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post #1 of 26 (permalink) Old 12-03-2014, 11:01 Thread Starter
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overheating issue

Since some time the TF is overheating.

When it happened the first time I noticed a low coolant level - then cleaned the system (some scaling washed out), refilled, bleed twice.

Everything ok, no leaks to spot, no coolant loss.

A few days later it started to get hot again - gauge started to raise and smoke from the expansion tank. Coolant was boiling already.

When switching on again the temp gauge fell to normal again (below middle mark) and car was running normal.

Same this morning, when switching off and on again within a few seconds the coolant gauge dropped immediately back to normal.
Rear fan was running, front fan was off.

Fan fuses are both OK, also fan relay is new. Coolant level is ok.

Will fit a new coolant temp sensor these days.

I do not expect the worst case as no coolant loss is to spot, oil and coolant are clean, no smoking.
Seems more related to the coolant system, circulation...

But what I really donít understand is why it is overheating only every few days and cools down immediately when switching off and on again?

Could it be the thermostat?

Any thoughts?
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post #2 of 26 (permalink) Old 12-03-2014, 11:44
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How old is your expansion tank cap?
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post #3 of 26 (permalink) Old 12-03-2014, 11:51 Thread Starter
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no idea, I assume it's original.

doesn't look faulty but gives a little whistling sound...

Could the cap only be the reason?
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post #4 of 26 (permalink) Old 18-03-2014, 10:02 Thread Starter
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After I spent two hours changing the thermostat yesterday IT OVERHEATED AGAIN this morning!

Happened after driving for about half an hour, when the engine went hot the heater blower blew
quite cold - an indicator that the thermostat does not open the bypass correctly and no hot coolant
reaches the front, is my thought correct here?

Also the front fan did not kick in while the rear one was running - as I'm quite sure the fan is working
this would mean no hot coolant around the temp sensor (front), am I right?

I checked the new thermostat before I fitted it, system should be bleed correctly (no bubbles on three bleeding points).

Also fitted a new expansion tank cap.

I'm at a loss, any suggestions from you guys??
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post #5 of 26 (permalink) Old 18-03-2014, 10:15
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Quote:
Originally Posted by Bertl View Post
Happened after driving for about half an hour, when the engine went hot the heater blower blew
quite cold - an indicator that the thermostat does not open the bypass correctly and no hot coolant
reaches the front, is my thought correct here?

Also the front fan did not kick in while the rear one was running - as I'm quite sure the fan is working
this would mean no hot coolant around the temp sensor (front), am I right?

I checked the new thermostat before I fitted it, system should be bleed correctly (no bubbles on three bleeding points).

Also fitted a new expansion tank cap.

I'm at a loss, any suggestions from you guys??
The coolant circulates around the engine AND heater regardless of thermostat position. The thermostat only brings the radiator into circuit.
The fact that your heater runs cold means either a massive airlock or no circulation.

Has the coolant pump been changed recently?
When the engine is idling, is coolant returning to the header tank via the thin return pipes? (should be a jet of coolant visible into the top of the tank).

I am surprised that your engine bay fan comes on so often. This normally only happens when the engine bay is really hot - maybe 45 minutes in a traffic jam.
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post #6 of 26 (permalink) Old 18-03-2014, 10:18
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Change both CTS's and expansion cap.

Mine was over heating until I changed the ECU CTS. Only a tenner too
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post #7 of 26 (permalink) Old 18-03-2014, 10:22 Thread Starter
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the waterpump was changed approx. 12k mls ago.It does overheat just occasionally, no abnormalities when I let it run for one hour yesterday.

Let me check the return flow later today - if there's none the waterpump may be faulty again, am I right??

Airlock - bleed again may help?

What I'm really unsure about is that it happens only every few days while I'm driving the same route every day...
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post #8 of 26 (permalink) Old 18-03-2014, 10:28 Thread Starter
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Have the coolant temp sensor at home already, only the right spanner was missing...
But does this explain the cold heater?

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post #9 of 26 (permalink) Old 18-03-2014, 10:40
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Lack of flow into the coolant tank normally indicates blocked jiggle valves - particularly the one in the inlet manifold. A blockage will allow build up of air in the head (and other parts of the system) and will stop the coolant from circulating properly. When you then stop the engine the airlock can move so that when you restart the engine all appears to be OK.

Faulty sensors will have no effect on the cold heater.
But a faulty CTS could cause overheating as the engine will run richer for longer.
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post #10 of 26 (permalink) Old 18-03-2014, 10:58 Thread Starter
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Quote:
Originally Posted by Ricky146a View Post
Lack of flow into the coolant tank normally indicates blocked jiggle valves
Where do I find these valves?
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post #11 of 26 (permalink) Old 18-03-2014, 11:13
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If you follow the thinner pipe from the top of the coolant bottle, you will come to a 'T' connection. One side goes to a plastic connector on top of a thicker hose. There is a jiggle valve inside the plastic connector although this does not normally cause a problem.
The other side of the 'T' leads to the inlet manifold. With the engine cold and not under pressure, undo the clip and pull the hose off. You should get a flow of coolant from the inlet manifold. If not then you really need to take off the inlet manifold and clean out the valve.

