18 replies to this topic

[tangerine_sedge]

I don't think this question has been asked before, and it definitely didn't come up in a search, so..... After I've driven my VX NA and got it up to normal temperature (i.e. ~88)., If I turn off the engine, then turn the iginition back on again, the temperature is displayed much higher, i.e. ~102. If I then start the engine it returns to the normal running temperature. What does the temperature shown during the ignition on, but engine not started mean? Why is it higher? I wondered if it was a peak temperature, but it's a long time since I got the engine so hot - probably summer last year! This has been buggin me for months now

[Sutol]

don't know why but mine does exactly the same.

[Garry.L]

I don't think this question has been asked before, and it definitely didn't come up in a search, so.....

After I've driven my VX NA and got it up to normal temperature (i.e. ~88)., If I turn off the engine, then turn the iginition back on again, the temperature is displayed much higher, i.e. ~102. If I then start the engine it returns to the normal running temperature.

What does the temperature shown during the ignition on, but engine not started mean? Why is it higher? I wondered if it was a peak temperature, but it's a long time since I got the engine so hot - probably summer last year!

This has been buggin me for months now

Could be because....

When you have switched off your 'hot' engine heat is Still transfered to the coolant, but because this coolant is now stagnent, ie water pump not turning, then the coolant temp will rise....... known as 'Heat soak'.

Once you start the engine again and the water pump is moving the coolant , the temp then drops..

Edited by Garry.L, 25 March 2008 - 09:11 AM.

[Chris_VX]

Mine too, but again, don't know why...

[ianrm]

I don't think this question has been asked before, and it definitely didn't come up in a search, so.....

After I've driven my VX NA and got it up to normal temperature (i.e. ~88)., If I turn off the engine, then turn the iginition back on again, the temperature is displayed much higher, i.e. ~102. If I then start the engine it returns to the normal running temperature.

What does the temperature shown during the ignition on, but engine not started mean? Why is it higher? I wondered if it was a peak temperature, but it's a long time since I got the engine so hot - probably summer last year!

This has been buggin me for months now

Could be because....

When you have switched off your 'hot' engine heat is Still transfered to the coolant, but because this coolant is now stagnent, ie water pump not turning, then the coolant temp will rise....... known as 'Heat soak'.

Once you start the engine again and the water pump is moving the coolant , the temp then drops..

[burnerblowout]

I don't think this question has been asked before, and it definitely didn't come up in a search, so.....

After I've driven my VX NA and got it up to normal temperature (i.e. ~88)., If I turn off the engine, then turn the iginition back on again, the temperature is displayed much higher, i.e. ~102. If I then start the engine it returns to the normal running temperature.

What does the temperature shown during the ignition on, but engine not started mean? Why is it higher? I wondered if it was a peak temperature, but it's a long time since I got the engine so hot - probably summer last year!

This has been buggin me for months now

Could be because....

When you have switched off your 'hot' engine heat is Still transfered to the coolant, but because this coolant is now stagnent, ie water pump not turning, then the coolant temp will rise....... known as 'Heat soak'.

Once you start the engine again and the water pump is moving the coolant , the temp then drops..

Spot on. Thermodynamics in action. Engine off, no fluid dynamics and heat transfer capability. Temp rises initially then reduces slowly from a peak threshold value.

[fishboy]

isn't it also do do with the fact that the car isn't moving as in when you are driving the air is sucked in cooling the car at the same time. As soon as you stop moving the air flow itsn't getting to the engine which is why loads of cars overheat in traffic jams. When i am in slow heavy traffic in my vx even with the engine ticking over the temperature rises from a nor of between 89-91 up to around 95.

[burnerblowout]

isn't it also do do with the fact that the car isn't moving as in when you are driving the air is sucked in cooling the car at the same time. As soon as you stop moving the air flow itsn't getting to the engine which is why loads of cars overheat in traffic jams. When i am in slow heavy traffic in my vx even with the engine ticking over the temperature rises from a nor of between 89-91 up to around 95.

Absolutely. Not moving with the engine on is a slighly different set of conditions though.

[tangerine_sedge]

I don't think this question has been asked before, and it definitely didn't come up in a search, so.....

After I've driven my VX NA and got it up to normal temperature (i.e. ~88)., If I turn off the engine, then turn the iginition back on again, the temperature is displayed much higher, i.e. ~102. If I then start the engine it returns to the normal running temperature.

What does the temperature shown during the ignition on, but engine not started mean? Why is it higher? I wondered if it was a peak temperature, but it's a long time since I got the engine so hot - probably summer last year!

This has been buggin me for months now

Could be because....

When you have switched off your 'hot' engine heat is Still transfered to the coolant, but because this coolant is now stagnent, ie water pump not turning, then the coolant temp will rise....... known as 'Heat soak'.

Once you start the engine again and the water pump is moving the coolant , the temp then drops..

I did consider this, but I'm suprised at how fast this is - literally seconds to go from 88 to 102! And, if I turn the engine back on, it drops to 88 instantly.

If I remember, I'll do a test tonight and check the temperature every few minutes. Hopefully it should cool down quickly...

Edited by tangerine_sedge, 25 March 2008 - 10:55 AM.

