Cooling system upgrade

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Re: Cooling system upgrade

Postby CJH » 03 Jul 2018, 12:57

captain Byrne wrote:There will be an optimum flow rate. Too fast and the water won't cool down enough as it passes through the radiator, too slow and the cooler water already passed through the radiator takes too long to reach the engine.


Water temperature feels like it ought to be the most important thing here, but actually what's more important is how much heat energy the cooling system can take away from the engine. The rate that heat energy leaves the system via the radiator is a function of the average temperature of the radiator, its surface area, and the airflow over it (temperature and speed). For a given radiator size and airflow, the performance of the cooling system improves as the average temperature of the radiator increases, i.e. more heat energy is removed if the temperature difference between the radiator and the air is greater.

It doesn't matter how fast the water is passing through it (ignoring issues such as turbulence (good) and cavitation (bad)), except that it affects the average temperature of the radiator. If the water is flowing so fast that the temperature drop is small, that is (more than) compensated for by the extra volume of (slightly cooled) water reaching the engine. Would the engine benefit more from a dribble of cold water or an infinite supply at, say, 95 degrees?
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Re: Cooling system upgrade

Postby 937carrera » 03 Jul 2018, 13:27

I don't mind pedant mode at all it's usually a didactic experience.

I think I agree with you, mostly, after doing some background reading where it appears I may have fallen foul of an Internet myth. Still trying to get my head around the deeper rad and whether there is an effect on that from the dimension or not. A wide river runs slower than a narrow river for the same flow.

With regard to the oil cooler position, wouldn't it have been better if it was separate to the rad ? Reasoning is that you have an additional volume of air to cool the oil. Of course in many cases rad, intercooler and oil cooler all occupy broadly the same space for packaging reasons, sizing being adjusted to reflect (bigger than if separate)?
Last edited by 937carrera on 03 Jul 2018, 13:38, edited 1 time in total.
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Re: Cooling system upgrade

Postby CJH » 03 Jul 2018, 13:38

937carrera wrote:With regard to the oil cooler position, wouldn't it have been better if it was separate to the rad ? Reasoning is that you have an additional volume of air to cool the oil. Of course in many cases rad, intercooler and oil cooler all occupy broadly the same space for packaging reasons, sizing being adjusted to reflect (bigger than if separate)?


I'm sure it would, yes, but the (easy) options were limited. I wanted it to benefit from the radiator fan (whether I was misguided or not, that's what I wanted!), and I had the brackets :D

Air flows through the oil cooler matrix, so it's not like the old-style cardboard blanking sheets that people used to use in the winter - it doesn't block that section of radiator completely. The air that reaches the water radiator via the oil matrix will be a little bit slower and a little bit warmer, but it will still cool the water. Applying my 'thought experiment', I imagined that air passing through both matrices will be warmer than air passing through just the water matrix, so the net effect would be more heat removed.
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Re: Cooling system upgrade

Postby captain Byrne » 03 Jul 2018, 13:40

CJH wrote:
captain Byrne wrote:There will be an optimum flow rate. Too fast and the water won't cool down enough as it passes through the radiator, too slow and the cooler water already passed through the radiator takes too long to reach the engine.


Water temperature feels like it ought to be the most important thing here, but actually what's more important is how much heat energy the cooling system can take away from the engine. The rate that heat energy leaves the system via the radiator is a function of the average temperature of the radiator, its surface area, and the airflow over it (temperature and speed). For a given radiator size and airflow, the performance of the cooling system improves as the average temperature of the radiator increases, i.e. more heat energy is removed if the temperature difference between the radiator and the air is greater.

It doesn't matter how fast the water is passing through it (ignoring issues such as turbulence (good) and cavitation (bad)), except that it affects the average temperature of the radiator. If the water is flowing so fast that the temperature drop is small, that is (more than) compensated for by the extra volume of (slightly cooled) water reaching the engine. Would the engine benefit more from a dribble of cold water or an infinite supply at, say, 95 degrees?


Isn't that pretty much much what I've said?
If you leave out the technical side of the workings of the radiator, It's all about having the water at the correct temperature at the correct flow. The thermostat controls the flow rate, slowing the water flow rate down when the engine is cold, and increasing the flow when it's hot. I'd definitely say It would be better to have an infinite supply of warm water than a dribble of cold.
To get back to the OP problem. He thinks by adding an oil cooler to the system this will prevent the engine from getting too hot. It probably will, but It's plainly obvious that there's a problem that he's not addressing which is that there's either a restriction in the system or a faulty thermostat.
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Re: Cooling system upgrade

Postby CJH » 03 Jul 2018, 13:53

captain Byrne wrote:To get back to the OP problem. He thinks by adding an oil cooler to the system this will prevent the engine from getting too hot. It probably will, but It's plainly obvious that there's a problem that he's not addressing which is that there's either a restriction in the system or a faulty thermostat.


Agreed. Assuming the fan switch is near the radiator inlet (I don't know, is it?), it means the water is arriving too hot most of the time. Could be a restricted thermostat or an inefficient (i.e. worn out) pump I guess. I saw a video about pump pulley sizes (checking my facts earlier) - is it possible someone's fitted a larger pump pulley and slowed down the water flow rate?

