Another overheating issue

Another overheating issue

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cornet

Original Poster:

1,469 posts

157 months

Monday 30th March 2015
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Another issue similar to http://www.pistonheads.com/gassing/topic.asp?h=0&a...

Here is the full story.

Car is 03 plate Celica T-Sport (2ZZ-GE engine) with 97k miles on the clock. About 6 weeks ago I went to pick up mate to drive up to Edinburgh, after a few miles I noticed that no heat coming through the cabin. Mile or so later and temperature gauge went up to max and just as I was about to pull over heat started coming through the heaters and temp dropped.

Then started blowing cold again, temp goes up, heaters kick in and drops again.

Not wanting to risk it we I left car at mate's and we got the train up.

However since then very occasionally the heaters have blown cold when driving around town but temp of engine has been fine. Done some longer journeys (30 miles or so) on motorways an no issues at all.

So Friday I drive up to Edinburgh again - no issues at all, car feels as it should.

Saturday drive to Oban - again no issues.

Sunday we drive around Oban and it;s blowing cold air again, as soon as temp gauge goes up I stop and let it cool down and then drive to somewhere less precarious and ring RAC who take me and the car back to Edinburgh. While RAC are arriving I check coolant level (since engine is now warm - and it looks fine).

Garage look at it today, their "test" was to leave it idling for a period of time - heaters run fine, temp is fine. They did say they would test it again tomorrow morning and see what happens.


So what do we think the issue is ?

I don't believe it's a leak since coolant level fine. Coolant hasn't been replaced in ages so can't see it being air lock. Now we are down to the water pump and thermostat.

Water pump seems obvious candidate since coolant should circulate through the heater matrix if the thermostat is closed according to the diagrams in this https://www.ddperformanceresearch.com/admin/pdf_fi...

However how would the water pump be failing in such a way that it was intermittent? If the whole cooling system was a single loop I would be suspecting the thermostat getting stuck.

If they don't find anything tomorrow morning I'm looking at a 250mile drive home with effectively no RAC cover (since they will consider it the same breakdown).


If it does make it home, what tests can I do ? - or should I just replace the water pump and thermostat (if I'm doing one of them there isn't that much extra work involved to do the other).

BritishRacinGrin

24,602 posts

159 months

Tuesday 31st March 2015
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First things first, stop driving the car it clearly has a cooling system problem and you're asking for trouble.

stevesingo

4,848 posts

221 months

Tuesday 31st March 2015
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Thermostat sticking open/closed? over cooling some of the time, undercooling at other times.

BritishRacinGrin

24,602 posts

159 months

Tuesday 31st March 2015
quotequote all
There's gas in it.

There's either air in it because it's displacing coolant which is getting out

or

There's air in it because the system isn't holding pressure.

Alternatively, there's combustion gasses in it.

And if there aren't combustion gasses in the coolant system already, there will be very soon unless you stop driving the car as it clearly has a cooling system problem.

Edited by BritishRacinGrin on Tuesday 31st March 08:55

cornet

Original Poster:

1,469 posts

157 months

Tuesday 31st March 2015
quotequote all
stevesingo said:
Thermostat sticking open/closed? over cooling some of the time, undercooling at other times.
This is my theory but how does it explain the cold air in the cabin. Surely if the thermostat was sticking closed I would still get hot air in the cabin ?



BritishRacinGrin said:
First things first, stop driving the car it clearly has a cooling system problem and you're asking for trouble.
Yes maybe I shouldn't have driven the car up to Edinburgh in hindsight but it I'd done a number of longer journeys during the week before with no issues what so ever (even had ODB meter plugged into car displaying current coolant temp - steady 89C as is normal).

I'm here now and could do with getting back this week. I've got no real space or tools to work on the car myself and the garage don't seem interested as it's not presenting the fault to them.

BritishRacinGrin

24,602 posts

159 months

Tuesday 31st March 2015
quotequote all
The garage's reluctance to road test it is unsurprising, what they could do is pressure test the system or sniff test it for combustion gasses, half hour's work.

cornet

Original Poster:

1,469 posts

157 months

Tuesday 31st March 2015
quotequote all
BritishRacinGrin said:
The garage's reluctance to road test it is unsurprising, what they could do is pressure test the system or sniff test it for combustion gasses, half hour's work.
Their response yesterday was "it seems fine to us - nothing wrong with it as far as we can see - come and collect it" which is why I'm somewhat frustrated.

Assuming both tests pass what is the next step - start stripping the thermostat and water pump out to check them for faults ?

Edited by cornet on Tuesday 31st March 09:14

BritishRacinGrin

24,602 posts

159 months

Tuesday 31st March 2015
quotequote all
If it's passed a sniff test and a pressure test...

There is never any harm doing a waterpump and thermostat if you have no idea when and if they were replaced previously. This'd be preventative maintenence in my opinion, parts should be cheap enough that once you've got everything off to check / inspect, refitting new parts is a no brainer. It's a good opportunity to check belts and hoses too.

Flush the system, refill as per owner's forum recommendations, carefully bleed it up and cap it off with a new expansion tank.. cap...

PhillipM

6,515 posts

188 months

Tuesday 31st March 2015
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Definately sounds like air in the system.