Overheating 2.5 auto?

Forestgreen · 19th July 2015, 21:29

Combination of hot sunny day with aircon on max and lowest setting, and a 100 mile motorway drive with cruise control set to 70. Halfway along I noticed the temp gauge start to rise slowly until a brief "engine overheat" flashed upon the message centre. I immediately turned the aircon off and slowed down to 55, at which point the gauge fell back to 9 o'clock, the normal position.

Pulled off at the next service station and checked the (hot) water level opening the cap as carefully as possibly to find water sloshing around the max level. So I carried on the journey at a steady 55 and the engine never indicated that it was overheating again except for a brief trial at 70 which on dropping back to 55 caused the temp gauge to go to normal again.

I let the engine cool down all afternoon then checked the water level only to find that none was visible in the chamber. So I topped up with around 200ml which got it to above the max line, and put the car in diagnostic mode. I put the aircon on full demist and a very noisy fan immediately kicked in (I'm assuming that's supposed to, though I had been getting the impression for the past couple of weeks that the fan sounds a lot louder than usual, is that normal in hot weather?)

The engine temperature driving at a constant 60mph on the way home read a steady 99. I then drove for a while at 70 and it rose to 102 but no higher.

I'll take it in to be looked at this week but in the meantime wondered if anyone can suggest any problems to consider? I had the thermostat replaced three years ago and there is no coolant visible to me so unlikely to be that. I don't often have to top the coolant up but 200ml didn't stricke me as excessive given I probably haven't checked the levels in a few months (I drive a V6 after all, not a 1.8!) Am wondering if it's me or it the fan is noisier than usual, though at the same time I had the thermostat done I had something done to the fans I forget exactly what but seem to recall one or more of the motors had packed up. At the last service it was mentioned that there might be a slight radiator leak in as much as there was a trace of dried coolant visible apparently but I have rarely if ever had to top the car up since that service.

StephenEssex · 19th July 2015, 21:37

99 to 102 seems quite high if your cruising along at 60/70MPH.

I monitor mine and even without a working fan it holds around 92ºC at cruising speed, I guess because of the air getting in through the front of the car.

Today was very hot though...

T-Cut · 19th July 2015, 22:52

If the fan sounds 'louder' maybe it is. The slow speed should start and run continuously whenever aircon is engaged. I suspect the slow speed has packed in and you're hearing the higher speed (is it a 2-speed or the older 3-speed?). Low speed engine cooling trips on at 100C, so your readings suggest it's not working - or the engine is really working hard.

I suggest you run the Demist test with the cold engine on tickover and take it from there.
You might also check for coolant leakage into the engine V (thermostat housing failure is No1 cause of coolant loss in the V6).

If you can't do either check, tell the garage what to do.

TC

Wayne2015 · 19th July 2015, 23:06

Quote:

Originally Posted by T-Cut

If the fan sounds 'louder' maybe it is. The slow speed should start and run continuously whenever aircon is engaged. I suspect the slow speed has packed in and you're hearing the higher speed (is it a 2-speed or the older 3-speed?). Low speed engine cooling trips on at 100C, so your readings suggest it's not working - or the engine is really working hard.

I suggest you run the Demist test with the cold engine on tickover and take it from there.
You might also check for coolant leakage into the engine V (thermostat housing failure is No1 cause of coolant loss in the V6).

If you can't do either check, tell the garage what to do.

TC

+1

Mine went to 107 before fan kicked in and brought it down to 99.

Everyone on here said that was too high and asked me to do the demist test - which shown mine low speed fan did not kick in....so either a new fan or repair needed...

SD1too · 19th July 2015, 23:08

Quote:

Originally Posted by Forestgreen

Pulled off at the next service station and checked the (hot) water level opening the cap as carefully as possibly to find water sloshing around the max level.

If you were able to remove the cap immediately after a 70 mph cruise and without scalding yourself, then your system isn't pressurising properly and that's why it overheated briefly.

You need to look for that elsuive radiator leak (and check in the 'V' too as advised already).

Simon

MrDoodles · 20th July 2015, 08:58

Do you know how old the thermostat is?

As it sounds to me the beginnings of V6 thermostat failure (ie; sticking shut) to me!

kaiser · 20th July 2015, 09:17

The fan should not come on at motorway speeds, at all.
So, assuming your story is correct, you can only have two problems causing what you have seen, and that is a lack of coolant or a stuck thermostat.

I would as a first step look for water in the V near the thermostat.

(not even considering more exotic failures like a blockage and or a water pump problem)

My first guess is that you have lost water, and that would be considerably more than 200ml!! So I think you have not filled the system correctly.

The other option is a stuck thermostat, which in itself would also lead to water loss, because of temperature and pressure increases.

In short, fill up you water level for starters and then monitor. If overheating persists, change the thermostat.

Forestgreen · 20th July 2015, 10:30

Thanks, car booked in for service and insepection in a week's time and will only be doing local driving inbetween. Thermostat was replaced (due to coolant loss) three years ago and I can't see any fluid in the engine V gully so would be surprised if it has gone so soon, but my local expert ex-Rover mechanic will undoubtedly sort things out.

Stag>75 · 20th July 2015, 10:42

Quote:

Originally Posted by kaiser

The fan should not come on at motorway speeds, at all.

There was a thread in the last week or so. The question was raised as to whether the cooling fan is ever off when the Air Conditioning is on. The thinking was that perhaps it never turns off. So the OP may need to ensure air conditioning is either off or at least on ECON in order to test fan operation at motorway speeds.

kaiser · 20th July 2015, 11:05

It is possible that the fan is on if the A/C is switched on. It would not have any effect on the engine cooling at these speeds however, as the ram effect (from the car moving) will exceed the ability of the fan to pump air by far at motorway speeds.

