Intermittent Engine Temp Warning

AndyJacobs · 8th October 2017, 19:57

Evening all

My ZT 190 has just started doing something weird. I first noticed it the other day on a longish trip where the engine temp light suddenly came on. I checked the gauge and it was already moving down back towards normal.

I've just driven to Heathrow and back - 2 x 60 miles with a 45 min break. On the way there it happened once. On the way back it also happened once but I was keeping an eye on the gauge and I noticed that on 2 more occasions the gauge went up 1 or 2 segments and then came back down.

The worst it is is that the gauge goes up very quickly - in less than 5 seconds, sits right at the top for probably 2 or 3 seconds and then comes back down just as quickly.

When it's behaving, the temp sits at the 9.00 position and doesn't move a millimetre.

If it was really overheating, I'd expect it to creep up and then come back down slowly - say if it was a fan or sensor problem. But the whole cycle only takes about 10 seconds.

The only other thing I've noticed and I'm not sure if it's because I've only just started watching is the time it takes to get up to temp in the mornings. I only drive a couple of miles to the station and it goes from cold to the normal position well before I'm there.

Any ideas?

Cheers
Andy

SD1too · 8th October 2017, 21:13

Andy,

The fast warm-up is a deliberate design feature of the K series.

Regarding the excessive temperature, start by checking the coolant level when the engine is stone cold. Follow that by testing that your radiator fan is working on its low speed by performing the 'demist test'.

The 'nine o'clock' position is meaningless. The needle will remain there for the temperature range 75 to 115 degrees C!

Simon

AndyJacobs · 9th October 2017, 06:41

Nice one. Thanks for that. The coolant level is fine. I'll check the fan situation later. I'll probably only do 15 miles this week so probably Saturday.

I just read a long thread on a similar situation that seemed to end up with the guy scrapping his car so I'm hoping mine is something simple. Do you reckon it's worth getting an OBDII thing to see if that tells me more? I was looking at them on Amazon but they seem to get very mixed reviews.

Cheers
Andy

SD1too · 9th October 2017, 08:06

Quote:

Originally Posted by AndyJacobs

Do you reckon it's worth getting an OBDII thing to see if that tells me more?

No.

Activate the built-in instrument pack diagnostics to display the actual coolant temperature instead.

Simon

Simondi · 9th October 2017, 08:36

Here's the link for diagnostics

AndyJacobs · 9th October 2017, 10:19

Cheers for the link. I'll give that a try as well.

cb750chris · 9th October 2017, 12:17

As Simon has suggested, the normal position covers a huge temperature range, I seem to remember that the red on the temperature gauge is 125°.

So what I suspect is happening is that you engine is getting to >115°, so your needle is going up, then the fan is kicking in on high speed and reducing the temperature to 115 (or less) so your needle is falling quickly. This can be confirmed in the diagnostics screen linked to in the post by Simondi.

Does you fan work on low speed? (start engine, and enable air con on the "heaters", then check if the cooling fan is running)
Does you car have a resistor fitted, or is it a 3 speed fan?

Chris

Geoff130 · 4th April 2019, 16:11

Did you ever get to the bottom of this, my ZT190 does exactly the same.
The fan works fine and the coolant level is correct. It has always had an issue with blowing one of the engine bay fuses if it hits a pothole hard and it's something on my to do list as somewhere there is an incorrectly routed ( and damaged ) cable loom, I don't know if this has anything to do with it but I've never had both happen together.

T-Cut · 4th April 2019, 16:50

I'd suggest that rapid temperature fluctuations noted in these cases is due to air bubble circulation. Rather than a stagnant air lock, the air can form circulating bubbles which occasionally reach the pump. This reduces/stops the flow temporarily, which raises the head temperature. The bubble is then displaced with coolant, which pumps it into the head where it may then leave the sensor exposed/dry, causing an apparent drop on the gauge. This passes through and everything settles back to normal. Basically, there's already air in or getting into the system. The obvious fix is a good bleed/top up and to fix any leaks which repeated events will suggest.

TC

8th October 2017, 19:57	#1
AndyJacobs Regular poster MG ZT 190 Join Date: May 2013 Location: Andover Posts: 73 Thanks: 14 Thanked 5 Times in 4 Posts	Intermittent Engine Temp Warning Evening all My ZT 190 has just started doing something weird. I first noticed it the other day on a longish trip where the engine temp light suddenly came on. I checked the gauge and it was already moving down back towards normal. I've just driven to Heathrow and back - 2 x 60 miles with a 45 min break. On the way there it happened once. On the way back it also happened once but I was keeping an eye on the gauge and I noticed that on 2 more occasions the gauge went up 1 or 2 segments and then came back down. The worst it is is that the gauge goes up very quickly - in less than 5 seconds, sits right at the top for probably 2 or 3 seconds and then comes back down just as quickly. When it's behaving, the temp sits at the 9.00 position and doesn't move a millimetre. If it was really overheating, I'd expect it to creep up and then come back down slowly - say if it was a fan or sensor problem. But the whole cycle only takes about 10 seconds. The only other thing I've noticed and I'm not sure if it's because I've only just started watching is the time it takes to get up to temp in the mornings. I only drive a couple of miles to the station and it goes from cold to the normal position well before I'm there. Any ideas? Cheers Andy __________________ --- 2003 MG ZT 190 in Trophy Blue

