B operation

[SD1too]

Dorset Bob, T-Cut & Colvert,

I think what you're all overlooking is that in the case of the 75/ZT, the coolant must reach 115 degrees before the fan runs in this way. You surely don't believe that that coolant temperature is normal? It is on the brink of sending the temperature gauge to maximum and illuminating its red LED.

It doesn't matter what other vehicles do. On the 75/ZT it warns us that there is something wrong with the cooling system. I was driving my 75 last Thursday in an ambient temperature of 35 degrees and the fan did not run-on after I stopped the engine.

Please can we concentrate on helping Charlie find the fault because there clearly is one.

Simon

[COLVERT]

Simon. The fan does not come on with the R75 because of a fault in the cooling system either.

T-cut explained why it could come on in his post. Heat-soak.

Have another read of his post. It is a 'design feature' that kicks in under certain circumstances in very hot weather.----

The reason being it stops the coolant from boiling off AFTER the engine is switched off.

There's a large lump of metal attached to the cylinder head. The exhaust manifold.--If you check this on a dark night after a fast run you will actually see it glowing dull red. Heat transfer from this item into the water jacket will effect quite a rise in temperature after the engine is switched off.

[Dorset Bob]

Originally Posted by SD1too

………….That tells us that you have a fault. The KV6 should run below 100 degrees C.

Simon, you are getting confused with normal running operating temperatures and heat soak temperatures.

Without intervention, when an engine stops running so does the coolant flow, oil flow, fan and air cooling.

In a nutshell, this can cause a rapid increase in temperature of various engine components. This has nowhere to escape, except mainly into the coolant.

In this situation, this causes a significant increase in coolant temperature. This is why on many vehicles, including the Rover 75 / MGZT, have systems designed to reduce the temperature after shutdown and during the heat soak.
In the case of the Rover 75 the fan is set to run as per T-Cut’s information.

This is normal operation.

I hope the graph below illustrates what we are referring to:-

“Afterboil” is the same as “Heat Soak”

[COLVERT]

Dorset Bob.

Snap-----

Great minds think alike.------------

[SD1too]

Originally Posted by COLVERT

T-cut explained why it could come on in his post. Heat-soak.

Colvert, T-Cut & Dorset Bob,

I'm disagreeing with T-Cut. As Bob says, "heat soak" is when hot parts of the engine rise in temperature due to the removal of the cooling effect of a running engine and/or moving vehicle. You are all claiming that this causes the coolant temperature to rise and trigger the fan to run as highlighted in the chart reproduced by T-Cut.

For this to be true and there to be no other fault with the cooling system as you all contend, at the moment that the engine is stopped the fan should not be running (unless the air conditioning is switched on). This would show that the cooling system is functioning correctly and the temperature is below 100 degrees. This is the purpose of the fan control regime, to keep the temperature below 100 degrees. Then, as "heat soak" takes place, time passes and the coolant temperature rises. Provided that the coolant reaches 115 degrees C the fan will then start running. This is very much an emergency provision since the trigger temperature is so high, as I have already explained. I'd say that it is stretching credulity to believe that an engine below 100 degrees can increase in temperature by as much as 15 degrees simply due to "heat soak".

But this is not what has been reported with Charlie's car. He says that the fan continues running after he has stopped the engine. That proves that the coolant temperature is already much too hot, at 115 degrees in fact, or he has another fault which is running the fan unnecessarily.

The chart which T-Cut has reproduced is from RAVE. It does not mention the term "heat soak" or the rationale for providing that particular fan sequence. So Jon, Bob and T-Cut, you may have your interpretation but it is not corroborated by any MGR documents and I disagree with it.

Since the three of you believe that Charlie doesn't have a fault, it would be appreciated if you could allow me and anyone else to continue a dialogue with him on the basis that he does.

