antwan
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| posted on 10/9/11 at 10:17 AM |
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Cooling system temperatures query
Hi can someone help me figure this out?
I have an MNR Vortx, BMW 1.8 16v powered on standard fuel injection system/ECU. No other mods.
Standard new polo rad and fan switch supplied by MNR.
Two large hoses connected to the new polo radiator, 1 small bore hose from top of rad back to top of reservoir, 1 small filler hose from bottom of res
connects back into original plumbing between heater circuit (heater removed) and water pump.
My digital temp reading is taken from where the heater used to be i.e. as the hot water comes out of the block. Fan switch in radiator
Case 1
94 deg C - normal road speeds - fan not operating
rises to 96 deg C - when sat at traffic lights - fan will kick in around this temp
start driving again and temp drops back to 94 deg C but struggling to get the fan to stop (unless i drive like a granny for 5 mins).
Case 2
94 deg C - normal road speeds - fan not operating
rises to 98+ deg C - when stuck in traffic (start to get a bit worried). Although the fan comes on, the temp guage seems to rise slowly as if fan is
undersized.
start driving again and temp drops back to 94 deg C but cant get the fan to stop.
As typically this car is not driven for fuel efficiency  temp typically is at 95 deg C and once the fan is on it never goes off until i get home.
Any opinions, fan undersized, radiator undersized?
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craig1410
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| posted on 10/9/11 at 10:59 AM |
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Hi,
Do you have pipes connected between heater connections? If so then blank them off as the flow is bypassing the radiator and not losing heat. Also fit
a flow restrictor in the pipe from rad to res for same reason. Just a bit cut off an M8 or M6 bolt with a 3mm hole drilled through middle. Still
allows air to bleed but less water flow.
Hope this helps.
Craig.
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antwan
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| posted on 10/9/11 at 11:22 AM |
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Yes when the heater was removed, I just shortened the hoses and connected together. These hoses are about 15mm ID.
What your saying makes sense to me now!
Although if im restricting this 15mm ID hose, will this affect the cooling system before the thermostat opens?
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antwan
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| posted on 10/9/11 at 11:23 AM |
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Also what is different about just removing the heater and connecting the lines together. Does the heater matrix provide some resistance to flow?
Thanks
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craig1410
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| posted on 10/9/11 at 12:24 PM |
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Yes the matrix and longer hoses will restrict flow but also the matrix will remove some heat. Even so, the heater matrix isn't as good at
removing heat as the main radiator which is usually in free flowing cool air. For this reason, if you have a car which is overheating, often the worst
thing you can do is move the heater control to hot. It might give you a very brief cooling effect as the cooler water in the matrix moves to the
engine but after a few seconds the car will be even worse. Of course this is assuming the main radiator is large enough and is moving through cool
air. In traffic, the internal heater might indeed help to cool the engine as long as you can get the heat back out of the cabin.
If you are worried about getting air locks in the blanked off heater hoses then connect them together but again use a restrictor to reduce water flow.
Then restrict the radiator bleed hose in the same way. This will ensure that almost all water flow will go through the radiator and promote
cooling.
Regarding flow before the thermostat opens, I would always recommend having 3 x 3mm holes drilled in the thermostat skirt but your engine should have
a bypass mechanism built in somewhere. I'm not familiar with your engine type so hopefully someone else can confirm this.
Cheers,
Craig.
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Dusty
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| posted on 10/9/11 at 01:40 PM |
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Your fan switch will have two built in trigger points. 95degrees to switch it on and something like 88 degrees to switch it off. As it never cools to
88 degrees it will not switch off once triggered on. Try a different fan switch. Possibly look at getting a lower opening thermostat. This assumes you
have some cooling capacity in reserve.
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antwan
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| posted on 10/9/11 at 02:34 PM |
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I have the water temp sensor in the heater circuit so to ensure this keeps working correctly, i will restrict the flow but not blank off and see if
this improves things. I dont think its massively far off as the engine has never overheater as such so i'll give restriction a go.
