ZX in summer heat problems

[lighteninguk]

well as the heat has pushed in my zx is showing some signs of cooling problems which I obviously want to have sorted before things start to get heated, warped and damaged.

my symptoms are that after being out driving on one of those rare warmer days (of which we've had quite a few recently in uk) I will park my car up at my house to which everything looks normal. I will come back to my car in say 5 minutes and its pissing coolant out of the radiators pressure cap hose. to which its been doing this to such an extent that its gone from max to minimum on the coolant header (on the radiator) in the past two hot weeks.

this leads me to think maybe the car boils itself whilst it comes to a standstill and has no airflow through what seems to be a new radiator.

I soon thought "have I ever heard the radiator fan go?"

on the driveway I have started the car and allowed it to warm up once up to temperature instead of having the fans click on it starts to trickle coolant out of the radiator pressure cap hose.

one idea was that maybe its lost its head gasket to the heavens, but it doesn’t bubble inside the header tank whilst the engine is going, nor does it do the hiss when engine off radiator cap off then on, engine on for short while, engine off, see if cap hisses as removed.

I soon went back to the idea of the fan. I looked over the electronics diagram for the fan and it’s just a simple temp switch and relay and no concern taken for road speed. I am able to "short" the temperature switch connector which causes the fan to fire up. so the fan and relay work.

today I replaced the temperature switch on the radiator to see if it makes any difference but this made no difference to the fan triggering.

one test I made was letting engine run with this new switch in place and connected, the engine got warm and a small trickle from what’s becoming the "usual" hose again no fan kicking in yet. I unplug the switch and short it to cause the fan to kick in. quite quickly it soon it stops trickling out of the hose, hence I think the cars getting warm!

I’ve felt the radiator whilst it gets warm and it does have the slight feeling of it getting warm first at the bottom of it then the rest following suit which doesn’t make sense as the intake to the radiator is at the top (along with the temperature switch) which is starting to make me think the radiator has some blockage possibly?

there is my problem and my thoughts on it,

should I remove the radiator, flush it (and the engine?) through, and refit?

p.s the cabin heater works a treat lovely toasty and warm which isn’t nice for this weather but am forcing myself to have it running slightly to help dissipate some of the engines heat. so im assuming the coolant is going through the engine properly without an air block.

[nick]

should I remove the radiator, flush it (and the engine?) through, and refit?

I would certainly do that first before suspecting anything more serious. It sounds like a case of a blocked radiator to me, or possibly an air lock. Is there an air bleed screw in the top of the rad?
It should be getting very hot at the top before you get any heat at the bottom.

[jeremy]

Sounds like little or no flow through the radiator. Is the thermostat opening? Start it from cold, and feel the temperature of the hose leading from the thermostat housing to the radiator. it should stay cold until the thermostat opens at (about 82 degrees c?) then suddenly get very hot indeed. If it doesn't then I'd suspect the thermostat has failed shut.

When the car is travelling (and everything is in order) the fans are largely redundant and they should not run. The airflow through the radiator is far greater at 30 MPH than what any fan could provide. This is why the control of the fan is simply a thermostatic switch. From what you say you have a fan switch in the radiator. The flow in the radiator is from side to side and the switch is at the 'cold' end.

The problem with crossflow radiators is that they have the headers at the ends rather than top and bottom - and so any sludge tends to collect in and block the bottom tubes, progressively working up - till it doesn't cool properly and the car boils.

[Peter.N.]

If you fill the header tank to the top you will always get some coolant loss as it expands on heating, but once the level has dropped an inch or so it should stop. If the cooling is sufficient while the car is in motion but boils over when you stop, providing that the cooling fan is cutting, the most likely problem is a clogged radiator especially if the car has done 100k miles or more. Replacement is the only real cure.

[alan s]

I'd be inclined to agree with Jeremy with the possibility of a thermostat having failed.
In the past, I have seen people clain these later type thermos should be changed as a matter of course every 3 - 4 years as they reckon that's their life expectancy.
To test, just do as you have been doing and let engine run until it begins to get warm. Keep hanging onto the top hose. At a temp around the mid 80s the top hose should just get suddenly hot, just like turning a hot water tap on. If the radiator was blocked so badly so as to prevent total circulation, the coolant would be gushing out of the radiator cap very early in the piece as the cap has a rating of only around 1 bar, which is why I tend to think more on the lines of the thermostat. I would guess that it works in a kind of a way but nowhere as efficiently as it should.
Once a new one is fitted just be certain to bleed the system thoroughly and back flush the radiator while you have the coolant out replacing the thermostat.

Alan S

[lighteninguk]

Just finished the job, flushed the radiator which had a bit of scum but not as much as i would have thought, but it gets hot evenly over now so it is all positive.

The act of the cap pissing out fluid seemed to be a case of a bad radiator cap which wasent sealing properly. i realised this when i was flushing the radiator i was running liquid through it in at all angles to try and clear it so had the radiator cap on for a couple of them but found it was leaking from the cap when it was upside down which showed it really wasent sealing properly as the weight of the water would push past the cap.

the new thermostat has made a big difference, the hot flow to the radiator is more sudden and happens slightly later. i tested the old one against the new one in a pan on the hob and it showed the old one opened much earlier but didnt even open properly compared to the new one.

all in all the fan fires up the cabin heater still going strong so a good job me thinks.

Thanks for the advice guys!

[victor xt]

Hi, i cleaned my radiator when i did the engine rebuild, i changed the thermostat with a new nissan thermostat, i still think that japan quality outperforms the french quality , if i remember well, it was 82 celsius degrees, i used a cold water pressure washers like karche* and it was incredible the amount of junk coming out of the radiator, i did this several times and still the junk was coming out, i did the same with the 2 hoses that goes to the cabin for the heater inside it, more junk was coming out, after all of this, the engine temperature was great here in chile where in summer we have around 34 celsius degrees top in the rush hour, the temperature was around 95 degrees celsius, all of this with 10w-40 liqu* mol*leichtlauf oil, same in motorways, at 80 mph or 120 km/hr the temperature was about sometimes at 95 celsius degrees, perferct i thought but when i swithched to synthetic with 5w-40 there was a huge improvement, the engine runs cooler , in motorways and city traffic hardly the temperature clock go beyond of the middle of it, like 90 celsius degrees

Hope this helps

[lighteninguk]

well having the lowest spec zx i have no temperature/pressure guages at all, all the wiring appears to be there at the engine end and at the cables that plug into the dash unit so in theory it could be installed.....