[Sutol]

I can understand that the temp will rise if the pump is not running but what i don't understand is that the ignition is off and the temperature sensor apparently still has a voltage to it in order to record the rise. Alternatively could this be part of some sort of self check on start up?

[Garry.L]

I can understand that the temp will rise if the pump is not running but what i don't understand is that the ignition is off and the temperature sensor apparently still has a voltage to it in order to record the rise. Alternatively could this be part of some sort of self check on start up?

Have you never heard your rad fan running 'After' you have turned the engine off?....

System still needs to be live to allow the rad fan to kick in if needed, without the iginition being on...

[Sutol]

I can understand that the temp will rise if the pump is not running but what i don't understand is that the ignition is off and the temperature sensor apparently still has a voltage to it in order to record the rise. Alternatively could this be part of some sort of self check on start up?

Have you never heard your rad fan running 'After' you have turned the engine off?....

System still needs to be live to allow the rad fan to kick in if needed, without the iginition being on...

fair comment, but when turning on the ignition from cold you still, for a moment, get a temp flashed up which is generally above a 100. So could it be that this is the temperature it reachs before it starts to fall which then deactivates the circuit involved if you get my jist?

[Buchos]

Does anyone think there would be any benefit to rigging the little electric water pump to run on a few minutes after killing the ignition?

[tangerine_sedge]

I also noticed that from cold, on just turning on the ignition (but not starting the engine), the temperature briefly flashed up 90 degrees. I would have thought the temperature would have been ambient? Therefore, I don't think it's an actual temperature, but must be some other indicator? A limit or trigger value perhaps?

[Garry.L]

Does anyone think there would be any benefit to rigging the little electric water pump to run on a few minutes after killing the ignition?

This is something Lotus already do/did on the Lizzy IIRC, to help with the problem of 'Heat Soak'.
Due to the K-Series unique construction and type of heat treated alloy used, it was found that after turning off a very Hot engine the heat still being transferd to the coolant would cause localised boiling, resulting in softening of the cylinder head alloy causing HGF..... so a small electric pump was fitted which 'runs-on' after ignition switch off to remove this super heated coolant.

The above it not such a problem in the more conventional front-engined, front Radiator type cars as thermal movement of the coolant will remove some of this hot coolant (Hot water is like hot air and rises) however as the coolant pipes both dip down on the rear-engined/front radiator type set up like ours, this thermal movement is greatly reduced....... I know from my days of F/TF ownership that if I had given the car a good thrashing I would always let the car idle for a minute or so just to help return some cooler coolant from elsewhere in the system, before swtiching off...... much like turbo owners do.

No expert on the Vauxhall lumps fitted to the VX, but given there don't seem to be any reports of HGF type problems etc, then it would seem that 'Heat-Soak' is much less of a problem, or at least does not appear to cause any damage.

Edited by Garry.L, 26 March 2008 - 09:50 AM.

[slindborg]

no real need on such a cool running engine and bay tbh. it was needed on the Omega V6 as it got bastard hot and stayed hot for a long time so needed the secondary pump (which I'm sure you could make that part fit the VX if you really really wanted to

[Garry.L]

no real need on such a cool running engine and bay tbh.

it was needed on the Omega V6 as it got bastard hot and stayed hot for a long time so needed the secondary pump (which I'm sure you could make that part fit the VX if you really really wanted to

This was an after-Market Solution one the MGF owners came up with....

http://www.mgf.ultim...coolant/ewp.htm

But, as you say it would appear not to be needed on the VX lumps, and if anyone is that concerned just leaving the engine to idle for a short while if VERY hot should be enough.

Edited by Garry.L, 26 March 2008 - 10:17 AM.

[Buchos]

But, as you say it would appear not to be needed on the VX lumps, and if anyone is that concerned just leaving the engine to idle for a short while if VERY hot should be enough.

There is already one of these electric pumps fitted in the VXT (not sure about NA). It seems to only run when the ignition is on, so i'm not really sure what purpose it serves, unless it activates like the fan if the temperature is above a certain level.

[Jase_MK]

I don't think this question has been asked before, and it definitely didn't come up in a search, so.....

After I've driven my VX NA and got it up to normal temperature (i.e. ~88)., If I turn off the engine, then turn the iginition back on again, the temperature is displayed much higher, i.e. ~102. If I then start the engine it returns to the normal running temperature.

What does the temperature shown during the ignition on, but engine not started mean? Why is it higher? I wondered if it was a peak temperature, but it's a long time since I got the engine so hot - probably summer last year!

This has been buggin me for months now

Could be because....

When you have switched off your 'hot' engine heat is Still transfered to the coolant, but because this coolant is now stagnent, ie water pump not turning, then the coolant temp will rise....... known as 'Heat soak'.

Once you start the engine again and the water pump is moving the coolant , the temp then drops..

Nah, I don't buy that. If you switch off at 88 degrees and switch back on again it is immediately 102 or whatever. A couple of seconds after the engine has started it pops straight back to wherever it was. I'm sure it's just a startup routine, a bit like the battery/oil/airbag light coming on when you first switch on the ignition. All three of my VXs have done the same.

I don't deny that the coolant will warm up a little after you turn off the engine due to being stationary, but the immediate engine off and on again jump from 88 to over 100 then immediately back to 88 I'm sure is just a startup procedure.