Cooling system - help anyone?

R

RIDDLER

Well-Known Forum User
Need a bit of advice please! I have reported before that when I start my Z from cold the temp gauge climbs steadily, passed the centre, until it reaches the 250 mark where it sits for a couple of minutes then suddenly starts coming down again. It returns to the centre (normal) position then remains there for the rest of the journey.
I had put this down to a late-opening thermostat but I replaced that and it has not solved the problem. Mr F advised me that if it was only remaining at a high temp for a short time I shouldn't really worry about it.
BUT .. . I have also noticed recently that I have started to use a bit of water - I keep needing to top it up from time to time. My trusty mechanic Mark Warburton said he could find no trace of a leak and did not believe there was any sign of a head gasket problem. Water was just disappearing.
Today I have seen for myself what is happening - and this is where I need someone to unravel the mystery for me!
I started the car from cold and sure enough the temp gauge got to the top. I opened the bonnet to have a look. The top hose on the radiator was cold and hard and the radiator was cold.
Suddenly there was a bubbling and I saw water come out of the clear overflow tube that runs from the top of the radiator cap. About half a pint at least came out of the tube and discharged onto the ground. About the same time the top hose became soft and warm and, of course, the temp gauge dropped back down,
So that is how I am losing water. But what is going on? And how do I solve it? Thinking of trying another thermostat - but don't know what else to do.
 
Last edited by a moderator:
sounds a bit weird, I would take the thermostat out and check it, there should be the temperature range stamped on it for opening, I was given one for my car and it was the wrong temp rating
 
RIDDLER it seems to me that your thermostat is opening far too late. This is resulting in the water in your engine (cylinder head) reaching boiling point and then the thermostat opens and the force of the boiling water and steam is opening the rad pressure cap and discharging water.

That's all a bit excessive and unusual - are you sure the thermostat is fitted correctly?

One of my Zs has a thermostat that is a bit too hot for the car I think (it was supplied to me by a local motor factor). All I get is the gauge going a little high (3/4 scale) and then settling down and no loss of water so not really an issue.
 
Last edited by a moderator:
Hi just remove the thermostat completely, and see if fault dissapears.
It looks to me like some massive air lock try doing the above with the radiator cap removed and run to remove air from system.
Its definately not right though!!:eek:
 
I had a problem with a brand new thermostat and had to change it. Just cause its new does not mean it not at fault.
 
It may be that the water isn't circulating quickly enough so the thermostat is not getting hot enough to open until too late, such as with a blocked radiator core, for example or slipping water pump. This would allow the cap to vent off the excess pressure as the water in the engine block would get very hot.
 
Thanks guys for all your help. Going to get the car to Mark on Friday and get the thermostat out. I will then try running it for a week and see what happens. Mark is getting me a replacement thermostat as well with a lower temp rating. The one in there, which was supplied to me by Mike Feeney, opens at 88degrees I believe (or is supposed to). I believe you can get them that open at 84 so may try one of those.
Hope it is not a slipping pump or blocked radiator core as that sounds expensive. If it was, why would it then right itself?
 
RIDDLER said:
Thanks guys for all your help. Going to get the car to Mark on Friday and get the thermostat out. I will then try running it for a week and see what happens. Mark is getting me a replacement thermostat as well with a lower temp rating. The one in there, which was supplied to me by Mike Feeney, opens at 88degrees I believe (or is supposed to). I believe you can get them that open at 84 so may try one of those.
Hope it is not a slipping pump or blocked radiator core as that sounds expensive. If it was, why would it then right itself?
Click to expand...

The good thing is that nothing mechanical on a standard Z is expensive compared to modern cars. :thumbs:
 
I think it is def possible to put the thermostat in the wrong position - if it's not the correct orientation the whatsit that opens can foul on the thermostat housing lower and prevent it opening properly.
 
my 2p worth,

a) Thermostat jamming closed after car has cooled down and then opening a bit as the pressure and temp rises to high level - then working normally until it goes stone cold again and 'jams'.
b ) big airlock in system - air expanding and escaping ( blowing coolant out with it ) on heating from cylinders and then normal operation continues once air mostly escaped ( heater matrix leaking letting air in, possible only leaking when cold ? ) - quite possible due to age of car.
c) less likely is small head gasket leak on cylinder seal or hairline crack in head that initially pressurises cooling system on stone cold start up and then as engine cylinder comes up to temp in couple of minutes then leak mostly seals itself and no longer puts any real pressure on water system..i've seen this on old rover 200/400/800's with poor factory head gaskets and or poor quality heads.

your mechanic needs to pressure test the cooling system both when cold and hot while you look for leaks and also check for combustion gases in coolant ( using chemical test )
and has been said above, take stat out and run car for a few days to see if problem goes away - some stats have a drilled hole in stat to act as a bleed and this requires certain orientation to work properly.


cheers
Ash
 
Ok - just an update. Thermostat now removed. Car starting and running fine with no noticeable difference. The temp gauge is barely moving from zero even when the car has been running half an hour. So does look like a thermostat issue. Mark now trying to source me one with a lower temp threshold. Believe the one I had in was 88 degrees? Looking for something around the 84 mark to try that.
 
The 84 degree thermostat is the standard one I believe about 180f, I think there was a 190f option which you must have had fitted, both should be ok but you do need a working one. Test it in boiling water before fitting as they can be faulty even when new!!
 
I took my 260z out for the first time this year yesterday and it did exactly as Riddler is describing. Temperature climbs steadily almost to the top, then drops quite quickly down to normal temperature where is stays.

The overflow pipe on my car is pretty perished so when I stopped it was clear to see that it had spurted some coolant out which had then been blown all over the place by the engine fan.

The Thermostat and Temp sender were new last year and only done a few hundred miles.

I will keep an eye on it and wondering if it was just stuck after its winter slumber and will be fine now....
 
Russell said:
I took my 260z out for the first time this year yesterday and it did exactly as Riddler is describing. Temperature climbs steadily almost to the top, then drops quite quickly down to normal temperature where is stays.

The overflow pipe on my car is pretty perished so when I stopped it was clear to see that it had spurted some coolant out which had then been blown all over the place by the engine fan.

The Thermostat and Temp sender were new last year and only done a few hundred miles.

I will keep an eye on it and wondering if it was just stuck after its winter slumber and will be fine now....
Click to expand...
I hope so! Will let you know how my car is after the new thermostat is fitted on Friday.
 
Please do let me know.

Mine only lost a tiny bit of coolant but looks like a massacre where the fan has blown it everywhere. I can see how only a few trips would make a difference though.

I'm going to take it out for a drive the next dry evening we get and see if it does it again.
 
Latest update: Problem completely solved! The new thermostat I have had fitted is brilliant. The temp gauge rises from cold to about 2mm past the centre then after about 20 seconds drops back to absolute dead centre! For those who are interested, the thermostat I fitted was rated at 81 degrees and is made by First Line, part number FTK001. Thanks to all of you who offered help and advice.
 
You must log in or register to reply here.
Back
Top