A jiggle valve is just a ball bearing in a cage that stops too much coolant from flowing past but allows air to pass back to the coolant bottle thus ensuring that air is always at the highest point of the system (i.e. Header tank)

If you idle the engine with the tank cap off then you should see a flow of coolant. Try squeezing each part of the thin pipe in turn and the coolant flow should slow but not stop. When the coolant does stop you have found the blocked valve.
Do not run the engine for too long with the cap removed - the car operates on a pressurised basis.

Also try squeezing the coolant pipes at the front radiator - lay on the floor and reach underneath. You should not hear anywhooshing noise as this indicates air in the hoses or radiator. constant air in the radiator could indicate a blocked radiator and the best cure to this is a new radiator coupled with a thorough flushing of the system.
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post #12 of 26 (permalink) Old 18-03-2014, 18:47
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I think you need to check the cap and jiggle valves as described above. If this doesn't show up anything change the cap and bleed, bleed and bleed again ensuring the heater is set to hot. Make sure you bleed all 3 points at the radiator, the heater matrix and the metal inlet pipe to the cylinder head. This can take some time so be patient. Once all is good things should work ok. If you are certain things are circulating ok and your gauge is still playing up change that.

If you cant get coolant to circulate there is a problem with thermostat (make sure it isn't backwards) .....although not sure if it is possible to fit backwards from memory or if not a block in the heater return pipe it would be the vanes on the water pump although sounds unlikely.
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post #13 of 26 (permalink) Old 19-03-2014, 15:48 Thread Starter
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thanks guys.

plan for the weekend is to check the jiggle valves, bleed, bleed, bleed and fit a new fan temp sensor.

Let's see what happens...
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post #14 of 26 (permalink) Old 19-03-2014, 17:29
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Quote:
Originally Posted by Bertl View Post
thanks guys.

plan for the weekend is to check the jiggle valves, bleed, bleed, bleed and fit a new fan temp sensor.

Let's see what happens...
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im having the same problem, i guess i will too just continue bleeding without worring about wating too much coolant. in my case i removed the thermostat and closed the housing again so to have constant flow of coolant. i didnt really understand where the jiggle valve from intake manifold was but as i have flow into water tank i think they are unblocked.

i wish you luck, i hate having these overheating problems.
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post #15 of 26 (permalink) Old 19-03-2014, 20:37
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Having the exact same problem!! Im sure its the jiggle valve as said above. Bleeding and refilling coolant soon so that's my weekend sorted.
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post #16 of 26 (permalink) Old 20-03-2014, 08:57
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when you bleed the system start at the radiator then the heater matrix. Once all looks good here then go to the inlet pipe bleed screw.........then repeat and repeat. There should be a stream of water with no bubbles.
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post #17 of 26 (permalink) Old 10-04-2014, 09:56 Thread Starter
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After some weeks of rain I finally did some work on the car.

So overall I fitted a new thermostat, cleaned both jiggle valves (but were not blocked anyway),
fitted a new temp fan sensor, flushed the cooling system, refilled, bled, bled, bled again, new expansion tank cap.

Drove to work this morning - most stressful trip I ever did, pure paranoia!
No overheating!

But the temp gauge seems to be more sensitive than in the past. So far it was quite steady below the half mark,
no matter if driving on the motorway or sitting in city traffic.
Now it clearly moves when driving in the city or waiting in a queue. Not alarming but it reaches the middle mark then.
(Guess how my blood pressure rose when I noticed this!)

Of course I'd expect the engine to get a little warmer in slower traffic - I'm just wondering why the gauge is more sensitive now?
Or is this just a symptom of my paranoia?


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Last edited by Bertl; 10-04-2014 at 10:10.
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post #18 of 26 (permalink) Old 10-04-2014, 10:21
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Probably cos the coolant is flowing freely!
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post #19 of 26 (permalink) Old 10-04-2014, 18:55 Thread Starter
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OVERHEATED AGAIN ON THE WAY HOME TWICE!!

I'm absolutely at a loss...

The first time the temp gauge did not rise but was around the middle mark permanently. The heater blew hot the whole time.
But there was steam from the expansion tank, the water inside was boiling!

Let it cool down, after a few miles the heater went cold, the temp gauge rose slightly (but not up to the red mark) and it boiled again.

Had to refill nearly two litres but do not see any leaks.
Evaporated?

Is there any problem with the circulation? Water pump?
Any other ideas?


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post #20 of 26 (permalink) Old 10-04-2014, 19:59
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You could be blowing coolant out from a hose whilst you are driving.
Give every hose joint a good inspection for signs of coolant including the underfloor pipes and under the pump.
It could be that youstill have an airlock - they can be difficult to find.

It could also be either a blocked radiator or the pump.
Sometimes new caps have been found to be faulty as well.

Sorry I cannot be of any more help but ongoing cooling problems like this usually have only one cause.
The trick is finding it.

Did you bleed it at all 3 points??
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