3.6 overheating apparent coolant loss ?

[whippetpaul]

Hi, My car recently overheated, within 2/3 miles. On investigation water was dripping from below the radiator. But on opening the expansion tank there was normal water level. And obviously no warning light for low coolant. The upper and lower hoses appear ' flat', I have no idea how to check the level or how to top up the radiator ?

Paul

[AndyF]

Hi Paul

I hope you have found a solution to you overheating issues - just seen your post. My first thought is about the "flat" comment on your hoses - this sounds like the system is under some sort of vacuum and that they have collapsed.

What is the condition of your radiator / expansion tank caps? Are they in a good condition - are they sealing properly?

Overheating within 2/3 miles sounds odd - assuming that you started the car from cold and then drove away without waiting for it to warm up, it would unlikely be overheating in 10 mins or so.... so perhaps it is more about the thermostat jamming closed and not opening as the car was warming up... this could give the impression of overheating.

My suggestions would be:
- Check condition of radiator - clear of debris and sealing foams in place around it?
- Check condition of belts - is water pump belt in place? Is the fan belt in place and tight enough?
- Check operation of thermostat - does it open and close in and out of hot water?
- Check condition of all hoses - are they secure?
- Fill and bleed the cooling system

And - because it has overheated, check that there has been no damage to the head gasket by checking the oil filler cap for emulsion / mayo gunk....

All the above comes from my experiences with the V12 (and one exciting adventure with an AJ16 4.0 to Spa which overheated multiple times due to a blocked rad - but ran fine once fixed while we were there - lying on the ground, in the dirt next to the track at Pouhon corner... - the straight 6 seems to be as tough as old boots!)

I am sure other 3.6 owners will know more than I - any comments all?

Stay safe

Andy

[davidr]

Andy - I would agree that the prime suspects on a car that overheats within such a short time would be the water pump or the thermostat.

[steve_m]

What was the indication for overheating?
Was there steam?
Was it a high temperature gauge?

[JimMann]

Hi Guys, An interesting conundrum. A couple of thoughts here!

1. The 'flat' radiator hoses are pointed out as being due to a vacuum, a realistic idea, but what could potentially pull a vacuum in a pressurised cooling system? As coolant is not compressible, we can determine that there is no coolant in the hoses and potentially the entire cooling system. This could point to the fact that the cooling system has been ejecting the coolant over a period of time as the manner of hoses becoming flat is for the vapour in a container (sealed system) to be heated (excess vapour and / or water to be ejected) and the container allowed to cool - remember the hot water in the plastic drinks bottle -, thereby creating a low pressure (vacuum) in a 'sealed' system, i.e. the water has not been drawn back from the expansion tank. The ejection of the coolant has to have been via a relief point, i.e. not a hole in the system, otherwise air would be drawn in and the hoses would not collapse. If the hoses were flat on inspection at the time of the reported overheating above, they had to have been flat prior to the overheating, pointing again to a problem over time.
2. If there is no coolant in the cooling system, then an overheating indication within a few miles would be the obvious outcome.

The question now therefore is how does the coolant escape / be ejected in an otherwise sealed system? Could the route to / from the expansion tank be worth investigating? As the coolant heats up in the sealed system, the expanded volume is supposed to be taken to the expansion tank. As the sealed system cools down again, the volume is returned from the expansion tank. If this process is repeated over time BUT the coolant is not being returned from the expansion tank due to a fault over the same period, you get a reduction of the coolant volume in the sealed system and that can result in the outcome described above.

Probably all hypothetical rubbish, but passed an otherwise quiet Sunday morning stuck at home!

Jim

[whippetpaul]

Hi, everyone.. thank you for your suggestions on this problem... The first indication of the problem was a rise in temperature on the dashboard guage, which is normally constant at N. I returned home and opened the bonnet to find vapour pouring from the back of the engine ? not really ' steam' I also noticed the auxilliary electric fan was not running . The expansion tank is still refusing to empty back into the system....

[ptjs1]

Paul,

As others have suggested, it seems that coolant is escaping from the system, under pressure, and then the system is unable to pull back coolant, either from the expansion bottle, or alternatively air from atmosphere from the leak source. Can you verify the vacuum theory by carfeull releasing the filler cap and witnessing an inrush of air?

If there is a vacuum lock, I guess it implies that a seal, such as the filler cap neck seal, is failing allowing vapour/ coolant to escape but preventing a suction back of air. Or alternatively that there is a hose leak which then closes as air attempts to pull back into the vacuum. Perhaps you could verify that by starting with the system appropriately filled, and seeing if you can identify a leak under pressure when warm or a filling of the expansion bottle which then does not return back to the system?

Good luck

Paul

[whippetpaul]

Hello, as I have had to top up the coolant I was concerned about the antifreeze situation... but obviously I have no way of knowing how much coolant is in the system. Or how to get antifreeeze in ? The expansion tank is still refusing to empty back into the system... So I dont know how much water there is in it ?
I have used the car a few times and the temperature guage has remained just below N.
I also can not find where the drain tap is ?

Paul.