought, would an engine be using more fuel than normal if it's moving? I know it revs a little higher at idle but when driving does that actually make a difference these days?

matt_gsxr - 9/2/12 at 06:55 PM

I read that the "recirculate air button" results in the inside warming quicker and so will your engine.

Maybe worth an experiment.

coyoteboy - 9/2/12 at 11:01 PM

quote:

Just a thought, would an engine be using more fuel than normal if it's moving? I know it revs a little higher at idle but when driving does that actually make a difference these days?


I think all port injected engines require more fuel at startup to increase the fuel in the puddle at the back of the valves. Normally there's a fixed quantity of wet walls with a steady rate of evapouration off the intake walls, when it's cold that fuel/air mix evapourates less freely, meaning more needs to be thrown in to keep the engine running OK (amongst other effects). I THINK (though I'll have to consult my books) even direct injection engines will require more fuel as the cold block/cyl walls will affect combustion quality in the cyls.

Recirc will indeed help as you are heating warmer and warmer air up to your target temp, instead of heating outside air from -10 to +25 constantly. It has the minor issue that it tends to make you steam up a bit but it's good initially.

nick205 - 9/2/12 at 11:40 PM

Someone above made the point that car makers have teams of trained, experienced engineers who develop these things under big budgets. This is true and in reality I guess the diesel heater solution will be the best compromise (all design is after all a compromise) taking account of all aspects; economy, reliability, cost etc.

On the other hand someone (Steve M?) also recalled the old method of drawing intake air over the exhaust manifold to prevent carb icing etc. (I vaguely remember a childhood family car having this feature). Someone also mentioned the "recirculate" feature which helps warm the cabin quicker and allows the engine to warm quicker.

Could the same principles not be applied by directing the coolant flow through the exhaust manifold to capture the heat and recirculate it back into the block...?

(Of course this may already be widely done for all I know!)

austin man - 9/2/12 at 11:50 PM

water will always flow through the stat as a safety measure hence the small hole in them so water will get to the rad. There is also no doubt that the extenal temperature will continue to cool the engine as it enters the engine bay and also flows arount the sump etc . Olser cars where supplied with a grill muff for really cold winters which cut down air flow by 50 to 60 %. Ah the good old days when you could fix something without having to renew it

PSpirine - 9/2/12 at 11:58 PM

One (of many) reasons why a water cooled exhaust doesn't work is that this issue mainly crops up on diesel engines which have a turbo. The efficiency loss by cooling down the exhaust manifold (before the turbo) will be so great to make any temperature related fuel increase negligible.

Modern engines still have a warm-up rich map right up to running temp. Even at 70 degrees the car will use more fuel (we're talking a couple of percent only but it still translates to real mpg loss) than if it's at running temperature.

Some other methods for getting more heat into the engine quickly are:

1) Block heaters - available from most manufacturers for cars sold in cold climates

2) Recirculate coolant in engine block only. This is slightly different to the "Recirculate air" suggestion above which has only a limited benefit as there's still coolant going through the heater. If recirculating engine block coolant, then an electric heater element is required in the heater unit to generate the heat for cabin. This consumes ridiculous amounts of electricity but works well for the few minutes it takes to warm up the engine. It also means you can clear your windscreen instantly whilst the engine is warming up.

3) Heated catalysts. This doesn't heat up the engine any quicker, but heats up the component that most requires it at start-up. The majority of emissions problems relate to start-up and warm-up. Again, these solutions tend to use ridiculous amounts of power (1-2kW).


A fuel burning heater, if fitted, is done so for a very good reason. They're not simple or cheap bits of kit even for the OEMs so it's only done when required.


Also remember that depending on the homologation/economy cycles performed by OEMs, the fuel burning heater may not actually cause a drop in mpg as it doesn't kick in on a combined cycle run, but only on start-up and in very cold climates. The start-up homologation requirement may well be NOx related or a separate test.

coyoteboy - 10/2/12 at 12:03 AM

quote:
water will always flow through the stat as a safety measure hence the small hole in them so water will get to the rad.


The hole in the stat is generally about 1-2mm diameter and it's designed to ensure there's no air locks so that the stat always sees block-temp water. That's why it's imperetive you install it with the hole to the 12 oclock position. You're likely to see flow rates through that hole of about 0.5 litres a min, hardly additional cooling. It's _not_ there for safety to ensure the engine stays cool even if the stat fails.

[Edited on 10/2/12 by coyoteboy]

[Edited on 10/2/12 by coyoteboy]