Simon

[clf]

Simon, the original post states 'engine is switched of at 100c plus '

By T-Cut's chart, slow speed fan cuts in at 100 degrees +, medium speed fan cuts in at 106+. So at the point of switching the engine off, in the absence of a definitive reading, let's say that the temp is 110 (since there is no mention of change of pitch of fan speed), therefore we can expect the fan to be running at medium speed. Would it not be reasonable to expect the temp to rise quite suddenly around the coolant sensor in the absence of coolant flow - causing the fan to stay on. I would also wager that MGR engineers have factored a rise of temp at standstill after ign off, to add a margin of error to allow for this situation. (ie to avoid this, switch off at 110, fan goes off, heat soak comes and raises the temp, forcing the fan on perhaps a minute or two after switching the car off - therefore making an owner suspect something was amiss with the electrical system).

You suggested elsewhere, that the fact that it is over 'normal operating temperature' indicates a fault. (because of the lack of mention of a change in pitch, I am making an assumption - I know I shouldnt lol - that the temp is over 106). With the addition of the various fan speeds, and the fact that the speeds can be ramped up during different temperatures, all suggest to me 'normal operating temps' which must account for ambient temperatures of different markets.

Which brings me to another point you mention, you driving in 35 degree ambient temps whilst maintaining 'normal operating temp' (I assume you mean to be less than 100 degrees?). I am guessing you were driving with AC on, which will help dissipate some of the heat, but more importantly, there is no mention of neither yours, nor Charlie's driving styles, loads or distances etc. (as well as coolant condition and concentration etc ie too many potential variables to compare directly). You cannot use your car and driving as a reference for this. T-Cut also alluded to the load issue in a previous post too.

From what I have read with V6s through this and in the past, whilst it is not what we would call normal, it does appear to be within acceptable limits. I would agree with you though, that if there is a need to add more coolant, (100ml) it would suggest a potential issue. For that amount I would suggest checking for an air lock, but nothing more than this.

[SD1too]

Originally Posted by clf

Simon, the original post states 'engine is switched off at 100c plus '

Thanks Alan; it does indeed. That reinforces my point. Charlie's engine is running too hot, it's as simple as that and that's what we need to address.

Charlie, have you carried out the official refilling and bleeding process yet? If not, please can you activate the instrument pack diagnostics and monitor your coolant temperature. I would like to see some readings both when you're moving and stationary in a queue of traffic, preferably with the air conditioning off.

Simon

[Avulon]

And don't forget the A/C requirements will you chaps?
:getcoat:

[clf]

Originally Posted by SD1too

Thanks Alan; it does indeed. That reinforces my point. Charlie's engine is running too hot, it's as simple as that and that's what we need to address.

Charlie, have you carried out the official refilling and bleeding process yet? If not, please can you activate the instrument pack diagnostics and monitor your coolant temperature. I would like to see some readings both when you're moving and stationary in a queue of traffic, preferably with the air conditioning off.

Simon

Simon it doesn't reinforce the point, it suggests the potential. As we dont know if there it has been a misfilled system, which in the absence of a comment of leak stains, I am inclined to think, for now. The car could still operate quite correctly as it has been, with 100ml shy of full. Simply topping up and bleeding will eliminate any doubts. The temperatures are all within limits and no indication of faults.

Sent from my SM-A600FN using Tapatalk

[T-Cut]

Originally Posted by SD1too

Since the three of you believe that Charlie doesn't have a fault

Since you've drawn me into your argument, I'll add more. Charlie expressed concern that his fan continued running, so I posted the chart to help him understand why. I did not comment on whether he has a coolant fault and your assumption is incorrect. Indeed I suspect there is an issue, but too many cooks as they say. You make a point that MGR don't mention 'heat soak' on the chart. So if you think I've invented it for some purpose is your problem, but believe me the term is widely used in MGR circles and no doubt by MGR themselves. I'm sure it's there if you do some research.

I described a similar event with my own car. In that case there was no coolant fault. Whether there is or isn't a fault, the chart describes fan operation. As to whether coolant temperature can rise significantly after shutdown depends on how much work was being done just before and the thermal inertia of the engine. Consider a V6 being turned off in last week's heatwave with the fan running at 110°C and the exhaust manifolds glowing bright orange. Other parts of the engine will also be at temperatures way above the coolant. With little external cooling available, that heat gets conducted to the stagnant coolant which is at the lowest temperature of all and so it may boil. Head boiling in this situation can generate safety issues which the pressure cap is specifically designed to mitigate. By all means Sherlock out Charlie's cooling problems, but do avoid arguing with the physics.

TC