Coolant loss when running with heater on 'cold'

[Ludwik]

Hello!

I run a 1968 Series 4.2 FHC E-type.

I am having an odd coolant problem with the car. I always start off with the heater on ‘hot’ and then once the car has warmed up I turn the heater down to ‘cold’. If I run in ‘cold’ for say a couple of hundred miles the car loses coolant, sometimes as much as a litre over that distance. I don’t have the problem if I keep the heater on ‘hot’. I change the coolant every couple of years and flush each time. I also only use distilled water. I have checked all the hoses and connections, including the heater control valve, and all is in good condition and no signs of leaks.

Any idea what is causing the coolant loss when running with the heater on ‘cold’?

Thanks in advance for your thoughts!

[greensimonc]

Hi,

I confess I haven't investigated my heater much - only that if I push the lever down with some force there is "clunk", which tends to suggest it's in need of some lubrication! But I would imagine that hot water circulates through it all the time and that it's only opening the vent and putting the fan on that directs hot air it into the cabin? So I doubt that operating the heater would have any effect of the circulation - maybe someone will correct me!

You say there is no evidence of a leak - so how do you know you're losing coolant? - is the header tank empty or are you losing coolant out of it via the expansion pipe? - cos that would suggest there's too much coolant in the system and as it warms up, it's got nowhere else to expand to other that out.....

Now it's getting colder I've been meaning to have a poke around the heater - if I come across anything I'll let you know.

Cheers, Simon.

[stuarthardy]

Hi Ludwik

Do you notice any difference in running temperature when the heater is on and off? Does the heater work as you would expect?

Are you absolutely sure there are no leaks anywhere? There are 3 metal pipes that run through the bulkhead and are notorious for leaking. As standard these pipes were mild steel and rusted severely, especially where people had failed to use good quality anti freeze or inhibitor. Replacements in either copper or stainless steel are available and advisable but its a pig of a job to do and best done during a major rebuild. Any leakage from these will go straight into your bulkhead and rot it from the inside out. Check your carpets aren't wet.

There is a valve that controls coolant flow through the heater matrix, I would suspect that the heater itself is not leaking as you would be experiencing the opposite problem of coolant loss when heater is on. So it is possible that the heater matrix is providing just enough extra cooling to prevent overheating.

Have you checked that you have the correct pressure cap on the header tank and that a plain cap is fitted to the radiator? Service manual states 7 psi cap for standard equipment car and 13 psi where air con is fitted.

That's all I can think of at this time.

Regards

[e600]

Hi Ludwick

When you turn to cold are you operating the flap or the heater valve, if the heater valve, then water should stop circulating through the heater, if the flap then water will continue to circulate but air is directed out of the bottom of the heater.

I can only think you may have a air lock of some sort, perhaps a slow fill, run, top up, run etc to ensure all air is purged and try again.

Regards
Pat


www.patsetypes.co.uk