8th October 2017, 21:13	#2
SD1too Doesn't do things by halves Rover 75 2.5 Connoisseur Auto (1999) Dealer launch model. Join Date: Mar 2007 Location: Former Middlesex Posts: 20,344 Thanks: 1,587 Thanked 3,749 Times in 3,181 Posts	Andy, The fast warm-up is a deliberate design feature of the K series. Regarding the excessive temperature, start by checking the coolant level when the engine is stone cold. Follow that by testing that your radiator fan is working on its low speed by performing the 'demist test'. The 'nine o'clock' position is meaningless. The needle will remain there for the temperature range 75 to 115 degrees C! Simon __________________ "Whatever is rightly done, however humble, is noble." Sir Henry Royce.

9th October 2017, 06:41	#3
AndyJacobs Regular poster MG ZT 190 Join Date: May 2013 Location: Andover Posts: 73 Thanks: 14 Thanked 5 Times in 4 Posts	Nice one. Thanks for that. The coolant level is fine. I'll check the fan situation later. I'll probably only do 15 miles this week so probably Saturday. I just read a long thread on a similar situation that seemed to end up with the guy scrapping his car so I'm hoping mine is something simple. Do you reckon it's worth getting an OBDII thing to see if that tells me more? I was looking at them on Amazon but they seem to get very mixed reviews. Cheers Andy __________________ --- 2003 MG ZT 190 in Trophy Blue

9th October 2017, 08:36	#5
Simondi Regional Secretary MGTF, MG ZS EV Exclusive Join Date: Sep 2007 Location: Kilwinning Posts: 14,046 Thanks: 1,460 Thanked 3,563 Times in 1,857 Posts	Here's the link for diagnostics __________________ Simondi FAQ How do you do that? Club Flyers Looking for a car seen in a film or on TV? Fancy a change in colour or wheels - paint configurator OBD - Trip Meter Ultimate Buyers Guide Post YouTube videos

9th October 2017, 10:19	#6
AndyJacobs Regular poster MG ZT 190 Join Date: May 2013 Location: Andover Posts: 73 Thanks: 14 Thanked 5 Times in 4 Posts	Cheers for the link. I'll give that a try as well. __________________ --- 2003 MG ZT 190 in Trophy Blue

9th October 2017, 12:17	#7
cb750chris Trader Rover 75 Tourer Join Date: Apr 2011 Location: Portsmouth Posts: 849 Thanks: 201 Thanked 292 Times in 200 Posts	As Simon has suggested, the normal position covers a huge temperature range, I seem to remember that the red on the temperature gauge is 125°. So what I suspect is happening is that you engine is getting to >115°, so your needle is going up, then the fan is kicking in on high speed and reducing the temperature to 115 (or less) so your needle is falling quickly. This can be confirmed in the diagnostics screen linked to in the post by Simondi. Does you fan work on low speed? (start engine, and enable air con on the "heaters", then check if the cooling fan is running) Does you car have a resistor fitted, or is it a 3 speed fan? Chris __________________ Now offering T4 services in the Fareham area Replacement keys programmed / supplied / cut Diesel 135 upgrade available IPK virginisation and T4 matching available Sorry, due to a big change in home circumstances, I am unable to do any large jobs at present, but can still offer evening time diagnostics.

4th April 2019, 16:11	#8
Geoff130 Loves to post MG ZT 190, Rover 75 CDTi, Honda VFR 750, Honda CB550F Join Date: Aug 2010 Location: Derby Posts: 393 Thanks: 75 Thanked 36 Times in 28 Posts	Did you ever get to the bottom of this, my ZT190 does exactly the same. The fan works fine and the coolant level is correct. It has always had an issue with blowing one of the engine bay fuses if it hits a pothole hard and it's something on my to do list as somewhere there is an incorrectly routed ( and damaged ) cable loom, I don't know if this has anything to do with it but I've never had both happen together.

4th April 2019, 16:50	#9
T-Cut This is my second home Rover75 and Mreg Corsa. Join Date: Nov 2006 Location: Sumweer onat mote o'dust (Sagin) Posts: 21,752 Thanks: 341 Thanked 3,660 Times in 2,924 Posts	I'd suggest that rapid temperature fluctuations noted in these cases is due to air bubble circulation. Rather than a stagnant air lock, the air can form circulating bubbles which occasionally reach the pump. This reduces/stops the flow temporarily, which raises the head temperature. The bubble is then displaced with coolant, which pumps it into the head where it may then leave the sensor exposed/dry, causing an apparent drop on the gauge. This passes through and everything settles back to normal. Basically, there's already air in or getting into the system. The obvious fix is a good bleed/top up and to fix any leaks which repeated events will suggest. TC