2 Speed Fan Poser will my woes end!

[Jules]

Originally Posted by T-Cut

So does this mean the low speed first trips on at 106C and then off when it's cooled to 100C - and the same principle for high speed?

Sorry to appear dim, but 'from 100C to 106C' is heating up, whereas from 106C to 100C is cooling down, which I assume is what happens.

The high speed (presumably) changes to low speed at 106C on the cooling down curve?

TC

No
Low speed on at 99- 100
Off at 95-96

Low speed stays on up to 105-106 when high speed takes over.
IRRC

[Dragrad]

Threads merged as they are related.

[T-Cut]

Originally Posted by RayH

Sorry TC, it wasn't a dig, your input is always appreciated. I just couldn't see where you were coming from with that.

That's OK. What I meant is the cooling systen isn't working whatever fan speed is running. The independent '100mph' fan blast didn't cool the engine under load. That suggests to me that the high/low speed question is irrelevent to the overheating issue. There's simply not enough cooling capacity. Logically, coolant flow (through the radiator) is too low, hence the suggestion to replace the radiator. Clearly the hi/lo fan issue is separate.

TC

[DerekS]

I noticed that whenever towing in foreign parts up long inclines and passes , the wind was always behind me . And usually , as you found , there were large heavy lorries going slowly. Meaning that there was no ( or very little) ram effect air through the radiator to cool it down . It never occured to me that the rad fan would not be working ( couldnt have heard it anyway due to engine noise ) but that might have happened in your case .

[rovertone]

Originally Posted by T-Cut

That's OK. What I meant is the cooling systen isn't working whatever fan speed is running. The independent '100mph' fan blast didn't cool the engine under load. That suggests to me that the high/low speed question is irrelevent to the overheating issue. There's simply not enough cooling capacity. Logically, coolant flow (through the radiator) is too low, hence the suggestion to replace the radiator. Clearly the hi/lo fan issue is separate.

TC

Hi T-Cut,
Just to clarify, by using the high velocity fan on the dyno test the temperature held at 105deg and it was much slower getting there, whereas without it and for a similar duration run the temp was heading off the scale. This suggests that the cooling system is working ok when there is more fan power.
I am not sure whether it would have increased beyond 105 if the run had been longer but the difference was so noticeable that it was clear that the problem lay with the fan.

I guess that if I can solve that problem and I still have a overheating problem then i must question whether the car is capable of towing in such exceptional conditions and/or there is a cooling system problem. I am still 'kicking myself' that when I was overheating I didn't short out the trinary switch to force the 2nd speed which would have given me the answer........benefit of hindsight.
Thanks for your input.
Tony

[SD1too]

Originally Posted by rovertone

... by using the high velocity fan on the dyno test the temperature held at 105deg ... This suggests that the cooling system is working ok ....

No it doesn't Tony. Your cooling system should not require a high velocity fan and it should be capable of maintaining a temperature way below 105° with the slow speed fan operating.

When the temperature rises above 100° grasp the bottom radiator hose. Does it feel hot or cool?

Simon

[RayH]

Originally Posted by SD1too

No it doesn't Tony. Your cooling system should not require a high velocity fan and it should be capable of maintaining a temperature way below 105° with the slow speed fan operating.

Simon

Even when under heavy load? Real or simulated.

Leaving that aside for a moment, I was giving some more thought to the fan speed issue.

If the information here has not been disputed then for a 3 speed setup cut-in temps are:

Low 100-105
Med 106-111
High 112-119

So when the fan was replaced with a 2 speed I suspect the low and high speed relays were used rather than low and medium.

Given the information above it is quite possible that 115 can be reached without activating the high speed relay and therefore the higher fan speed.
It would explain why demist and trinary tests work normally but there is no additional cooling at higher engine temperature.

Tony - if that is the case you will simply need to rewire to the other relay, but let's see what you have in there first.

[SD1too]

Originally Posted by RayH

If the information here has not been disputed then for a 3 speed setup cut-in temps are:

Low 100-105
Med 106-111
High 112-119

Ray,

That post from Keith dates from 2006 and we know more now.

The way you have expressed the temperatures above is incorrect. I believe that they have come from the MGR 'Electrical Library' section of RAVE and are unreliable. There is only one nominal cut-in temperature for each speed and for the three speed fan they are (according to the main RAVE text):

Low 100°
Medium 106°
High 112°

The cut-out temperatures are, of course, lower than these figures.

For the two speed diesel fan there may be a slight variation from these low and high speed cut-in points due to different component values on the control box PCB (source: French Mike's investigation).

Simon

[rovertone]

Originally Posted by SD1too

No it doesn't Tony. Your cooling system should not require a high velocity fan and it should be capable of maintaining a temperature way below 105° with the slow speed fan operating.

When the temperature rises above 100° grasp the bottom radiator hose. Does it feel hot or cool?

Simon

I am not sure I follow that logic Simon, why then do we need a higher fan speed(s) at all. I agree with what you say when it comes to light loads, as I proved on the fast idle test as I couldn't get the temp to rise above 97, as soon as I hit that mark 1st speed stopped it rising further, hence the trip to the dyno.

I think a good starting point is as Ray suggests, having a look inside the control box I'll do that and get back with my findings.

[T-Cut]

Originally Posted by rovertone

Just to clarify, by using the high velocity fan on the dyno test the temperature held at 105deg and it was much slower getting there, whereas without it and for a similar duration run the temp was heading off the scale. This suggests that the cooling system is working ok when there is more fan power.

An unknown factor in the dyno tests is how hard the engine was having to work. It may have exceeded the ability of the cooling system to maintain the correct temperature. Perhaps the dyno loading exceeded what the car is designed to accomodate. Undr such conditions, no fan speed would cool it. Even so, the lack of sufficient cooling when caravan towing suggests an underlying issue apart from the lo/hi speed fan behaviour. Radiator, water pump, thermostat, there's not much else involved.

TC