19th July 2015, 21:29	#1
Forestgreen Gets stuck in Rover 75 Connoisseur SE 2.5 V6 saloon Join Date: Dec 2011 Location: Birmingham Posts: 770 Thanks: 47 Thanked 105 Times in 54 Posts	Overheating 2.5 auto? Combination of hot sunny day with aircon on max and lowest setting, and a 100 mile motorway drive with cruise control set to 70. Halfway along I noticed the temp gauge start to rise slowly until a brief "engine overheat" flashed upon the message centre. I immediately turned the aircon off and slowed down to 55, at which point the gauge fell back to 9 o'clock, the normal position. Pulled off at the next service station and checked the (hot) water level opening the cap as carefully as possibly to find water sloshing around the max level. So I carried on the journey at a steady 55 and the engine never indicated that it was overheating again except for a brief trial at 70 which on dropping back to 55 caused the temp gauge to go to normal again. I let the engine cool down all afternoon then checked the water level only to find that none was visible in the chamber. So I topped up with around 200ml which got it to above the max line, and put the car in diagnostic mode. I put the aircon on full demist and a very noisy fan immediately kicked in (I'm assuming that's supposed to, though I had been getting the impression for the past couple of weeks that the fan sounds a lot louder than usual, is that normal in hot weather?) The engine temperature driving at a constant 60mph on the way home read a steady 99. I then drove for a while at 70 and it rose to 102 but no higher. I'll take it in to be looked at this week but in the meantime wondered if anyone can suggest any problems to consider? I had the thermostat replaced three years ago and there is no coolant visible to me so unlikely to be that. I don't often have to top the coolant up but 200ml didn't stricke me as excessive given I probably haven't checked the levels in a few months (I drive a V6 after all, not a 1.8!) Am wondering if it's me or it the fan is noisier than usual, though at the same time I had the thermostat done I had something done to the fans I forget exactly what but seem to recall one or more of the motors had packed up. At the last service it was mentioned that there might be a slight radiator leak in as much as there was a trace of dried coolant visible apparently but I have rarely if ever had to top the car up since that service.

19th July 2015, 21:37	#2
StephenEssex Loves to post 2000 Rover 75 2.5 V6 Connoisseur Join Date: Jul 2014 Location: Gibraltar Posts: 385 Thanks: 222 Thanked 75 Times in 48 Posts	99 to 102 seems quite high if your cruising along at 60/70MPH. I monitor mine and even without a working fan it holds around 92ºC at cruising speed, I guess because of the air getting in through the front of the car. Today was very hot though...

19th July 2015, 22:52	#3
T-Cut This is my second home Rover75 and Mreg Corsa. Join Date: Nov 2006 Location: Sumweer onat mote o'dust (Sagin) Posts: 21,753 Thanks: 341 Thanked 3,660 Times in 2,924 Posts	If the fan sounds 'louder' maybe it is. The slow speed should start and run continuously whenever aircon is engaged. I suspect the slow speed has packed in and you're hearing the higher speed (is it a 2-speed or the older 3-speed?). Low speed engine cooling trips on at 100C, so your readings suggest it's not working - or the engine is really working hard. I suggest you run the Demist test with the cold engine on tickover and take it from there. You might also check for coolant leakage into the engine V (thermostat housing failure is No1 cause of coolant loss in the V6). If you can't do either check, tell the garage what to do. TC

20th July 2015, 08:58	#6
MrDoodles Banned MG ZT+ V6 190 Join Date: Nov 2011 Location: Spalding Posts: 13,245 Thanks: 369 Thanked 1,196 Times in 818 Posts	Do you know how old the thermostat is? As it sounds to me the beginnings of V6 thermostat failure (ie; sticking shut) to me!

20th July 2015, 09:17	#7
kaiser This is my second home 75 Tourer 2.5 Auto, 1.8T, 75V8ZT Join Date: Jun 2007 Location: Johannesburg ZA Posts: 6,200 Thanks: 1 Thanked 859 Times in 613 Posts	The fan should not come on at motorway speeds, at all. So, assuming your story is correct, you can only have two problems causing what you have seen, and that is a lack of coolant or a stuck thermostat. I would as a first step look for water in the V near the thermostat. (not even considering more exotic failures like a blockage and or a water pump problem) My first guess is that you have lost water, and that would be considerably more than 200ml!! So I think you have not filled the system correctly. The other option is a stuck thermostat, which in itself would also lead to water loss, because of temperature and pressure increases. In short, fill up you water level for starters and then monitor. If overheating persists, change the thermostat.

20th July 2015, 10:30	#8
Forestgreen Gets stuck in Rover 75 Connoisseur SE 2.5 V6 saloon Join Date: Dec 2011 Location: Birmingham Posts: 770 Thanks: 47 Thanked 105 Times in 54 Posts	Thanks, car booked in for service and insepection in a week's time and will only be doing local driving inbetween. Thermostat was replaced (due to coolant loss) three years ago and I can't see any fluid in the engine V gully so would be surprised if it has gone so soon, but my local expert ex-Rover mechanic will undoubtedly sort things out.

20th July 2015, 11:05	#10
kaiser This is my second home 75 Tourer 2.5 Auto, 1.8T, 75V8ZT Join Date: Jun 2007 Location: Johannesburg ZA Posts: 6,200 Thanks: 1 Thanked 859 Times in 613 Posts	It is possible that the fan is on if the A/C is switched on. It would not have any effect on the engine cooling at these speeds however, as the ram effect (from the car moving) will exceed the ability of the fan to pump air by far at motorway speeds.