Could also be timing I suppose - too retarded and the engine runs hotter.
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Re: Cooling system upgrade

Postby CJH » 03 Jul 2018, 14:45

This discussion has got me interested in a replacement electric water pump (not 'seriously' interested, just interested). Some of them look very sophisticated - independent control of the pump speed to achieve a desired water temperature, increased engine power due to not having to turn a mechanical pump*, ability to run on after the engine is turned off to avoid hot spots. I could imagine that circulating the water faster than a mechanical pump would when idling in traffic could help get the best out of the radiator in that scenario - hearing the fan kick on and off in traffic still makes me nervous as I'm only a fuse or dodgy switch away from overheating.

*but since you don't get anything for nothing, I'm sceptical - surely the current draw for this pump would make the alternator work harder.
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Re: Cooling system upgrade

Postby 937carrera » 03 Jul 2018, 15:41

CJH wrote:
*but since you don't get anything for nothing, I'm sceptical - surely the current draw for this pump would make the alternator work harder.


Yep, unless a perpetual motion machine has been invented. Also why modern cars have alternators which switch off based on battery condition / load. You are then into the energy efficiency of a mechanical pump vs an electrical pump, if that's what you want your focus to be.

Back to the OP's question, he needs to let us know what rad is actually fitted before concluding anything else is wrong. If he has a naff rad, then that might be the only problem, remembering his issues arose on what we call a hot day.
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Re: Cooling system upgrade

Postby 937carrera » 03 Jul 2018, 16:39

and now I'm back at a computer here's some links

One that got me a little better educated today

https://www.eng-tips.com/viewthread.cfm?qid=432703

The one that I went astray with because I didn't read the last post properly :roll: I was carrying around with me a view that you could angle a radiator up to 17 degrees, in the end I could only find a source supporting 15 degrees and this was en route

https://www.f1technical.net/forum/viewtopic.php?t=9093
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Re: Cooling system upgrade

Postby Da dan » 03 Jul 2018, 22:32

So I like what your all saying and it got me thinking. Tired water pump, it works or not? Timing? Much heat difference really? If when you accelerate the pump pumps harder thus water runs faster what about a bigger water pump. I do think everything is working well on my van. So no major panic but it’s when I hit traffic and it’s hot I do just worry a little. It’s never over heated but I just feel its running little hot. Thermo will be looked at and I like the thinking it may not be totally open?
Do these thing make you feel a little more assured when stuck in traffic on hot day?
Thanks


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Re: Cooling system upgrade

Postby bigherb » 04 Jul 2018, 05:58

Increasing the water flow can lead to overheating just as too slow a flow will. The coolant has to be in the engine long enough for the heat to be transferred away from the hot bits through all of the coolant, otherwise, only a small part of the coolant in contact with the hot bits gets heated which can cause localised hotspots although will show up as a cooler running engine on the gauge because all the coolant has not been heated. The thermostat also acts as a baffle to slow the water flow when fully open taking out thermostats can be death to an engine.
VW did know what they were doing and sold these vans for vans in hot countries without problems, if the system is working as it should there should be no problems. Did the engine actually overheat?

When was the fan on? Slow moving traffic? That what it was designed to do and is perfectly normal. If you are trying to cool water down from 100+ degrees with air that is at 30 deg the fan will be on a lot longer than if the air temp is only 10 degrees it is perfectly normal.

Before you start making modifications. As CB says check your cooling system first, have you got a thermostat fitted, are the baffles around the radiator in place they are there to stop the fan sucking in the air it has just heated getting sucked back through the radiator, have you blocked the rear vents they are to let radiated heat from the engine out.
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Re: Cooling system upgrade

Postby Ian Hulley » 04 Jul 2018, 10:51

bigherb wrote: have you blocked the rear vents they are to let radiated heat from the engine out.


On a DG the offside vent is blocked anyway as standard by the warm air unit so clearly Uncle Volkswagen didn't think it was too critical.

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Re: Cooling system upgrade

Postby bigherb » 04 Jul 2018, 11:30

Ian Hulley wrote:On a DG the offside vent is blocked anyway as standard by the warm air unit so clearly Uncle Volkswagen didn't think it was too critical.

Ian

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Re: Cooling system upgrade

Postby Mocki » 04 Jul 2018, 16:55

Both of mine are blocked , battery one side and my kero tank the other side for the heating , air flow over a wbx makes no difference as far as I can tell




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Re: Cooling system upgrade

Postby Cobra88 » 04 Jul 2018, 17:37

Neither are blocked on my DG :?

What's missing from my Caravelle then :roll:
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Re: Cooling system upgrade

Postby Da dan » 04 Jul 2018, 20:53

It’s not over heated, I am just thinking it runs hot. But the thermostat is normal. It gets to temp very quick after a short drive, 5 mins up the road. How can I check the pump or thermostat to see if they both working correctly? I’m going to have a look at the weekend and see what I can find.


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