Great thanks chaps... Im off to the garage!
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britishtrident
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| posted on 10/9/11 at 07:02 PM |
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Very important don't not block off or excessively restrict the by-pass connection.
Looks like you have a 94c thermostat which is a wee bit on the hot side I would advise trying to find a slightly cooler thermostat.
It also looks to me like the fan switch drop out temperature is too low below the thermostat fully open temperature. If you keep the existing
thermostat you need a fan switch that goes on at at 98 off about 95c
A lot of builders worry too much about temperature gauge readings. If the cooling system is holding pressure then a modern engine only gets into the
over heat zone over about 120c.
On modern tintops the temperature gauge readings are driven by the engine ecu which alters the readings so as not to needlessly alarm the the
driver. If you click on the link to the graph below you will see the temperature gauge needle will not move (ie be on "N" between
70 and 120c
http://www.locostbuilders.co.uk/photos.php?action=showphoto&photo=rovertemp.jpeg
[Edited on 10/9/11 by britishtrident]
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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antwan
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| posted on 10/9/11 at 09:08 PM |
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Hi again,
I have just tried restricting the heater circuit using a plug 17 diameter with a 4mm hole in it.
The car seem to run upto temperature a little quicker.
I have the digital temp reading just after the restriction.
The temps being seen on the guage are now between 85 to 87 when idling on the driveway rather than the 94 to 96 before. The fan came on at around 87
and shut off at 85. It appeared to me as if the temp reading was a little numb and only really responded with some revs (presumably due to lack of
flow past the sensor with the thermostat open??).
I think I may open the restriction up to say 8mm from the 17mm original ID. Hopefully this will give a happy medium of cooling through rad and flow
down the bypass.
I have also noticed that due to the fan being mounted 15mm off the face of the rad, a huge amount of air is lost through this gap before the air gets
to the radiator surface. I have ordered some universal radiator zip ties so the fan can be mounted to the face of the radiator which should speed up
the removal of heat.
ant
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britishtrident
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| posted on 10/9/11 at 10:27 PM |
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If you look up the workshop manual you will see what the standard thermostat temperature is 92c with an 88c option, the thermostat
should maintain this as a minimum temperature so your 84c temperature gauge reading is meaningless. The gauge reading is foobarred because the
flow over the sensor is drastically throttled.
You have to think logically your problem is simply a mismatch between the fan switch and thermostat temperature.
A decent by-pass flow is essential to ensure an even temperature distribution around lower half of the engine.
Incidentally some BMW engines run at much higher temperatures with 97 degree thermostats.
[Edited on 10/9/11 by britishtrident]
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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craig1410
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| posted on 10/9/11 at 10:35 PM |
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BT, are you saying the heater flow IS the bypass on this engine or are you guessing? In my experience the bypass on most engines is separate. As I
said earlier, I don't know the BMW engine. Is it an M10 by the way?
If in doubt I would far rather drill a couple of holes in the stat to act as bypass than have my heater circuit open as the reduction in cooling
caused by an open heater circuit can be severe.
Temperature should not ideally be measured in the heater circuit. Better to measure as close to the stat as possible, ideally on the engine side of
the stat.
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antwan
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| posted on 11/9/11 at 10:25 AM |
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Nope still not getting this...
I have had a think for a good couple of hours before ploughing ahead.
I understand the cooling system as follows:
When the engine is cold, the water starts off at the pump (100% flow), makes its way round the engine and back to the pump. A couple of auxilary
circuits are present i.e. heater circuit and inlet manifold connection. If 100% starts off at the pump and 80% returns to the pump via the block, and
the 20% goes through the aux circuits, surely a total of 100% returns to the pump whether it be via the block or other circuits. Therefore restricting
or blocking the heater circuit should have no effect on engine cooling as a greater percentage just returns to the pump via the block.
If 100% always returns to the pump, surely 100% ends up going through the rad when the stat opens.
The cross sectional area of the radiator hoses is far greater than the aux connections therefore my assumption that most of the coolant returns inside
the block to the pump should be correct.
