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Author Topic: Possible air lock?  (Read 117 times)

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Omega Nige

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Possible air lock?
« on: 24 November 2021, 13:53:45 »

Hi, I have just changed my cam belt on my V6, new water pump and new thermostat. Refilled the coolant as per Haynes filling the pipe to the heater first and then filling via the reservoir. Squished rad hoses, ran and then topped up. I have no heat in the cabin and temp gauge doesn't read. Is it an air lock or a dodgy thermostat? Hopefully an air lock (how to cure it, thanks?) as I don't want to strip it all down again to fit a new thermostat! Thanks.
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Doctor Gollum

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Re: Possible air lock?
« Reply #1 on: 24 November 2021, 15:12:22 »

The rules for refilling the coolant are straightforward.

1. Cap off.
2. Add 5 litres of red Dexcool.
3. Fill to MAX mark with distilled water.
4. Start engine and leave idling.
5. Set cabin temp to max/HI. Both sides if ECC/face-lift.
6. Ensure cabin blower is set to one bar.
7. Wait until the radiator fans kick in twice.
8. Top up to MAX with distilled water.
9. Refit cap.
10. Wait for the radiator fans to kick in twice.
11. Re check level and top up with distilled water if required.
12. Switch off.

If the heater doesn't work after this, then the matrix is blocked or the HBV/associated vacuum system is faulty.
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Enceladus

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Re: Possible air lock?
« Reply #2 on: 24 November 2021, 15:34:57 »

Likely it's still air-locked.
The temp gauge sender is at the back of the V. It's the single pole (single wire) brass bodied sensor. As I recall it's screwed into the coolant bridge. So if it was working before you started than likely you didn't reconnect it when you replaced the thermostat. Or the wire terminal got pulled off during reassembly. Or perhaps the wire got fractured where the female terminal end is. This sensor does not feed the engine management so the engine still runs properly, just the gauge on the dash doesn't work.

Nor will it stop the cabin heater working.

If the heater was working before you started work but not now, then it might be a loss of vacuum to the HBV (heater bypass valve). Located behind the offside cylinder head underneath the scuttle. Did you pull of the vacuum hose when you were working on the thermostat? Maybe forgot to reconnect it.

Or if the heater wasn't working before you started then perhaps the HBV is stuck (common problem) or the heater matrix is blocked with scale and gunge. Lot's on the forum about flushing it out. You don't really want to replace the matrix unless you absolutely have to.
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Nick W

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Re: Possible air lock?
« Reply #3 on: 24 November 2021, 16:15:44 »

DG's list takes far too much time and effort for me:


Fill the cooling system using the expansion tank until the level settles at the max mark


Start the car, and check for leaks with the cap off


Put the tools away


Turn the heater on full, and top up the level. Fit the cap


Drive the car until it is thoroughly warmed through


Add coolant to correct the level once it has cooled down completely - I usually do this the next day before driving the car.


This has always worked for me after replacing  the various parts of the cooling system - radiator, HBV, water pump, hoses, heater matrix, head gaskets, thermostat - without any problems.


It's a self bleeding system, so there's no need to fill individual components. It does have a massive radiator and takes ages to warm up at idle, which is why I adopted the procedure above.
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Doctor Gollum

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Re: Possible air lock?
« Reply #4 on: 24 November 2021, 16:21:38 »

It is indeed a straightforward process ;)

My 'list' ensures that the heater is set for max coolant flow with minimal heat loss from the cabin.

People always overlook the heater settings and then wonder why it has an airlock ::)
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TheSoulDoctor_123

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Re: Possible air lock?
« Reply #5 on: Yesterday at 22:29:58 »

I'd definitely gi with Dr Gollum's refill procedure, it worked well for me the last time I had to flush the heater. That was after the RAC had to fix a blown coolant hose, and the heater wasn't right from that day, which I suspect was an airlock combined with a stilted matrix.  It really doesn't take much air to be stuck in there to cause big problems.
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