Make sense? or am i barking
Engine is an M42 bmw fuel injected
[Edited on 11/9/11 by antwan]
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britishtrident
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| posted on 11/9/11 at 07:30 PM |
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Cooling systems are designed to keep engine at as close as possible to an constant even temperature both in terms of the temperature at the
cylinder head and an even spread of temperature through both the block and cylinder head.
The idea of by-pass flow is to keep the coolant flowing rapidly through the block to created a turbulent flow which improves mixing and improves
heat transfer and to prevent over cooling of the bottom end of the engine. The engine temperature is controlled by the thermostat, at the rated
nominal opening temperature the thermostat only starts to open it will only fully open about 6 or 7 degrees above the rated temperature i.e. an 88c
thermostat will approach fully open at about 94c and and 91 degree thermostat at about 97c. If you don't have a by-pass flow when the
thermostat opens a slug of over cooled coolant will get drawn into water pump from the radiator resulting in drastic over cooling of the cylinder
block, which will continue until the slug of cold water works its way up to thermostat. Without a by-pass connection the flow of coolant over the
thermostat is reduced or in some cases non-existent so the opening of the thermostat in response to increasing temperature will be greatly delayed.
As a result the coolant temperature with swing between near boiling and over cooling.
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craig1410
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| posted on 11/9/11 at 09:08 PM |
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quote:
Originally posted by britishtrident
Cooling systems are designed to keep engine at as close as possible to an constant even temperature both in terms of the temperature at the
cylinder head and an even spread of temperature through both the block and cylinder head.
The idea of by-pass flow is to keep the coolant flowing rapidly through the block to created a turbulent flow which improves mixing and improves
heat transfer and to prevent over cooling of the bottom end of the engine. The engine temperature is controlled by the thermostat, at the rated
nominal opening temperature the thermostat only starts to open it will only fully open about 6 or 7 degrees above the rated temperature i.e. an 88c
thermostat will approach fully open at about 94c and and 91 degree thermostat at about 97c. If you don't have a by-pass flow when the
thermostat opens a slug of over cooled coolant will get drawn into water pump from the radiator resulting in drastic over cooling of the cylinder
block, which will continue until the slug of cold water works its way up to thermostat. Without a by-pass connection the flow of coolant over the
thermostat is reduced or in some cases non-existent so the opening of the thermostat in response to increasing temperature will be greatly delayed.
As a result the coolant temperature with swing between near boiling and over cooling.
Yes I'm aware what bypass flow is but what I was asking earlier was if you know if the heater connections are used for this purpose (very
unlikely in my opinion) on this specific BMW M42 engine? Bypass flow is intended to keep water moving to avoid localised hot spots and to give the
pump somewhere to push water round until the stat opens. When the stat does start to open, flow will be very small initially and the cooler water from
the bottom of the radiator will only be introduced slowly thus avoiding any rapid temp fluctuations. The stat is an "analogue" actuator
and does not snap open and shut and this is how it keeps a generally steady temperature under varying loads and speeds.
So in summary, yes bypass flow is important, hence my suggestion to drill some holes in the stat if there is any doubt over it, but I think it will be
perfectly safe and desirable to block the heater connections off and thus get more coolant flow through the radiator. This should be confirmed with
someone more familiar with this enginee though.
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NS Dev
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| posted on 12/9/11 at 07:34 AM |
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your problem is wrong fan switch, look in the intermotor book for another one with higher switchoff temp. Could do with an accurate probing (oo-err)
to check the guage accuracy, and don't worry basically, if it goes over 105 deg when driving under load, then worry a bit but other than that
just sort the fan switch so its not running all the time and drive it!
I have over 200hp and a polo 1.0 rad and another chap on here has a 280hp supercharged 4age engine with the same rad too so you're not exactly
taxing it! Mine has to be standing in traffic for 10 mins on a red hot summer day before the fan even kicks in.
here's the catalogue.........
intermotor catalogue link
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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